Slides Shared Resource

1. HEMISPHERE DECONNECTION AND UNITY IN CONSCIOUS AWARENESS J R. W. SPERRY California Institute of Technology T HE following article is a result of studies my Episodes of…
of 11
All materials on our website are shared by users. If you have any questions about copyright issues, please report us to resolve them. We are always happy to assist you.
Related Documents
  • 1. HEMISPHERE DECONNECTION AND UNITY IN CONSCIOUS AWARENESS J R. W. SPERRY California Institute of Technology T HE following article is a result of studies my Episodes of status cpilcpticus (recurring seizures colleagues and I have been conducting with that fail to stop and represent a medical emergency some neurosurgical patients of Philip J. Vogel with a fairly high mortality risk) had also begun to of Los Angeles. These patients were all advanced occur at 2- to 3-month intervals. Since leaving the epileptics in whom an extensive midline section of hospital following his surgery over 51/<> years ago, the cerebral commissures had been carried out in an this man has not had, according to last reports, a effort to contain severe epileptic convulsions not single generalized convulsion. It has further been controlled by medication. In all these people the possible to reduce the level of medication and to surgical sections included division of the corpus obtain an overall improvement in his behavior and callosum in its entirety, plus division also of the well being (see Bogen & Vogel, 1962). smaller anterior and hippocampal commissures, plus The second patient, a housewife and mother in in some instances the massa intermedia. So far as her 30s, also has been seizure-free since recovering I know, this is the most radical disconnection of from her surgery, which was more than 4 years the cerebral hemispheres attempted thus far in hu- ago (Bogen, Fisher, & Vogel, 1965). Bogen related man surgery. The full array of sections was that even the EEG has regained a normal pattern in carried out in a single operation. this patient. The excellent outcome in the initial, No major collapse of mentality or personality apparently hopeless, last-resort cases led to further was anticipated as a result of this extreme surgery: application of the surgery to some nine more in- earlier clinical observations on surgical section of dividuals to date, the majority of whom are too the corpus callosum in man, as well as the results recent for therapeutic evaluation. Although the from dozens of monkeys on which I had carried out alleviation of the epilepsy has not held up IQO% this exact same surgery, suggested that the func- throughout the series (two patients are still having tional deficits might very likely be less damaging seizures, although their convulsions are much re- than some of the more common forms of cerebral duced in severity and frequency and tend to be surgery, such as frontal lobotomy, or even some of confined to one side), the results on the whole con- the unilateral lobotomies performed more routinely tinue to be predominantly beneficial, and the overall for epilepsy. outlook at this time remains promising for selected The first patient on whom this surgery was tried severe cases. had been having seizures for more than 10 years The therapeutic success, however, and all other with generalized convulsions that continued to medical aspects are matters for our medical col- worsen despite treatment that had included a leagues, Philip J. Vogel and Joseph E. Bogen. sojourn in Bethesda at the National Institutes of Our own work has been confined entirely to an ex- Health. At the time of the surgery, he had been amination of the functional outcome, that is, the averaging two major attacks per week, each of behavioral, neurological, and psychological effects which left him debilitated for another day or so. of this surgical disruption of all direct cross-talk 1 between the hemispheres. Initially we were con- Invited address presented to the American Psychological Association in Washington, D. C., September 1967, and to cerned as to whether we would be able to find in the Pan American Congress of Neurology in San Juan, these patients any of the numerous symptoms of Puerto Rico, October 1967. Original work referred to in hemisphere deconnection that had been demon- the text by the writer and his co-workers was supported strated in the so-called "split-brain" animal studies by Grant MH-03372 from the National Institute of Mental Health, United States Public Health Service, and by of the 1950s (Myers, 1961; Sperry, 1967a, 1967b). the Hixon Fund of the California Institute of Technology. The outcome in man remained an open question in 723
