Poststimulation excitability of ventral pallidum self-stimulation neurons

The degree of neural recovery from refractoriness was inferred in rats self-stimulating with pairs of pulses in the ventral pallidum. The prerecovery intrapair interval varied from 0.5 to 1.0 ms, depending on brain site. At some sites, recovery reached its maximum within less than 1.6 ms whereas, at the majority of sites, a substantial amount of recovery occurred at delays longer than 1.2 ms. The shortest recovery estimates were not fundamentally different from those obtained from sites lying along the medial forebrain bundle. The longest recovery estimates were similar to those obtained from cortical and basal forebrain sites. The differences in recovery noted between sites and the presence of step-like patterns in the recovery curves suggest the presence of neural heterogeneity within the ventral pallidal substrates of reward.