Different Psychological Status in the Two Hemispheres of Two Split-Brain
Fredric Schiffer, M.D.1
Eran Zaidel, Ph.D.2
Joseph Bogen, M.D.2,3
Scott Chasan-Taber, Ph.D.4
From the 1Department of Psychiatry, Harvard Medical School at the McLean Hospital, Belmont, Massachusetts, 02178; 2Department of Psychology, University of California, Los Angeles, CA 90095-1563; 3Department of Neurological Surgery, University of Southern California, Los Angeles, CA 90033;4 Boston Biostatistics, Inc., Framingham, MA 021702
Address for Reprint Requests: Fredric Schiffer, M.D., McLean Hospital, 115 Mill Street, Belmont, MA 02178
Running Title: Differential Hemispheric Psychological Status
Corresponding Author: Fredric Schiffer, M.D., McLean Hospital, 115 Mill Street, Belmont, MA 02178, (617) 237-9620
Acknowledgement: The authors acknowledge the advice of David Bear, M.D. and the research assistance of Linda Capetillo-Cunliffe
Support: This work was supported by NIH (NINDS) Grant NS20187
In : Neuropsychiatry, Neuropsychology, and Behavioral Neurology 1998; 11:151-156
Questions of a psychological nature were presented to two split-brain patients from the California series encouraging each hemisphere to respond simultaneously and independently. The responses of both patients indicated that their hemispheres were responding independently. For the first patient, his right hemisphere appeared to be more disturbed than his left by childhood memories of being bullied. The right hemisphere of the second patient seemed to regard himself more positively, but it also seemed to feel more negative emotions such as loneliness and sadness. We discuss the possible significance of the findings.
Key Words: Split-brain, Cerebral Dominance, Cerebral Laterality, Lateral Visual Fields, Emotion, Hemispheric Specialization, Hemispheric Independence, Self-image.
Split-brain patients, subjects who earlier had undergone a commissurotomy
for intractable epilepsy, have been extensively evaluated in regard to
the cognitive abilities of their left and right hemispheres. Sperry,
Gazzaniga, and Bogen () suggested that in split brain patients there exists
a duality of mind. Sperry, Zaidel, and Zaidel () offered a glimpse
of the psychological properties of the right hemisphere in split-brain
patients and found it to demonstrate a sense of self and a sense of humor
as it functioned beyond the awareness of the left hemisphere. LeDoux
et al () also found the right hemisphere in split-brain patient PS to have
a sense of self-awareness and to hold opinions separate from those of the
left side. They found that when the two hemispheres were in agreement
the patient was in a happier mood, but when they were in disagreement,
he was anxious and aggressive.
Bogen (, ) and Zaidel et al () have suggested that a duality of mind may extend to normal, intact individuals, and Schiffer (,) has recently elaborated on this theme and proposed that each hemisphere may have different psychological properties, with one side often being less mature and more disturbed by past traumas.
In an attempt to learn more about the psychological nature of the right hemisphere in split-brain patients, we undertook the following study in which we sought to examine whether the two hemispheres, left and right, might differ in their sensitivity to past traumas and whether they might each hold different perceptions, attitudes, or feelings.
We asked two male split-brain patients well known to the laboratory to come in for the study. Each signed informed consent and was paid for his assistance. Both patients previously had complete cerebral commissurotomy (including the entire corpus callosum as well as anterior and hippocampal commissures) (). The two patients both had physical limitations which required that each be studied with an individualized procedure. Both subjects underwent a brief psychiatric interview, and both were found to have a normal mental status examination. Both appeared euthymic, cooperative, and pleasant. Neuropsychiatric and neurological data on these two patients have been presented in detail elsewhere (). More recent data has shown no significant change.
We expected that the left hand would respond to questions posed to the LVF (right hemisphere) and that the right hand would respond to questions to the RVF (left hemisphere). This is based on the well known lateralized anatomy of the motor cortex. We expected pattern of the patientsí answers to substantiate this assumption.
