Basic Neurosciences · Paper A
Aphasias and language localisation
Aphasia (a language disorder from brain damage, not a problem with the mouth or tongue) differs strikingly depending on which language centre is damaged. Two patients after a stroke show the contrast clearly: one speaks in short, effortful, broken phrases but understands everything said to them, while the other speaks fluently and confidently yet the words make no sense and they cannot understand questions. That contrast alone tells you which brain region is damaged.
Broca's (expressive) aphasia comes from damage to the inferior frontal gyrus. It gives non-fluent, effortful, telegrammatic speech with preserved comprehension, and the patient is aware of the deficit and often frustrated. Wernicke's (receptive) aphasia comes from damage to the superior temporal gyrus instead. It gives fluent but empty, paraphasic (word-substituting) speech, with impaired comprehension and poor insightA person's awareness and understanding that they are unwell and need help.Read more → into the problem. Conduction aphasia (arcuate fasciculus damage) gives fluent speech and good comprehension but disproportionately poor repetition, e.g. a patient who converses normally but stumbles badly when asked to repeat a sentence word for word. Testing repetition specifically in a fluent, comprehending patient is therefore the discriminating step once fluency and comprehension have already been assessed.
A fresh doctor might try to memorise "Broca's equals expressive, Wernicke's equals receptive" as a fact to recall. What actually gets tested is whether you can extract three variables (fluency, comprehension, and repetition) from a patient's speech and use them to localise the lesion, without ever being told the anatomical location directly. Hold the phrase THREE VARIABLES, ONE LOCALISATION through every section below.
Aphasia is an acquired language disorder caused by brain damage, not a problem with the mouth, tongue, or vocal cords themselves: the machinery of speech works, but the language content is disrupted. Language is governed by the dominant hemisphere, usually the left, and different aphasia subtypes localise to different parts of that hemisphere depending on which combination of fluency, comprehension, and repetition is affected.
A common mistake is assuming poor repetition always means conduction aphasia. Global aphasia also impairs repetition, but alongside severe deficits in both fluency and comprehension, whereas conduction aphasia impairs repetition in relative isolation with fluency and comprehension both intact. Conversely, a patient with impaired fluency or comprehension but genuinely SPARED repetition should point toward a transcortical variant, not toward Broca's or Wernicke's aphasia.
Two patients after a stroke can sound completely different: one speaks in short, effortful, broken phrases but understands everything said to them, while the other speaks fluently and confidently, yet the words make no sense and they cannot understand questions. Testing fluency (is speech effortful or flowing), comprehension (can they follow instructions), and repetition (can they repeat a spoken phrase back accurately), in that order, is the systematic way to localise any aphasia.
Broca's (expressive) aphasia comes from damage to the inferior frontal gyrus and produces non-fluent, effortful, telegrammatic (short, grammatically stripped) speech with comprehension preserved; the patient is typically aware of the deficit and frustrated by it. Wernicke's (receptive) aphasia comes from damage to the superior temporal gyrus instead and produces fluent but empty, paraphasic (word-substituting) speech, with impaired comprehension and, notably, poor into the problem: the patient may not realise their speech makes no sense.
Conduction aphasia, from damage to the arcuate fasciculus (the white-matter tract connecting Broca's and ), gives fluent speech and good comprehension but disproportionately poor repetition, for example a patient who converses normally but stumbles badly when asked to repeat a sentence word for word. Global aphasia, from more extensive damage affecting both regions, impairs fluency, comprehension, and repetition together. Transcortical aphasias are the exception to the repetition rule: despite fluency or comprehension deficits resembling Broca's or Wernicke's patterns, repetition is characteristically SPARED, because the arcuate fasciculus itself is undamaged.
Broca's aphasia (non-fluent, comprehension preserved) should not be confused with Wernicke's aphasia (fluent, comprehension impaired): the discriminator is comprehension, not fluency alone, since both can sound abnormal to an untrained listener. Conduction aphasia's isolated repetition deficit should not be confused with the transcortical aphasias' spared repetition despite other language deficits. Global aphasia, affecting all three variables, should not be confused with any single-variable-deficit subtype. Aphasia as a whole should also be distinguished from dysarthria (a motor speech problem causing slurred but linguistically normal speech) and from apraxia of speech (difficulty planning the movements for speech despite intact language and intact muscles).
Diagnosis is clinical, built from bedside assessment of fluency, comprehension, and repetition, using standardised aphasia screening tools where available (such as the Frenchay Aphasia Screening Test) and supported by imaging (CT or MRI) to confirm the causative lesion, most often an ischaemic stroke in the dominant middle cerebral artery territory. Naming and reading/writing testing add further detail once the three core variables have localised the broad subtype, and repeat assessment over the following days to weeks helps distinguish a fixed deficit from one that is evolving or resolving.
Management is multidisciplinary: speech and language therapy is the first-line intervention for all aphasia subtypes, alongside treatment of the underlying cause, such as standard stroke management pathways for acute ischaemic stroke (including thrombolysis where eligible), and structured communication support for the patient and family, following standard neurology and NICE stroke-rehabilitation guidance. Early, intensive speech and language therapy in the first few months after stroke is associated with the best functional recovery, which is why referral is prioritised rather than left until later in the rehabilitation pathway.
The high-yield pearl: fluency alone is a trap: always check comprehension before naming a subtype. Vignettes often describe a patient with fluent but nonsensical speech and expect Wernicke's, not Broca's, aphasia to be identified: fluency alone is a common false lead. Another trap gives a patient with normal fluency and comprehension but a striking repetition deficit and expects recognition of conduction aphasia specifically. A further trap describes impaired fluency alongside genuinely preserved repetition and expects the candidate to name a transcortical variant rather than defaulting to Broca's aphasia.
Localise any aphasia by testing three variables in order: fluency, comprehension, repetition. Broca's aphasia (inferior frontal gyrus) is non-fluent with preserved comprehension; Wernicke's aphasia (superior temporal gyrus) is fluent with impaired comprehension; conduction aphasia (arcuate fasciculus) has isolated poor repetition; global aphasia impairs all three; and the transcortical variants are the exception where repetition stays spared despite other deficits. Diagnosis is bedside and clinical, confirmed with imaging, and speech and language therapy is the first-line management for every subtype.