Phencyclidine discoordinates hippocampal network activity but not place fields

Abstract

We used the psychotomimetic phencyclidine (PCP) to investigate the relationships between cognitive behavior, coordinated neural network function and information processing within the hippocampus place cell system. We report in rats that PCP (5mg/kg i.p.) impairs a well-learned hippocampus-dependent place avoidance behavior in rats that requires cognitive control, even when PCP is injected directly into dorsal hippocampus. PCP increases 60-100 Hz medium gamma oscillations in hippocampus CA1 and these increases correlate with the cognitive impairment caused by systemic PCP administration. PCP discoordinates theta-modulated medium and slow gamma oscillations in CA1 local field potentials (LFP) such that medium gamma oscillations become more theta-organized than slow gamma oscillations. CA1 place cell firing fields are preserved under PCP but the drug discoordinates the sub-second temporal organization of discharge amongst place cells. This discoordination causes place cell ensemble representations of a familiar space to cease resembling pre-PCP representations, despite preserved place fields. These findings point to the cognitive impairments caused by PCP arising from neural discoordination. PCP disrupts the timing of discharge with respect to the sub-second timescales of theta and gamma oscillations in the LFP. Because these oscillations arise from local inhibitory synaptic activity, these findings point to excitation-inhibition discoordination as the root of PCP-induced cognitive impairment.\n\nSIGNIFICANCE STATEMENTHippocampal neural discharge is temporally coordinated on timescales of theta and gamma oscillations in the local field potential, and the discharge of a subset of pyramidal neurons called \"place cells\" is spatially organized such that discharge is restricted to locations called a cells \"place field.\" Because this temporal coordination and spatial discharge organization is thought to represent spatial knowledge, we used the psychotomimetic phencyclidine (PCP) to disrupt cognitive behavior and assess the importance of neural coordination and place fields for spatial cognition. PCP impaired the judicious use of spatial information and discoordinated hippocampal discharge, without disrupting firing fields. These findings dissociate place fields from spatial cognitive behavior and suggest that hippocampus discharge coordination is crucial to spatial cognition.