The effect of unilateral and bilateral frontal lobe extirpation on the behavior of monkeys.

Abstract

Two cebus (Cebus capucina) monkeys (one died before conclusion of the expt., the remaining animal) and 2 rhesus (Macaca mulatta) monkeys were ob- served in an investigation of the influence of unilateral and bilateral prefrontal lobectomy upon the following previously learned tasks (1) A simple black-white discrimination (animal trained to select black stimulus patch when black-white were presented in the form of small squares). (2) A complex discrimination function (animals required to select the black stimulus patch when the stimuli were small; the white patch when they were larger; they were tested on large and small stimulus patches of other shapes to determine extent of generalization). (3) Instrumentation (animal trained to use one rake in order to obtain food, or to obtain another rake which in turn could reach either food or a longer rake, etc. This was done first with a single platform, then modified so that the animal obtained the first rake at one platform, the next from another, the next from the first, etc., until food was finally obtained. Finally 3 platforms were introduced). Unilateral injury had little or no effect upon either the simple or complicated visual discrimination habit, although bilateral injury resulted in loss of the simpler habit which was relearned with difficulty, while the complex discrimination habit was not relearned in 1000 trials. Unilateral injury had no effect on the single platform instrumentation problem, although some disturbance was noted in the more complex stages of the double and triple platform tasks. Bilateral removal had no effect on the single platform problems, but resulted in serious disturbance of the more complex problems, the triple platform habit never being relearned, and "only the simplest levels of the double platform habit" being retained.