DISORDERS OF LANGUAGE

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CHAPTER 3 DISORDERS OF LANGUAGE

There are two main schools of thought in the history of neurogenic language disorders, both of which have relevance to modern aphasiology. The first, the Wernicke-Lichtheim-Geschwind tradition, emphasized that primary language functions are represented in discrete regions of cortex (“centers”) and that the activities of these loci are integrated through connecting fiber tracts. The Wernicke-Lichtheim scheme consisted of a center for motor images of words, located in the posterior third of the inferior frontal convolution (Broca’s area), as well as a center for acoustic images of words (Wernicke’s area). A fiber tract (arcuate fasciculus) joined the two centers, with the flow of information running from posterior to anterior. A third center for concepts was located in the extrasylvian cortex, with an outflow to Broca’s area and input from Wernicke’s area. There was an output from Broca’s area to the motor cortex and an input to Wernicke’s area from the auditory cortex. This simple scheme systematized the main perisylvian and transcortical aphasia syndromes observed before 1885 and predicted the existence of a syndrome as yet unobserved at that time: conduction aphasia. The Wernicke-Lichtheim model was later refined by members of the Boston School, principally Frank Benson and Norman Geschwind, with the addition of three new syndromes, and the inclusion of the inferior parietal lobule as language cortex (see Benson and Ardila, 1996).

The second main stream is represented by neurologists such as Hughlings Jackson, Sigmund Freud, and Aleksandr Luria who conceived of language as represented in broader hierarchical cortical zones or gradients, organized around the centers of the Wernicke-Lichtheim model. The role of connecting tracts was deemphasized. Luria’s aphasiology preserves the anteroposterior schema of the Wernicke-Lichtheim model but redefines localization of language as hierarchical and distributed. Modern clinical aphasiology is based on the classical syndromes described in the Wernicke-Lichtheim tradition and their modifications. Concepts of their localization, however, have come to be shaped further by ongoing clinicopathological observation and functional neuroimaging, and current views on the localization of language are not too distant from those of the Jackson-Freud-Luria tradition. Linguistic ideas have also become part and parcel of modern aphasiology. A glossary of important linguistic terms and concepts is given in Table 3-1.

TABLE 3-1 Essential Linguistics Concepts

Phonological	Phonology is the study of the structure and patterning of the sounds of language. Many of the clinical features of language disorders are phonological. The units of analysis are phonemes, which can be defined as the basic meaning-distinguishing sounds (essentially consonant and vowel sounds) of the language.
Lexical	Whereas phonology is concerned with the patterning of sounds within a word, and is therefore a sublexical discipline, lexicology is concerned with the whole word as a single entity. At a lexical level, there is a dichotomy that is fundamental to the understanding of aphasic disorders, because aphasic variants affect the two classes of words differentially. The open class, so-called because it is conceptually unlimited and new items are steadily added as vocabularies increase, consists principally of nouns, verbs, adverbs, and adjectives—that is, words that refer to specific objects, actions, and attributes and that convey substantive content. The closed class, which is conceptually limited and does not increase in size as vocabularies increase, consists of articles (e.g., “a,” “the,” “that”), conjunctions (e.g., “and,” “but”), pronouns (e.g., “you,” “they”), and prepositions (e.g., “up,” “along,” “below”). The distinction between open- and closed-class words parallels the distinction between the meaning of a sentence (semantics) and the form or sequential structure of a sentence (syntax).
Morphological	Morphology concerns the internal structure of words. The aspect of morphology that is most important for understanding language disturbances is word formation, or the construction of a new word from an existing word by adding an affix. This can be derivational, whereby an adjective such as “good” is converted to a noun such as “goodness,” or inflectional, whereby a word is changed to suit the grammar of a sentence; for example, “run” might become “running,” or “pencil” might become “pencils.” Because the suffixes “-ing” and “-s” cannot stand alone, they are referred to as bound morphemes.

LANGUAGE PRODUCTION

At a clinical level, language disorders are more easily recognized and identified in language production, either spoken or written, than in disturbances of comprehension. Production consists of three broad stages: conceptualization, formulation, and overt execution. The first two of these stages are described in detail in the following sections. From a neuroanatomical perspective, conceptualization (the development of an intention to speak, and a decision about what will be said) depends on the dorsolateral prefrontal cortex. Formulation (the conversion of ideas into the structure of spoken language) depends on Broca’s region. Execution is the production of physical speech and depends on all of the motor mechanisms associated with speech (see Duffy, 2005).

Conceptualization

This is a largely prelinguistic phase that involves the development of an intention to speak and a decision as to what will be said. Development of an intention and a decision about the message to be conveyed is often referred to as macroplanning. From that point on, the message must be reshaped into a particular set of logical relationships (propositions) that can be expressed in terms of the syntactic and semantic structure of language. This is often referred to as microplanning. Propositions form a link between thought and its expression in language. It is noteworthy that this concept was anticipated by the British neurologist Hughlings Jackson, who regarded it as essential for understanding the relationship between thought and speech in aphasia. Conceptualization depends on connectivity between extrasylvian association cortex and the classical perisylvian language axis, a concept borne out by functional neuroimaging (see Blank, Scott, Murphy, et al, 2002).

Formulation

This phase deals with the conversion of propositions into actual sentences (sentence encoding). It is governed directly by the rules of syntax and semantics and consists of two important components. The first involves the selection of appropriate open class of lexical items (see Table 3-1) to convey the intended meaning. The linguistic concept of selection is of central importance in aphasic disorders. Selection implies the possibility of choice among alternatives, and errors in selection manifest clinically as paraphasias. A paraphasia has two essential features: (1) It is an error of selection resulting in the substitution of a word or part of a word with a frequently incorrect or inappropriate alternative, and (2) it is unintended. Selection processes occur at the phonemic and the semantic levels (see Table 3-1). In neuroanatomical terms, selection processes are heavily, but not exclusively, dependent on posterior perisylvian association cortices. The second component of formulation involves the genesis of correctly ordered positional slots into which the words of the sentence are inserted. These sequentially ordered schemas are often called sentence frames, and their construction is contributed to and defined by closed class (function) words and bound morphemes (see Table 3-1) Sentence frames are constructed according to the rules of syntax (see Table 3-1). The functional neuroanatomy of syntactic processing is complex, involving a network of left perisylvian structures, and it appears that Broca’s area is a key nodal structure within this network. Disorders of syntax, including Broca’s aphasia, occur most prominently with lesions involving the anterior aspects of the perisylvian language zone.

