ABSTRACT
The present work, using two intact-brain and two split-brain baboons, investigated the role of forebrain commissures in the performance of a choice-RT task, in which one of two equiprobable left and right visual dots served as stimulus, and the response consisted of a binary choice between hands.
In Experiment 1, it was found that the two split-brain monkeys were unable to carry out the choice task, whereas the two control monkeys reached fairly high accuracy scores.
In Experiment 2, conducted in the two split-brain monkeys, it was shown that their choice inability resulted not from a deficit in some input stage, but clearly from a deficit in the ability to select the response from a bimanual motor repertoire.
A double channel interpretation of this result, which assumed that the deficit was due to the inability of the stimulated hemisphere to prevent its irrelevant competitor from making the erroneous response, was not supported by the results of Experiment 3. In this experiment, while one go signal was dispatched to one hemisphere, one no-go signal was simultaneously dispatched to the other hemisphere. Such additional information left the accuracy scores unimproved in both split-brain monkeys.
Finally, an alternative model was proposed, based on the general assumption that the two cerebral hemispheres are alternately activated in bilateral tasks. This model accounted for the dramatic choice deficit observed in the split-brain monkeys by hypothesizing that commissurotomy critically reduces the speed of the attentional interhemispheric switching mechanism, thereby prohibiting the fast correction of erroneous lateralized motor set.
Preliminary tests, through the analysis of sequential effects and of latencies of correct and incorrect responses in both operated and control animals, yielded reasonable support of this model. In turn, the model may provide a new look at some classical results in the field of split-brain studies.
