Differential learning-related changes in theta activity during place learning in young and old rats.

The participation key role of the hippocampus in place learning ability as well as the decline of cognitive functions associated with aging, have been established in experimental and clinical studies. On the other hand, hippocampal theta activity has been proposed as a part of the cerebral phenomena underlying hippocampal-dependent learning processes. In the present study, the relative power of low, high, and maximal frequency components of hippocampal CA1 theta activity during a 6-day training period (four daily trials; basal, searching, and platform stages) and the probe trial of a place learning paradigm (Morris water maze) were analyzed in young and aged rats. An increase in high frequency, and a decrease in low frequency relative power of theta activity during the searching stage, which were correlated with shorter swimming path lengths and predominant hippocampal-dependent allocentric strategies, were observed in young rats as became trained in place learning and memory tasks, in the Morris water maze; while, under these conditions, no changes in theta activity and predominant non hippocampal-dependent egocentric strategies occurred in the old rats. Besides, an overall (theta activity recorded during the three behavioral stages) increase of low frequency and an overall decrease of high frequency theta bands in the old group as compared to the young group were observed. These electrophysiological data suggest that old rats process information relevant for cognitive functions in a different manner, possibly leading to the use of different learning strategies, than young rats.