RIGHT AND LEFT BRAIN HEMISPHERES ACTIVATION IN THE REPRESENTATIVES OF TWO DIFFERENT CULTURESVadim S. Rotenberg vadir@post.tau.ac.ilAbarbanel Mental Health Center, Tel-Aviv University, Israel V. V. Arshavsky, Medical Institute, Riga, Latvia HOMEOSTASIS VOL 38 JULY 1997, 2: 49-57. A routine EEG combined with alpha-index and spatial synchronization (SpS) analysis was performed in two different populations, native citizens of the Far North-East of Russia and new immigrants to the Far North-East. The investigation was performed in the initial resting state, in the process of mental arithmetic and of imagination of a natural landscape. According to the significant increase in spatial synchronization during task solution, all subjects were divided into 3 groups:
INTRODUCTION The research of brain hemisphere functional asymmetry has a complicated history. According to the initial investigations performed on the split-brain patients (Sperry et al, 1969, Gazzaniga, 1970) it was suggested that the function of the left hemisphere is the handling of verbal material, of signs and symbols which ensures verbal communication. The function of the right hemisphere is the handling of non-verbal material: the perception of images, melodies, intonations, space and body position orientation, field dependence, identification of complicated patterns (human faces) and the performance of kinaesthetic functions (Springer & Deutch, 1985). However, recent data refute this construction as too simplified:
According to another assumption (Zaidel, 1984) the basic function of the left hemisphere is a consecutive analysis of information, whether verbal or non-verbal, while the function of the right hemisphere is "grasping" of many elements of information as a single whole, even before it is analyzed. However, it was shown (Polich, 1982) that the left hemisphere is also able to "grasp" a series of data simultaneously, and as rapidly as the right hemisphere, but only if the differences between the elements of such a series are very definite and easily expressed. If these differences are vague and indefinite, being dependent on many interrelations between elements, the advantage is on the right side. The "novelty- routinization" dichotomy of hemispheric specialization (Goldberg, Costa 1981) suggests that the left hemisphere is critical for any process mediated by well routinized, stored, generic representations, linguistic and non-linguistic alike. However, the left hemisphere is crucial for analytical process which can lead to new knowledge, consequently it is difficult to speak about this hemisphere in terms of "routinization". According to Kosslyn (1978) the fundamental dichotomy is between organization of information along categorical lines in the left hemisphere, and according to spatial coordinates in the right hemisphere. However, this concept has also some limitations. For instance, is a human face with a definite uncommon feature organized along categorical lines, in contrast to the usual human face? How is it possible to explain in Kosslyn's terms that the right hemisphere damage prevents the creative solution of a mathematic task, while the routine mathematic tasks are solved successfully? (Zenkov, 1978). Are metaphors, which are processed by the right hemisphere (Winner & Gardner, 1977) organized according to spatial coordination? By taking into consideration all of the above mentioned data and contradictions, we have suggested that in its most general form the difference between the two strategies of thinking is reduced to opposite modes of organizing the contextual connections between elements of information (Rotenberg, 1979, 1985, 1993). "Left-hemisphere" mode of thinking so organizes any sign material (whether symbolic or iconic) as to create a strictly ordered and unambiguously understood context. Its formation requires an active choice, out of the real and potential connections between the multiform objects and phenomena of a few definite connections, which would not create internal contradictions and would facilitate an ordered analysis. Such a strategy of thinking makes it possible to build a pragmatically convenient but simplified model of reality. The latter is build on probability forecasting (Meerson, 1986) and a search for concrete cause-and-effect relations, and it is precisely for this model that the vector of time orientation exists. In contrast, the function of "right-hemispheric", "image" thinking is a simultaneous capture of an infinite number of connections and the formation due to this capture of an integral but ambiguous context. In such a context, the whole is not determined by its components since all specific features of the whole are determined only by interconnections between these parts. On the contrary, any concrete element of such a context bears a determining stamp of the whole. A new experience is incorporated in this holistic picture of the world. Individual facets of images interact with each other on many semantic planes simultaneously. Examples of such contextual connections are the connections between images in sleep dreams or in work of art. The advantages of this strategy of thinking manifest themselves only when the information itself is complex, internally contradictory and basically irreducible to an unambiguous context (Rotenberg & Arshavsky, 1991). This theoretical conceptualization is a basis for the experimental operationalization. According to the nomination of the polysemantic context it was possible to predict that the right hemisphere has a broader field of associations and is more sensitive to metaphors (due to their polysemantic nature), in comparison to the left hemisphere. Actually, both predictions were confirmed (Chiarello & Richards, 1992, Winner & Gardner, 1977). It is also possible to predict that the nonambiguous geometrical figure is processed by the left hemisphere while a typical human face is processed by the right hemisphere. There are some reasons to suggest that these two opposite cognitive styles are differently distributed in populations of different cultures. According to the analysis of the psychology of consciousness performed by Ornstein (1972), it is the Western civilization which stimulates the development of the left hemispheric functions, while Eastern civilization is more dependent on the abilities of