Fluency

The division of language disturbances into fluent and nonfluent is the most fundamental and clinically appreciable dichotomy in diagnostic aphasiology. The major aphasia syndromes are encompassed within the distinction of fluent versus nonfluent (see Table 3-2).

TABLE 3-2 The Fluent-Nonfluent Distinction

	Nonfluent Production	Fluent Production
Anatomical	Anterior (prerolandic) language areas	Posterior (postrolandic) language areas
Fundamental disorder	Sequential organization (conceptualization, formulation)	Selection
Syndrome	Perisylvian	Perisylvian
	Aphemia	Pure word deafness
	Broca’s aphasia	Wernicke’s aphasia
	Extrasylvian	Conduction aphasia
	Transcortical motor aphasia	Extrasylvian
		Transcortical sensory aphasia
		Anomic aphasia

Note: Mixed transcortical aphasia and global aphasia are associated with clinically nonfluent production but also involve an underlying selection disorder.

Fluent language output in an aphasic patient is defined by the use of sentences that are syntactically intact but are semantically compromised because of a selection disorder. The following example, taken from a description of a severe form of fluent dysphasia, namely jargonaphasia (a variant of Wernicke’s aphasia), illustrates this point:¹

“This guy has got to this thing, this thing made out in order to slash immediately to all of the windpails. … This is going right over me from there, that’s up to is 5 station stuff from manatime, and with that put it all in and build it all up so it will all be spent with him conversing his condessing.”

The sequential relationships between grammatical entities in the passage are preserved. It is the closed class entities that are primarily affected by errors in selection, resulting in phrases that are devoid of meaning, and jargonistic substitutions (neologistic paraphasias) such as “manatime,” and “condessing.” Prosodic features are characteristically retained. Prosodic features are rhythmic and emphatic aspects of language production that allow the listener to appreciate whether the speaker is, for example, asking a question or making a statement.

Nonfluent aphasic output, in contrast, is characterized by a dissolution of syntactic structure; in particular, the production of closed class words is affected. The following are examples of nonfluent language:

1. A soldier talking about a bullet wound to his head on the battlefront: “Well … well … front … well … advance … well … bullet … well … nothing much … hospital … operation … well … speech … speech … speech. …”²

2. In response to the question “Have you played no games?”: “Played games, yes, played one, daytime, garden.”³

3. Explaining a readmission to hospital: “Ah … Monday … ah, Dad and Paul and Dad … hospital. Two … ah, doctors … and ah … thirty minutes.”⁴

In contrast to the fluent output, these utterances are devoid of syntactic structure, exemplified by the lack of closed class words, and the relative excess of open class words. This pattern constitutes agrammatism. Nevertheless, there is appropriate selection of open class words (nouns and verbs), and as a consequence nonfluent output does not entirely have the “empty” character of fluent output. The length of phrases is heavily reduced in agrammatic disorders.

Paraphasia and Other Deviations

Paraphasias

Paraphasias are defined as unintended utterances. In essence, there is a failure of selection at the phonemic level, producing a phonemic (literal) paraphasia (e.g., “I drove home in my lar”) or at a word (lexical) level (e.g., “I drove home in my wagon”), producing a verbal paraphasia (Table 3-3). Paraphasias are said to be neologistic when the unintended word is heavily contaminated with extraneous phonemes and, as a result, contains juxtapositions of sublexical fragments that are not characteristic of the language (phonemic neologisms) and are nonsensical in context. For example:⁵

TABLE 3-3 Paraphasias and Other Selection Errors

Type	Examples
Phonemic (literal)	“glear” instead of “clear”
	“spink” instead of “sphinx”
	“gedrees” instead of “degrees”
	“tums” instead of “tongs”
Conduit d’approche (successive phonemic approximations to a target word)	“trep”→“tretz”→“fretful”→“pretzel”
Verbal
Formal (similar form, different meaning)	“dare” instead of “pear”
Morphemic (assembled from legal morphemes)	“man-a-time,”^* “summer-ly”
Semantic (substituted word belongs to the same general category)	“train” instead of “car”
	“Taj Mahal” instead of “pyramid”
	“cloth” instead of “blanket”
	“seahorse” instead of “unicorn”
Circumlocutions (word substituted with a phrase of the same meaning)	“drinking container” instead of “cup”

* Morphemic assemblies that do not produce acceptable words are called neologisms.

EXAMINER: Are you feeling better than this morning?

PATIENT: Not too melsise, I don’t think.

EXAMINER: Pardon me?

PATIENT: I motsumsirs, orie.

Morphemic neologisms occur when valid morphemes are assembled in a manner that does not produce an acceptable word (e.g., “man-a-time”).

Unintended substitutions also occur in writing (paragraphias). Like paraphasias, they can be literal or they can involve semantic substitutions (see Table 3-3).

APHASIA SYNDROMES

Contrary to earlier views, more recent tractography findings indicate that the arcuate fasciculus consists of two components. The first is a direct tract connecting the posterior segments of the inferior and middle temporal gyri with Broca’s area (Brodmann’s areas 44 and 45), as well as with parts of the middle frontal gyrus and inferior precentral gyrus. The second component is an indirect tract with anterior and posterior segments. The posterior segment connects Wernicke’s area with the inferior parietal lobule (Brodmann’s areas 39 and 40), whereas the anterior segment connects the inferior parietal lobule with frontal language cortex (see Catani et al, 2005). Structures connected by the arcuate fasciculus are somewhat more extensive than classical views suggested, and this broader concept of the perisylvian region accommodates the clinicopathological studies of fundamental language disorders since the 1950s more successfully. Furthermore, it suggests that the arcuate fasciculus might be important in uniting perisylvian and extrasylvian language regions.

