Intensity generalization with positively reinforcing intracranial stimulation.

Rats were implanted with electrodes in positively reinforcing areas of the septal region or medial forebrain bundle. Rewarding brain stimulation, at an intermediate intensity, was established as a conditioned stimulus for a shuttle box avoidance response. When the avoidance response was learned, test trials were run using stimulation intensities 10 and 20 μa above or below the original CS intensity. Later, self-stimulation rates were collected at each current level employed in the generalization tests. The degree of stimulus intensity generalization correlated highly with changes in “reinforcement strength” demonstrating that the latter can be a salient perceptual dimension.