Biological Psychology 5 (1977) 245-255 © North-Holland Publishing Company
VISUAL EVOKED RESPONSE CORRELATES OF CEREBRAL SPECIALIZATION A F T E R HUMAN COMMISSUROTOMY PEGGY S. GOTT *, VALERIE S. ROSSITER, GARY C. GALBRAITH t , and RONALD E. SAUL
Division of Biology, California Institute of Technology, Pasadena, California 91109; Department of Psychology, University of Southern California, Los Angeles, California 90007; Department of Neurology, Los Angeles County- USC Medical Center, Los Angeles, California 90033 Accepted for publication 21 January 1977
Visual evoked responses (VERs) were recorded from commissurotomy patients and normal subjects in order to investigate the electrophysiological correlates of cerebral lateralization and independent hemispheric processing. A verbal task consisted of detecting rhyming words and a spatial task consisted of comparing matching shapes. Stimuli were delivered, by means of a computer graphic display, into the right visual field, the left visual field, or both visual fields. Behavioral results and evoked response waveforms showed lateralization for verbal processing in the left hemisphere for the patient group. Analysis of variance of product moment correlation coefficients between VER waveforms indicated significant differences between unilateral and bilateral stimulation for both patients and normals. Commissurotomy and normal VERs showed similar patterns of correlation when verbal stimuli were delivered to the left hemisphere, but differed during right hemisphere stimulation. The results are discussed in terms of VER correlates of visual-verbalprocessing.
1. Introduction Lateralized tests with patients who have undergone surgical section of the forebrain commissures for control of intractable epilepsy confirm that, in most righthanded individuals, the two hemispheres of the brain are specialized for different cognitive functions. Hemispheric lateralization has been described in terms of a superiority of speech, calculation and related linguistic or analytic activities for the hemisphere, and configurational, spatial, and synthetic activities for the right hemisphere (Bogen and Gazzaniga, 1965; Sperry and Gazzaniga, 1967; Levy-Agresti * Present address and reprint requests: PeggyGott, Ph.D.,Department of Neurology, Los Angeles County/University of Southern California Medical Center, 1200 N. State Street, Los Angeles, California 90033. t Present address: Neuropsychiatric Institute-Pacific State Hospital Research Group, University of California at Los Angeles, Pomona, California 91768. 245
246
P.S. Gott et al. / VER after commissurotomy
and Sperry, 1968). Studies with these patients have further demonstrated that each disconnected hemisphere may independently process sensory information and, for the most part, is unaware of information presented exclusively to its opposite mate (Sperry, 1974). Although results on hemispheric specialization agree with and reinforce conclusions drawn from studies on left-right field differences in normals (White, 1969), the electrophysiological correlates of cerebral lateralization are currently the subject of much investigation and some controversy (Friedman, Simpson, Ritter and Rapin, 1975; Galambos, Benson, Smith, Schulman-Galambos and Osier, 1975). In the present study, therefore, visual evoked responses (VERs) were recorded from commissurotomized and normal individuals to directly investigate the electrophysiological correlates of hemispheric specialization and 'split-brain' phenomena. Commissurotomy patients lacking direct interhemispheric communication offer special advantages in differentiating brain activity related to specific modes of information processing. For example, electrical activity from each hemisphere can be independently assessed during tasks involving verbal or spatial stimuli. In a previous paper (Gott, Rossiter, Galbraith and Saul, 1975) we presented the results of within- and between-hemisphere correlations during unilateral visual field stimulation. Compared with normals, the commissurotomy patients had significantly higher within-hemisphere correlations during both spatial and verbal stimulation, and significantly lower between-hemisphere correlations during verbal stimulation. In the present paper, however, unilateral visual field stimulation is compared with bilateral field stimulation, the latter condition being more analogous to the normal viewing process. Results provide some electrophysiological indication of the extent to which each hemisphere is involved in linguistic functioning and suggests that the electrical activity from the left parietal area provides a possible marker for visualverbal processing.
2. Method 2.1. Subjects
Five commissurotomy patients (L.B., C.C., N.G., N.W., and R.Y.) and five normal subjects were tested. The commissurotomy patient~ (3 male and 2 female) had undergone presumed complete surgical section of the forebrain commissures including the corpus callosum, anterior and hippocampel commissures, and massa intermedia when present. Surgery was performed to help control intractable epilepsy (Bogen, Fisher and Vogel, 1965; Bogen, Sperry and Vogel, 1969). All of the patients tested were predominately right-handed both before and after surgery. Some additional pertinent facts are summarized in table 1 ; more complete histories of these patients have been published elsewhere (Sperry, Gazzaniga and Bogen, 1969; Milner and Taylor, 1972).
247
P.S. Gott et aL / VER after commissurotomy
Table 1 Commissurotomy patients * Patient
Sex
Estimated time of injury lesion
Probable side of epileptogenic lesion
Age at operation
Age when tested
L.B. C.C. N.G. N.W. R.Y.
