Cognitive Activity of the Right Hemisphere: Possible Contributions to
Fredric Schiffer, M.D.
From the Department of Psychiatry, Harvard Medical School at the McLean
Hospital, Belmont, Massachusetts, 02178
Address for Reprint Requests: Fredric Schiffer, M.D., McLean Hospital, 115 Mill Street, Belmont, MA 02178
Running Title: Right Brain Cognition
Corresponding Author: Fredric Schiffer, M.D., McLean Hospital, 115 Mill Street, Belmont, MA 02178, 617) 237-9620
Published In: Harvard Review of Psychiatry, September/October,
The author reviews evidence from split brain and more recent studies
which have enriched and advanced our understanding of the cognitive
and emotional abilities and characteristics of the right hemisphere.
In addition to surgical studies the author includes research on unoperated
subjects employing Wada tests, unilateral videos, and functional imaging,
as well as neurophysiological studies on dissociated states such as multiple
personality disorder and hypnosis.
The literature continues to support the view that in intact individuals the right hemisphere has significant mental faculties which can operate with some independence from those of the left hemisphere. The author then reviews relevant psychodynamic literature and discusses the theoretical and the dynamic and biological therapeutic implications of the existence of these partially autonomous right hemispheric mental faculties.
Key Words: Cerebral Dominance; Laterality; Amytal Test; Tomography,
Emission-Computed; Hypnosis; Unconscious (Psychology); Psychotherapy; Psychopharmacology.
It has been known since at least the days of Hippocrates () that the brain is composed of two hemispheres, and there have been attempts for centuries to exploit this in explanations of psychological function. This enterprise was particularly active toward the end of the 19th century as described in detail by Harrington (,). For a variety of reasons enthusiasm for this approach died away. One reason for the eclipse of the two brain view was the increasing knowledge of left hemispheric dominance for language and related behaviors (), leaving the right hemisphere relegated to the role of the "minor" hemisphere. Another reason was the skepticism aroused by claims about the double brain from unstructured research into hysteria and hypnosis during the latter part of the 19th century (2). About mid-20th century, neurologists gradually began to understand that the left hemispheric dominance for language was complemented by right hemispheric dominance for other abilities (). Meanwhile, interest in the partial independence of the hemispheres was reawakened by the split-brain experiments in animals by Myers and Sperry (). A few years later it was shown by split-brain studies in humans that complementary hemispheric specialization and partial hemispheric independence could co-exist (,). It was based on these considerations that Bogen (), Galin (), and Hoppe () asserted that in normal individuals, the right brain has intelligent and autonomous mental functions often beyond the awareness of the person's verbal, left-sided mentation.
The full nature of the mental functions of the right brain has been difficult to evaluate because in split brain patients the right hemisphere almost always lacks fluent linguistic abilities and because in intact subjects it is difficult to separate the contributions of each hemisphere since both operate simultaneously. Nevertheless, a large body of scientific work bearing on right-sided cognition exists, and the author will review and discuss some of the relevant literature with an emphasis on recent findings. Additionally, the paper will discuss the significance of right-sided mentation to human psychology and psychopathology. In so doing, the paper will expand on the seminal work of Bogen (9), Galin (10), Hoppe (11) and others (,,,) by including recent evidence reflecting on this issue. The literature search included, but was not limited to, review articles on "laterality" and on "cerebral dominance" in English from 1968 until 1995 on Medline as well as chapters and books on "cerebral dominance" on PsycLIT from 1987 until 1995. For "laterality" and "cerebral dominance" the subheadings "physiology" and "drug effects" between 1991 and 1996 were also searched.
Basics of Cortical and Hemispheric Connectivity
There are three types of connectivity fibers in the neocortex: association, projection, and commissural neurons (). Association fibers consist of long fiber bundles, which connect more distant areas, and of short subcortical U-fibers, which connect adjacent areas. Projection fibers provide afferent and efferent connections between cortical and subcortical centers such as the thalamus. Commissural fibers connect the two hemispheres and mainly comprise the anterior commissure, the corpus callosum, and the hippocampal commissures. The anterior commissure primarily connects the anterior portions of the left and right temporal lobes and amygdalae. The corpus callosum provides the major connections between the neocortices. The anterior portion of the corpus callosum, referred to as the genu, connects the prefrontal lobes. Fibers in the middle portion mainly connect the sensory and motor areas and the parietal lobes of both hemispheres. The posterior portion, the splenium, interhemispherically connects the temporal and occipital lobes. It was the section of the corpus callosum which led to the split brain studies.
Split Brain Studies
In the forties and then in the early sixties, as a treatment for intractable epilepsy, neurosurgeons performed several commissurotomies (,,), in which the corpus callosum was severed, separating left and right cerebral hemispheres. The patients were noted to have an improvement in their epilepsy. Remarkably, they appeared psychologically to be little changed by the operation (). That is, the patient's personal identity and sense of personal continuity remained in tact.
