Effects of Nembutal in Baboons With Frontal Lesions

Abstract

STUDIES CONCERNING the effects of barbiturates on the delayed-response and delayed-alternation performance of primates with frontal lesions have yielded discrepant results. An experiment on four monkeys by Blum et al. (1) failed to confirm the findings of improvement with sedation obtained on two monkeys by Wade (4) and on two baboons by Pribram (2). Two consistent differences among the experimental ,conditions employed in these studies have been noted by Blum and co-workers. Their animals were tested late, two at six months and two at two years postoperatively, and all scored significantly above chance prior to injection of the drug. In contrast, Wade's and Pribram's animals were tested early, three months postoperatively, and performed at only a chance level before drug administration. Blum and co-workers suggest that in the latter animals Nembutal may have hastened an improvement which would have occurred without the use of sedatives if sufficient time and training had been allowed following operation. To test this hypothesis, an experiment on the effects of Nembutal was performed on a group of baboons who had received six months of intensive postoperative training on delayed-response and delayed-alternation problems. At the end of this period, which was comparable to that allowed two of the monkeys studied by Blum and co-workers, the delayed-alternation scores of half the animals were at a chance level and of the other half at a level significantly above chance. A finding of improvement with sedation., par-ticuIarly in those animals who were already performing reliably better than chance, would be inconsistent with the interpretation advanced by Blum et al. METHODS Six baboons (Papio papio) were used in this experiment. All had been subjects in an

Analysis of the effects of frontal lesions in monkey: II. Variations of delayed response.

“…This striking achievement of frontal operates in a delay situation differs from that obtained with experimental manipulations which have been attempted in the past, in that criterion performance was quickly established in all operates. Elimination of interference factors during delay (4), use of predelay reinforcement (1), and injection of barbiturates (6,8) have not consistently improved performance l.o a control level; and in most instances, the improvement that did occur appeared only after lengthy training. In the cue-and-responsevaried problem described in the present study, all frontal operates attained a level of 90 per cent correct in less than 250 trials, and they continued to perform well above chance with relatively long intratrial delays.…”

The Neuropsychology of Attention

“…Furthermore, performance can be facilitated by increasing the salience of the cues used during the learning procedure, a finding indicating that attentional factors account for much of the memory dysfunction. If the level of hyperactivity and nonrelevant motor behaviors is reduced, an improvement in task performance can also be obtained (Mishkin, Rosvold, & Pribram, 1953;Pribram, 1950).…”

Brain damage and the overlearning reversal effect

“…The findings in these studies would suggest that the frontal cortex is in some way involved with higher order learning, or with a general factor which is essential for good discriminative performance under difficult conditions (Brush, Mishkin, & Rosvold, 1964). The deficits displayed by these animals may, for example, be due to increased distractability, difficulties in attention span, or problems in overcoming spontaneous preferences (Brush et al, 1961;Maher, 1955;Malmo, 1942;Mishkin, Rosvold, & Pribram, 1953). The large number of perseverative errors and position habits displayed by the animals in this group would be consistent with such an interpretation.…”