BRAIN STIMULATION, EXPERIENCE, AND BEHAVIOR

An apparatus was constructed for the electrical stimulation of the brain by a modified radio frequency carrier wave to a receiving unit fastened subfascially over the cranium of 8 rhesus monkeys (4 with brain lesions) and 6 cats. The uni-or bipolar electrodes were stereotactically implanted in the median forebrain bundle or the septal, thalamic, hypothalamic or mesencephalic reticular areas. Animals with varied preceding experiences were subjected to conflict-inducing air blast or shock stimuli while discriminating external (tone, light) vs. internal (brain stimulation) cues, and developed adaptational conflicts characterized by the disruption of learned skills, persistent and generalized aversions, organic dysfuctions, loss of body weight and other deviations of conduct. All behavior patterns were evaluated on highly reliable rating scales. Our results were as follows:

1. "Threshold" stimulation of various regions of the brain did not interfere with previously established auditory-visual discriminations.

2. Intracranial self-stimulation (ICS) was variously ignored, avoided, or sought for prior to its establishment as a discriminative cue.

3. The response patterns to ICS were not significantly correlated with anatomical location or species (except that cats uniformly ignored it) but were influenced by prior preferences, and were reversible as the externally applied electrical brain stimulation (EBS) became differentially meaningful.

4. All animals readily learned to discriminate liminal EBS from a tone or light signal, but facility in this varied directly with the general adaptability of each animal.

5. Discrimination of brain stimulation was retained up to 4 months without practice and could be transferred immediately to the interruption of a continued squaredpulse stimulation.

6. Adaptational conflicts produced generalized "neurotic" behavioral deviations which included "conditioned anxiety" reactions to EBS, but these effects again varied with the length and adequacy of each animal's laboratory adaptation.

7. Stimulus generalization gradients for EBS frequency were similar in animals with different brain lesions, but varied greatly with each animal's previous experiences.

8. Chemotherapy with Ritalin and Librium failed to mitigate behavioral deviations and showed no essential interactions with EBS.