Glucose effects on firing rate of neurons of the locus coeruleus: another attempt to put memory back in the brain.

After a generation of research into the biological mechanisms of memory, the essential nature of the engram remains as elusive as ever. Many investigators have reorganized their conceptual framework to emphasize the role of physiological responses elicited by a learning experience in modulating memory for that event. This approach has generated a long list of correlations between physiological functions and memory performance. The papers comprising the present section have the common theme of contributing to that list, but the remarkable fact which they emphasize is that these correlations are much greater in the aged rat than in young animals, suggesting that it is a parallel degeneration of several physiological functions which mediate deficits in memory performance.