Human declarative memory and the medial temporal lobe : evidence from patients with medial temporal lobe lesions

The medial temporal lobe supports declarative memory, the capacity to consciously recollect facts and events. This capacity has traditionally been thought to be separable from other perceptual and cognitive functions, as patients with medial temporal lobe lesions exhibit circumscribed impairment in declarative memory. Several current issues surrounding the organization of memory and the medial temporal lobe were addressed in three separate studies. The first study tested whether the medial temporal lobe is necessary for visual perception. Patients with medial temporal lobe damage exhibited intact visual perception, even when perception was challenged with difficult discriminations. The second study tested whether a new measure of working memory (distraction) that is independent of a traditional measure of working memory (performance of memory-impaired patients with medial temporal lobe damage), would support the long-standing idea that working memory is independent of the medial temporal lobe. The finding was that the method of distraction corresponded with the traditional measure of working memory (performance of memory-impaired patients) and was consistent with the idea that working memory is independent of the medial temporal lobe. The third study tested whether path integration ability (a form of spatial cognition) is dependent on the medial temporal lobe not only when demands are made on long-term memory, but even when performance can be maintained within working memory. Patients with medial temporal lobe damage succeeded in path integration when they could effectively use working memory and were impaired when working memory capacity was exceed and performance depended on long-term memory. It is concluded that the medial temporal lobe supports long-term declarative memory, and that this capacity is separable from other cognitive function