Patient 1, AA, born November 20, 1950, was operated October 14, 1964. He was right handed. Prior to surgery a left hemispheric epileptic focus was indicated by convulsions sometimes beginning in the right hand and by the bilateral EEG abnormalities being more marked over the left hemisphere. He was said to be keeping up in school until 4th grade when he fell behind. In 1982 he was found to have difficulty reading unfamiliar words greater than 2 syllables. Because of this reading limitation, he was not asked to attempt to read complex words flashed to the lateral fields as we did with the second patient. The procedure used for him was as follows: a series of 49 questions were verbally asked by an experimenter standing behind him. Each question had the same basic format as the following sample question: How much on the scale from none to extreme would you like to be admired? The patient responded to each question by touching one of five pegs set up in a row in front of each hand. The pegs were behind a screen and not visible to the patients, but with practice and with a visible diagram of the pegs, he learned that the pegs were arranged in a straight line running left to right in front on each side. The peg furthest to the left was designated as "none," and each peg to the right increased in value to "mild," "moderate," "quite-a-bit," and "extreme." In this way the patient could respond to our questions simultaneously with both hands, by touching the intended pegs with each index finger.
In a brief psychiatric interview before the formal testing, one of the authors (FS) learned that Patient 1 had been persistently bullied as a child. During the brief interview Patient 1 verbally reported [left brain] that he was not at all upset by the bullying which he pointed out occurred about 30 years earlier. We sought to learn if this patient would respond to questions about the bullying differently with his right hand than his left hand, each responding for its contralateral hemisphere. In this way we sought to determine whether this patients' separated hemispheres might have different feelings about his traumatic childhood experience. Fourteen questions related to the bullying. For example, the patient was asked how cruel he felt the bullies were, how scared he was of them, and how angry he felt at them.
In addition to questions about the bullies, the patient was also asked 35 questions addressing his beliefs, his aspirations, his enjoyment of different activities, and his present relationships. For example, he was asked if he believed in the soul, in God, in cheating, and/or in abortion. He was asked if he enjoyed shopping, going to the movies, eating, sex, romance, puzzles, work and/or taxes. He was asked if he would like to be powerful, to be poor, to be president, to be loved, and/or to be a movie star. He was asked also about his feelings about his girlfriend, mother, and father. We sought to determine if his left and right hands would respond similarly or differently to each of these questions. We also sought to see if the patient's responses to questions about the bullies would be different from his responses to the other questions which we categorized as "general" questions.
Patient 2, LB, was born May 15, 1952, and was operated on April 1, 1965. He was right handed. He was having a major seizure every week for a year preceding the operation, and had a dramatic improvement from the surgery. The only lateralizing evidence for a seizure focus were some left sided Jacksonian attacks during the third year after the complete cerebral commissurotomy. This patient also has been well studied over many years in the UCLA laboratory, and was known to be capable of reading complex words in both hemispheres, and we used a different procedure when testing him. This patient sat before a computer monitor with his eyes fixed on a + sign at the mid-point of the screen. One of the authors would ask the patient the beginning of a question such as "On our scale, how much are you now . . . ?" As soon as the verbal part of the question was asked, then a different word was flashed for 0.15 second to each lateral visual field. One field might receive the word "confident" and the other "alone." In this way we intended to lateralize simultaneously different questions to each hemisphere.
As with the first patient, the second was asked to respond by touching one of the five pegs set up in a row in front of each hand. In this way this patient could respond to our questions simultaneously with both hands by touching the intended pegs with each index finger.
On the first run, 93 words were flashed to each lateral field following a verbal introduction. All words were flashed to each lateral field in a different order. Examples of paired words are:
Admired - Disrespected
Ashamed - Admired
Attractive - Dishonest
Confident - Confident
Cruel - Friendly
Despondent - Attractive.
