Changes of behavioral strategy as a mechanism of relearning instrumental responses after cerebral lesions.

Several examples of functional recovery of instrumental responding after cerebral lesions are reviewed. Small incision on the boundary between the sensory and the motor cortex of a dog changed the saliency not only of the tactile but also of the auditory conditioned stimuli, eliciting the preoperatively acquired alimentary instrumental response. Prefrontal lesions in cats affected differently each of the several learning processes involved in the performance of the avoidance response: they enhanced the classically conditioned component, attenuated the motivational role of fear but left the motor component intact. Preoperatively acquired interrelations of these components underwent substantial changes, leading to the restoration of the previous level of avoidance of pain. However, a highly adaptive mode of behavior, namely avoidance of the state of fear, was permanently impaired. After small electrolytic lesions of amygdalar nucleus centralis cats were handicapped in the acquisition of escape from pain responses. The responses to low shock intensities were especially diminished. Improvement of the escape from pain responses was observed after a prolonged increase of the intertrial response frequency. The effectiveness of both escape and avoidance learning depended on the duration of the postoperative recovery period prior to instrumental training. All these data indicated that cerebral lesions changed the interactions between different parts of the neuronal circuitry participating in the learning and performance of a given instrumental response.