Abstracts

Rationale: To better understand the functional aspects of memory deficits observed in temporal lobe epilepsy, we investigated the temporal coding of hippocampal neurons, i.e. the way they process information in time, as well as their firing relationship with brain oscillations. In the rat hippocampus, pyramidal cells encode the temporal sequence of the locations visited by the animal in a compressed time window relevant for synaptic plasticity. This encoding is believed to be accomplished through phase precession, a phenomenon whereby neuronal action potentials are linked to the ongoing theta oscillation.Methods: Hippocampal single unit activity and EEG were recorded in rats running back and forth on a linear track for food reward. Two months before the recordings, rats underwent status epilepticus by i.p. injection of lithium pilocarpine.Results: We found that both phase precession and the compression of temporal sequences were significantly altered in epileptic rats. In addition, the same animals were markedly impaired in the water maze spatial memory task.Conclusions: These results show that the temporal coding and the oscillation-related firing of hippocampal neurons are altered in a pathological state associated with memory impairment.