  • 2. 724 AMERICAN PSYCHOLOGIST summarized as an apparent doubling in most of the realms of conscious awareness. Instead of the normally unified single stream of consciousness, these patients behave in many ways as if they have two independent streams of conscious aware- ness, one in each hemisphere, each of which is cut off from and out of contact with the mental experi- ences of the other. In other words, each hemisphere seems to have its own separate and private sensa- tions; its own perceptions; its own concepts; and its own impulses to act, with related volitional, cognitive, and learning experiences. Following the surgery, each hemisphere also has thereafter its own separate chain of memories that are rendered inaccessible to the recall processes of the other. This presence of two minds in one body, as it luo. 1. Apparatus for studying laleralization of visual, tactual, lingual, and associated functions in the surgically were, is manifested in a large number and variety of separated hemispheres. test responses which, for the present purposes, I will try to review very briefly and in a somewhat streamlined and simplified form. First, however, view of the historic Akelaitis (1944) studies that had set the prevailing doctrine of the 1940s and let me take time to emphasize that the work re- ported here has been very much a team project. 1950s. This doctrine maintained that no important functional symptoms are found in man following The surgery was performed by Vogel at the White even complete surgical section of the corpus cal- Memorial Medical Center in Los Angeles. He losum and anterior commissure, provided that other has been assisted in the surgery and in the brain damage is excluded. medical treatment throughout by Joseph Bogen. Bogen has also been collaborating in our behavioral These earlier observations on the absence of be- testing program, along with a number of graduate havioral symptoms in man have been confirmed in students and postdoctoral fellows, among whom a general way to the extent that it remains fair M. S. Gazzaniga, in particular, worked closely to say today that the most remarkable effect of with us during the first several years and managed sectioning the neocortical commissures is the ap- much of the testing during that period. The pa- parent lack of effect so far as ordinary behavior is tients and their families have been most coopera- concerned. This has been true in our animal studies tive, and the whole project gets its primary funding throughout, and it seems now to be true for man from the National Institute of Mental Health. also, with certain qualifications that we will come to later. At the same time, however—and this is Most of the main symptoms seen after hemisphere in contradiction to the earlier doctrine set by the deconnection can be described for convenience with Akelaitis studies—we know today that with ap- reference to a single testing setup—shown in propriate tests one can indeed demonstrate a large Figure 1. Principally, it allows for the lateralized testing of the right and left halves of the visual number of behavioral symptoms that correlate di- field, separately or together, and the right and left rectly with the loss of the neocortical commissures hands and legs with vision excluded. The tests can in man as well as in animals (Gazzaniga, 1967; be arranged in different combinations and in as- Sperry, 1967a, 1967b; Sperry, Gazzaniga, & Bogen, sociation with visual, auditory, and other input, 1968), Taken collectively, these symptoms may with provisions for eliminating unwanted stimuli. be referred to as the syndrome of the neocortical In testing vision, the subject with one eye covered commissures or the syndrome of the forebrain com- centers his gaze on a designated fixation point on missures or, less specifically, as the syndrome of the upright translucent screen. The visual stimuli hemisphere deconnection. on 35-millimeter transparencies are arranged in a One of the more general and also more interesting standard projector equipped with a shutter and are and striking features of this syndrome may be then back-projected at 1 /jo of a second or less—too
  • 3. HEMISPHERE DECONNECTION 725 fast for eye movements to get the material into the wrong half of the visual field. Figure 2 is merely a reminder that everything seen to the KEY i CASE left of the vertical meridian through either eye is projected to the right, hemisphere and vice versa. The midline division along the vertical meridian is found to be quite precise without significant gap or overlap (Sperry, 1968) . When the visual perception of these patients is tested under these conditions the results indicate that these people have not one inner visual world any longer, but rather two separate visual inner worlds, one serving the right half of the field of vision and the other the left half—each, of course, in its respective hemisphere. This doubling in the visual sphere shows up in many ways: For example, after a projected picture of an object has been identified and responded to in one half field, we find that it is recognized again only if it reappears in the same half of the field of vision. If the given visual stimulus reappears in the opposite half of the visual field, the subject responds as if he had no recollection of the previous exposure. In other words, things seen through the right half of the visual field (i.e., through the left hemisphere) are registered in mental experience and remembered quite separately from things seen