Proactive interference in patients with amnesia resulting from anterior communicating artery aneurysm

Diencephalic and temporal amnesics display an excessive sensitivity to proactive interference (PI) in memory tasks of the AB/AC kind. There exists considerable controversy about the nature of this sensitivity to PI. Moreover, it is an open question whether such sensitivity to PI is an obligatory feature of amnesia, or rather an incidental result of frontal damage often reported in amnesics. This question was reexamined by enrolling patients with an operated aneurysm of the anterior communicating artery (ACoA) and matched controls for an AB/AC learning task of two lists of 12 paired-associate words. It appeared that ACoA patients, like diencephalic and temporal amnesics, did indeed display a marked sensitivity to PI when compared to normals (Exp. I), even when performance of both groups in the learning of the first list was equated (Exp. II). The distribution of errors made in learning the second list, as well as the correlations between performance in learning the second list and a Stroop test, suggest that sensitivity to PI in ACoA amnesics could be the consequence of an inability to suppress irrelevant information at retrieval due to defective inhibitory attentional mechanisms. Complementary data collected in a small sample of Korsakoff's amnesic subjects are also described.