Speech and higher function

Published on 09/04/2015 by admin

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Speech and higher function

Speech and higher function are not formally examined in every neurological patient. This should be undertaken in patients who report difficulties or if an abnormality is suggested by the history. Abnormalities in these areas can explain difficulties in obtaining a clear history. If in doubt, test.

Speech

Speech is required for the patient to give a history and it therefore constitutes the first part of the examination. The processes in language and terms used to describe abnormalities are summarized in Figure 1. Speech processing occurs in the dominant hemisphere. The process of understanding occurs in Wernicke’s area in the supramarginal gyrus of the parietal lobe and the upper temporal lobe. This is linked by the arcuate fasciculus to Broca’s area in the inferior frontal gyrus where speech output is generated. This then requires motor output involving corticospinal tracts, the basal ganglia and cerebellar inputs. The larynx is innervated by the vagus nerve to produce the voice, and then the tongue and lips, innervated by the hypoglossal and facial nerves, produce articulated speech (Fig. 1).

image

Fig. 1 Process of language.

Aphasia

There are two main types of aphasia, which have been given different names in different classifications.

1. Fluent aphasia = Wernicke’s aphasia = receptive aphasia = sensory aphasia

Patients have impaired understanding and do not answer questions appropriately and do not obey commands. The speech output is fluent but is often meaningless because they cannot edit their own output. This pattern of aphasia results from lesions in Wernicke’s area. Patients with a milder fluent aphasia may seem normal superficially, especially on social pleasantries. However, any attempt at more meaningful questioning will highlight the difficulties. This pattern of aphasia is frequently misinterpreted as confusion.

2. Non-fluent aphasia = Broca’s aphasia = expressive aphasia = motor aphasia

Patients have preserved comprehension and will obey commands. Speech is non-fluent with difficulties finding words. In milder deficits this particularly affects less commonly used words. This results from lesions in Broca’s area.

These patterns of aphasia can occur in isolation but there is often a mixed picture affecting comprehension and speech production, which, if severe, is referred to as global aphasia. Smaller lesions can produce more subtle speech problems: for example, lesions of the arcuate fasciculus impair repetition; smaller lesions within Broca’s area can lead to subtle difficulties in word finding or impaired spontaneous speech; nominal aphasia, difficulty in finding names for objects, occurs in lesions of the angular gyrus.

Assessment

Assessment of aphasias follows the pathway of language processing given above. Establish that patients can hear you. Give instructions of increasing complexity to determine the degree of comprehension. Listen to spontaneous speech (patients may need to be asked to describe something, for example their work) – is it fluent? Are they using the words correctly? Assess word finding ability by asking them to name objects (watch, strap, buckle), to list animals (normally >18 in 1 min) or words beginning with F or S (normal >12 in 1 min). Other facets of language can also be tested, for example reading and writing. Intriguingly, with dominant occipitoparietal lesions, reading can be lost without losing the ability to write (alexia without agraphia) so patients can write but not read their own writing!

Higher function

Higher function is the term used to include all the processes of thought, memory, interpretation and comprehension of visual, auditory and sensory information. The objectives are:

image to determine if there are abnormalities in higher function
image to determine if these are focal or diffuse
image to assess their severity.

Factors affecting assessment of higher function

1. The testing needs intact speech and attention. If these are affected, testing has to be more limited and interpretation is more difficult. Non-verbal communication can sometimes be used to a limited extent with abnormal speech.
2. The level of premorbid intelligence needs to be considered, and some estimation made of expected level of function.
3. Other neurological deficits such as visual or hearing difficulties affect the results. Formal assessment of higher function needs to be undertaken after conducting a full neurological examination.
4. The mental state of a patient will affect higher function testing. Anxiety or depression can impair performance.

The interpretation of higher function deficits should incorporate information from the mental state examination. Patients with frontal lesions have marked behaviour changes, with altered personality, apathy or disinhibition and perseveration, but may have relatively modest abnormalities of higher function. Patients with parietal lobe abnormalites have normal mental state examinations but many abnormalities in higher function. Higher function can be divided into the following areas.

Attention and orientation

Attention can be tested using digit span – the number of digits that the patient can repeat both forward and backward (normal: 7 forward, 5 backward). Orientation is given in terms of time (time, day, date, month, year), place (ward, hospital, town) and person (what is your name?). Abnormal orientation is non-specific and has no localizing value; it simply indicates an abnormality either of attention or memory.

Memory

Memory is complicated and can be classified in several ways (Fig. 2). The content of the memory can be divided into:

image episodic memory: the recall of particular events
image semantic memory: the knowledge of objects, facts, concepts, words and meanings
image motor or procedural memory: i.e. how to juggle and tie knots.
image

Fig. 2 Types of memory. Memory disturbances (pp. 52–55) may be for past events (retrograde amnesia) or storage of new information (anterograde amnesia).

For bedside testing, the following scheme is useful, but is only the beginning of the assessment of memory:

image Immediate memory: tested with digit span or giving the patient a name and address to repeat.
image Short-term memory: ask the patient to repeat the name and address after 5 min.
image Long-term memory: general information is easiest to test and needs to be adjusted according to knowledge that the patient could be reasonably expected to know, e.g. dates of World War II, name of Prime Minister, etc.

Memory is represented bilaterally in the temporal lobes and is usually lost in diffuse rather than focal lesions. Loss of short-term memory occurs in early dementia and rarer amnestic syndromes (e.g. Korsakoff’s psychosis). Long-term memory is usually only involved in severe organic brain disease; isolated abnormalities of this are usually functional.

Calculation

This can be tested using serial 7s (taking 7 away from 100 repeatedly), doubling 3s or other simple calculations. This usually reflects a generalized disturbance in higher function but can be involved in isolation in dominant hemisphere abnormalities.

Abstract thought

This is a test of frontal lobe function. Ask the patient to interpret proverbs (e.g. people in glass houses shouldn’t throw stones). If the metaphor is not understood this indicates concrete thinking.

See if the patient can give you reasonable estimates of, for example, the weight of an elephant (5 tonnes) or the length of a jumbo jet (70 m). Outlandish estimates and concrete thinking suggest frontal lobe dysfunction.

Spatial perception

This can be tested by asking the patient to draw a star or clock. Inattention can be revealed when only half the clock is drawn, and inability to draw anything is a constructional apraxia; both indicate a contralateral parietal lobe lesion.

Visual and body perception

Agnosias are abnormalities of perception despite being able to demonstrate that the sensory modality is intact: for example, the inability to recognize faces despite normal vision (prosopagnosia) or an inability to recognize an object put in the hand despite normal sensory testing (astereognosis). These indicate parietal lobe lesions. In some instances the patient fails to recognize half his or her own body (usually the left side) – asomatagnosia. More marked is the phenomenon of neglect when the patient completely ignores one side, again almost always the left side. These too reflect contralateral parietal lobe lesions.

Apraxias

An apraxia is when an action cannot be carried out even though the necessary motor and sensory functions are intact. Examples include dressing apraxia (the patient cannot organize clothes to allow dressing) or ideomotor apraxia (cannot mime an action, e.g. striking a match). These abnormalites can reflect either frontal premotor or dominant parietal lobe lesions.

Speech and higher function

image Speech is usually assessed informally while taking the history.
image Intact speech is needed to test other aspects of higher function.
image Test speech more formally if there are specific complaints, if there is difficulty getting the history or if there is a suggestion of other higher function deficit.
image Simple bedside testing can categorize most speech abnormalities.
image Higher function testing aims to quantify any deficit and distinguish between focal and generalized higher function loss.

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