the right hemisphere. This is the reason why the altered states of consciousness (yoga, meditation) which, according to Ornstein, are based on the right hemispheric skills, are mostly used in the Eastern civilizations. It was even shown that in Japanese and Chinese the recognition and discrimination of the patterns of the written text is performed by using the right hemisphere (Hatta, 1977, Huanda & Jones, 1980). However, a systematic psychophysiological investigation of the hemisphere functions in the representatives of the different cultures has not been performed, and it was one of the main tasks of the present study. Another task was to analyze the functional meaning of the different types of the physiological activation of the brain hemispheres in the process of tasks solving. Psychophysiological aspects of brain hemisphere activity are very ambiguous due to some methodological difficulties. It is a general consensus that percentage of EEG alpha-waves, "alpha-index", reflects the level of non-specific activation caused by the brain stem reticular formation: there is a negative correlation between the alpha-index and the degree of involvement of the corresponding cortical area in mental activity (Wertheim, 1974). However, alpha-index is increased during the successful process of the solution of creative tasks performed by a creative person (Whitton, 1978). During altered states of consciousness (meditation) alpha index and alpha wave amplitude are also increased in comparison with the ordinary state of consciousness (Hirai, 1974), although mental activity in meditation is present (Ornstein, 1972). In an attempt to overcome the above-mentioned contradictions, it is reasonable to compare the alpha-index to the so-called spatial synchronization of brain biopotentials (crosscorrelation analysis of the first EEG derivate, Livanov, 1972) under functional loads addressed predominantly to one or the other hemisphere. The increase in spatial synchronization of brain biopotentials recorded from different points of the scalp reflects the contribution of definite cerebral mechanisms in the functional system which ensure the performance of the corresponding functions (Livanov, Sviderskaya, 1984). Usually there are no differences in the amount of spatial synchronization between the two hemispheres during quiet wakefulness but such differences are obvious if the subject is involved in mental activity: spatial synchronization is increased in the right or in the left hemisphere according to the quality of the task (Livanov & Sviderskaya, 1984), and characterizes the functional activity of the corresponding part of the brain. The aim of the present study was to compare the spatial synchronization and alpha-index in the right and left hemispheres in the representatives of different cultures in the process of tasks solution in order to check whether different styles of thinking determine also different types of brain activation. SUBJECTS AND METHODS Brain biopotentials were recorded on EEG apparatus Galileo. Reference electrode was placed in the mid-line of the head between the ears (vertex), other electrodes were placed according to the 10/20 scheme. The resistance of the reference electrode was no more than 20 kOhm, the resistance of the functional electrodes was 7- 10 kOhm. EEG recording was performed in a dark sound-proofed room. EEG artifacts, including eye movement artifacts, have been detected visually and the corresponding parts of EEG have been excluded from the subsequent analysis. Spatial synchronization was assessed using the number of correlations (cross-correlations) between brain potentials recorded from two different points of the cortex. Cross-correlation analysis of the first EEG derivative was performed. Coefficients of correlation have been measured automatically for 4-second epochs during the 60-second EEG recording, and the highest correlations in the right and left hemisphere have been selected automatically and displayed. Correlograph was working according to the cosinusoidal formula proposed by Bernstein (1946) R = -cos(m/n) (R - coefficient of correlation, m - the number of phases of the bio-potentials which correspond in their directions, n - the number of measurements performed with 50 msec intervals). The highest, automatically selected correlogram was compared with a standard auto-correlogram (R =1). The highest level of correlation during rest and during task performance have been used for the comparison between hemispheres. This comparison was based on the mentioned finding (Livanov & Sviderskaya, 1984) that the increase in the spatial correlations reflects the functional activity of the corresponding brain area. Correlograms for the left and for the right hemisphere were recorded on two channels, simultaneously with the EEG signal. Alpha-index was calculated manually for various functional states, in both occipital channels, for further analysis it was used only in adults (after the age of 18), in order to avoid problems with the age-dependent maturation of brain potentials. A minimal alpha-rhythm amplitude used for analysis was 25 microV. A minimal duration of the alpha-rhythm spindle was 0. 5 sec. Alpha-index was used as a single unit without its differentiation according to the real frequency. Mental task included:
The tasks have been presented subsequently, one after another, after a short (1 minute) rest, in a balanced order, each task only once. EEG was recorded during the 60-second task solving period. Only after the end of EEG recording the subject was asked to describe the picture. In the preliminary study we have found a similar dynamic pattern of the spatial synchronization irrespective of the localization in the visual field. Thus, it was quite sufficient to expose the task in the mid-line. Heart rate was measured in order to assess the emotional involvement of the subject in the task. Subjects. Two groups of subjects were tested: native citizens of the Far North-East (Chukotka) of the previous USSR, and people who migrated to this district from the European part of USSR. Obviously left handed subjects have been excluded in order to avoid the additional problem of the relationships between left-handedness and hemispheric specialization. The distribution of Ss according to sex and age is represented in the Table 1. Table 1.
