Motor aphasia (frontal Broca's aphasia)
The motor form of aphasia develops when the lesion focus is localized in the inferior frontal gyrus of the left hemisphere. The basic physiological mechanism of this disorder involves a disruption of systemic efferent processes responsible for speech formation.
The clinical picture of motor aphasia consists of the following features:
- Spontaneous speech: The patient almost completely loses the ability to speak. Speech is extremely difficult or absent altogether. The patient cannot pronounce a single meaningful word.
- Speech comprehension: Cognitive perception is unimpaired. The patient adequately understands the interlocutor and speech addressed to them.
- Vocalization: The ability to produce sounds is preserved. Patients can scream or reproduce individual sounds, but forming them into words is impossible.
- Reading: The ability to read aloud is lost. At the same time, comprehension of the read text (silent reading) may be preserved.
Sensory aphasia (temporal Wernicke's aphasia)
The sensory form of aphasia occurs when the posterior pole of the superior temporal cortex is damaged. The mechanism of this pathology is based on the impairment of the action result acceptor. The patient loses the ability to evaluate the achieved result of their mental activity, which leads to severe communicative disorders.
The symptomatology of sensory aphasia is radically different from motor aphasia:
- Perception: Totally impaired. Patients cease to understand both audible (oral) and written speech.
- Spontaneous speech: The physical ability to articulate phrases is not lost. On the contrary, patients become excessively talkative. However, their speech is distorted, completely incomprehensible to others, and represents a meaningless «word salad».
Sensory aphasia is often accompanied by associated disorders:
- Alexia — complete loss of the ability to read silently.
- Amusia — loss of the ability to perceive music.
Comparative characteristics of aphasias
For quick memorization of the differences between the two main forms of aphasia, it is convenient to use a comparative table.
| Sign | Motor aphasia (Broca) | Sensory aphasia (Wernicke) |
|---|---|---|
| Localization | Inferior frontal gyrus of the left hemisphere | Posterior pole of the superior temporal cortex |
| Comprehension of others' speech | Preserved | Disrupted |
| Spontaneous speech | Lost (cannot say a single word) | Preserved, but distorted («word salad») |
| Reading | Cannot read aloud (comprehension preserved) | Loss of the ability to read silently (alexia) |
| Mechanism | Impairment of efferent speech processes | Impairment of the mechanisms of the action result acceptor |
Briefly: answers to topical questions
In which cerebral hemisphere is Wernicke's center located?
Wernicke's center is located in the cortex of the dominant cerebral hemisphere.
The exact anatomical localization includes the following structures:
- Wernicke's center — posterior part of the superior temporal gyrus (posterior pole, cytoarchitectonic area 22).
- Adjacent structures — the pathological process often involves adjacent areas of the cortex of the inferior parietal lobule (areas 42 and 40).
Damage to this area of the dominant hemisphere leads to sensory receptive aphasia (Wernicke-Korsakoff/Wernicke-Kozhevnikov aphasia), characterized by impaired comprehension of spoken language.
What is conduction aphasia and where is the lesion localized in this condition?
Conduction aphasia is a speech disorder that occurs when the associative fibers connecting the cortical speech centers are damaged.
Anatomical features of lesion localization:
- Arcuate fasciculus — a branch of the superior longitudinal fasciculus that curves around the posterior end of the lateral (Sylvian) sulcus.
- Subcortical white matter — the level of passage of the arcuate fasciculus in the hemisphere.
- Connected structures — fibers connect the speech centers of the frontal and temporal lobes (Broca's and Wernicke's centers).
Broca — «Silence» (motor, cannot say words himself, but understands everything). Wernicke — «Vinaigrette» (sensory, produces word salad without understanding the meaning of what is said and heard).
Class and exam questions
Is a patient with Broca's motor aphasia capable of producing any sounds?
Yes, vocalization is preserved. The patient is capable of screaming and producing separate articulate or inarticulate sounds, but cannot pronounce a single meaningful word.
What is alexia and in which form of aphasia does it occur?
Alexia is the complete loss of the ability to read silently. This symptom is an associated disorder in Wernicke's sensory aphasia.
What is the underlying mechanism of sensory aphasia?
It is based on the impairment of the systemic mechanisms of the action result acceptor. The patient loses the ability to evaluate the achieved result of their mental activity, which turns their speech into an incoherent stream.
What else to study on this topic
- Mechanisms of formation of systemic efferent speech processes
- The role of the action result acceptor in higher nervous activity
- Physiological foundations of music perception and the development of amusia
- Neurophysiological differences between reading aloud and reading silently
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