During this trial we observed that all of this patient's right-handed
responses were limited to the first 3 pegs. Because we suspected
that he might have had some difficulty responding with his right hand,
we repeated a run of the first 29 words in which we asked the patient to
respond verbally to verify his right handed responses. The patient
responded to each set of questions with both hands, immediately following
which he gave a verbal response. His verbal responses covered a full
range from "none" to "extreme" although his right hand responses were still
limited to the first 3 pegs. We attributed this limitation his recently
acquired, non-progressive, mild right hand uncoordination of undetermined
origin, and relied on his verbal responses in our data analysis.
It is unlikely that this pure motor problem significantly affected his
affective states. For the patient's left handed responses, in our
data analysis, we used the average of his responses on each of the 2 trials
to each of the 29 questions. We did not repeat the full set of 93
questions because the patient was beginning to experience fatigue.
We categorized the flashed words as either "positive" or "negative." Positive words described desirable attributes such as "admired" or "honest," and negative words described undesirable attributes such as "disrespected" or "dishonest."
We also categorized the words as "about" or "feel" words. "About" words consist of those which described how he felt others regarded him, words such as "disliked" or "admired." "Feel" words consisted of those which articulated the patient's emotional feelings, words such as "happy" or "sad."
In addition to the 29 questions asked in both lateral fields, we reviewed the left handed responses to the 64 questions on the first trial on which the right hand responses were unreliable and on which we did not perform a second trial with verbal responses.
For both patients, two experimenters observed the patients' hand responses and recorded the peg pointed to by the patients' index fingers of both hands. With the second patient, they also recorded his verbal responses.
We analyzed the second patient's responses as they related to the lateral fields and to the types of questions asked. Because the responses of both patients were ordinal and not normally distributed, we used non-parametric statistical tests.
For the 35 "general" questions both hands responded exactly the same 74% of the time and 17% of the time the left hand responded one point more than the right. None of the differences on the general questions reached 3 or 4 points. For the 14"bully" questions, responses to only 29% were the same; the left hand responses were greater than the right 64% of the time with 44% of these responses 3 or 4 points greater.
Using the Wilcoxon Rank Sum Test, we compared the differences between the right and the left hand responses for "Bully" questions v. "General" questions and found a statistically significant difference at p=0.0078, Mean Rank Score for the differences between the left and right hand responses for Bully questions was 32.54, and that for General questions was 21.98.
We used a Marginal Homogeneity Test, an extension of the McNemars Test (), to compare the left handed responses of the first run with those of the second run. The test gave a p-value of 0.3931 indicating that there was no significant difference between the two trials in regard to the left hand responses.
We used the Wilcoxon Rank Sum Test to compare responses to positive versus negative words measured as the differences between the left hand and the verbal responses. As shown in figure 1, comparing the 15 "Negative" words (Mean Rank Score = 11.77) and the 14 "Positive" words (Mean Rank Score Mean = 18.46), the difference was statistically significant (Z = 2.11, p = 0.0347), with a higher left-handed response for positive words and a higher verbal response for negative words. Typical of patient 2's responses, his verbal response was that he was "quite a bit" evil, although his left handed responses rated his evilness as "none." Verbally he rated himself as "extremely" disrespected, although his left hand responses rated him as "mildly" disrespected. His left hand rated him as "quite a bit" on "friendly" and "important," but verbally he rated himself as "none" on both words.
Among negative words, we compared the responses to "feel" words versus "about" words and found that for the 8 questions on negative feelings the mean left hand minus the verbal response was 0.50 ± sd 1.58 and for the 7 negative attribute questions it was -0.93 ± 1.51. Positive numbers indicate larger left handed (right hemispheric) responses. By the Wilcoxon Rank Sums Test the differences between these two groups were significant at p = 0.045 (mean score for "feel" words = 10.187 and for "about" words =5.500, Z = 2.002). As examples of the patient's responses, his left hand responses were higher than his verbal responses on "hopeless," "lonely," "sad," and "unhappy," although his verbal response was higher on "frustrated."
Because there were only 3 positive "feel" words a similar analysis for positive "feel" versus "about" words was not possible.
