Vascular disorders

Two types of vascular disorder can particularly affect memory, as opposed to general cognitive functioning, namely thalamic infarction and subarachnoid haemorrhage.

In an elegant CT scan study, von Cramon et al.{39) showed that damage to the anterior thalamus was critical in producing an amnesic syndrome. When the pathology was confined to the more posterior regions of the thalamus, memory function was relatively unaffected. The anterior region of the thalamus is variably supplied by the polar or paramedian arteries in different individuals: both of which are, ultimately, branches of the posterior cerebral artery, that also supplies the posterior region of the hippocampi. When there is a relatively pure lesion of the anterior thalamus, anterograde amnesia without an extensive retrograde memory loss commonly results. However, cases in whom there is also retrograde memory loss, or even a generalized dementia, have been described following thalamic infarction, and this presumably relates to the extent to which thalamic projections are also implicated in the infarction.

Subarachnoid haemorrhage following rupture of a beri aneurysm can result in memory impairment, whether the anterior cerebral or posterior cerebral circulation from the Circle of Willis is involved. Most commonly described in the neuropsychological literature have been ruptured aneurysms from the anterior communicating arteries, because these affect ventromedial frontal structures and the basal forebrain. Gade (31> has argued that it is whether or not the septal nuclei of the basal forebrain are implicated in the ischaemia which determines whether a persistent amnesic syndrome occurs in such patients. Others have attributed the florid confabulation, which these patients often exhibit, to concomitant ventromedial damage. (32>

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