Sperry and his associates (8,), however, in the early 1960's, examined these patients with sophisticated experimental techniques. They devised a method of flashing images so they could be seen by only one hemisphere. In this way they could flash a picture, perhaps, of a spoon to the left brain and ask the patient to verbally identify the item. The patient could do this with ease. However, when the experimenters flashed a picture of an item to his right brain, the patient said he saw nothing. Yet, with his left hand, connected to his right hemisphere, he was consistently able to retrieve the item which had been flashed to his right brain. This work demonstrated that the right hemisphere was capable of understanding the experimenter's instructions, identifying the object from the picture, and retrieving the object with the left hand, all without the direct awareness of the left hemisphere. Although the specific pathology causing the intractable epilepsy varied from case to case, all of the patients examined by Sperry and his associates demonstrated these lateralized abilities. Bogen and Vogel (19) performed the surgery in these patients. Initially they performed a complete callosotomy and section of the anterior commissure. Later, they modified their procedure by sparing the splenium.
In one study using a special contact lens apparatus () which allowed prolonged viewing restricted to the right hemisphere, although the patient's verbal left brain reported that it could not see photographs presented to the right side, the patient's right hemisphere was easily able to express opinions about the photographs using a thumbs up or down signal. For example, although the patient verbally reported that he could not see the images, to the first photograph his left hand signaled thumbs up, to the second thumbs down, and to the third his thumb motioned horizontally. The first image was of Johnny Carson, the second, Adolph Hitler, and the third, Richard Nixon. The patients' right hemispheres also could recognize and respond to photographs of themselves, indicating a clear sense of a personal identity.
In another experiment (), an exceptional split brain patient had the ability to answer the experimenter's verbal questions by spelling his replies with scrabble chips with his left hand. Apparently he had some expressive language ability on his right side, and the experimenter was able to interview both hemispheres separately. When asked what he wanted to be when he grew up, his left brain verbally replied, "a draftsman," but to the same question his right brain spelled out that it wanted to be a race car driver. On a five point scale, from "like very much" to "dislike very much," he was able to rate his feelings (on both his left and his right sides) for a number of people including himself, his mother, and the president. At times the opinions of his left and right brains differed, and, in general, he felt emotionally more irritable on those days on which his hemispheres tended to disagree more strongly.
Evidence that the right brain is capable of having its own intentions and actions is offered by the post-commissurotomy syndrome. In this disorder, which has been observed in several commissurotomy patients for a brief period following surgery, the right brain appears to initiate behaviors which are distinct from the intentions of the left brain. For example, one female patient () wanted to wear a particular dress and reached to retrieve it from the closet. Her left hand, however, grabbed another dress and refused to release it. The patient literally had to struggle against her autonomously driven left hand. Similarly, another split brain patient () tried forcibly to grab his wife with his left hand, while his conscious self and his right hand defended her. Another patient (12) was unable to smoke because whenever he lit a cigarette, his left hand, acting against the patient's conscious intentions, would grab the cigarette and put it out.
Bogen () offers a number of examples of cross-cuing in split brain patients from the right to left hemispheres. For example, one patient was able to accurately name which of 3 items, a sphere, a cube, and a pyramid, was being placed in his left hand, out of sight. The experimenters later noted that the patient's right hemisphere was providing information through behavioral cues to his verbal left hemisphere. When the sphere was placed in his left hand, the patient would at the clock, when it was the cube, he would look at the door, and when it was the pyramid, he would look at the ceiling. When the experimenters blind-folded him, preventing him from looking around the room, he was unable to name the objects. Thus, the patient's left brain was able to understand, for example, that when his eyes were moved toward the clock by his right hemisphere, the left hand was holding the sphere. Bogen (26) pointed out that such cross-cuing indicated that the patient's right hemisphere autonomously controlled this reasonably intelligent, purposeful behavior, supporting the idea of mental duality in split-brained patients.
Other studies show that the right hemisphere can directly influence the affect of the left hemisphere. For example, one split brain patient's right brain was shown a picture her conscious, verbal, left brain could not see (8). The patient suddenly felt a sense of embarrassment and giggled. When she was asked why she was laughing, she said, "Oh, Doctor, you have some machine!" The experimenters had just shown a picture of a nude to her right brain. Her left brain responded with emotion appropriate to the picture, but without a correct understanding of the cause of the emotion. Sperry () proposed that this reaction was due to the transfer of affective information via a "cross-integration systems of the intact brainstem" which remained intact following the surgery.