Among the 64 questions with only left handed responses, Patient 2 rated his mother and father as quite-a-bit or extremely good, but his ex-wife as not good. He rated his divorce as quite-a-bit upsetting, but rated his past and his seizures as not upsetting. His left hand indicated that he did not believe in God or in Christ, but that did believe moderately in the soul and quite-a-bit in abortion and justice. His left hand indicated he extremely liked reading, sex, puzzles, math, shopping, and movies, but did not like work or taxes.
The data from Patient 1. showing differences between the "Bully" questions and the "General" questions are consistent with our hypothesis that patient's right hemisphere may have felt more upset about his traumatic childhood experiences with the bullies than did his left hemisphere.
Considering the data from the second patient, since his left hand responses gave consistent, reasonable responses which were different from his verbal responses, the data support the assumption that his left hand was responding for his right hemisphere and his verbal responses for his left hemisphere. That the differences between his left hand and his verbal responses were significant for "positive" versus "negative" words and for negative "about" versus "feel" words is also in support of our hypothesis that the types of responses represented different hemispheric responses. The picture that emerges from our data from Patient 2 is one of a right hemisphere which sees himself as a good person, but seems to feel somewhat sad and lonely and of a left hemisphere which sees himself as a somewhat inadequate person, but who also seems to feel a greater emotional sense of general well-being.
The data from the two patients, taken together suggest that we were able to obtain separate responses from each hemisphere. Further, they suggest that the hemispheres may have different cognitive and emotional characteristics. In the first patient, his right hemisphere seemed to be more affected by his past traumas. This idea is consistent with work in intact patients recalling traumatic memories and monitored by evoked potentials () or by PET scans (). That the right hemisphere of the second patient appeared to feel more hopeless, lonely, sad, and unhappy is consistent with a large literature suggesting a relationship between the right hemisphere and negative emotion or primary emotion and depression (,,).
That the left hemisphere of the second patient seemed to think about himself more negatively than his right hemisphere is consistent with the findings of Bear and Fedio () that in patients with temporal lobe epilepsy, the patients' opinions about themselves were "tarnished" in those with left-sided foci and "polished" in those with foci on the right side. Fedio and Martin () evaluated 9 left and 10 right temporal lobectomy patients and reported that left sided patients judged themselves less harshly after surgery, but still more harshly than right lobectomy patients who more resembled a normal control group. This report suggests that the left sided ìtarnishersî in Bear and Fedioís original unoperated group manifest their interictal symptoms through a relative left-sided hyperactivity. This is consistent with our Patient 2 who appeared to have a ìtarnishedî view of himself when responding from his left hemisphere. In patient 2, our data suggest a right hemisphere with an interesting combination of high esteem but low mood.
Some have argued that split-brain data should be disregarded because the patients who all suffered epilepsy may manifest undetected brain defects which would complicate the interpretation of data. Although a majority patients who have had a split-brain operation show evidence of severe cognitive impairments both before and after surgery, that is not true of all the patients, and is specificially not true of these two patients. But, all split-brain patients most importantly manifest mental duality which cannot be attirbuted to epilepsy because epilepsey is not a single syndrome and does not usually affect mentation when controlled. The manifestation of duality is not reasonably attributed to epilepsy, and moreover is the same duality which is seen in cat and monkeys (5).
The right hemispheres of both patients appeared to hold religious and moral opinions, and both seemed to dislike taxes and to enjoy sex. The extent to which the specific emotional characteristics we observed in the independent hemispheres in our two patients can be generalized will require much further study, but our findings do support the evidence put forth by Sperry, Zaidel and Zaidel (2), and LeDoux, et al (3) that the right hemisphere in split brain patients is capable of complex mentation and affect and that it can operate with considerable independence from the left hemisphere. Recently, Schiffer (7) has speculated, as have Galin (), Joseph (), and Watt (), that in unoperated, intact people, autonomous right hemispheric mentation, similar to that observed in these patients, could have an important role in normal and abnormal psychological processes.
Figure 1. The mean left hand and verbal responses (none to extreme) on "positive" and "negative" questions for Patient 2.
Figure 2. The differences between the mean left hand and verbal responses to negative "about" and "feel" words for Patient 2.
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