Chantal Stern, an associate professor of psychology, studies working memory in people using functional magnetic resonance imaging (see also Research Briefs, October 25, 2002, for related studies by Sargent College Professor Gloria Waters). Psychology Professor Howard Eichenbaum studies the brains of rats as they solve complex problems. John White, a biomedical engineer and Michael Hasselmo, a psychology professor, examine the intricacies of working memory on a cellular level.

Recent studies by Hasselmo and his colleague, Angel Alonso, at the Montreal Neurological Institute and McGill University, reveal that contrary to previous expectations, individual neurons in the entorhinal cortex (an area of the brain near the hippocampus) fire single electrical impulses, or spikes, not only when they are activated by sensory input, but for several seconds after sensory input ceases. This sustained neuronal activity indicates working memory, says Hasselmo.

The researchers’ most recent studies reveal that neurons in the deep layers of the entorhinal cortex not only sustain activity, but do so at graded firing rates. If they start firing at five spikes per second (five Hz) they maintain firing at five Hz; if additional input pushes them to seven Hz, they maintain a seven Hz level, and so forth. This ability, says Hasselmo, is important for storing information about continuous dimensions, such as keeping track of compass headings and distant landmarks as you navigate a kayak, for instance.

The researchers are now examining the relationship between sustained neuronal activity and the neurochemical acetylcholine — a substance known to activate neurons but which is depleted in the brains of individuals with Alzheimer’s disease. By better understanding the cellular processes underlying working memory, the researchers hope to find mechanisms that lead to effective treatments for Alzheimer’s disease.

This research was published in the November 14, 2002 issue of the journal, Nature. It can be found online here.

Image: neurons.