Some physical and pharmacological factors affecting delayed response performance of baboons following frontal lobotomy.

Abstract

HUNTER (13) devised the delayed response test as a method to evaluate, in animals, the variables intervening between the exposure of the subject to a stimulus configuration and that response of the subject which alters the stimulus configuration. Essentially, the method interposes a time interval between exposure and opportunity for such response. The investigations of Jacobsen and co-workers (15) demonstrated that the ability to perform adequately on delayed response can be used as an index of frontal lobe function in monkeys. These studies were interpreted as indicating that the frontal' cortex is essential to bridging the temporal gap interposed in the test situation. On the other hand, Nissen (29) and his co-workers interpreted their studies to indicate that delayed response performance is difficult for operated animals because of some failure which occurred at the time of stimulus presentation. Support of this viewpoint comes from Lashley (23) who, in describing the conditional reaction, pointed out that performance of this test depends on the animal's ability to take cognizance of the context in which the discriminanda appear. The failure of animals with frontal lesions to perform this test (34) adds credence to the view that such lesions limit an animal's ability to perform any test whenever performance depends on the animal's reaction t to an element in the stimulus configuration which is. not immediately altered by this reaction. Malmo (28) tested these alternative suggestions as to the temporal locus of the failure, and, using the indirect technique, demonstrated that if distractions are kept at a minimum during the test procedure, performance of the delayed response test is possible for frontal lobectomized animals. When distractions were interposed during the delay period the animals failed. These experiments again shifted attention to the delay period as the critical one for interpretation of frontal lobe function. Wade (32) sought to reduce distractibility by pharmacological means. She used barbiturates to