I. Steele Russell

Neocortical lesions and pavlovian conditioning

Abstract A conditional nictitating membrance response was elaborated in normal, hemidecorticate and decorticate albino rabbits. The acquisition of conditional responses was not retarded in either of the lesioned groups nor was there any correlation between size of lesion and rate of conditioning. Both hemidecorticates and decorticates, however, failed to produce short latency conditional responses, which in normal animals became more frequent as acquisition progressed. The amplitude of both conditional and unconditional responses was greater in the hemidecorticate group than either the decorticate or normal animals. These results were discussed in relation to the differential effect of neocortical lesions on Pavlovian conditioning and instrumental learning.

The effects of unilateral frontal eye field lesions in the monkey: Visual-motor guidance and avoidance behaviour

Macaque monkeys were tested on a visual-motor guidance task and observations of avoidance behaviour were made following unilateral frontal eye field lesions. Visual-motor guidance was assessed by speed and accuracy of reaching to press recessed, illuminated buttons arrayed in a 90 degree arc in front of the monkey. Unilateral frontal eye field lesions produced a marked neglect of stimulus lights contralateral to the side of the lesions, as shown in greatly increased errors and response latencies. Responses to the most peripheral of the ipsilateral stimulus lights were also affected, although not to the same degree. Partial to complete recovery occurred, usually within a month. A unilateral lesion of the principal sulcus did not cause symptoms of neglect in the visual-motor guidance task. Section of the cerebral commissures partially restored the visual-motor guidance deficit in the frontal eye field-lesioned monkeys, with recovery again occurring. Commissurotomy and the unilateral frontal eye field lesion performed in a single-stage operation produced an initially more severe neglect than the two-stage operation, but recovery was no less rapid. The unilateral frontal eye field lesions resulted in a severe neglect of contralateral threat objects when the monkeys were threatened from both sides (avoidance-avoidance tests). Avoidance was normal when the threat was presented to one side. Commissurotomy fully restored the avoidance-avoidance deficit and made it permanent. These and other recent findings suggest that the contralateral visual field defect and the other symptoms resulting from frontal eye field lesions represent an impairment in directing and sustaining attention in regions of the visual field arising from disruption of a corticothalamotectal sensorimotor integration system.

Role of encoding unitization in cued recognition memory

A cueing effect, defined as the facilitation of recognition of a to-be-remembered (TBR) word by the reinstatement of an item which accompanied it at encoding, was found in two studies after learning with imagery instructions but not with associative instructions. The cueing effect was found with imagery instructions when the cues were either concrete nouns unrelated to the TBR or pictures of an ordered walk (the method of locations). In the case of recall, a cueing effect was found using associative learning instructions with unrelated concrete nouns. It is argued that imagery instructions produce strong unitization of encoding, requiring redintegration of the unitized pair at the time of testing along with decoding of the TBR.

Differential and reversal conditioning in partially neodecorticate rabbits

Abstract Normal rabbits and rabbits with extensive unilateral or bilateral neocortical lesions were required to differentiate between visual and auditory stimuli in a Pavlovian situation and then to reverse that differentiation. It was found that neocortical ablations had no effect on the initial differentiation and that the lesioned animals were superior to normals in their performance on the reversal task. The lesioned animals in particular did not show the same tendency as normals to continue responding to the negative stimulus under reversal conditions. Possible sources of the apparently greater efficiency shown by the neodecorticates are discussed.

Binocular vision in the rabbit

Two experiments are reported where rabbits were trained on both an Either- Or and a Same-Different visual discrimination task. A system of coloured patterns and light filters ensured that information was accessible only by binocular vision. The results showed that the animals were able to solve both types of discrimination problems under these conditions.

The role of the cortex in acquisition and retention of a classically conditioned passive avoidance response

Abstract A classically conditioned passive avoidance response was found to transfer in the functional split-brain which suggested a lack of cortical involvement in this type of learning. It was found, however, that training during functional decortication produced no indication of true conditioning. On the other hand animals showed perfect retention if they were decorticated after conditioning was established. These experiments show that subcortical storage and retrieval systems are independent of cortical function. Nonetheless the cortex is essential for the encoding of the information input.

Some Studies of Interhemispheric Integration in the Rat

The most central problem of the study of the commissures and hemispheric integration is the question of whether or not a single or a duplex record of experience is established in the brain. In other words when an animal is trained on a visual problem with binocular vision, is the information stored as two separate and independent records in the two hemispheres, or as a single record across both hemispheres? The interest in the question derives from the early work of Sperry (1961) which established the essential point that monocular visual training in the cat with both chiasm and commissures sectioned resulted in memory lateralisation to one hemisphere. By contrast, monocular training in either the chiasm-sectioned or the callosum-sectioned animal did not produce memory lateralisation. These findings were interpreted to imply that in the normal intact brain the visual information is integrated during binocular vision by both the chiasm and the commissural system to result in two separate records, one in each cerebral hemisphere. This is what is known as the bureaucratic theory of the brain, where everything is stored in duplicate form at least at a cortical level. If we consider the colliculi, it may even be necessary to think in terms of quadruplicate storage.

Specificity and savings of behavioural habituation over a series of intra- and inter-modal stimuli

A series of four tone stimuli, differing either in tonal frequency or in melody, was presented at the rate of one presentation per day to a group of rats. Habituation was specific to the frequency of simple auditory stimuli and to the melody of patterned stimuli, as shown both by the distraction to stimulus change, and by the trials to habituate to the new stimulus. Savings in habituation occurred when a series of tone stimuli was presented, but was not found for a series of inter-modal stimuli.

Task difficulty and lateralization of learning in the functional split-brain rat

Abstract The present experiment was concerned to evaluate whether or not task difficulty determines lateralization of learning in the functional split-brain animal. Complete lateralization was obtained at all difficulty levels not only for integrated escape responses but also for all instrumental components of the behaviour. Classically conditioned CERs failed to lateralize, but they did not facilitate the acquisition of escape behaviour with the new hemisphere. Analysis of the learning pathways taken by each hemisphere indicated that in the split-brain the two hemispheres learn in different ways. The presence of a hemidecorticate learning deficit for escape learning was confirmed and evidence for a retention deficit found. The relationships between classical conditioning and instrumental learning were discussed.

RETENTION OF CONDITIONED INHIBITION OF THE NICTITATING-MEMBRANE RESPONSE IN DECORTICATE RABBITS

Rabbits were trained on a Pavlovian conditioned inhibition (CI) task using light as the reinforced conditional stimulus (CS) and the same light compounded with a tone as the non-reinforced CS. The conditional response was the nictitating membrane response (NMR). The subjects then received an extensive neocortical lesion or a sham operation. After 9 weeks postoperative recovery, the animals were retrained on the CI task. Sham operated control animals showed immediate and high levels of CI retention but the decorticates showed a profound initial loss, showing that there is a cortical influence in CI. Reacquisition of CI by the decorticates was rapid and showed considerable savings over de novo acquisition. This supports our earlier finding that the neocortex is not essential for the acquisition of CI.