Aphasias caused by anterior (prerolandic) lesions are associated with nonfluent language production, whereas those caused by posterior lesions (postrolandic) are associated with fluent disorders. There are two major nonfluent aphasias: Broca’s aphasia, in which repetition is disturbed, and transcortical motor aphasia (TMA), in which repetition is normal. The fluent aphasias are Wernicke’s and conduction aphasias, in which repetition is disturbed, and anomic and transcortical sensory aphasias (TSA), in which repetition is preserved (Table 3-4) (see LaPointe, 2005). In addition, there are two aphasias in which the dysfluency typical of anterior dysphasias is combined with the impaired comprehension typical of posterior dysphasias: global aphasia and mixed transcortical aphasia.

TABLE 3-4 Classification of Aphasia by Fluency and Comprehension

Impaired Repetition	Normal Repetition
Nonfluent
Broca’s^*	Transcortical motor
Global^†	Mixed transcortical
Fluent
Conduction^*	Anomic
Wernicke’s^†	Transcortical sensory

* Comprehension preserved.

† Comprehension impaired.

Nonfluent Production with Impaired Repetition: Speech Dyspraxia and Broca’s Aphasia

Speech Dyspraxia (Aphemia)

The syndrome of speech dyspraxia occurs quite separately from the other anterior aphasias. There is, however, a widely recognized dictum in aphasiology that lesions restricted to Broca’s area do not necessarily cause Broca’s aphasia. Embolic infarctions of Brodmann’s areas 44 and 45, often involving subjacent white matter and extension into the anterior insula, cause a wide spectrum of acute effects ranging from subtle hesitancy to mutism. Recovery is rapid—within days, weeks, or months—and in some cases, minimal residual dysfluency may be the only detectable language feature. Dyspraxia of facial, oropharyngeal, lingual, and respiratory functions is an associated feature that might persist beyond the resolution of language deficits, manifesting, in many cases, with some features reminiscent of the syndrome of speech dyspraxia. The chronic picture is “deficits in the smoothness with which vocalization of one phoneme in a series can be ceased and changed to the next, in precise control of the respiratory component of vocalization, and/or in precise positioning of the oral cavity to produce desired phonemes … better explained by inadequacy in skilled execution of movements, an apraxia in speaking … but not an associated disorder in language usage.”⁶ This resembles Luria’s idea of efferent motor aphasia, in which the primary disorder relates to skilled sequential movements or kinetic melodies in which the patient is able to position the articulators correctly but is not capable of moving smoothly from one articulatory position to the next.⁷ Originally, Pierre Paul Broca used the term aphemia to refer to this condition. There appears to be a revival in the use of this term in relation to progressive speech disturbances. Michael Alexander’s group at Boston University has taken the view that aphemia is a distinctive syndrome arising from small lesions in the left inferior frontal gyrus (pars opercularis), inferior precentral gyrus, and underlying white matter.⁸

The main features of speech dyspraxia are shown in Table 3-5.

TABLE 3-5 Main Features of Speech Dyspraxia (Aphemia)

Effortful articulatory approximations and attempts at self-correction

Dysprosody

Articulatory inconsistency

Difficulty initiating speech, sometimes with unproductive articulatory groping

Often preserved articulation of automatic speech

Preserved syntax and semantics

Functional neuroanatomy of speech dyspraxia

It is now recognized that articulatory function depends on a hierarchically organized network of structures involving cerebellum, thalamus, striatum, anterior insula, and sensorimotor cortex. Current concepts of Broca’s area, particularly the posterior portion (Brodmann’s area 44) abutting on the precentral sulcus (Brodmann’s area 6), include the view that it mediates the encoding of phonological word forms into articulatory plans. This places it at the apex of the articulatory hierarchy. Broca’s area also shows increased activity during syntactic processing, although lesions restricted to this area cause impairments in speaking rather than language,⁶ a view dramatically foreshadowed by the neurologist Pierre Marie in 1906 with a paper titled “The Third Frontal Convolution Does Not Play Any Special Role in the Function of Language” (see Harrington). Functional neuroimaging findings have raised the possibility that Broca’s area represents a bridge between articulation and language production.

The Syndrome of Broca’s Aphasia

The term Broca’s aphasia is applied to a syndrome that occurs after more extensive infarction in the territory of the superior division of the middle cerebral artery. A core clinical feature is the production of sentences that lack syntactic structure. In its milder forms, affected patients produce simplified phrase structures, with a loss of the prosodic (melodic) aspects of speech. In its more severe forms, speech becomes telegraphic with strikingly effortful articulation. The effort involved in articulation results in highly economical phrases, usually restricted to nouns and verbs (e.g., “money. … send”).

Loss of fluency in Broca’s syndrome is the combined effect of an impairment at the linguistic level (agrammatism) and an impairment of articulatory programming (speech dyspraxia). Agrammatism, or a dissolution of grammatical form, is characterized by greatly reduced use of open class words (articles, conjunctions, prepositions) and of morphemic structure (affixes), with relative preservation of words that convey substantive content (open class words such as nouns and verbs). The writing disturbance in Broca’s aphasia parallels spoken language in that it is sparse, effortful, clumsy, agrammatic, and paragraphic.

Repetition is impaired and reflects essentially the same pattern of nonfluency as is that in spontaneous language. Written language is also agrammatic, with graphemic and graphomotor errors. Comprehension in Broca’s aphasia is not unscathed, but it nevertheless serves the patient comparatively well in daily life, and comprehension deficits are not a particularly noticeable feature of the clinical encounter. Some authorities have argued that there is a unitary impairment that produces both expressive agrammatism and syntactic comprehension deficits. There are cases, however, in which expressive agrammatism and comprehension dissociate, which suggests that there are separate mechanisms for elaborating syntactic form in language production and for appreciating syntactic form in heard or read language and that these mechanisms can be separately impaired. Gesture and communicative pragmatics (i.e., all of the nonverbal behaviors that accompany language appropriate the communicative context) are usually preserved.

The syndrome of Broca’s aphasia can be observed as a later consequence of infarction. The initial clinical picture resembles a global aphasia. After weeks or months, there is a gradual emergence of the dyspraxic and agrammatic features, and these evolve slowly toward the long-standing features of the syndrome of Broca’s aphasia (see Mohr,⁶ page 230).

