Roger W. Sperry’s research while affiliated with California Institute of Technology and other places

Right-handed patients with surgical disconnection of the cerebral hemispheres cannot report verbal input to the left ear if diferent verbal stimuli have been channeled simultaneously to the right ear. With monaural stimulation, they show equal accuracy of report for the two ears. These findings highlight the dominance of the contralateral over the ipsilateral auditory projection system. Suppression of right-ear input is obtained in nonverbal tests. Dissociation between verbal and left-hand stereognostic responses indicate a right-left dichotomy for auditory experience in the disconnected hemispheres.

In respect to their agility and muscular coordination, monkeys in which the corpus callosum has been sectioned are hardly distinguishable from normal animals. Nevertheless, certain movement patterns involving the use of both hands might be expected to depend on direct connections between the hemispheres since the main cortical motor centers for each hand lie in opposite hemispheres. In these experiments a behavioral test was used to measure the proficiency in aim and timing of hand movements where the sensory information for direction, distance, and timing of the target came from proprioceptive and kinesthetic cues originating in the other arm. Testing of monkeys with various midline brain lesions showed that section of either the corpus callosum or tectal cross-connections alone produced only a transient loss of skill in the task. If forebrain and midbrain commissures were both severed, however, a long-lasting deficit became apparent when the task was attempted without vision. With visual guidance of hand movement, performance remained essentially normal. With continued postoperative practice over several months the accuracy of spatial coordination of hand movements slowly improved until even when working blind, performance scores were once again normal and further were unaffected by an almost complete midline division of the cerebellum.

The BASIC picture of the cerebral deconnection or split-brain syndrome1 has been extended and elaborated in recent years through the study of some patients in whom cerebral commissurotomy had been carried out by P. J. Vogel at the White Memorial Medical Center, Los Angeles, in an effort to curb severe epileptic seizures not controlled by medication.2,3 Earlier descriptions of these cases dealing with visual, tactual, and language functions primarily indicate that the two separated hemispheres function quite independently with respect to most mental or gnostic activities.4-8 In brief, speech, writing, and calculation, plus visual gnosis for the right half visual field and stereognosis of the right hand, were found to be lateralized in the dominant left hemisphere, while stereognosis of the left hand and visual gnosis of the left half visual field were found restricted to the right minor hemisphere. Other functions including some aspects of language

7 pigtail monkeys were trained to perform an intermanual size discrimination and tested after split-brain surgery. Exp. I required Ss to pull the larger of 2 cylindric levers presented simultaneously, 1 by each hand. Postoperative scores for 2 Ss working with 4 lever pairs from 5 sizes were good initially, but declined gradually. Scores of 2 Ss working with 9 lever pairs from 10 sizes fell abruptly to chance level after surgery and remained there. Exp. II required Ss to use 1 hand to pull 1 of 2 levers that matched in size a lever presented to the other hand; postoperative scores from 3 Ss were at chance level, even with gross size difference. Evidently cross-communication of manual stereognostic size information was eliminated by the surgery.

The performance of 2 choice reactions, 1 with each hand, in response to 2 visual discrimination tasks presented simultaneously, 1 in each ½ of the visual field, normally takes much longer than the performance of either 1 alone. In commissurotomized human patients, however, the double task was performed as rapidly as the single task. The results conform with the view that the neocortical commissures serve to unify adjustment to the visual world and their presence tends to prevent the 2 half brains from making discordant volitional decisions. (PsycINFO Database Record (c) 2012 APA, all rights reserved)

It has long been considered a general rule for nerve regeneration that the reinnervation of skeletal muscle is nonselective. Regenerating nerve fibers are supposed to reconnect with one skeletal muscle as readily as another according to studies covering a wide range of vertebrates (Weiss, 1937; Weiss & Taylor, 1944; Weiss & Hoag, 1946; Bernstein & Guth, 1961; Guth, 1961, 1962, 1963). Similarly, in embryogenesis proper functional connexions between nerve centers and particular muscles are supposedly attained, not by selective nerve outgrowth but rather through a process of ‘myotypic modulation’ (Weiss, 1955) that presupposes nonselective peripheral innervation. Doubt about the general validity of this rule and the concepts behind it has come from a series of studies on regeneration of the oculomotor nerve in teleosts, urodeles, and anurans and of spinal fin nerves in teleosts (Sperry, 1946, 1947, 1950, 1965; Sperry & Deupree, 1956; Arora & Sperry, 1957a, 1964).

During the past decade we have been engaged in studies in which the brain is surgically divided down the middle into right and left halves. The behavioral performances of cats and monkeys following brain bisection have led to the conclusion that each of the surgically separated hemispheres must sense, perceive, learn, and remember quite independently of the other hemisphere [Sperry, 1961a, 1961b; 1964a, 1964b].

Fish were trained to jump at the correct (rewarded) one of two differently colored feeders and to avoid feeders of other colors and different shades of gray. It was found that the fish could discriminate the colors red, blue, yellow, and green both in the normal state and after complete section and regeneration of the optic nerve.When the color preferences were trained prior to optic nerve section, regeneration of the nerve resulted in reinstatement of the same color preferences, no relearning being necessary. Some of the implications regarding specificity of the optic fibers and factors governing their central synapsis in the optic tectum are discussed.