VISUOSPATIAL SHORT-TERM RECOGNITION MEMORY AND LEARNING AFTER TEMPORAL-LOBE EXCISIONS, FRONTAL-LOBE EXCISIONS OR AMYGDALO-HIPPOCAMPECTOMY IN MAN

Three groups of neurosurgical patients with temporal lobe excisions, frontal lobe excisions or unilateral amygdalo-hippocampectomy were assessed on a computerized battery of tasks designed to investigate visuo-spatial short-term recognition memory and learning. A double dissociation is reported between deficits of pattern recognition memory and spatial recognition memory which were observed in the two posterior groups and frontal lobe patients, respectively. In addition, both the temporal lobe and amygdalo-hippocampectomy patients were also impaired on a delayed matching-to-sample paradigm whilst frontal lobe patients performed at an equivalent level to controls. Finally, whilst the impaired performance of the three groups was indistinguishable on a test of paired-associate learning, quite different patterns of deficit were observed on a test of spatial working memory. These results are discussed with reference to recent suggestions that visual recognition memory is mediated by a neural system which includes, as major components, the inferotemporal cortex, the medial temporal lobe structures and particular sectors of the frontal lobe, and are compared to previous findings from patients with idiopathic Parkinson's disease and dementia of the Alzheimer type.