Functional neuroanatomy of Broca’s aphasia

Broca’s aphasia is typically produced by fairly large lesions in the territory of the superior division of the left middle cerebral artery. Right hemiparesis, particularly involving the face and arm, is typically present as a neighborhood sign. Broca’s area, the anterior insula, and the basal ganglia are often all damaged, and the lesion usually also includes the middle frontal gyrus and the anterior parietal lobe. Involvement of Broca’s area alone is not a sufficient condition for the emergence of the syndrome of Broca’s aphasia. Neuroimaging findings have suggested that damage to Broca’s area impairs the production of all forms of speech (propositional and nonpropositional; see Blank et al, 2002). Propositional speech refers to newly formulated language output that conveys an idea, as opposed to nonpropositional speech, which is more automatic in nature and conveys nonideational content such as feeling states. At a clinical level, it is well accepted that propositional speech is most severely affected and that automatic nonpropositional aspects of speech are often preserved. Grammatical output depends on the interaction between Broca’s area and other cortical regions. Functional neuroimaging in normal subjects demonstrates that the middle frontal gyrus is commonly activated by language tasks that activate Broca’s area, which suggests that this region should also be included in a language production network (see Blank et al., 2002). Tractography of the arcuate fasciculus suggest that this pathway terminates in the middle frontal and inferior precentral gyri (Fig. 3-1), as well as in classically defined Broca’s area (see Catani et al., 2005).

Figure 3-1 Terminations of the arcuate fasciculus suggested by tractography.

(From Catani M, Jones DK, Ffytche DH: Perisylvian language networks of the human brain. Ann Neurol 2005; 57:8-16, Fig. 3. Copyright © 2006 Wiley-Liss, Inc., A Wiley Company. Reprinted with permission of John Wiley & Sons, Inc.)

Nonfluent Production with Normal Repetition: Transcortical Motor Aphasia

Like all actions, language output, whether in the form of speech or writing, must be planned. Planning is a complex and multilevel process, ranging from the intention to produce propositional output (conceptualization) to the specification of appropriate syntactic structure and semantic forms (formulation) and then to the specification of phonology and articulatory patterns (overt execution). Cognitive capacity for planning is limited and dependent on normal frontal lobe function. The cardinal clinical manifestations of TMA can be conceptualized as a pathological disruption in planning of language output.

The Syndrome of Transcortical Motor Aphasia

TMA is a nonfluent aphasia. The quantity and complexity of speech and of written output are reduced, but repetition, writing in response to dictation, reading, confrontation naming, and comprehension are well preserved. This pattern reflects the notion that TMA is a disorder of spontaneous, self-initiated language output, with facilitation of output when external supports are provided.

There is general agreement that there are two variants of TMA.¹⁰ The first often manifests initially as mutism, which resolves to poorly initiated and nonfluent output, characterized more by an articulatory disturbance than by a language disturbance. Output is normal during repetition. Comprehension and naming are also well preserved. There is some debate as to whether this form of TMA is a true aphasia. It occurs with infarcts in the territory of the left anterior cerebral artery, particularly with involvement of the supplementary motor area. It also occurs after resection of the left supplementary motor area. This variant of TMA has been ascribed to isolation of the supplementary motor area from frontal perisylvian language mechanisms. In this view, isolation of the supplementary motor area results in impaired motor programming before the overt execution of language output.¹¹

The second variant of TMA is characterized by very sparse language production, which gives the impression of a reduced intention or motivation to speak. What speech is produced is well articulated but with impoverished syntax and narrative. Nevertheless, repetition is normal, even for long and complex sentences. Although patients with this form of TMA do not initiate routine series (e.g., naming the months of the year, nursery rhymes) on request, they freely complete the series after the examiner has provided the first few elements. Similarly, they are able to fill in sentence frames provided by the examiner (e.g., “the day is __________ and the sun is __________”). Luria referred to this condition as dynamic aphasia.⁷ He believed that the underlying impairment was an inability to elaborate the linear scheme of sentences or, in current terms, an inability to elaborate propositions. Luria’s description of the production difficulties of this group of patients is instructive:¹²

“As a rule, these patients answer simple questions relatively easily, frequently prefacing their reply with an echolalic^* repetition of the question, but they have difficulty as soon as they are asked to read a text and relate it to the examiner, or to compose a story from a picture given to them, and they are completely helpless if they have to write an essay on any freely chosen subject. In these cases they state that their thoughts will not move, that nothing enters their head, and they usually abandon the task or do nothing more than reproduce some habitual verbal stereotype, usually taken from their past experience.”

The dynamic variant of TMA occurs with damage to the left frontal cortex anterior or superior to Broca’s area, involving the middle or superior frontal gyrus or both.

Fluent Production with Impaired Repetition and Comprehension: Wernicke’s Aphasia and Pure Word Deafness

The Syndrome of Wernicke’s Aphasia

The disturbance associated with Karl Wernicke’s name is perhaps the prototypic fluent aphasia. Nevertheless, disagreements about the exact features of Wernicke’s aphasia continue, and it should be recognized that there are a number of variants, which range from a lexical agnosia (pure word deafness) to jargonaphasia. From a diagnostic perspective, this condition is sometimes confused with psychiatric disturbances or even delirium in a busy emergency room.

The following is a list of core features accepted in current practice:

Output is fluent, often empty of substantive meaning, with an excess of closed class words and circumlocutions.

Paraphasias are common. These may be phonemic (literal) or semantic, but the former is held to be the most frequent type. Paraphasias may be so severe that jargon is produced (jargonaphasia). Similar output features are seen in writing, which, however, displays preserved penmanship.

Patients appear to be unaware of or unconcerned about their highly disturbed and often nonsensical output, in contrast to the frustration shown by those with Broca’s aphasia.

Comprehension is severely impaired, predominantly because of a difficulty in discriminating between phonemes. The profundity of the comprehension impairment makes this the most disabling feature of Wernicke’s aphasia. As a consequence of the comprehension difficulty, output during attempts at conversation is seldom related to the conversational context. Some patients respond on the basis of incidental nonlinguistic cues.

Repetition of words and sentences is impaired.

The following is an example of the fluent output disorder of a patient with severe Wernicke’s aphasia, illustrating runs of paragrammatism:¹³

I feel very well. My hearing, writing been doing very well; things that I couldn’t hear from; in other words, I used to be able to work cigarettes I didn’t know how. The pay I didn’t know how. I can write, cheesterfeela for over twenty years I can write it. Chesterfeel, I know all about it, I can write it.

