Correct Answer: D. Fluent
The posterior superior temporal gyrus (Wernicke's area and surrounding temporal cortex) is the primary language comprehension zone. Lesions here produce fluent aphasia — characterized by preserved speech fluency, normal articulation, and intact prosody, but with profound comprehension deficits and semantic paraphasias. The patient speaks in long, grammatically intact but meaningless sentences ("jargon speech"). Repetition is impaired because the lesion disconnects auditory input processing from motor speech output. This contrasts sharply with Broca's area (inferior frontal) lesions, which cause non-fluent aphasia with effortful, agrammatic speech but relatively preserved comprehension. The posterior temporal location is critical: damage here spares the motor speech pathways (arcuate fasciculus and Broca's area remain intact), allowing fluent output despite severe comprehension impairment. In Indian clinical practice, fluent aphasias are often underrecognized because patients appear to speak normally until content is analyzed. The Wernicke-Broca-arcuate fasciculus circuit is the anatomical foundation for understanding aphasia classification in neurology examinations.
Why the other options are wrong
A. Anomic — Anomic aphasia (word-finding difficulty with preserved fluency and comprehension) results from lesions in the angular gyrus or temporal-parietal junction, not the posterior superior temporal gyrus. While anomia may be present as a feature in Wernicke's aphasia, the defining characteristic of posterior temporal lesions is fluent speech with comprehension deficit, not isolated naming difficulty. Anomic aphasia is the mildest form and does not match the severity profile of posterior temporal damage. B. Non fluent — Non-fluent (Broca's) aphasia arises from lesions in the inferior frontal gyrus (Broca's area), not the posterior superior temporal gyrus. Non-fluent aphasia is characterized by effortful, agrammatic, telegraphic speech with relatively preserved comprehension. The posterior temporal location specifically preserves motor speech pathways, resulting in fluent output — the opposite of non-fluent aphasia. This is a classic anatomical trap in aphasia classification. C. Conduction — Conduction aphasia results from lesions of the arcuate fasciculus (white matter tract connecting Broca's and Wernicke's areas), not the posterior superior temporal gyrus itself. Conduction aphasia presents with fluent speech and relatively preserved comprehension, but markedly impaired repetition. Posterior temporal gyrus lesions produce fluent speech with impaired comprehension and impaired repetition, making them Wernicke's (fluent) aphasia, not conduction aphasia. The anatomical distinction is critical.
High-Yield Facts
- Posterior superior temporal gyrus = Wernicke's area: lesions here produce fluent aphasia with comprehension deficit and semantic paraphasias.
- Fluent aphasia hallmark: preserved speech rate and articulation, but meaningless content ('jargon speech') and impaired comprehension.
- Repetition is impaired in Wernicke's aphasia because the lesion disrupts the sensory-motor language circuit despite intact motor output pathways.
- Broca's area (inferior frontal) lesions produce non-fluent aphasia — the opposite of posterior temporal lesions — with effortful, agrammatic speech.
- Arcuate fasciculus lesions cause conduction aphasia (fluent + preserved comprehension + impaired repetition), distinct from Wernicke's aphasia.
- Anomia is a feature, not a defining characteristic: anomic aphasia is a separate entity arising from angular gyrus/temporal-parietal lesions.
Mnemonics
WBAF Circuit Wernicke (posterior temporal) → comprehension; Broca (inferior frontal) → production; Arcuate Fasciculus → connection. Wernicke lesion = fluent but don't understand. Broca lesion = understand but can't speak fluently. Fluent vs Non-Fluent Back (Wernicke) = Fluent (speaks easily, doesn't understand). Front (Broca) = Non-fluent (understands, struggles to speak). Posterior temporal = back = fluent.
NBE Trap
NBE often pairs "posterior temporal" with "comprehension deficit" to lure students into choosing anomic or conduction aphasia, which also involve temporal regions but have different clinical profiles. The key discriminator is that posterior superior temporal gyrus specifically produces fluent speech with comprehension loss — not isolated naming difficulty or preserved comprehension.
Clinical Pearl
In Indian hospital settings, patients with Wernicke's aphasia are often initially misdiagnosed as "confused" or "delirious" because they speak fluently and appear alert. The key bedside finding is asking them to point to objects or follow commands — they cannot, revealing the comprehension deficit. This distinction is critical for localizing the lesion and ruling out metabolic encephalopathy.
_Reference: Harrison Ch. 27 (Aphasia); Robbins Ch. 28 (CNS pathology); Guyton & Hall Ch. 57 (Language)_