Groups of subjects distributed according to gender and age.
The native population of Chukotka developed in a cultural context which is quite different from the European one. Many people in this district are still hunters and owners of reindeers. Although young and middle-aged generations are school - educated and some of them achieved a professional education or a high education, the style of life is generally almost the same as centuries ago. All cultural traditions are strong. Most representatives of the native population are highly skilled in space orientation, in non-verbal communication and in special kind of art, like carving bones. The proportion of people with a low education (less than 8 years) and simple job (workers in agriculture) is significantly higher in native population than among immigrants. The communication between native citizens is also very special: verbal communication is limited, laconic and rigorous, while there are many nonverbal ritualized actions. RESULTS In the state of quiet wakefulness (basic state), the crosscorrelations ranged 0. 33 - 0. 45 and did not differ statistically in the left and right hemisphere. According to the spatial synchronization, the subjects have been divided into 3 groups:
Table 2.
Alpha-index %(group mean and standard deviation ) in the left (L) and right (R) hemisphere during mental task solution in subjects with different hemispheric dominance. Statistical significance of the difference between task solution and initial level: *-p< 0. 05, ** - p < 0.01, t-test for paired values.
Table No 2 displays the change of alpha-index in these 3 groups. There were no signs of linear relationships between the alpha-index and spatial synchronization. In the subjects of the 1st group, alpha-index was reduced in the left hemisphere even during the rest period before the task performance, when the spatial synchronization was low. During the imagination, alpha-index in this hemisphere was the same as in the initial state. Spatial synchronization increased in the right hemisphere although alpha-index in this hemisphere did not decrease. The arithmetic task produced a decrease in the alpha-index in both hemispheres, while spatial synchronization remained low. In the second group, spatial synchronization was increased in the left hemisphere during mental arithmetic. It was not accompanied by a marked diminution of alpha-index in either left or right hemisphere; only in the left hemisphere the alpha-index was slightly but significantly reduced. During imagination alpha-index was reduced in both hemispheres although spatial synchronization was not increased. In the balanced group, mental arithmetic caused a slight (but significant) reduction of alpha-index in the left hemisphere in parallel with an increase in the spatial synchronization, while mental imagination was not accompanied by alpha-index reduction although spatial synchronization in the right hemisphere was increased. Table 3 demonstrates the distribution of the types of brain hemisphere activity according to the age and to the type of the population. The majority of all age groups of the native citizens (in comparison to immigrants) is formed by subjects with an increased spatial synchronization in the right hemisphere during imagination. Age has also a definite influence on the brain hemisphere activity. Under the age of 10, increased spatial synchronization in the right hemisphere during imagination was found not only in the representatives of the native population but also in immigrants. Table 4 demonstrates the distribution of the types of brain hemisphere activity in immigrants and in native citizens according to the gender. In native citizens the increase of the spatial synchronization in the right hemisphere was less often seen in men then in women. Table 3.
Distribution of the hemispheric dominance in immigrants (IMM) and native citizens (NC) in individual age groups
Table 4.