Neuroanatomy of Wernicke’s Aphasia

Wernicke’s aphasia is caused by lesions in the posterior segment of the superior temporal gyrus. Persistent and very severe forms, such as jargonaphasia, involve the supramarginal gyrus as well.

Because Wernicke’s area falls within the territory of the inferior division of the middle cerebral artery, it is seldom accompanied by hemiparesis as a neighborhood sign. It may, however, be accompanied by a right superior quadrantanopia as a result of damage to the temporal portion of the optic radiation in subjacent white matter.

Pure Word Deafness

The hallmark of this condition is an inability to recognize the phonology of language, despite normal hearing and normal ability to recognize nonlanguage sounds. The fundamental disturbance is at a phonemic rather than a lexical level, as evidenced by normal comprehension of written language. Repetition and writing in response to dictation are impossible. Spontaneous writing, however, is intact. Pure word deafness is, in effect, a phonemic agnosia.

Pure word deafness is caused by damage to the region of the posterior insula and temporal isthmus. The condition is also encountered in epileptic aphasia (Landau-Kleffner syndrome).

Fluent Production with Normal Comprehension and Impaired Repetition: Conduction Aphasia

The syndrome of conduction aphasia is perhaps the most controversial of the aphasias. It was postulated as a theoretical possibility from the Wernicke-Lichtheim model. In essence, Wernicke assumed that if the pathway connecting Broca’s and Wernicke’s areas were to be interrupted, speech would be fluent but paraphasic, and comprehension would be preserved, but the patient would be unable to repeat what he or she heard. This disconnection concept was challenged, principally by Sigmund Freud, who held that conduction aphasia, to the extent that this syndrome actually existed, was more likely to be the result of cortical damage and that its exact character would depend on the proximity of the lesion to either Broca’s or Wernicke’s areas. This notion has been revisited in light of tractography studies of the arcuate fasciculus (see Catani et al, 2005).

Conduction aphasia is fundamentally a disorder of repetition. The breakdown in repetition has two underlying causes, giving rise to two variants of the syndrome: reproduction conduction aphasia and repetition conduction aphasia. Reproduction conduction aphasia is a specific disorder of phonological processing in which the processes by which the perceived phonemic representation of a word is converted into articulatory sequences are impaired. Repetition conduction aphasia, or acousticomnestic aphasia in Luria’s classification,⁷ is considered to be a disorder in a particular aspect of short-term memory: namely, reduced capacity to pass information from a short-term acoustic store to the output system. From a cognitive perspective, both forms of the syndrome involve a breakdown in a privileged communication channel. From a neuroanatomical perspective, the notion that this channel is necessarily the arcuate fasciculus, a deep white matter pathway that was initially thought to connect Broca’s and Wernicke’s areas, has been remarkably persistent in neurological thinking, but the clinicoanatomical literature indicates that there is no reason to believe that arcuate fasciculus interruption is a more feasible explanation for conduction aphasia than are lesions in the perisylvian language cortex.

The Syndrome of Conduction Aphasia

The core clinical features of reproduction conduction aphasia are as follows:

Output is fluent, with phonemic paraphasias and with normal or near normal comprehension.

Against this background, repetition of words, phrases, and sentences, as well as writing in response to dictation, is very impaired and is hampered by prominent phonemic paraphasias. Phonemic paraphasias are also seen in naming and reading.

Characteristic attempts are made to correct the phonemic selection errors by successive approximations, or conduit d’approche (see Table 3-3). This phenomenon suggests that the representation of phonological knowledge is intact in conduction aphasia and that the impairment lies in the integration of phonology with articulatory processing.

Repetition conduction aphasia is easily recognized on neuropsychological evaluation from a severe inability to repeat sentences, against a background of fluent spontaneous output and normal comprehension. Because of the absence of overt language symptoms, these cases rarely come to medical attention. In contrast to reproduction conduction aphasia, language is devoid of paraphasic errors. Affected patients usually exhibit a severely reduced digit span.

The following example of fluent output in a conduction aphasic illustrates the profuse phonemic paraphasias and conduit d’approche:¹³

EXAMINER: Tell me what’s going on in this picture.

PATIENT: Oh … he’s on top o’ the ss … ss … swirl … it’s a … ss … sss … ss … sweel … sstool … stool.

Neuroanatomy of Conduction Aphasia

Most cases with conduction aphasia have lesions centered on the supramarginal gyrus. The lesion can include white matter deep to the supramarginal gyrus, involving the posterior end of the arcuate fasciculus. Whether involvement of the posterior arcuate fasciculus is a necessary condition is debatable. Anterior transection of the arcuate fasciculus does not produce conduction aphasia. Lesions in the insular cortex, including subinsular white matter, are also an important cause of conduction aphasia. It is recognized that conduction aphasia can occur with pure suprasylvian or pure subsylvian lesions (see Benson and Ardila, 1996).

Fluent Production with Normal Repetition and Impaired Comprehension: Transcortical Sensory Aphasia

TSA is a rather controversial condition. It is similar to all posterior aphasias in the sense that it manifests as a fluent language disturbance, which ranges from severely paraphasic and circumlocutory speech to relatively normal output with occasional semantic paraphasias. The hallmark of TSA is impaired comprehension but well-preserved repetition. Patients with TSA are able to repeat long and complex sentences that they cannot comprehend. The pattern of cognitive breakdown in TSA is variable, which suggests that this is not a single entity. Location of the causative lesion is also not certain and might be more widely distributed than classical aphasiologists suspected. Computed tomographic evidence suggests that lesions producing TSA tend to overlap in the inferior region of the temporo-parieto-occipital junctional cortex, as well as occipitotemporal cortex and underlying white matter. This inferior and medial distribution implicates the posterior cerebral artery.¹⁴ Other affected patients have lesions that are more superolateral, lying in the posterior watershed region between the posterior and middle cerebral arteries.¹⁴ TSA is also associated with degenerative conditions, such as the posterior cortical atrophy variant of Alzheimer’s disease.¹⁵

TSA is noted for its frequent association with other posterior focal neighborhood signs, such as Gerstmann’s syndrome, agnosia, alexia, constructional impairments, and ideational apraxia, in both focal and degenerative etiologies.

