Abstract
It has been suggested that cases of amnesic syndrome following rupture of an aneurysm of the anterior communicating artery (basal forebrain amnesia) exhibit the following aspects (Damasio et al. 1985). Firstly, patients are able to learn separate stimuli, but cannot properly integrate those differently learned components. Secondly, patients do not develop a time-tag for the separate stimuli that they learn. Lastly, cueing strongly benefits recall and recognition, of both anterograde and retrograde memories. But more recently, retrosplenial amnesia was shown to be impaired in acquiring temporal information about new stimuli (Bowers et al. 1988) , thereby suggesting that memory impairment for temporal order may not occur in basal forebrain amnesia alone. In our study, to clarify Damasio's hypothesis, 11 amnesic patients of various types (4 basal forebrain, 5 Korsakoff, 1 retrosplenial, 1 temporal lobe) were examined for memory for temporal order. Results showed that recognition memory and memory for temporal order varied among the basal forebrain amnesia cases, that not only basal forebrain amnesia but also Korsakoff patients lose memory for temporal order, and that retrosplenial amnesia does not cause a decrease in memory for temporal order. Three out of four basal forebrain patients who showed decrease in memory for temporal order had not only basal forebrain lesion, but also orbitofrontal cortex lesion. Therefore, memory disorders for temporal order may require an orbitofrontal cortex addition to the basal forebrain lesion.
