Speech and higher function

Published on 09/04/2015 by admin

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Last modified 09/04/2015

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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).

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!

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