Theta Rhythms Coordinate Hippocampal–Prefrontal Interactions in a Spatial Memory Task
(A) mPFC tetrodes targeted deep layers of prelimbic and infralimbic cortices. Photograph shows a typical lesion site (triangle) marking the tip of a tetrode. The partial brain section is superimposed on a schematic of a coronal section taken 3.7 mm rostral of bregma, showing the boundary of the prelimbic cortex (denoted by PrL).
(B) Spike amplitude clusters for a typical mPFC tetrode. The cluster in red was for the neuron shown in D. The points in the six panels plot extracellular-action-potential amplitude on wire 1 of the tetrode versus wire 2, wire 1 versus wire 3, etc.
(C) and (D) Activities of a typical CA1 place cell and two mPFC pyramidal cells, respectively (see also Figure S2). The upper mPFC neuron in D was recorded simultaneously with the CA1 neuron in C. Spikes were binned into positional pixels, and mean pixel firing rate was color-coded to generate the firing-rate maps on the left. Graphs show corresponding inter-spike interval distributions (10 Hz marked by the blue line; note logarithmic time scale). Waveforms show averaged extracellular action potentials recorded on a single wire of each tetrode (horizontal and vertical scale bars, 1 ms and 400 μV, respectively).
(E) Overlap in the distributions of spatial information carried by spikes from CA1 (black) and mPFC (blue) populations.