Aphasia

For medical students2 min readUpdated 2026-10-10

Aphasia is a systemic impairment of language functions resulting from injury to specific areas of the cerebral cortex. Depending on the precise localization of the lesion, a patient may lose the ability to produce words while fully understanding others, or conversely, lose the comprehension of speech while producing an incoherent stream of sounds.

Motor formLesion of the inferior frontal gyrus of the left hemisphere

Sensory formLesion of the posterior pole of the superior temporal cortex

Broca's symptomInability to utter a single meaningful word

Wernicke's symptom"Word salad" and impaired speech comprehension

Motor Aphasia (Broca's Frontal Aphasia)

Motor aphasia develops when the lesion 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 production.

The clinical presentation of motor aphasia includes the following features:

Spontaneous speech: The patient almost completely loses the ability to speak. Speech is extremely labored or absent altogether. The patient cannot produce a single meaningful word.
Speech comprehension: Cognitive perception remains intact. The patient adequately understands the interlocutor and speech addressed to them.
Vocalization: The ability to produce sounds is preserved. Patients can shout or produce isolated sounds, but cannot organize them into words.
Reading: The ability to read aloud is lost. However, comprehension of the written text (silent reading) may be preserved.

Sensory Aphasia (Wernicke's Temporal Aphasia)

Sensory aphasia occurs due to damage to the posterior pole of the superior temporal cortex. The underlying mechanism of this pathology is a disruption in the functioning of the action result acceptor. The patient loses the ability to evaluate the achieved result of their mental activity, leading to severe communication disorders.

Symptomatology of sensory aphasia differs radically from motor aphasia:

Perception: Totally impaired. Patients stop understanding both heard (spoken) and written speech.
Spontaneous speech: The physical ability to pronounce 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, use the comparison table below.

Feature	Motor Aphasia (Broca)	Sensory Aphasia (Wernicke)
Localization	Inferior frontal gyrus of the left hemisphere	Posterior pole of the superior temporal cortex
Speech comprehension	Preserved	Impaired
Spontaneous speech	Lost (cannot say a word)	Preserved, but distorted ("word salad")
Reading	Cannot read aloud (comprehension preserved)	Loss of ability to read silently (alexia)
Mechanism	Impairment of efferent speech processes	Impairment of action result acceptor mechanisms

Mnemonic

Broca = "Broken speech" (motor, cannot speak words himself, but understands everything). Wernicke = "Word salad" (sensory, produces incomprehensible speech without understanding the meaning of what is said or heard).

Frequently asked questions

In which cerebral hemisphere is Wernicke's center located?

Wernicke's center is located in the cortex of the dominant cerebral hemisphere.

Precise anatomical localization includes the following structures:

Wernicke's center — the posterior part of the superior temporal gyrus (posterior pole, cytoarchitectonic area 22).
Adjacent structures — pathological involvement often spreads to adjacent cortical areas of the inferior parietal lobule (areas 42 and 40).

Damage to this area of the dominant hemisphere results in sensory receptive aphasia (Wernicke-Kozhevnikov aphasia), characterized by impaired spoken language comprehension.

What is conduction aphasia, and where is the lesion localized?

Conduction aphasia is a language disorder that occurs when associative fibers connecting cortical speech centers are damaged.

Anatomical features of the lesion:

Arcuate fasciculus — a branch of the superior longitudinal fasciculus that loops around the posterior end of the lateral (Sylvian) sulcus.
Subcortical white matter — the level through which the arcuate fasciculus runs within the hemisphere.
Connected structures — fibers connecting the speech centers of the frontal and temporal lobes (Broca's and Wernicke's areas).

Is a patient with Broca's motor aphasia able to produce any sounds?

Yes, vocalization is preserved. The patient is able to shout and produce isolated articulated or non-articulated sounds, but cannot utter 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 a concurrent disorder in Wernicke's sensory aphasia.

What is the mechanism underlying the development of sensory aphasia?

It is based on a disruption of the systemic mechanisms of the action result acceptor. The patient loses the ability to evaluate the achieved result of their mental activity, turning their speech into an incoherent stream.

Go deeper

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 silent reading