Post-stimulation excitability of diencephalic self-stimulation neurons.

We used the double-pulse technique with moveable electrodes to estimate the refractory periods of self-stimulation neurons within the rat's dorsal diencephalon and surrounding areas. Refractory period estimates varied substantially depending on the site of stimulation. For some sites, recovery from refractoriness was noted at post-stimulation intervals as short as 0.5 ms, an estimate similar to that reported for the MFB axis and the dorsal raphe and periaqueductal grey. The longest recovery intervals were similar to those reported for the prefrontal cortex, caudate, and substantia nigra. Step-like recovery (believed to indicate the presence of neural populations with non overlapping refractory periods) was also noted in several sites. The large range of recovery intervals found in the present study may suggest that the diencephalon plays an integrative role for rewarding signals arriving from various brain areas.