Both types of task produced heart rate acceleration in all groups, and it confirms that the subjects have been motivated to solve the tasks. Heart rate acceleration differed in subjects with the different patterns of the brain hemisphere activation. In subjects of the 1st group HR acceleration was more prominent during mental arithmetic, and it could indicate that this task was more difficult for these subjects. In the second group heart rate was increased more during imagination. DISCUSSION The central point of the present investigation is the relationship between brain hemisphere activity displayed in spatial synchronization, and the additional physiological activation of the brain which is reflected by the reduction of alpha-index during task performance. The increase in the spatial synchronization in a brain area corresponds to the successful performance of the task relevant to the functional activity of this area (Livanov & Sviderskaya, 1984; Sologub, 1973; Gofman, 1972). It is possible to suggest that an increase in the spatial synchronization in a hemisphere during the task solution indicates a cognitive set to use a particular strategy related to the particular hemisphere (Bryden, 1979; Butler & Glass, 1987). One of the limitations of the present investigation is the impossibility to compare both tasks with respect to the difficulty. Different heart rate reaction to the tasks in different groups argues that the EEG differences found cannot be ascribed to the different difficulties of tasks. The most pronounced decrease in the alpha-index took place during the arithmetic task performance in subjects with the predominating readiness to use the right hemisphere. In subjects with the functional domination of the left hemisphere for the arithmetic tasks (left hemispheric cognitive set) the process of imagination caused a greater activation (desynchronization of the EEG) than arithmetic task solution. However, the latter also caused a moderate but significant reduction of alpha index. The process of imagination in subjects with the right hemispheric cognitive set occurred without additional brain activation, this conclusion is in an agreement with data of Jones-Gotman & Milner, 1977, Grossman, 1988, and De Pascalis & Palumbo, 1986. We suggest that the reduction in the alpha-index is especially pronounced in the condition which produces dissociation between initial brain capability and the nature of the task to be resolved. The nonspecific additional activation reflects an effort to compensate for the relative functional insufficiency of the left or right hemisphere during the task solution. The reduction of the alpha-index reflects the additionally increased arousal (it is confirmed also by the increased heart rate), while the increase in the spatial synchronization in one of the hemispheres reflects the processing style (Kinsbourne, 1970). Processing style and arousal are mutually supplemental. Verbal skills are aquired earlier and to a higher level by females (Bryden, 1978). Thus it is possible to suggest that in those cases when alpha-rhythm suppression is increased over the left hemisphere in males during verbal tasks (Glass, Butler, Alien, 1975) it reflects the additional effort to achieve the cognitive strategy which is opposite to the initial cognitive set. At the same time, according to our data, arithmetic task produces a moderate brain activation (alpha-index reduction) even in subjects who are predisposed to the solution of such tasks. These data confirm the results of other investigators (Butler & Glass, 1976). The task that might rely on the cognitive specialization of the right hemisphere is not regularly accompanied by EEG activation. We shall discuss these data according to our theoretical approach. We suggest that only the organization of the monosemantic context produced by the left hemisphere requires the additional brain activation. The formation of the polysemantic context produced by the right hemisphere does not require additional effort in subjects who are initially prepared for such activity. Moreover, additional activation cannot essentially compensate for the functional insufficiency of image thinking, for instance in subjects with the incomplete lateralization of speech (Yanson & Kenga, 1984). While additional activation of the left hemisphere during the solution of the left hemispheric tasks represents an adaptive strategy of the brain, additional activation of the brain in subject with dominant left hemisphere functions during the solution of the "right hemispheric" tasks does not help, because the right hemisphere is not able to improve its functions in conditions of an additional physiological activation, and this activation does not help in the organization of the polysemantic context. From our point of view, organization of the polysemantic context by the right hemisphere is based on the mechanism which makes different probabilities subjectively equivalent. It helps to pay attention to the "weak" relationships between objects and events and thus to create a new approach to the task. The most probable combinations and consequencess of events are not preferred to less probable combinations and consequences. On the other hand, the additional activation of the left hemisphere is important for the organization of a definite forecast based on the estimation of different probabilities, as well as for the restriction of the number of connections between objects and events. The role of the left hemisphere in probability forecast was confirmed by Meerson (1986). Our data help to create a new physiological method for the estimation of the right hemisphere function. This function is optimal if during the task solution the pronounced spatial synchronization in the right hemisphere is combined with a high alpha index. Conversely, the insufficiency of the right hemisphere strategy manifests itself in reduced spatial synchronization of the brain biopotentials combined with the reduced alpha-index. Another important question is the distribution of different hemispheric strategies in different populations. Ornstein (1972) was one of the first who suggested that the Western civilization is oriented to the cause and effect relationships and requires a high activity of the left hemisphere, while traditional Eastern society (especially if it is using meditation and yoga) stimulates the development of the right hemisphere functions and is adapted to its domination. We have found that the representatives of the Eastern civilization (the native citizens of the Far North East) are characterized by the right hemispheric cognitive set. The initial predisposition to the right hemispheric style of thinking which characterizes children of both populations is rarely replaced by the left hemispheric style in native citizens. In immigrants from Europe, the adult type of the brain hemisphere activity is established already after an age of 10, possibly in the process of school education. It is possible to speculate that school education in the context of left-oriented culture is more capable to replace the right hemispheric style by the left one in comparison with school education in the context of right -hemisphere oriented culture. This conclusion is confirmed by the data that many children of the native population who have failed in the process of the Western-oriented school education and as a result have been supposed to be mentally retarded, are characterized by the right-hemispheric style of thinking (spatial synchronization in the right hemisphere is increased during mental imagination), rather than by mental retardation (Arshavsky, 1988). The difference between genders according to the brain hemisphere activity is less prominent in Western population in comparison to native citizens of the Far North-East. This lack of difference between genders corresponds to the results of other studies performed on the European population (see Butler and Glass, 1987). 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