Behavioral parameters of the spatial memory correlate with the potentiation of the population spike, but not with the population excitatory postsynaptic potential, of the CA1 region in rat hippocampal slices.

Rats were tested for spatial performance in a water maze with further in vitro investigation of short-term and long-term potentiation (STP and LTP) in the CA1 region of the hippocampus. Recordings of the population spike in stratum pyramidale and population excitatory postsynaptic potential (EPSP) in stratum radiatum were made with extracellular electrodes after stimulation of the radiatum and oriens inputs in the region. It was found that for both inputs, STP and LTP of the population spike amplitude correlated with behavioral parameters of memory: latency of reaching the hidden platform (escape latency) and percent of time which the animal spent inside the quadrant with the platform. Potentiation of the initial slope of EPSP, in contrast, did not correlate with these parameters. These data support the hypothesis that hippocampal LTP may underlie spatial performance and show that potentiation of the output characteristic of the hippocampus (population spike), but not of the EPSP, is a physiological correlate for spatial memory.