In another experiment with a split brain patient (), an apparatus was developed which could show a movie exclusively to one hemisphere or the other. When an anxiety provoking movie of an accident was shown to the right brain, the person consciously (though she said she saw nothing of the movie) felt extreme anxiety. Thus, the right hemisphere, beyond the awareness of the patient's verbal, left-sided mind, was able to see a provocative photograph or video and then evoke an emotional reaction, without correct insight, in the patient's verbal, left-sided mind.
Zaidel () in two split brain patients measured the vocabularies of both sides and found that the right brain scored only about three years less than did the left side. The right mind understands complex phrases () such as "kitchen utensil," "container for liquids," "used for slicing." If shown a picture of a cigarette it picks an "ash tray" or "matches" among 9 choices. If it is given a spoon it will choose from a list of related words, "fork," "soup," "silverware" and "cook" (). It was not able to choose "nutrition." The right mind understands verbs, but not long sequences of instructions such as, "Touch the small blue circle and the large green circle (29)."
Studies on Handedness and Laterality
Intracorotid sodium amytal tests indicate that in over 95% of right handers, the left hemisphere is dominant for speech. Similarly, in over 70% of left handers speech is lateralized to the left hemisphere (). In the remaining 30%, about half had bilateral speech representation, and half had a right-sided localization (). It has been suggested that a large portion of this minority of left handers with right hemispheric speech representation may have had an insult to their left brains early in development (33). There is some indication that left handers, in general, show a smaller degree of functional asymmetry between the left and right sides (,). Associations between left handedness and inferior (,,) or superior (38,) intellectual abilities, occupations (architects (), mathematicians (), or artists()), psychotic illnesses (,), and premature death (,) have been found to be inconsistent ().
The significance of the findings on handedness in terms of cerebral laterality is not yet well understood, and the further elucidation of the intellectual and psychological consequences of left handedness or of right-sided speech representation as well as of the etiology of left handedness will require further study. With one exception, the split-brain patients were right-handed. The single left-handed patient reported in the literature () demonstrated right sided language. Her right hemisphere was superior for traditional right-sided tasks such as face recognition. Most interesting, however, is the fact that this left-handed patient manifested the same duality of mind suggested in the right-handed patients. That is, both her left and her right hemispheres were able to understand the experimenters' instructions and to respond each independently of the other.
Left Hemispherectomy Patients
There are a few cases reported in the literature (,,) in which the entire left cortex in adults was removed because of glioma. Although they lost many of their linguistic abilities, these patients were able to function somewhat independently. They could do such complex tasks as tell time and keep appointments, and use the elevator. Their personality characteristics seemed similar to the personalities they had before the operation.
I.Q. and memory quotient scores of patients with left hemispherectomies done earlier in life are comparable to those of patients with right sided hemispherectomies. Vargha-Khadem and Polkey () state, "Only in regard to language processes is there a consensus regarding the differential effects of left and right hemidecortication, and here the differences are apparent only in the relatively subtler aspects of language."
Implications from Neurosurgical Patients
These observations indicate that the cognitive faculties of the right brain in split brain and in left hemispherectomy patients can be fairly well developed. They demonstrate that the isolated right hemisphere has a capacity for autonomous perception, memory, thought, emotion, and volition. The right brain can also induce affect or behavior without a correct, conscious left-sided direct understanding of the reason behind it, as occurred in the experiment with the anxiety provoking movie and in the post-commissurotomy patient whose left hand prevented him from smoking. All this suggests that the right hemisphere has an intact mental faculty, separate from and generally beyond the awareness of the patient's verbal, conscious left-sided mind.
Gazzaniga () has argued that from his own experience 90% of split brain patients have right brains are "extremely passive mental systems capable of performing at best, simple match-to-sample nonverbal perceptual tasks." But, Myers () reviewed Gazzaniga's patients and found that this conclusion was based on a series of patients who had predominately right sided pathology. Levy (), and Zaidel () disagree and from their experience believe that most split brain patients have right hemispheres with a high degree of cognitive function. The broad scope of the literature including the post-commissurotomy syndrome, left hemispherectomy patients, and the Wada studies discussed below suggest that the isolated right hemisphere generally functions at a sophisticated level.
Myers and Sperry (6) and Trevarthen () and others have demonstrated that bisection of the cerebral commissures and the optic chiasm in cats or monkeys leads to an animal with independent cerebral hemispheres, each capable of being taught operant tasks of which the other remains untrained.
In related experiments () in rats, each half of the animal's brain was inactivated for several hours with a direct application of potassium chloride onto the surface of the hemisphere. The awake hemisphere could be taught a task. When the chemical effect wore off, and the potassium chloride was applied to the other side, the animal could not perform the task taught to the other hemisphere, but can be instructed in a new task of which the anesthetized half will be naive when it wakes.
