Integration of Information Between the Cerebral Hemispheres

, Nl-MBPR I, FFBKl.'.XRY 1^98

ity in dichotic perception of vocal nonverbal Nitschke, J.B., Heller, W., & Miller, G.A. (in press). sphere dysfunction in nonverbal learning dis- . sounds. Canadian Journal of Psychology, 26,111- The neuropsychology of arwiety. In J.C. Borod abilities: Social, academic, and adaptive func- 116. (Ed.), The neuropsychology of emotion. New tioning in adults and children. Psychological Ladavas, E., Uimlta, C, & Ricci-Bitti, P.E. (YiW). York; Oxford University Press. Bulletin, 107, 196-209. Evidence for sex differences in right- Nitschke, J.B., Heller, W., Palmieri, P.A., & Miller, Spielberger, CD. (1968). Self-evaluation question- hemisphere dominance for emotions. Neuro- G.A. (1998). Contrasting patterns of brain activity naire. STAl Form K-2. Palo Alto, CA: Consult- psychologia, 18, 361-366. in anxious apprehension and anxious arousal. ing Psychologists Press. Landis, T., Assal, G., & Perret, E. (1979). Opposite Manuscript submitted for publication. cerebral hemispheric superiorities for visual Papez, J.W. (1937). A proposed mechanism of Suberi, M., & McKeever, W.F. (1977). Differential associative processing of emotional facial ex- emotion. Archives of Neurological Psychiatry, 38, right hemispheric memory storage of emo- pressions and objects. Nature, 278, 739-740. 725-743. tional and non-emotional faces. Neuropsycholo- Lang, P,J., Bradley, M.M., & Cuthbert, B.N. (1990). Robinson, R.G., Kubos, K.L., Starr, L.B., Rao, K., & gia, 15, 757-768. Emotion, attention, and the startle reflex. Psy- Price, T.R. (1984), Mood disorders in stroke Tucker, D.M., Watson, R.T., & Heilman, K.M. chological Review, 97, 377-398. patients: Importance of location of lesion. (1977). Discrimination and evocation of affec- Ley, R., & Bryden, M.P. (1982). Hemispheric dif- Brain, 107, 81-93. tively intoned speech in patients with right pa- ferences in processing emotions and faces. Rourke, B.P. (1988). The syndrome of Nonverbal rietal disease. Neurology, 27, 947-958. Brain and Language, 7, 127-138. Learning Disabilities: Developmental manifes- MacLean, P.D. (1949). Psychosomatic disease and tations in neurological disease, disorder, and Wapner, W., Hamby, S., & Gardner, H. (1981). The the "visceral hrain": Recent developments dysfunction. Clinical Neuropsychologist, 2, 293- role of the right hemisphere in the apprehen- bearing on the Papez theory of emotion. Psy- 330. sion of complex linguistic materials. Brain and chosomatic Medicine, 11, 338-353. Semrud, CM., & Hynd, G.W, (1990). Right hemi- Language, 14., 15-33.

Integration of Information Between the terhemispheric interaction appears to have emergent properties, in Cerebral Hemispheres that under certain conditions, one cannot deduce how the hemispheres Marie T. Banich^ interact based solely on how each The Beckman Institute and Department of Psychology, University of Illinois at hemisphere operates in isolation. Urbana-Champaign, Urbana, Illinois Researchers attempting to understand interhemispheric interaction have generally concentrated on two major lines of inquiry. The Despite 30 years of research mation about how these two rela- first examines how information is clearly demonstrating fhe comple- tively distinct portions of the brain represented as it is transferred mentary functions of the cerebral interact to provide the seamless be- from one hemisphere to the other. hemispheres, we have little infor- havior we all exhibit in everyday Thought of differently, this line of life. So striking are some of the inquiry attempts to understand the demonstrations of lateralization of "language" that the hemispheres use to communicate with one an- ;!Recommended Reading function in splif-brain patients (i.e., individuals in whom the corpus other. The second line of inquiry 1, M.T. (1995). Interhemi- callosum, which connects the cere- examines how transfer between the spheric processing: Theoretical hemispheres affects the brain's in- • and empirical considerations. In bral hemispheres, has been sev- I RJ. Davidson & K. Hugdahl ered) that philosophers and neuro- formation processing capacities (Eds.), Brain asymmetry (pp. 427- scientists alike have paused to and strategies. Thaf is, this line of \ 450). Cambridge, MA: MIT Press. consider whether humans might research attempts to understand Helhge, J.B. (1993). Chapter 6: Vari- have two separate and unique con- what mental processes are modu- , eties of interhemisplieric interac- lated or influenced by interhemi- , tion. In J.B. Hellige, Hemispheric sciousnesses, rather than a single asymmetry: Wfiat's right and what's mind. Recent work has helped to spheric interaction. left (pp. 168-206). Cambridge, expand our understanding of the Most interaction between the ce- MA: Harvard University Press. exquisite interplay between the rebral hemispheres occurs via a Lassonde, M., & Jeeves, M.A. (Eds.). hemispheres that provides us with very large neural band of fibers (1994). Callosal agenesis: A natural split brain? New York: Plenum unified thought. It has become known as the corpus callosum (see Press. clear that interhemispheric interac- Fig. 1), which is composed of more Milner, A.D. (Ed.). (1995). Neuropsy- tion has some unanticipated func- than 200 million nerve fibers. Al- chological and developmental tions, such as playing a role in per- though there are other neural path- studies of the corpus callosum ceptually binding together disparate ways by which information can be ' ISpecial lssuej Neuropsyihologia, parts of an object or modulating at- transferred between the hemi- % 921-1007 tentional ability. Furthermore, in- spheres (see Fig. 1), the vast major-

