FIGURE 1.

Electrophysiological identification of striatal single-units responding to cortical stimulation: medium-sized spiny projection neurons (MSNs) and fast-spiking interneurons (FSIs). (A) Traces show typical cortically-evoked responses from isolated MSNs (left) and FSI (right). Ten consecutive overlaid responses are shown. Insets show a single event (1 epic) representative of the cortically-evoked responses. FSIs often discharge trains of spikes in response to cortical stimulation, whereas MSNs typically fire in single spikes. (B) Left: Representative waveform of a cortically-evoked spike from an antidromically-identified striatonigral MSNs (SNr+MSNs). Middle: Representative waveform of a cortically-evoked spike from an electrophysiologically-identified FSI. Right: Overlay of MSN and FSI waveforms showing the differences in waveform duration between the cell types. (C) Left: All or none current intensity threshold for activation (responses are never observed at sub-threshold current intensities, but always observed at supra-threshold currents). Right: responses always exhibit a fixed latency to SNr stimulation. Ten consecutive overlaid responses are shown. (D) Constant fixed latency firing during high frequency antidromic stimulation.