Fluent Production, Normal Repetition, and Preserved Comprehension: Anomic Aphasia

The main feature of anomic aphasia is a supramodal word-finding difficulty, with little effect on comprehension. Supramodal implies that the anomia is present regardless of the sense modality through which the item to be named is presented. Language production is fluent, but it is devoid of substantive content, circumlocutory, and paraphasic. Repetition is normal, which means that anomic aphasia is a transcortical disorder, and it has been suggested that it is on a continuum with TSA.

Norman Geschwind’s adaptation of the Wernicke-Lichtheim model attributed the role of name retrieval to the angular gyrus, which is widely recognized as a zone of convergence for visual, auditory, and tactile information and a repository for semantic information. It is anatomically well placed as a nodal structure for the activation of semantically specified concepts. It is richly interconnected with the posterior temporal region, where activated concepts are converted to phonemic form. Angular gyrus lesions produce the features of anomic aphasia, but it is recognized that dysnomic features can arise from multiple loci and are therefore poorly localizing. In the author’s own experience, however, extra-angular lesions seldom produce the prominent fluent and circumlocutory output disturbance of anomic aphasia. For example (in which the patient attempts to convey that he suffered a stroke after aortic surgery):¹³

EXAMINER: Can you tell me about your illness?

PATIENT: I had a. … I had a one or two three … There’s one … I had a … a … I know the exact part of it.

EXAMINER: And it was after the operation?

PATIENT: Right, about a day later, while I was under whatchmacall. …

EXAMINER: Anesthesia?

PATIENT: Under where they put you, just two or three people, an’ you stay in there for a couple o’ days.

Nonfluent Production, Normal Repetition, and Impaired Comprehension: Mixed Transcortical Aphasia

The syndrome of mixed transcortical aphasia was initially described in 1948 by Kurt Goldstein, although the condition had been anticipated by the classical aphasiologists. There is a severe reduction in the quantity of spontaneous output; comprehension is also severely impaired, but repetition remains intact. This pattern of impairment was ascribed to isolation of the speech area, a concept that was later to be confirmed by Geschwind in his classic study of a case of carbon monoxide poisoning. Repetition is made possible by the integrity of the perisylvian language axis: namely, Broca’s and Wernicke’s areas and the connections between them. Broca’s and Wernicke’s areas are, however, disconnected from anterior and posterior association cortices that mediate the ideational basis of language. Functional neuroimaging findings support the notion of a widely distributed left-lateralized extrasylvian neocortical system involved in the formulation of propositional language before its conversion to articulated speech (see Blank et al., 2002). Echolalia is a prominent component of mixed transcortical aphasia and, like intact repetition, can be thought of as reflecting the preservation of the automatic aspects of language, devoid of an ideational context.

The lesions producing mixed transcortical aphasia tend to be multifocal or diffuse and include hypoxic insults, large watershed infarctions or a combination of focal watershed and pial infarction, and degenerative processes. The mixed transcortical aphasia syndrome also occurs in thalamic infarction.

PRIMARY PROGRESSIVE APHASIA

Primary progressive aphasia refers to a gradually evolving aphasia, in the absence of other cognitive disorders. It is often the first symptom of neurodegenerative conditions such as one of the forms of frontotemporal dementia (see Chapter 73).

The term primary progressive aphasia is applied when the speech and language symptoms have progressed for about 2 years in the absence of any other cognitive or behavioral changes.¹⁶ Even when the underlying dementia begins to manifest, the aphasic disturbance remains the most prominent and disabling symptom. Although some studies suggest that 50% to 60% of primary progressive aphasia cases have a fluent disturbance, at least two variants (fluent and nonfluent forms) are currently acknowledged. A third logopenic variant (characterized by slow and halting word production in the context of highly simplified but grammatically correct sentences) has also been proposed.

Mesulam ¹⁶ estimated that the underlying neuropathology in about 60% of patients with primary progressive aphasia is neuronal loss, gliosis, and spongiform change. Some cases are caused by frontotemporal dementia with parkinsonism linked to chromosome 17 (see Chapter 74), a genetic tauopathy. A further 20% have Pick’s disease, and fewer than 20% have Alzheimer’s disease.

Fluent Progressive Aphasia: Semantic Dementia

In semantic dementia, spontaneous language is fluent, dysnomic, and possibly circumlocutory, but production and comprehension of syntax are normal. The hallmark feature is a loss of word meaning, underpinned by a degradation of semantic function. On confrontation testing, for example, patients not only are anomic but also are unable to give any of the attributes of the object. The intended word is often replaced by a superordinate category (e.g., “flower” instead of “daisy”), which reflects an early loss of subordinate knowledge. Speech itself is normal in terms of rate of production and articulation. Published consensus criteria for the diagnosis of frontotemporal dementia link semantic dementia with disorders of object and face recognition (visual agnosia and prosopagnosia, respectively) as additional manifestations of semantic loss.¹⁷ This is controversial with regard to the definition of primary progressive aphasia mentioned previously.¹⁶

The earliest cerebral change in this variant is left anterolateral temporal atrophy. Semantic dementia is considered to be one of the clinical variants of frontotemporal dementia.

Nonfluent Progressive Aphasia

The nonfluent progressive aphasia variant manifests with nonfluent speech, agrammatism, and difficulties in comprehending complex syntactic structures but also with preserved semantic function, at least at a single-word level. Articulation is labored. Cases of progressive aphemia or of speech apraxia but without a true aphasia have also been described. The distinction between nonfluent progressive aphasia and progressive aphemia parallels the distinction between Broca’s aphasia and aphemia.

Most patients with nonfluent progressive aphasia and pure progressive aphemia have been shown to have Pick’s disease, with more restricted atrophy in the latter group.¹⁸ Both conditions are regarded as frontotemporal dementia variants¹⁷ and may represent a clinical spectrum reflecting varying degrees of damage to the anterior insular, inferior premotor cortex, and pars opercularis.