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Hippocatnpal commissure visual, auditory, and somatosen- sory information are transferred Corpus callosum through different sections of the Habenular commissure callosum (e.g., Risse, Gates, Lund, Maxwell, & Rubens, 1989). Intri- Posterior guingly, there is evidence for an commissure asymmetry in the speed of transfer of sensory information between the hemispheres: Such transfer is faster from the right hemisphere to the left than from the left hemisphere to the right (Marzi, Bisiacchi, & Nicoletti, 1991). Anterior commissure Collicular Because not all information commissures Massa intermedia transferred between the hemi- of the thalamus spheres is sensory in nature, researchers have also attempted to Fig. 1. A view of the brain cut down the middle so that the inside-most regions of the right hemisphere are shown. Labeled in this figure are the various pathways determine how higher order (e.g., through which information can be communicated between the hemispheres. Notice spatial, semantic) information is that the corpus callosum is by far the largest, and it is responsible for the vast communicated. This task can be majority of information transfer between the cerebral hemispheres. From Banich somewhat difficult because higher (1997). Copyright 1997 by Houghton Mifflin Company. Used with permission. order information could be transferred between the hemispheres in ity of information is transferred via the major types of sensory informa- a variety of ways. A word, for ex- the callosum. As Reuter-Lorenz tion (e.g., visual, auditory, tactile) ample, could be represented as a and Miller (this issue) discuss, only is processed by a distinct brain re- visual pattern, as a series of letters, rudimentary information can be gion, and because different higher as a series of sounds, or as a mean- transferred without a callosum. order representations of informa- ing. Hence, much of this research Such information includes coarse tion (e.g., abstract visual form vs. has focused not on the exact nature visual information regarding mo- meaning) are processed by differ- of information transferred, but tion but not visual form, binary in- ent brain regions as well, one rather on whether the representa- formation (yes/no, odd/even), might expect that the callosum con- tion of the information involved in general emotional tone (positive, sists of channels, each of w^hich is interhemispheric communication is negative), and information that al- responsible for transferring a dis- similar to or distinct from the rep- lows for the automatic orienting of tinct type of information. resentation employed by each attention. For the most part, this expecta- hemisphere. tion seems to hold. For example, A commonly utilized method in when a simple flash of light is di- such endeavors is to com^pare the HOW IS INFORMATION rected to one hemisphere and the processing that occurs when infor- REPRESENTED WHEN IT IS motor response is controlled by the mation is directed to only one TRANSFERRED BETWEEN other hemisphere, hoth sensory hemisphere with the processing THE HEMISPHERES? (i.e., visual) and motoric informa- that occurs when both hemispheres tion are transferred. Electrophysi- receive identical information. In ological recordings suggest that the the case of visual information, One of the guiding principles of motor signal is sent across middle stimuli are presented to only one interhemispheric interaction is that portions of the callosum that con- visual field (i.e., only to the left or different types of information are nect motor regions of the brain, right of fixation) on some trials and transferred across different sec- whereas the visual signal is sent to both visual fields (i.e., to both tions of the callosum. The callosum across posterior portions of the cal- sides of fixation) on other trials. In- is organized topographically, with losum that connect visual regions formation presented to a given vi- each section connecting nearby re- of the brain (Rugg, Lines, & Milner, sual field is processed initially by gions (i.e., the anterior callosum 1984). Furthermore, studies of pa- the opposite hemisphere. Thus, in- connects anterior brain regions; the tients with cailosal tumors or par- formation presented to the right vi- posterior callosum connects poste- tial section of the callosum provide sual field (RVF; i.e., to the right of rior brain regions). Because each of evidence that, for the most part. fixation) is processed initially by