in the other half of the field. Each half of the field of vision in the FIG. 2. Things seen to the left of a central fixation commissurotomized patient has its own train of point with either eye are projected to the right hemisphere visual images and memories. and vice-versa. This separate existence of two visual inner worlds is further illustrated in reference to speech and writ- We do not think the subjects are trying to be ing, the cortical mechanisms for which are centered difficult or to dupe the examiner in such tests. in the dominant hemisphere. Visual material pro- Everything indicates that the hemisphere that is jected to the right half of the field—left-hemisphere talking to the examiner did in fact not see the system of the typical right-handed patient—can be left-field stimulus and truly had no experience described in speech and writing in an essentially with, rior recollection of, the given stimulus. The normal manner. However, when the same visual other, the right or nonlingual hemisphere, however, material is projected into the left half of the field, did see the projected stimulus in this situation and and hence to the right hemisphere, the subject con- is able to remember and recognize the object and sistently insists that he did not see anything or can demonstrate this by pointing out selectively the that there was only a flash of light on the left side. corresponding or matching item. This other hemi- The subject acts as if he were blind or agnostic for sphere, like a deaf mute or like some aphasics, can- the left half of the visual field. If, however, instead not talk about the perceived object and, worse still, of asking the subject to tell you what he saw, you cannot write about it either. instruct him to use his left hand to point to a If two different figures are flashed simultaneously matching picture or object presented among a to the right and left visual fields, as for example a collection of other pictures or objects, the subject "dollar sign" on the left and a "question mark" has no trouble as a rule in pointing out consistently on the right and the subject is asked to draw what (he very item thai he has just insisted he did not he saw using the left hand out of sight, he regularly see. reproduces the figure seen on (he left half of the
  • 4. 726 AMERICAN PSYCHOLOGIST field, that is, the dollar sign. If we now ask him what obliged to retrieve such an object with the same he has just drawn, he tells us without hesitation hand with which it was initially identified. They that the figure he drew was the question mark, or fail at cross-retrieval. That is, they cannot recog- whatever appeared in the right half of the field. nize with one hand something identified only In other words, the one hemisphere does not know moments before with the other hand. Again, the what the other hemisphere has been doing. The second hemisphere does not know what the first left and the right halves of the visual field seem hemisphere has been doing. to be perceived quite separately in each hemisphere When the subjects are first asked to use the with little or no cross-influence. left hand for these stereognostic tests they com- When words are flashed partly in the left field monly complain that they cannot "work with that and partly in the right, the letters on each side of hand," that the hand "is numb," that they "just the midline are perceived and responded to sepa- can't feel anything or can't do anything with it," rately. In the "key case" example shown in Fig- or that they "don't get the message from that ure 2 the subject might first reach for and select hand." If the subjects perform a series of success- with the left hand a key from among a collection ful trials and correctly retrieve a group of objects of objects indicating perception through the minor which they previously stated they could not feel, hemisphere. With the right hand he might then and if this contradiction is then pointed out to spell out (he word "case" or he might speak the them, we get comments like "Well, T was just word if verbal response is in order. When asked guessing," or "Well, I must have done it un- what kind of "case" he was thinking of here, the consciously." answer coming from the left hemisphere might be With other simple tests a further lack of cross- something like "in case of fire" or "the case of the integration can be demonstrated in the sensory and missing corpse" or "a case of beer," etc., depending motor control of the hands. In a "symmetric upon the particular mental set of the left hemisphere handpose" test the subject holds both hands out at the moment. Any reference to "key case" under of sight symmetrically positioned and not in contact. these conditions would be purely fortuitous, assum- One hand is then passively placed by the examiner ing that visual, auditory, and other cues have been into a given posture, such as a closed fist, or one, properly controlled. two, or more fingers extended or crossed or folded A similar separation in mental awareness is into various positions. The subject is then in- evident in