These experiments have demonstrated repeatedly that in lower vertebrates, each hemisphere can function autonomously and is capable of independently learning and remembering complex tasks.
Can the findings from split brain and hemispherectomy patients be applied to intact people? Bogen (26) argues based on a thoughtful review of the literature that in normal individuals there is a duality of mind attributable to a partial hemispheric independence. He cites evidence that the corpus callosum is not capable because of its inherent anatomical and physiological limitations to offer a complete transfer of information from one hemisphere to the other. More recently, Ringo et al () suggested that hemispheric specialization arises from significant interhemispheric conduction delays. Bogen (26) reviewed a number of studies in intact animals and in intact human subjects which demonstrated that in many circumstances one hemisphere can be taught information which is not transferred to the opposite hemisphere. In another paper, Bogen () argued that it would be less reasonable to expect a commissurotomy to create a mind, rather it could only be expected to reveal a preexisting, independent mind.
The fact of hemispheric specialization, the fact that the specialized abilities of the right and left brains in split-brain patients, such as spatial versus linguistic capacities, are similar to the cerebral asymmetries found in intact people (,) also supports the possibility that the duality found in split-brain patients might apply to intact people. Objective evidence of autonomous, high level, mental functioning in the right hemisphere in unoperated patients comes also from the Wada test. This test is not performed on healthy individuals but those who are anticipating neurosurgery. Further, healthy individuals can be studied with methods to show videos to only one hemisphere.
The Wada Test
The Wada test () is a procedure performed by neurosurgeons prior to brain surgery to determine the side on which the patient's language and memory functions are located. In the procedure the patient's carotid arteries are separately injected with a fast acting anesthetic agent, sodium amytal. When one hemisphere is anesthetized, the other awake side is tested for language and memory functions. In a study by Risse and Gazzaniga (), while 8 patients' left hemispheres were anesthetized and their right brains remained awake, an object such as a spoon was put in their left hands. When the left hemisphere recovered, the patient would be asked what had been put in his hand. Typically, he would report that he had no memory of anything being placed in his hand, but when asked to point at a picture of the object from an array of several pictures, he could easily make the correct response. The best explanation for this observation is that the right brain was able to understand and remember what was put in the patient's hand while the left cortex was anesthetized and could later assist the patient in making the correct choice.
Ahern et al () used the Wada test to study two patients with temporal lobe epilepsy and a variant of multiple personality disorder. The right hemisphere is capable in some individuals, as in these two patients, of some limited speech. The first patient had been diagnosed as having a schizophreniform psychosis and a schizoid personality disorder. Post ictally the patient's personality became essentially normal. The patient had a left-sided seizure focus.When his left hemisphere was anesthetized during the Wada test his personality changed from his usual withdrawn psychological state to an affable state identical to his post-ictal personality. Although this patient was left handed, his language function was predominately left-sided. The significance of this patient's handedness is unclear.
The second patient had a normal baseline personality but post ictally became "verbally and physically abusive." His seizure focus was also on the left side, and when his left hemisphere was anesthetized and he manifest a right hemiplegia, he "cursed quite fluently (probably coming from the right hemisphere), and screamed profanities at the examiners. Some of the phrases were paraphasic, such as 'Let me lo my move!'(65)" The best explanation for these findings is that each hemisphere in these two patients is associated with a different personality, one that is released by the anesthetization of the other.
Taken together, these Wada studies suggest that the chemically isolated right hemisphere is capable at times of intact cognitive and emotional activity.
Unilateral Presentation of Films in Intact People
In a series of studies, Wittling, et al used an elaborate technique in which eye movements were yoked to a mask on a video monitor such that a film could be shown to only one half of the retina. This procedure allowed the experimenters to show to normal subjects an emotion laden film to either the left or right hemisphere at a given viewing. The subjects' objective physiological (,) as well as subjective emotional () responses were significantly greater when the films were shown to the right hemisphere. Wittling () argues that because of interhemispheric conduction limitations "neural activity evoked by unilateral visual stimulation remains largely lateralized . . . "
This author suggests that an additional explanation for Wittling's consistent findings may be that lateral visual stimulation may have some tendency to stimulate the opposite hemisphere and possibly inhibit the other. As in the divided visual field studies discussed below, differential hemispheric responses can be consistently observed in normal subjects, each with an intact corpus callosum. These studies do not demonstrate that there is no transfer between the hemispheres, rather they show that the hemispheres can function somewhat differently even in intact people.
Dimond, et al () using a specially constructed contact lens were also able to selectively show films to only one hemisphere in healthy subjects. They found that negative films viewed by the right hemisphere evoked a significantly greater emotional response than when viewed by the left side.