Copyright © 1998 American Psychological Society VOLUME?, \'i;VIi3i.-R !, FEfiRLiARY Vm the left hemisphere, and informa- errors are much more frequent on suggests that the individual hemi- tion presented to the left visual the third letter of the sequence than spheres employ a representation in field (LVF; i.e., to the left of fixa- the first, whereas this difference is which meaning and form are sepa- tion) is processed initially by the much reduced on RVF trials. The rable. right hemisphere. pattern of errors on BVF trials is The major finding of this line of intermediate between that of RVF inquiry is that the representation and LVF trials (Luh & Levy, 1995). HOW DOES invoked when both hemispheres These findings suggest that both INTERHEMISPHERIC are involved in processing can vary hemispheres contribute to perfor- INTERACTION across situations (see Hellige, 1993, mance so that the representation employed in the interchange of in- MODULATE chap. 6). In some cases, the repre- COGNITIVE PROCESSES? sentation employed when both formation is a blend of the different hemispheres receive information is representations utilized by the two similar to the representation used hemispheres. Researchers have also made by one hemisphere, but not the One of the m^ost interesting find- some progress in understanding other. For example, Hellige, Jons- ings of such research is that the how interaction between the hemi- son, and Michimata (1988) asked representation employed when spheres influences the ways in individuals to differentiate two both hemispheres receive informa- which the brain processes informa- faces that varied by a single feature tion can be completely distinct tion. Research with animals sug- (hair, eyes, mouth, jaw), and exam- from the representation employed gests that at least for the primary ined performance as a function of by either hemisphere in isolation. sensory areas of the brain (i.e., the which feature distinguished the In a series of studies, Karol and I region of the brain where informa- two faces. One might presuppose instructed individuals to decide tion from sensor receptors, such as that the representation employed whether either of two probe words the eye, is first received), integra- when both hemispheres saw the (which were positioned in the same tion of information across the cal- faces (bilateral-visual-field, or BVF, visual field on some trials and in losum allows for a unitary sensory trials) would be similar to the rep- different visual fields on others) world. Because the neural system resentation used by the hemi- rhymed with a previously pre- is organized so that information on sphere generally considered spe- sented target word. We found that the left side of space goes to the cialized for the task (in this case, when a rhyme was present, perfor- right half of the brain, and vice the right hemisphere, because it is mance on RVF trials, and to a lesser versa, there is a need to fuse these usually superior at face process- degree on BVF trials, was influ- two perceptual half-worlds. The ing). However, that was not the enced by whether the meaning of callosum seems to play a critical case. The pattern of performance the two probe words was identical role in this regard. Callosal connec- on BVF trials was identical to that (e.g., bee and bee) or different (e.g., tions in primary sensory areas are observed on RVF (left-hemisphere) bee and sea), an effect not observed often limited to those regions of the trials, but different from that for for LVF trials. We then changed the sensory world that fall along the LVF (right-hemisphere) trials. In task slightly, presenting the two midline, such as where the RVF fact, the representation employed words in different cases and fonts and LVF meet. on BVF trials is frequently similar (e.g., BEE and bee, BEE and sea) so Corroboration of the role of the to that of the hemisphere less adept that they would no longer look callosum in sensory midline fusion at the task. Perhaps when both identical. This manipulation did comes from studies of individuals hemispheres are involved, the not affect performance on RVF and who were born without a callosum, more adept hemisphere has to LVF trials, but changed the pattern a syndrome known as callosal "dumb down" to meet the other for BVF trials (Banich & Karol, 'agenesis. These individuals have hemisphere's ability. 1992, Experiments 4 and 5). Thus, interesting sensory difficulties, in- In other cases, the nature of pro- the words' meaning and form in- cluding a poor ability to discern cessing when both hemispheres are teracted to affect performance on which of two objects placed in cen- stimulated is a blend, or average, of BVF trials, suggesting that the rep- tral vision is closer or further away the processing that takes place resentation used when both hemi- (an ability that relies on the brain within each hemisphere. For ex- spheres are involved in processing computing slight differences in the ample, when the task is naming is one in which physical form and retinal images received by the two consonant-vowel-consonant se- meaning are linked. In contrast, the eyes), a poor ability to determine quences, the pattern of errors var- fact that font and case did not affect whether two points touched on ei- ies by visual field. On LVF trials. either LVF or RVF performance ther side of the trunk are different

