Figure 8.

Spatial selectivity and object responsiveness of dorsal subicular neurons. (A) Top left, action potentials from three subicular neurons are shown in red, blue, and green. Top right, the spikes are isolated by principal component clustering, of which two projections (labeled PC1 and PC2) are shown. Bottom, autocorrelogram for a principal neuron recorded during a choice trial. (B) Left, peri-event histograms for two novelty-responsive DS neurons, one on each row, during exploration of familiar and novel objects. Dashed lines indicate the onset of object exploration. Right, Plot of the normalized firing rate (mean ± SEM), 500–1000 ms after the start of exploration of familiar and novel objects for this subset of DS neurons. ^**p < 0.005 (t-test). (C) Firing rate maps of four DS neurons during the sequential stages of the NOR task showing broad place fields with several peaks of firing within the behavioral context. In these top views of the square chamber (30 cm on the side), gray circles indicate the locations of the objects. The color scales (at left of each map) specify the firing rates (spikes per sec) for the units. It is clear that subicular place cells exhibit spatial selectivity that does not appear to be modulated by the presence of objects nor their degree of novelty.