Correct Answer: C. Difficulty in identifying known faces
Prosopagnosia (from Greek "prosopon" = face, "agnosia" = failure to know) is a specific form of visual agnosia characterized by the inability to recognize familiar faces despite intact visual acuity and general cognitive function. The condition results from bilateral lesions in the fusiform gyrus (particularly the fusiform face area, FFA) and adjacent ventromedial temporal regions, which are critical for facial recognition. Patients can see the face clearly and describe its features (eyes, nose, mouth are present), but cannot identify who the person is—even their own family members or celebrities. This dissociation is the hallmark: perception is intact, but recognition fails. In Indian clinical practice, prosopagnosia is encountered in patients with posterior cerebral artery (PCA) territory strokes affecting the ventral occipitotemporal cortex, or in degenerative conditions like posterior cortical atrophy. The condition is distinct from other agnosias because it is highly specific to faces; patients typically recognize people by voice, gait, or clothing. Importantly, prosopagnosia does NOT impair consciousness, general object recognition, or insight into deficits—these are preserved, making it a pure recognition disorder rather than a global cognitive or consciousness disturbance.
Why the other options are wrong
A. Failure to identify objects — This describes visual object agnosia (inability to recognize common objects like keys, cups, or tools), not prosopagnosia. While both are agnosias, prosopagnosia is face-specific. Patients with prosopagnosia retain normal object recognition—they can identify a car, a phone, or a book. The NBE trap here is conflating 'agnosia' with 'any agnosia,' when the question specifically asks for the definition of the face-recognition variant. B. Impairment of consciousness — Prosopagnosia does NOT affect consciousness or alertness. Patients are fully awake, aware, and oriented. This option confuses prosopagnosia with disorders of consciousness (coma, stupor, delirium) or global cognitive decline. The lesion is in high-order visual cortex, not in reticular activating system or thalamus. This is a classic NBE distractor for students who think 'brain lesion = altered consciousness.' D. Being unaware of one's problems — This describes anosognosia (lack of insight into one's deficits), which is a separate neuropsychological syndrome typically seen with right hemisphere or anterior lesions. Prosopagnosia patients are usually aware they cannot recognize faces—they know something is wrong. This option tests whether students confuse different agnosias and neuropsychological syndromes, a common NBE strategy.
High-Yield Facts
- Prosopagnosia = face-specific agnosia from bilateral fusiform gyrus (ventromedial temporal cortex) lesions; perception intact, recognition fails.
- PCA stroke is the most common acute cause in Indian stroke patients; posterior cortical atrophy (PCA syndrome) is the most common degenerative cause.
- Patients can describe facial features and recognize people by voice, gait, or clothing—dissociation between perception and recognition is diagnostic.
- Consciousness, general object recognition, and insight are preserved—this is NOT a global cognitive or consciousness disorder.
- Covert recognition may occur: skin conductance or heart rate changes when viewing familiar faces, even though conscious recognition fails (detected in research settings).
Mnemonics
PROSO = Face PROSO-agnosia: PROSOpon (Greek for face) + agnosia (failure to know). Literally 'face-blindness.' Use this when you see 'prosop-' in any question—it always refers to faces. 3 Ps of Prosopagnosia Perception intact (can see features), Perception-recognition dissociation (key finding), Posterior cortex lesion (fusiform/ventral temporal). Helps distinguish from other agnosias.
NBE Trap
NBE pairs prosopagnosia with generic 'agnosia' or 'consciousness' to trap students who memorize 'agnosia = brain lesion' without learning the specific definition. The word 'agnosia' itself is a red herring—students must know that prosopagnosia is face-specific, not object-specific.
Clinical Pearl
In Indian stroke units, a patient post-PCA stroke who cannot recognize their spouse despite clear vision and normal alertness is a classic bedside presentation of prosopagnosia. The family often reports, "He can see, he can talk, but he doesn't know who I am"—this dissociation is pathognomonic and immediately localizes the lesion to ventral occipitotemporal cortex.
_Reference: Guyton & Hall Physiology Ch. 58 (Cerebral Cortex); Harrison Principles of Internal Medicine Ch. 27 (Disorders of Consciousness and Cognition)_