I'liblished by Cambridge University Press or the same, and difficulties in lo- to make a decision) than if both has been provided by the recent calizing sounds in space (a skill digits are presented to the same surge of brain-imaging studies. Al- that relies on the brain computing hemisphere (in which case, no in- though these studies are designed slight differences in the timing or teraction is required). In contrast, if to examine specific cognitive pro- intensity of sounds received by the the task is to decide whether two cesses (e.g., memory), the manipu- two ears). All these difficulties rely digits are identical (physical- lations employed often vary in critically on the comparison of in- identity task), interhemispheric in- complexity (e.g., in how many formation received separately by teraction does not yield a perfor- items musf be retrieved from the two hemispheres, and hence re- mance advantage. The summation memory). As task demands are in- quire integration across the callo- task is more con:\plex because not creased, often there is not only sum (Lassonde, Sauerwein, & Lep- only is perceptual processing of the greater activation of the brain re- ore, 1995). digits required (as in the physical- gion specialized for that task, but Recently, it has been proposed identity task), but then some iden- greater activation over both hemi- that the pattern of activation across tification and addition must be per- spheres as well (e.g.. Braver et al., the callosum may help bind to- formed as well These results are 1997). Such findings are consistent gether different parts of the visual consistent with others demonstrat- with the idea that as tasks get more world into unitary objects. When ing thaf performance is better difficult to perform, more re- stimuli on different sides of the vi- when operations are divided sources are recruited from both sual midline move in tandem, cells across the hemispheres (e.g., di- hen:\ispheres. in the two hemispheres fire syn- recting a digit to be added to a tar- Interhemispheric interaction chronously. This synchrony relies get to one hemisphere, while di- also seems to modulate fhe ability specifically on the callosum, as it recting another digit to be subtracted to select certain information for does not occur when the callosum from the target to the other hemi- processing (e.g., the words on this is severed. Because parts of an ob- sphere) than when bofh operations page) while filtering out other in- ject generally move together in the must be performed by the same formation (e.g., the background same direction and at the same hemisphere (Liederman, 1986). noise that occurs while you are speed, such temporal aspects of We believe this effect occurs be- reading). Using three well-known callosal firing may provide a cause the computational power of paradigms, Alessandra Passarotti, mechanism for binding together the brain may be increased by di- Joel Shenker, Daniel Weissman, parts of an object that appear on viding processing over as much and I have demonstrated that inter- either side of the midline (Engel, neural space as possible (in this hemispheric interaction aids task Konig, Kreiter, & Singer, 1991). Be- case, over the two hemispheres), performance when a high degree, cause people typically move their much the way that computational but not a low degree, of selection is eyes so that an object of interest power of computers is increased by required. In one of these para- falls in the center of gaze (and dividing a task over many sysfems. digms, the individual must pay at- hence spans the midline), such cal- Such a division is possible because tention to the overall shape (global losal connections may be important for most tasks (with the possible form) of an item and ignore the for object recognition. exceptions of speech output and small shapes (local form) of which Interaction between the hemi- phonetic processing), specializa- it is composed (or vice versa); in spheres not only influences sen- tion of the hemispheres is relative another, individuals must decide if sory processing, but also modu- rafher than absolute. Thus, even a pair of items matches, and that lates the processing capacity of the though one hemisphere may do a decision must be made by attend- brain. Belger and I (Banich & Bel- particular task less capably or effi- ing to one attribute of the pair (e.g., ger, 1990) found that fhe ability of ciently than the other, it nonethe- their shapes) but not another (e.g., inferhemispheric interaction to fa- less has the capacity to contribute their colors); and in the third para- cilitate performance increases as (see also Beeman & Chiarello and digm, the Stroop paradigm, an in- the computational complexity of Chabris & Kosslyn, this issue). As dividual must pay attention to the task, which we define as fhe tasks get more difficulf, any cost (and name) the color of the ink in number (and nature) of the steps overhead imposed by having to co- which a word is presented while involved, increases. For example, if ordinate processing between the ignoring the meaning of the word. it must be decided whether two hemispheres is more than offset by When there is no interference be- digits add to 10 (summation task), the increased computational capac- tween the two types of information performance is befter if one digit is ity provided by having both hemi- and thus little need for selection, presented to each hemisphere (so spheres involved. interaction between the hemi- that the hemispheres musf interact Indirect support for such an idea spheres does not aid performance.

