An analysis of the mean theta phase of population activity in a model of hippocampal region CA1.

In a recent study, Manns et al. (2007) showed that CA1 population spiking activity differs in mean phase between conditions of exposure to stimuli of varying levels of familiarity. Here, we provide an analysis of a computational model of the hippocampus from Hasselmo et al. (2002) to examine how an animal's history of exposures to stimuli affects CA1 population activity. We show how the model can reproduce the major findings from the study by Manns et al. Specifically, we show that differences in direction and magnitude of the mean phase of population activity between two stimuli in the model depend on the order of presentation of the stimuli and the duration of exposure during each presentation. The analyses also reveal that the model's learning rule results in stability and normalization of synaptic weights and show how dysfunction of neuromodulatory systems might lead to epileptic or amnestic type conditions.