These two groups of studies imply that each hemisphere in intact individuals was capable of understanding and responding to the film independently, and this is consistent with each hemisphere's having intact, autonomous cognitive and emotional capacities.
Controversies About the Interpretation of Split-Brain Studies
There are three primary areas of controversy. The first regards hemisphereisity, the purported tendency of the two hemispheres to have dichotomous cognitive properties. Orienstien (), for instance, proposed that the left hemisphere was more logical and sequential and more dominant in Western thought. The right brain was seen as more intuitive and mystical. Such interpretations became popular in the lay press, and led to accusations of "dichotomania" by a number of neuroscientists (,,) who felt that the proposed ideas far exceeded the reasonable assumptions which the available data would support. However, more recent reconsiderations of the available data by scientists such as Gordon () and Iaccino () suggest that the two hemispheres do have a number of dichotomous properties which persist throughout the experimental literature and which remain somewhat consistent with the popular notions. Corballis, whose 1980 article (74) was severely critical of dichotomous views about the hemispheres, more recently () suggested a new dichotomy in which the left hemisphere is specialized for what he refers to as the generativity of language. Efron (72) argued against accepting any hemispheric specializations, including those for language, and then proposed one based hemispheric differences in visual scanning. What certainly remains clear is that the precise nature of the functional properties of the hemispheres needs to be further elucidated.
A second area of controversy is whether in split-brained patients there is a duality of mind as proposed by Sperry (27) and by Bogen (9). Robinson (), Dennett (), and Eccles () argue against duality. Clearly, the idea of duality is counter-intuitive, but the findings of Sperry's group are of such great interest in part because they do run counter to our ordinary experience. The facts of Sperry's findings are incontrovertible; their psychological, philosophical, and religious significance will continue to be debated. In this paper, the author argues, like Bogen (9) and others (10-13), that there may be a duality of mind, not only in split-brained patients, but also in normal individuals.
A third area of controversy involves questions of experimental methodology, especially around techniques such as divided visual field studies in normal individuals. Young () has articulated some of these issues:
In all DVF studies investigators should pay careful attention to the strategies available to their subjects, and should normally aim to achieve a high degree of uniformity in the strategies actually used. They should be cautious in the inferences they draw from studies of asymmetries for processing visually presented stimuli, and beware of prematurely concluding that they constitute an index of some form of general "lateraisation".
Although the cautions of Young and of others such as Sergent ()
need to be followed, the fact remains that there are hundreds of published
divided visual field studies. There can be no doubt that divided
visual field studies have demonstrate repeatedly that differences exist
between the processing of material presented to one lateral field versus
the other (76). For example, verbal material present to the right
visual field is consistently found to be processed faster than that present
to the left visual field (). These findings are generally interpreted
as reflecting preferential hemispheric involvement of the side contralateral
to the visual field. Prominent among the questions which remain is,
how is it possible for any hemispheric differences to be found when the
corpus callosum is intact and capable of transferring information?
Two explanations have been offered. The first is that the transfer
of information through the corpus callosum is limited by its inherent conduction
properties (59,69), and may further be limited by possible transient, functional
neurologic inhibitions to conduction. Conduction pathways connecting
the visual cortices through the corpus callosum are more sparse than those
between most complimentary areas (16).
But, the more important additional explanation for the divided visual field findings may be that the presentation of the lateralized stimuli may differentially activate the hemispheres (76,,). For example, such unilateral presentations could affect cerebral dominance, and possibly activate one hemisphere while suppressing the other ().
These two explanations are not mutually exclusive, and they do not deny the
existence of intact connections between the hemispheres. Further, they account for the facts that the differences between the hemispheres are not absolute, but relative, and are not present in each individual trial (as in split-brained studies), but develop only with a large number of observations.
HEMISPHERIC ASYMMETRY AND DISSOCIATED STATES
Multiple Personality Disorder
In addition to Ahern's study discussed under the Wada test, other studies have also reported shifts in hemispheric dominance corresponding to different personalities in patients with duel personalities. For example, Henninger (87) reported a patient with a classic multiple personality disorder who was right handed in her dominant personality, but left handed when in her primary alter. This patient also demonstrated left hemispheric dominance on dichotic listening tests with verbal, linguistic stimuli when in her dominant personality. Her alter demonstrated right hemispheric dominance on those tests.
Putnam et al (88) found that 37 of 100 patients with multiple personality changed handedness with personality. Ischolondsky (89) reported two patients with dual personalities who had motor and sensory changes consistent with shifts in hemisphericity with personality. And Gott and associates (90) reported a woman who could voluntary change mental states. One state was superior at right sided tasks, the other with left sided tasks. The idea of a corresponding shift in laterality was supported by EEG changes.
