Definition and types of agnosia. Anosognosia, spatial agnosia, prosopagnosia. Gerstmann’s syndrome
1. Big picture
Agnosia is a higher cortical disorder: the patient can see, hear, or feel the stimulus, but cannot recognize its meaning. This is not a problem of the eye, ear, peripheral nerve, muscle power, or basic consciousness. It is a problem of sensory association cortex, especially in the parietal, temporal, and occipital association areas.
For the exam, the most important logic is:
Primary sensation is intact → perception reaches the cortex → but the patient cannot attach meaning to it.
So agnosia is different from:
| Disorder | Main problem |
|---|---|
| Blindness/deafness/sensory loss | Primary sensory input is impaired |
| Aphasia | Language comprehension or expression is impaired |
| Apraxia | Motor planning is impaired despite preserved strength |
| Agnosia | Recognition is impaired despite preserved basic sensation |
| Dementia/delirium | Global cognition or attention is impaired |
The examiner usually wants you to know: what agnosia means, which types exist, how to test them, and where the lesion is.
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