[Disorders of learning and memory in focal cerebral tissue lesions]

Memory and learning in man depend on complex cognitive systems, and thus on efficient associative information stores in different neocortical areas of our brain. In addition, phylogenetically older, "limbic" brain structures are needed, in order to manage these huge accociative stores in our telencephalon. This "operating system" manages memory and learning capabilities considering the "milieu interne", and especially biological and individual priorities. Our contribution attempts to sketch the anatomical outlines of this limbic operating system. Two interdependent neuronal networks may be of pivotal importance: 1. a medial limbic loop with Papez circuit as the main structure, and 2. a basolateral limbic loop including the amygdala, the subcallosal area (and the septum verum?) as well as the mediodorsal thalamic nucleus. Based on the anatomical evidence of (largely) selective, i.e. focal brain lesions the likelihood for all these relay stations as memory-related structures is discussed. Our working hypothesis assumes that combined, bilateral lesions of both limbic neuronal networks make severe, global and lasting deficits in memory and learning performance fairly likely. The lesion of only one of these limbic loops seems to cause modality-specific deficits. Unilateral lesions of the retrocommissural hippocampal formation may also account for lasting amnesia.