Mathew et al (91) measured cerebral blood flow in a patient with multiple personality disorder when the patient was in her dominant personality and in her primary alter. Compared to her dominant personality, her primary alter manifest a large increase in blood flow to her right temporal lobe. Saxe (92) et al using SPECT to measure the blood flow in another patient with multiple personality disorder found that for 3 of 4 personalities there was an increase in the left temporal lobe. These authors did not report which personality was dominant and which were alters.
Some have argued that multiple personalities cannot involve hemispheric divisions when the number of personalities exceeds the number of hemispheres. Henninger (87) suggests that in patients with multiple personality, the major division, involving the dominant and primary alter personalities is along hemispheric lines. She suggests that further splitting into minor alters "occurs within this subdivision."
Hypnosis And The Right Hemisphere
Some studies of hypnosis have indicated that in highly hypnotizable subjects there is increased right brain activity when the subject is not in trance. For instance, Bakan (93) and Gur and Rehyer (94) found that highly hypnotizable subjects had more left-looking eye movements compared to less hypnotizable subjects when face to face with the examiner. Gruzelier (95,96) found that in highly hypnotizable subjects, compared to low, there was neurophysiologic evidence (tactile processing and bilateral electrodermal orienting) of greater left-sided activity in non-hypnotized states. In these subjects, but not low hypnotizables, there was a significant shift to right-sided dominance when hypnosis was induced. Morgan, et al (97) found that highly hypnotizable subjects have a greater ability to enter alpha states, but have less alpha activity on the right side. However, overall in the literature the relation between resting alpha states and hypnotizeability has been contradictory (98,99).
Edmonston and Moscovitz (100), measuring total EEG power over the occipital areas, did not find an increase in right brain activity during hypnosis, and Sabourin, et al (101) found that highly hpnotizables have more 6-7 Hz theta activity (thought to be an index of focused attention), especially in the frontal area, during trance, but they did not find the activity significantly lateralized, although it was higher on the right side. Crawford (102), using this theta index of activity, found highly hypnotizeables had both significantly more theta than low hypnotizeables and significantly more right than left sided activity during focused activity without hypnosis.
In studies of subjects in trance, DePascalis, et al (103) found an increase in 40 Hz activity (a probable indicator of heightened brain activity) on the right side in highly hypnotizable subjects during the recall under hypnosis of emotionally negative events. Crawford (102) reported that 5.5-7.5 Hz power (high theta) was higher than controls (especially in the temporal regions) under hypnosis in subjects who were highly hypnotizable and were able to develop complete analgesia to ice water. Interestingly, these highly hypnotizable subjects demonstrated increased theta activity on the left side under hypnosis when asked to experience the pain, but shifted significantly to the right side when asked to experience analgesia. The control group of subjects who could not achieve hypnotic analgesia did not manifest any asymmetry.
Ulrich, et al (104) reported a 16% increase in right temporal blood flow during hypnosis. Crawford, et al (105) reported a bilateral increase in PET activity in highly hypnotizable subjects under three hypnotic conditions: 1. at rest, 2. with hand in ice water experiencing pain, and 3. with hand in ice water under hypnotic analgesia. A control group of low hypnotizable subjects did not show this increase in PET activity.
The author knows of no studies in the literature of hypnotized subjects performing a post-hypnotic suggestion under hypnotic amnesia, manifesting an explicit state of mental dissociation. We are beginning such a study in our laboratory to test our hypothesis that in this condition, the right hemisphere might be aware of the suggestion while the left is naive.
FUNCTIONAL IMAGING STUDIES
A number of investigators have explored hemispheric localization during cognitive activities in normal subjects. A number of authors have confirmed that rCBF increases from a resting state to a cognitively active state. Risberg (106) found the left anterior frontal area activity to increase with new problems which avoid habituation. Meyer (107) found increased activation with concentration, attention and apprehension, and (108) compared with a resting state the left side increased overall by 11% though the increases were bilateral in the frontal and most other areas.
Risberg found (109) significant hemispheric asymmetries only when he motivated subjects with payments for performance. In that case a verbal analogy test showed large increases in activity over Wernicke's area and a nonverbal perceptual test showed increased right frontal and parietal activity. Others also have found left posterior inferior frontal (Broca's area) increases during speech and right posterior increases during visual/spacial problem solving tasks. For instance using SPECT, Devous (110) found a bilateral increase, more on the left side, during a verbal Miller's analogies test, and right partial activation during a line orientation task. Arithmetic showed a mild left dominance.
But, Gur and Reivich (111) although they found the expected left sided PET activity increases during a verbal task they found only half the subjects predominately used the right side during a spatial task. And, Reivich (112), using PET imaging, found both verbal and spatial tasks were higher on the right side. There were no lateralized differences in the frontal poles or inferior frontal cortices. Increased activity on the right was noted in the frontal eye fields, superior temporal and inferior parietal lobes. Mazziotta, et al (113,114) found that strategy, whether analytic versus nonanalytic, affected hemispheric activation in response to music tasks. The analytic strategy increased the left-sided activity and the nonanalytic, the right.