An Intermediate Variant: Logopenic Progressive Aphasia

The logopenic progressive aphasia variant does not meet the criteria for semantic dementia or nonfluent progressive aphasia. Rate of speech output is reduced, with hesitancies suggestive of a word-finding difficulty and with impaired repetition. Articulation is normal. Grammar is simplified but correct. Semantic function is preserved, but syntactic comprehension is impaired. Logopenic progressive aphasia is associated with left temporoparietal atrophy. Together with a high frequency of the apolipoprotein E ε4 haplotype in this group, this anatomical distribution of atrophy suggests that logopenic progressive aphasia might be an atypical-onset form of Alzheimer’s disease.

Further definition of primary progressive aphasia variants is likely to continue (see Grossman, 2002). Because primary progressive aphasia is an evolving language disorder, distinctions between the variants might be stage related. On the basis of a longitudinal study, Kertesz and colleagues suggested that although the aphemic, logopenic, agrammatic, and semantic distinctions are useful, there is some tendency for outcomes to converge as the dementia progresses.¹⁹

ACQUIRED DISORDERS OF READING: THE ALEXIAS

Fundamental Concepts: The Dual-Route Model

In nonideographic writing systems—in which individual symbols do not themselves stand for concepts or ideas—all phonemes of the language have corresponding written representations, known as graphemes. Learning to read depends on acquiring knowledge of the phonemic equivalents of the graphemic system: that is, the rules of grapheme-phoneme correspondence. In sensory terms, this involves an integration between visual and auditory processing systems. Beginning and unskilled readers depend heavily on grapheme-phoneme correspondence and therefore on phonological pathways. This gives rise to the phenomenon of letter-by-letter synthesis: reading by sounding out each grapheme in turn before synthesizing the individual sounds into the word itself. This approach is considered to be sublexical because it depends on sequential identification of individual components of the word. It allows the individual to read any string that conforms to the phonological structure of the language and can therefore be “sounded out.” This would include all words with regular grapheme-phoneme correspondence, such as “cat,” “glint,” and “slap,” as well as pseudowords such as “rint,” “glaint,” or “lume.” But this does not allow the individual to read orthographically irregular words (written differently from the way they sound) such as “yacht,” “psalm,” or “thyme.” Words such as these can be read correctly only through a purely visual route; an attempt at using a phonological (grapheme-to-phoneme conversion) pathway would result in a mispronunciation. With increasing reading proficiency, all words come to be recognized visually (lexical or whole-word reading), but the sublexical route must still be recruited for pseudowords. This dual-route model is fundamental to understanding the acquired alexias.

The Dual-Route Model and Reading Disorders: Deep and Surface Alexias

Deep alexia and surface alexia are psycholinguistic “syndromes.” They do not necessarily correspond to particular loci of cerebral damage, but they are useful in systematizing patterns of reading impairment and relating these patterns to putative mechanisms of disruption.

Deep Alexia

The main features of deep alexia are as follows:

Normal reading of familiar and highly imageable words, regardless of whether they have regular (“desk”) or irregular (“yacht”) grapheme-phoneme correspondence.

Inability to read pseudowords correctly according to the usual grapheme-phoneme conversion rules of the language.

Visual reading errors (e.g., “patience” for “patients”) and semantic reading errors (e.g., “ship” for “boat,” “cash” for “money”) are common.

This pattern is brought about by a loss of the phonological or grapheme-phoneme conversion route. The patient is left with a residual ability to recognize familiar words but cannot recruit a phonological strategy to tackle unfamiliar words or pseudowords, which are, in effect, profoundly unfamiliar.

Deep alexia is seen in patients with severe aphasias and with widespread damage in a frontoparietal distribution.

Surface Alexia

Patients with surface alexia are able to read orthographically regular words (“rush,” “tint,” “same”) and pseudowords (“glant,” “sint,” “glame”) but are unable to read irregular words (“gaoled,” “subtle,” “colonel”). Pronunciation is regularized (e.g., “denni” for “deny”). This feature cannot be detected in languages with uniform, unambiguous grapheme-phoneme conversion rules (e.g., Spanish), but it is readily demonstrable in English. Reading is effortful, taking appreciably more time for long words than short words (word length effect). There is inability to recognize words at a glance.

Word meaning is accessed only after the word has been pronounced. If an error in pronunciation occurs, the meaning is deemed to be that of the unintended word. For example, if the word “pretty” is read as “pity,” its meaning is judged to be “compassion.”

This constellation of features implies preservation of the phonological route but loss of visual access to the semantic system.

Deep alexia and surface alexia are regarded as central alexias, because they represent a loss of access by visual representations of word forms to central phonemic and semantic mechanisms (Table 3-6).

TABLE 3-6 Central Alexia Syndromes

Psycholinguistic Syndrome	Deficit	Closest Equivalent Neurological Syndrome, or Lesion Location
Deep alexia	Loss of grapheme-to-phoneme conversion	Alexia with agraphia
Deep alexia	Loss of grapheme-to-phoneme conversion	Aphasic alexia
Surface alexia	Loss of visual word form access to semantic system	Left temporoparietal
		Generalized atrophy
		Primary progressive aphasias

Neurological Classification of Alexias

There is an alternative, nonpsycholinguistic classification system for the alexias. Although some syndromes are essentially the same in both (e.g., pure alexia), there really is no equivalent syndrome in the other classification system for others (see Benson and Ardila, 1996, for suggested correlations between the two classification systems).

Alexia without Agraphia (Pure Alexia)

Patients with pure alexia read by sequentially identifying the letters of the word (letter by letter reading). This is a slow and laborious process, and at least in the subacute phase, silent reading is not possible. Speed of reading depends on the number of letters in the word (word length effect); therefore, whole-word recognition is not possible. All other language functions are well preserved, giving rise to the term pure alexia. Writing is also intact, but the patient is not able to read what he or she has written. The classical lesion in pure alexia is infarction of the medial surface of the left occipital lobe and splenium of the corpus callosum. It is now accepted that splenial involvement is not a necessary condition for the emergence of pure alexia.

Pure alexia tends to evolve acutely from an inability to identify individual letters to recovery of letter identification and letter-by-letter reading and, in some cases, recovery of silent reading. Alexia without agraphia is regarded as a peripheral alexia because the deficit occurs at the level of visual processing without involving the more central mechanisms of grapheme-phoneme conversion or semantic processing.