M M F F M
Birth Birth Birth
VISUAL EVOKED RESPONSE CORRELATES OF CEREBRAL SPECIALIZATION A F T E R HUMAN COMMISSUROTOMY PEGGY S. GOTT *, VALERIE S. ROSSITER, GARY C. GALBRAITH t , and RONALD E. SAUL
Division of Biology, California Institute of Technology, Pasadena, California 91109; Department of Psychology, University of Southern California, Los Angeles, California 90007; Department of Neurology, Los Angeles County- USC Medical Center, Los Angeles, California 90033 Accepted for publication 21 January 1977
Visual evoked responses (VERs) were recorded from commissurotomy patients and normal subjects in order to investigate the electrophysiological correlates of cerebral lateralization and independent hemispheric processing. A verbal task consisted of detecting rhyming words and a spatial task consisted of comparing matching shapes. Stimuli were delivered, by means of a computer graphic display, into the right visual field, the left visual field, or both visual fields. Behavioral results and evoked response waveforms showed lateralization for verbal processing in the left hemisphere for the patient group. Analysis of variance of product moment correlation coefficients between VER waveforms indicated significant differences between unilateral and bilateral stimulation for both patients and normals. Commissurotomy and normal VERs showed similar patterns of correlation when verbal stimuli were delivered to the left hemisphere, but differed during right hemisphere stimulation. The results are discussed in terms of VER correlates of visual-verbalprocessing.
1. Introduction Lateralized tests with patients who have undergone surgical section of the forebrain commissures for control of intractable epilepsy confirm that, in most righthanded individuals, the two hemispheres of the brain are specialized for different cognitive functions. Hemispheric lateralization has been described in terms of a superiority of speech, calculation and related linguistic or analytic activities for the hemisphere, and configurational, spatial, and synthetic activities for the right hemisphere (Bogen and Gazzaniga, 1965; Sperry and Gazzaniga, 1967; Levy-Agresti * Present address and reprint requests: PeggyGott, Ph.D.,Department of Neurology, Los Angeles County/University of Southern California Medical Center, 1200 N. State Street, Los Angeles, California 90033. t Present address: Neuropsychiatric Institute-Pacific State Hospital Research Group, University of California at Los Angeles, Pomona, California 91768. 245
246
P.S. Gott et al. / VER after commissurotomy
and Sperry, 1968). Studies with these patients have further demonstrated that each disconnected hemisphere may independently process sensory information and, for the most part, is unaware of information presented exclusively to its opposite mate (Sperry, 1974). Although results on hemispheric specialization agree with and reinforce conclusions drawn from studies on left-right field differences in normals (White, 1969), the electrophysiological correlates of cerebral lateralization are currently the subject of much investigation and some controversy (Friedman, Simpson, Ritter and Rapin, 1975; Galambos, Benson, Smith, Schulman-Galambos and Osier, 1975). In the present study, therefore, visual evoked responses (VERs) were recorded from commissurotomized and normal individuals to directly investigate the electrophysiological correlates of hemispheric specialization and 'split-brain' phenomena. Commissurotomy patients lacking direct interhemispheric communication offer special advantages in differentiating brain activity related to specific modes of information processing. For example, electrical activity from each hemisphere can be independently assessed during tasks involving verbal or spatial stimuli. In a previous paper (Gott, Rossiter, Galbraith and Saul, 1975) we presented the results of within- and between-hemisphere correlations during unilateral visual field stimulation. Compared with normals, the commissurotomy patients had significantly higher within-hemisphere correlations during both spatial and verbal stimulation, and significantly lower between-hemisphere correlations during verbal stimulation. In the present paper, however, unilateral visual field stimulation is compared with bilateral field stimulation, the latter condition being more analogous to the normal viewing process. Results provide some electrophysiological indication of the extent to which each hemisphere is involved in linguistic functioning and suggests that the electrical activity from the left parietal area provides a possible marker for visualverbal processing.
2. Method 2.1. Subjects
Five commissurotomy patients (L.B., C.C., N.G., N.W., and R.Y.) and five normal subjects were tested. The commissurotomy patient~ (3 male and 2 female) had undergone presumed complete surgical section of the forebrain commissures including the corpus callosum, anterior and hippocampel commissures, and massa intermedia when present. Surgery was performed to help control intractable epilepsy (Bogen, Fisher and Vogel, 1965; Bogen, Sperry and Vogel, 1969). All of the patients tested were predominately right-handed both before and after surgery. Some additional pertinent facts are summarized in table 1 ; more complete histories of these patients have been published elsewhere (Sperry, Gazzaniga and Bogen, 1969; Milner and Taylor, 1972).
247
P.S. Gott et aL / VER after commissurotomy
Table 1 Commissurotomy patients * Patient
Sex
Estimated time of injury lesion
Probable side of epileptogenic lesion
Age at operation
Age when tested
L.B. C.C. N.G. N.W. R.Y.
M M F F M
Birth Birth Birth