Copyright © 1998 American Psychological Society For example, interhemispheric in- & Ron, 1995). The implications of alization of function, it will be tefaction is not especially useful such findings remain unclear at critical to understand interhemi- when the global and local form of present, but it is possible that some spheric integration, as research al- an item are the same, when a pair of the attentional difficulties ob- ready suggests that the whole is of items have the same form and served in people with these syn- more than the sum of its parts. the same color, or when the color a dronnes may be lir\ked to disrupted word names is concordant with its interhemispheric interaction. Acknowledgments—Preparation of this article was supported by National Insti- ink color (e.g., "red" is printed in The interplay between the hemi- tute of Mental Health Grant ROl red ink). However, when there is spheres may also be linked to MH54217. I thank Mark Beeman, Chris- conflicting information and indi- changes in cognitive processing topher Chabris, Emanue! Donchin, and Wendy Heller for helpful comments. viduals must select one type of in- with development. During child- formation over another, the degree hood, the speed with which infor- of interference engendered by the mation can be relayed between the conflicting information can be re- hemispheres increases because the Note duced by interhemispheric interac- fatty insulation around neurons, tion. For example, when an item's called myelin, continues to increase 1. Address correspondence to global and local shape lead to dif- in size around callosal neurons un- Marie T. Banich, Beckman Institute and ferent responses, when items til some time during the late teen Department of Psychology, University of Illinois at Urbana-Champaign, 405 match in form but not color, and years. In essence, the hemispheres N. Mathews, Urbana, IL 61801; e-mail: when the word "blue" is printed in of young children are more func- mbanich@s .psych.uiuc.edu. red ink, interaction between the tionally disconnected than those of hemispheres leads to superior per- adults. Children do not exhibit the formance. Furthermore, these re- same advantages of dividing pro- REFERENCES sults, for the most part, are rela- cessing across the hemispheres as Banich, M.T. (1997). Neiiropsychology: The neural tively independent of hemispheric observed in older individuals, but bases of menial function. Boston: Houghton Mif- asymmetries for the task, once that changes as they grow older flin. again suggesting that interhemi- Banich, M.T., & Belger, A. (1990). Inter hemispheric (Liederman, Merola, & Hoffman, interaction: How do the hemispheres divide spheric interaction may affect pro- 1986). Interhemispheric interaction and conquer a task? Cortex. 26. 77-94, cessing in a manner independent of Bdnich, M.T., & Karol, D.L. (1992). The sum of the may be disrupted in dyslexia (Mar- parts does not equal the whole: Evidence from hemispheric specialization. kee, Brown, Moore, & Theberge, bihemispheric processing, journal of Experi- mental Psycbologi/: Human Perception and Perfor- 1996), and may be atypical in atten- mance. 18, 763-784. tional deficit disorder (Giedd et al., Braver, T.S., Cohen, J.D., Nystrom, L.E., Jonides, J., 1994). Future work is likely to be Smith, E.E,, & Noll, D.C. (1997). A parametric study of prefrontal cortex involvement Ln hu- THE IMPORTANCE OF directed to more carefully explicat- man working memory. Neuroimage. 5. 49-62. INTERHEMISPHERIC ing the nature of the relationship David, A.5., Minne, C, Jones, P., Harvey, I., & Ron, M.A. (1995). Structure and function of the INTERACTION FROM A between interhemispheric interac- corpus callosum in schizophrenia: What's the CLINICAL OR tion and certain developmental connection? European Psychiatry, 1Q{\). 