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. Author manuscript; available in PMC: 2014 Jun 13.
Published in final edited form as: Brain Res. 2007 Apr 25;1156:46–58. doi: 10.1016/j.brainres.2007.04.053

Figure 5. Input/output functions of IC-evoked post-stimulus spike discharges (ICPSDs): Monotonic function of pulse number and stimulus intensity.

Figure 5

(A) The inset shows a representative extracellular recording of a VTA GABA neuron during high-frequency stimulation (10 pulses, 200 Hz) of the internal capsule (IC). VTA GABA neuron spikes not only accompany each IC stimulation pulse, but are elicited for hundreds of msec after the stimulus train has ended. The peri-stimulus histogram shows the average of 12 IC stimulations producing ICPSDs. (B) These representative peri-stimulus spike histograms demonstrate that VTA GABA neuron ICPSDs increase with increasing pulse number. (C) This graph summarizes the effects of pulse number on ICPSDs. Fitting these data with linear regression analysis reveals a slope of approximately 4, indicating that 4 discharges occur for every pulse. Moreover, a threshold of 4-5 pulses at half-maximum current intensity is needed to induce discharges. (D) This graph summarizes the effects of pulse number and current on VTA GABA neuron ICPSDs. The goodness of linear fit is shown next to each of the pulse # isobars.