Operant conditioning of amygdala spindling in the free chimpanzee.

Summary The aims of this paper are: (a) to show the practicality of 2-way radio communication between the brain of free animals and laboratory instrumentation; (b) to demonstrate the principle that telemetered brain waves can be pattern recognized by a computer in order to trigger contingent radio-stimulation of a determined area of the brain; and (c) to investigate amygdala spindling in the chimpanzee. The experiments were performed on a juvenile male chimpanzee equipped with intracerebral electrodes, stimoceiver for multichannel EEG telemetry and brain radio-stimulation, plus mobility recordings belt. Some of the studies were carried out with the animal completely free on a small artificial island in the company of 3 other chimpanzees. Throughout 24 h, peaks of mobility corresponded with peaks of spindle power when the animal was inside a building, and not when he was on the artificial island. In this case spindling peaks increased correspond with periods of grooming. Sensory excitation increased amygdala spindling. Visual sensation habituated while olfactory testing did not, suggesting a role of amygdala spindling in olfactory functions. Automatic radio-stimulation of the reticular formation contingent on amygdala spindling suppressed ipsilateral spindling to less than 1% of control value. Bilateral reticular stimulation produced bilateral suppression of spindling accompanied by decreased motivation and behavioral placidity. The same amount of reticular stimulation lacking the contingency factor did not modify amygdala spindling.