A number of investigators have studied patients with depression using dynamic imaging techniques, but their findings are generally inconsistent. A few studies (115-120), have shown a bilateral decrease in rCBF in depressed patients at rest. One of these studies (115) showed the left side to be more decreased than the right and one (117) showed a decrease greater on the right.
Some studies found unilateral changes. Uytdenhoef et al (121) and Drevets et al (122) found increased left-frontal activity, but Kuhl et al (123), Baxter (124), Bench et al (125), and Dolan et al (126) found decreased left-frontal activity. Devous et al (127) found differences in subtypes of depression. Unipolar endogenous depressives were lower bilaterally in the frontal areas; unipolar nonendogenous depressed patients were a little higher bilaterally than controls with the left side higher than the right. Bipolar depressed patients were the highest bilaterally.
Resting imaging abnormalities in depressed patients have been found (122,124,128) to revert to normal after successful treatment with medication or cognitive therapy (128).
Gur et al (129) did verbal and spatial activation studies in medicated depressed patients and controls. They found differences between males and females. Depressed female patients had higher rCBF''s than controls under all conditions, but depressed males had lower rates at rest and during spatial activity but increased to normal control levels during the verbal tasks.
A few studies have used psychologically significant provocations. Pardo, et al (130) found increased left sided frontal PET activity in 4 healthy men during self-induced dysphoria. Three healthy women had bilateral frontal increases (left greater than right). Rauch, et al psychologically provoked patients with obsessive compulsive disorder (131), and found activation primarily in the bilateral orbital frontal cortex, the right caudate nucleus, and the left thalamus. Provocative PET studies of simple phobia (132-134) have, in general, been inconsistent.
Taken together functional imaging studies of pathological conditions such as depression, obsessive depressive disorder, and simple phobia have not revealed consistent findings in terms of cerebral asymmetry. To date, these data suggest that in psychopathological states cerebral asymmetries do not play a consistent role. However, we must appreciate that although functional imaging reveals activated anatomical areas, it does not evaluate the qualitative aspects of the activation. For instance, activation might reveal areas which are either stimulating or inhibiting behaviors. Further, these studies cannot differentiate between areas which are initiating instructions as opposed to simply obeying them. Thus, these studies do not eliminate the possibility that qualitative changes in hemispheric activity may play a role in some psychopathological conditions.
THE RIGHT HEMISPHERE AND THE PSYCHOLOGICAL UNCONSCIOUS
Clinicians employing psychotherapy have long observed the existence and importance of the unconscious mind (135). In psychoanalytic theory the unconscious is generally not thought of as an autonomous personality, although discussions of unconscious determinism (136), unconscious aspects of the ego (136), and introjects (137-139), imply an autonomous, intelligent agent beyond consciousness. Erdelyi (140), Horowitz (141), Luborsky and Chits-Christoph (142), and Weiss (143) have suggested that the unconscious may operate as an intact cognitive and affective entity.
Galin has suggested (10) that the right brain may be intimately related to the unconscious. His views are supported and elaborated on in works by Joseph (12), Watt (13) and Levin (15), but this literature is not yet widely appreciated, and is generally regarded as interesting but not compelling because of a lack of experimental evidence.
A significant part of this difficulty is that there is no clear, firm definition of what authors (135,136) intend by the term "unconscious mind." The term is generally used to explain apparently intentional behavior and/or emotions whose motivations are not correctly appreciated by the person's conscious mind. The unconscious has been associated with emotionality and primitive thinking, both often connected with childhood stresses.
Since Galin's paper some studies have shown results consistent with, among other possibilities, a relation between the right brain and the unconscious mind as defined here. First, several studies (144-151) have shown a right brain superiority for the perception and for the expression of emotion. For example, Ross and associates (145) found in patients that when their right hemispheres were anesthetized with sodium amytal, their speech was fluent but lacked emotion.
A second group of studies (153,153) looked at cerebral asymmetry and emotional memories. These showed that patients with right sided lesions, compared to left sided lesioned patients, had a better factual memory but had a poorer recall of emotional issues.
Next, there are a group of studies relating the experiencing of emotion with asymmetrical brain activity. For example, Schwartz and associates (154) and Tucker and associates (155) found increased left lateral eye movements, an indication of right brain activity, as subjects reflected on emotion inducing questions. Tomarken, Davidson and Henriques (156) measured alpha EEG activity as a measure of left versus right frontal brain activity in nursing students shown an anxiety provoking movie. They observed that those who showed an increase in right sided brain activity on baseline (as reflected in an increased left to right alpha ratio), demonstrated heightened negative affect in response to the films. They also found a correlation between fear responses to the films and an increased measure of brain activity at the right frontal area.