Alexia with Agraphia

Strictly speaking, alexia with agraphia is diagnosed when reading and writing are impaired against a background of otherwise normal language functions. This pattern, however, is rare. The nature of the reading and writing impairment is variable. Alexia with agraphia is caused by lesions in the temporoparietal cortex and is often accompanied by mild features of Wernicke’s aphasia. In pure forms of alexia with agraphia, residual reading depends on whole-word recognition, and it therefore resembles the psycholinguistic syndrome of deep alexia.

Aphasic Alexia (Co-occurring with Broca’s or Wernicke’s Aphasia)

With severe Broca’s aphasia there is a profound disruption of grapheme-to-phoneme conversion, and residual reading occurs at the level of whole-word reading. This brings about a striking impairment of reading comprehension despite relatively well-preserved comprehension of speech. Like alexia with agraphia, alexia in Broca’s aphasia resembles the psycholinguistic syndrome of deep alexia. It is sometimes referred to in the neurological classification of alexias as the third alexia.

Wernicke’s aphasia causes impairments for spoken and written language. The comprehension impairment for speech tends to recover more rapidly than does reading comprehension, and the evolving clinical picture is one of alexia with agraphia.

ACQUIRED NEUROGENIC AGRAPHIA

Speech and writing are the two major output modalities for language. It is often assumed that language disorders in speech are paralleled by an equivalent pattern in writing, and, as a consequence, the agraphias have come to be overshadowed by the aphasias. Aphasic agraphias certainly can reflect the production disorder of the aphasic syndrome, but this is not always the case, and there is often overlap between writing disorders in fluent and nonfluent aphasias. Classical agraphic syndromology is therefore somewhat less satisfactory than classical aphasiology.

Most classifications have recognized agraphias associated with aphasic syndromes (aphasic agraphias), those associated with fundamental visuospatial disorders (e.g., neglect), and those associated with upper limb motor disorders and dyspraxic disorders. Benson and Ardila (1996) proposed a dichotomous classification, into aphasic and mechanical agraphias (Table 3-7).

TABLE 3-7 Classification of the Agraphias

Aphasic Agraphias

Agraphia in Broca’s aphasia

Agraphia in Wernicke’s aphasia

Agraphia in conduction aphasia

Agraphia in other aphasias

Mechanical Agraphias

Hyperkinetic agraphia

Based on Benson DF, Ardila A: Aphasia: A Clinical Perspective. New York: Oxford University Press, 1996, p 214, Table 12.1.

The mechanical agraphias raise the question as to whether writing impairments of nonsymbolic origin (such as dystonic, paretic, or apractic forms) should be regarded as true agraphias, which is, again, reminiscent of the question of whether speech dyspraxia should be regarded as aphasic or dysarthric. Perhaps the term agraphia should be reserved for language-based disturbances in writing and graphomotor impairment for nonlinguistic disturbances. Table 3-8 lists the main characteristics of some of the aphasic agraphias, and Table 3-9 lists characteristics of the higher-level mechanical agraphias.

TABLE 3-8 Characteristics of Aphasic Agraphia: Comparison with Spoken Output

Spoken Output	Written Output
Agraphia in Broca’s Aphasia
Sparse output	Sparse output
Effortful	Effortful
Poor articulation	Clumsy calligraphy
Short phrase length	Abbreviated output
Dysprosody	(No written equivalent)
Agrammatism (lack of closed class words)	Agrammatism (lack of closed class words)
Poor spelling	Poor spelling
Agraphia in Wernicke’s Aphasia
Normal vocal characteristics	Normal graphic characteristics
Noneffortful speech	Noneffortful writing
Good articulation	Well-formed letters
Normal phrase length	Normal sentence length
Normal prosody	(No written equivalent)
Lack of open class (substantive) words	Lack of open class (substantive) words
Paraphasias	Paragraphias

Adapted from Benson DF, Ardila A: Aphasia: A Clinical Perspective. New York: Oxford University Press, 1996, pp 218-219, Tables 12.3 and 12.4.

TABLE 3-9 Apractic and Spatial Agraphias

Apractic Agraphia

Fundamentally, a loss of ability to form normal graphemes

Profuse written spelling errors, despite a retained ability to spell orally

Profuse iterations, repairs, and other distortions

Writing difficulty evident in spontaneous writing, writing in response to dictation, and copying

Can occur in isolation from speech difficulties or upper limb apraxia and can therefore be regarded as a “pure” apraxia; this, however, is rare

Usually occurs in association with ideomotor dyspraxia or other inferior parietal signs

Spatial Agraphia

Loss of ability to utilize spatial constraints and organization in writing

Letters are reiterated

Spatial delimiters between words are not used correctly (“Th esunis shi ning” instead of “The sun is shining”)

Progressive enlargement of margins, heavily slanted writing, and other forms of malpositioning of writing

Impairments seen in automatized (for example, signature) and nonautomatized forms of writing

Occurs in association with other spatial impairments, typically in right hemisphere lesions

Neurocognitive Classification of Agraphias

Neuropsychological studies have resulted in an alternative classification of the agraphias, analogous to the psycholinguistic classification of the alexias. The distinction is made between central and peripheral agraphias, with matching of the concepts of central and peripheral alexias. Spatial and apractic agraphia can be regarded as peripheral because they do not involve fundamental language mechanisms. Table 3-10 summarizes the central agraphias.

TABLE 3-10 Central Agraphias

Syndrome	Linguistic Impairment	Neuroanatomy
Lexical agraphia (analogous to surface dyslexia)	Loss of whole word processing	Dominant angular gyrus, with sparing of immediate perisylvian region
	Inability to spell irregular or ambiguous words, with preserved spelling of regular words and graphemically legal nonwords
	Graphemic regularization (for example, “grayshus” instead of “gracious”)
Phonological agraphia (analogous to phonological dyslexia)	Loss of sublexical processing	Dominant supramarginal gyrus and insula
	Impairment of phoneme-to-grapheme conversion
	Inability to spell nonwords, with preserved ability to spell regular and irregular familiar words
Deep agraphia (analogous to deep dyslexia)	Inability to write nonwords or words with low imageability	Large supramarginal or insula lesions
Deep agraphia (analogous to deep dyslexia)	Semantic paragraphias with no visual similarity to the target (for example, “travel” instead of “car”)	Large supramarginal or insula lesions