Characteristics of stimulation-induced feeding sites in the sulcal prefrontal cortex

Double pulse tests were used to infer the refractory periods of the substrate underlying stimulation-induced feeding in the sulcal prefrontal cortex of the rat. Eleven sites were examined, of which five supported the behaviour at currents of 250 to 400 microA; pulse duration was 100 microseconds. The average profile indicates a recovery function that begins at 0.5 ms and ends at 3.0 ms, with no apparent contribution from local potential summations. The mean effectiveness value corresponding to the asymptotic portion of the curves was 91%. These results suggest that there is substantial overlap in the excitability of neurons underlying stimulation-induced feeding in the sulcal prefrontal cortex and that reported for the medial forebrain bundle, but unlike the latter structure, there is no evidence of self-stimulation from the same sulcal prefrontal cortex placements. Response rates were collected for a maximum of 21 days from each of the cortical sites at which feeding was recorded and at the same currents used to evaluate the refractory periods underlying stimulation-induced feeding. The rates averaged between 0 and 3 responses per minute whether the current was available or not. These data represent the first demonstration of a site that supports stimulation-induced feeding in the absence of brain stimulation reward, at least at these specific placements and stimulation parameters.