Reports of others that animals will seek electrical stimulation of certain regions of the central nervous system are confirmed. A method is presented whereby these ‘motivational’ aspects of central stimulation can be analyzed and shown to be capable of change by training and to have a different threshold from the animal's ‘perception’ of this stimulation. Cats were trained to press a bar to receive pellets of meat. When each bar-press was accompanied by stimulation through electrodes implanted in the caudate nucleus or anterior hypothalamus, the animals continued pressing. If the press was paired with stimulation of the septal or habenular regions, pressing was abolished. Foot-shock paired with pressing also produced avoidance but pairing with a startling buzzer did not. Caudatal stimulation of 0.2 ma, 50/sec., 2-msec. pulses, was adequate as conditional stimulus to establish conditioned foreleg flexions to avoid an electric shock. Subsequent to the latter training two animals would no longer press the bar if pressing resulted in caudatal stimulation. Other cats would press as often as 1000 times in a 20-minute period to obtain caudatal stimulation if it were allowed at rapid rates and intensities five times that required to evoke conditioned flexion reflexes. The evidence suggests that avidity develops for stimulation of certain neural structures only if the stimulus is adequate to initiate some form of excessive, seizure-like activity.
Which elements are excited in electrical stimulation of mammalian central nervous system: A review