28-35. LIFE-SPAN PERSPECTIVE Engel, A.K,, Konig, P., Kreiter, A.K,, & Singer, VV. syndromes. (1991). Interhemispheric synchronization of oscillatory neuional responses in cat visual cortex. Science. 152, 1177-1179. The nature of interaction be- Gale, S.D., Johnson, S.C., Bigler, E.D., & Bfatter, tween the hemispheres may also be D.D. (1995). Nonspecific white matter degen- CONCLUSION eration following traumatic brain injury, jour- important in a number of neuro- nal of the International Neuropsychological Soci- psychological syndromes, and may T ety, I, 17-28. Giedd, J.N., Castellanos, F.X., Casey, B.J., Kozuch, have implications for development In sum, the functionally distinct P., King, A.C, Hamburger, S.D., & Rapoport, and aging. For example, the corpus cerebral hemispheres appear to co- J.L. (1994). Quantitative morphology of the corpus callosum in attention deficit hyperac- callosum seems especially vulner- ordinate their performance in mul- tivity disorder. American journal of Psychiatry, able to damage caused by multiple tiple ways via the corpus callosum, 151, 665-669. Hellige, J.B. (1993). Hemispheric asymmetry: What's sclerosis (e.g., Rao et al., 1989) and which allows for dynamic inter- right and what's left. Cambridge, MA: Harvard closed head injury (Gale, Johnson, change of information. The nature University Press. Hellige, ).B., Jonsson, J.E., & Michimata, C. (1988). Bigler, & Blatter, 1995), and the of the representations used for Processing from LVF, RVF and BILATERAL morphology and function of the such communication is not well presentations: Metacontroi and interhemispheric interaction. Brain and Cognition, 7, 39- corpus callosum are different in elucidated at present, especially for 53, people with schizophrenia than in higher order information. How- Lassonde, M., Sauerwein, H.C, & Lepore, F, (1995). Extent and Umits of caliosal plasticity; neurologically intact individuals ever, it is clear that to further un- Presence of disconnection symptoms in cal- (e.g., David, Minne, Jones, Harvey, derstand the implications of later- losal agenesis. Neuropsychologia, 33. 989-1007.

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Liederman, J. (1986). Subtraction in addition to ad- perimental Psychology: Human Perception and connection in multiple sclerosis: Relationship dition: Dual task performance improves when Performance, 21, 1243-1258, to atrophy of the corpus caJlosum. Archives of tasks are presented to separate hemispheres. Markee, T., Brown, W,S,, Moore, L.H., & Theberge, Neurology, 46, 918-920, journal of Clinical and Experimental Neuropsy- D,C. {1996). Calossa! function in dyslexia: Risse, G,L., Gates, J-, Lund, G,, Maxwell, R, & chologi/, 8, 486-502. Evoked potential interhemispheric transfer Rubens, A, (1989), Interhemispheric transfer in Liederman, ]., Merola, ].L., & Hoffman, C. (1986), time and bilateral field advantage. Develop- patients with incomplete section of the corpus Longitudinal dat,a indicate that hemispheric mental Neuropsychology, 12, 409-428, callosum. Archives of Neurology, 46, 437-443, independence increases during early adoles- Marzi, CA., Bisiacchi, P,, & Nicoletti, R, (1991), Is cence. Developmental Neuropsychology, 2, 183- interhemispheric transfer of visuomotor infor- Rugg, M,D,, Lines, C.R, & Milner, A.D. (1984). 20L mation asymmetric? Evidence from a meta- Visual evoked potentials to lateralized visual Luh, K.E,, & Levy, ], (1995), Interhemispheric co- analysis, Neuropsychologia, 29, 1163-1177, stimuli and the measurement of interhemi- operation: Left Ls left and right is right, but Rao, S,M,, Bemadin, L,, Leo, G,J,, Ellington, L,, spheric transmission time. Neuropsychologia, sometimes the twain shall meet, journal of Ex- Ryan, S,B,, & Burg, L,S, (1989). Cerebral dis- 22, 215-225,

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