Selective dorsolateral frontal lobe dysfunction associated with diencephalic amnesia.
We report three cases with unilateral thalamic ischemic lesions that resulted in lasting material-specific memory impairments and concomitant selective frontal lobe-related cognitive deficits. In two cases the lesions were limited to the left thalamus, and in the third the right thalamus was involved. These deficits were associated with ipsilateral diencephalic, striatal, and dorsolateral prefrontal hypoperfusion. The damage implicated the ventral anterior nucleus, the mamillothalamic tract, and the rostroventral internal medullary lamina. These findings suggest that medial thalamic damage involving the ventral and rostral sector of the dorsal thalamus will concurrently affect functionally and neurally distinct limbodiencephalic pathways and diencephalic connections with the frontal cortex. A review of the neuropsychological and neuroimaging findings from previously reported cases with vascular lesions of the thalamus further supports this contention. The presence of frontal lobe-related cognitive deficits, though not obligatorily related to the memory problems, may contribute to some aspects of the memory deficits and affect the nature of the memory disorder observed in some cases with diencephalic amnesia.