Ladavas and associates (157) used measurements of subject's reaction times to lateralized visual stimuli as an index of lateralized brain activity. They found that when the subjects felt sad, the measurements indicated increased right brain activity.
Tucker and associates (158) used hypnosis and suggestions to induce feelings of depression in normal subjects. They found that in the emotional state there was a decrease in the subjects' ability to perform right sided tasks, yet an increase in right sided brain activity as reflected in alpha EEG suppression. Tucker's finding is consistent with a large literature on depression and cerebral asymmetry. In that literature, although many contradictions exist, the general trend is for studies to associate depression with decreased right sided functioning, yet increased EEG activation. Tucker (159) hypothesized that the right brain may be active in depression, but preoccupied with affective experiences and so less available for cognitive functions.
These studies imply a relation between the right brain and emotion, and they are consistent with the idea of a connection between the unconscious and the right brain, but they do not specifically address that association. Recently, Schiffer and associates (160) attempted to address this issue more directly by comparing cerebral lateralization during the recall of early traumatic memories in the context of an empathic psychiatric interview and comparing it to the lateralization during the recall of neutral memories. Using auditory probe evoked potentials as developed by Papanicolaou (161) as an indicator of brain activity, they studied 20 asymptomatic subjects, 10 of whom had suffered significant childhood trauma and 10 who had not. The trauma group manifest left sided activation during the neutral memory which very significantly shifted to the right side during the psychiatric interview. The control group had a similar, though non-significant shift. Analysis of co-variance indicated that the results were not due to the intensity of the subjects' emotional responses. These results suggest that the right hemisphere might be preferentially associated with painful childhood memories, accessible in an empathic interview.
More recently, Rauch and colleagues (162) performed a similar study using PET scans. They studied 8 patients with PTSD while they attended to 2 tape recorded scrips, one designed to evoke a neutral memory and one, a traumatic memory. Compared to the neutral memory, the traumatic memory manifest significant increases in activation on the right side. The increases were located most prominently in following right sided regions of interest: medial orbitofrontal cortex, insular cortex, anterior temporal pole, medial temporal cortex, and visual association cortex.
IMPLICATIONS FOR PSYCHOLOGY: A POSSIBLE CONNECTION BETWEEN NEUROPHYSIOLOGY
AND DYNAMIC PSYCHOLOGY
The author offers the following speculations and acknowledges the limitations of the literature on which they are based. He believes that much of what has been regarded as "the unconscious mind" may relate to some of the conscious functioning of the less verbal right brain. Clinically, we commonly see patients whose emotions and/or behaviors we consider "neurotic" or inappropriate. We frequently attribute such symptoms to "the unconscious," meaning that there is a psychological explanation which is beyond the patient's comprehension. This explanation often involves experiences in the patient's childhood which were at that time distressing. Even when "the unconscious" is made conscious, and the patient appreciates that his inappropriate feelings and/or behaviors relate to his childhood traumas or conflicts, the symptoms often persist. For instance, a patient may come to feel that his gambling is related to ridicule in his childhood, but still not be able to control his behavior. Indeed, clinically, "the unconscious" often becomes revealed without losing its autonomy. Thus, by the term "unconscious," as we commonly use it clinically, we often refer to mentation of which the person is conscious, but which he experiences as somewhat alien or archaic.
The author speculates that if the right hemisphere supports autonomous mental faculties associated with the concept of the unconscious mind, then this would lead to interesting theoretical and therapeutic implications. This view is ultimately testable and, if supported by scientific data, would clarify and enhance many psychoanalytic concepts. For instance, free association in this view might become a method of listening to the mental faculties or "mind" of the right brain. Psychological "interpretations" might then be the therapist's decipherment of the thoughts or feelings of the patient's right hemisphere. "Resistance" might occur when the mental faculties of the right hemisphere object to the therapist's therapeutic interventions. "Regression" may occur when the right mind takes a dominant role in the patient's personality. "Repression," as suggested by Levin (15) and Henninger (87), might be due to a lack of communication from the right to left mind.
Psychological treatment in this view becomes to a significant degree, the treatment of the "mind" of the right brain, addressing its misconceptions and associated emotional and physiological responses, helping it to surmount its past stressors.
This view is consistent with work suggesting asymmetric effects of some psychoactive medications (163-167), and of ECT (168), and may encourage further research into the understanding and development of physical and psychological treatments of the right hemisphere. This view offers an interesting integration of biological and of psychodynamic concepts, and encourages a respectful, informed cooperation between the major disciplines within psychiatry.
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