tests that deal with stereognostic or structed verbally or by demonstration to form the other somesthetic discriminations made by the right same pose with the other hand, also excluded from and left hands, which arc projected separately to vision. The normal subject does this quite ac- the left and right hemispheres, respectively. Ob- curately, but the commissurotomy patient generally jects put in the right hand for identification by fails on all but the very simplest hand postures, like touch are readily described or named in speech or the closed fist or the fully extended hand. writing, whereas, if the same objects are placed in In a test for crossed topognosis in the hands, the the left hand, the subject can only make wild subject holds both hands out of sight, forward guesses and may often seem unaware that anything and palm up with the fingers held apart and ex- at all is present. As with vision in the left field, tended. The examiner then touches lightly a point however, good perception, comprehension, and on one of the figures or at the base of the fingers. memory can be demonstrated for these objects in The subject responds by touching the same target the left hand when the tests are so designed that point with the tip of the thumb of the same hand. the subject can express himself through nonverbal Cross-integration is tested by requiring the patient responses. For example, if one of these objects to use the opposite thumb to find the corresponding which the subject tells you he cannot feel or does mirror point on the opposite hand. The com- not recognize is taken from the left hand and placed missurotomy patients typically perform well within in a grab bag or scrambled among a dozen other cither hand, but fail when they attempt to cross- test items, the subject is then able to search out locate the corresponding point on the opposite and retrieve the initial object even after a delay hand. A crude cross-performance with abnormally of several minutes is deliberately interposed. Un- long latency may be achieved in some cases after like (he normal subject, however, these people are practice, depending on the degree of ipsilateral
  • 5. HEMISPHESK DECONNECTION 727 motor control and the development of certain may compare it lo the visual sphere of the hcmi- strategies. The latter breaks down easily under anopic patient who, following accidental destruction stress and is readily distinguished from the natural of an entire visual cortex of one hemisphere, may performance of the normal subject with intact not even notice the loss of the whole half sphere callosum. of vision until Ihis has been pointed out to him in In a related test the target point is presented specific optometric tests. These commissurotomy visually as a black spot on an outline drawing of patients continue to watch television and to read the hand. The picture is flashed to the right or left the paper and books with no complaints about half of the visual field, and the subject then at- peculiarities in the perceptual appearance of the tempts as above to touch the target spot with the visual field. tip of the thumb. The response again is performed At the same time, I want to caution against any on the same side with normal facility but is impaired impression that these patients are better off mentally in the commissurotomy patient when the left visual without their cerebral commissures. It is true that field is paired with a right-hand response and vice if you carefully select two simple tasks, each of versa. Thus the duality of both manual stereognosis which is easily handled by a single hemisphere, and visuognosis is further illustrated; each hemi- and then have the two performed simultaneously, sphere perceives as a separate unit unaware of the there is a good chance of getting better than normal perceptual experience of the partner. scores. The normal interference effects that corne If two objects are placed simultaneously, one in from trying to attend to two separate right and left each hand, and then are removed and hidden for tasks at the same time are largely eliminated in retrieval in a scrambled pile of test items, each hand the commissurotomized patient. However, in most will hunt through the pile and search out selectively activities that are at all complex the normally uni- its own object. In the process each hand may ex- fied cooperating hemispheres still appear to do plore, identify, and reject the item for which the better than the two disconnected hemispheres. Al- other hand is searching. It is like two separate though it is true that (he intelligence, as measured individuals working over the collection of test items on IQ tests, is not much affected and that Ihe with no cooperation between them. We find the personality comes throu
  • We Need Your Support
    Thank you for visiting our website and your interest in our free products and services. We are nonprofit website to share and download documents. To the running of this website, we need your help to support us.

    Thanks to everyone for your continued support.

    No, Thanks