PSYCHOPHYSIOLOGICAL CHARACTERISTICS OF VISUAL PERCEPTION OF SCHIZOPHRENIC PATIENTS WITH POLARIZATION OF THE OCCIPITAL AND FRONTAL CORTEX UDC 612.821:616.895.8

I.A. Korsakov

The psychophysiological study of the features of the formation of the subjective image in schizophrenia constitutes a problem, the relevance of which extends both into the field of knowledge of the regularities characteristic of the reflection of the external world by healthy individuals and schizophrenic patients (schizophrenia is in this case a "natural model" of the distortion of these regularities), and into clinical practice, since data on the psychophysiological bases of the pathogenesis of schizophrenia may have a definite diagnostic value. The disturbances of cognitive activity in schizophrenia have for many years been the object of the unwavering attention of psychiatrists, as well as of psychologists and pathophysiologists. A number of fundamentally important regularities of perception have been identified in schizophrenia, relating to disturbances in selective attention and in the sphere of the preparatory set in perceptual function. The concrete physiological content of these disturbances is, however, of special interest. While it is the case that the definitive psychophysiological solution to this problem is still hardly possible today, the contemporary methodological foundation does permit us to approach the solution of a number of nodal questions in the analysis of cognitive activity in schizophrenia, and first and foremost, to approach the study of the functional-temporal structure of the perceptual act. In a previous investigation [7] of the dynamics of the psychophysicai indices of perception in directional shifts in the functional status of the visual and frontal cortex induced by their polarization, we demonstrated that selectivity of perception, reflected in the criterion of decision-making, is in many respects mediated by the frontal region of the cortex. Shifts in the potential of the cortex are one of the components of the active regulation of the sphere of perceptual set. The accumulation of data obtained to the present time, regarding the psychophysiological mechanisms of perception in healthy individuals, proves the suggestion that data, both on the pathogenetic bases of this illness and on the paths to the development of its objective diagnosis, may be obtained in the study of schizophrenic patients. The present report is in fact devoted to such an investigation. The investigation was carried out in 48 schizophrens patients (15 simple, 6 slowly progressive, ii paroxysmal, and 16 paranoid). The method of stimulation and calculation of psychophysiological indices is entirely identical to those used in our preceding investigation [7]. Therefore only the most important features of the method are described in the present report. The subject's task in the experiments to be described consisted in the discrimination of the brightness of a pair of light flashes. In half the cases the second flash in the pair was brighter than the first by a quantity negligibly exceeding the differential threshold. In other cases the flashes were identical in brightness. When the subject perceives the flashes to be different in brightness, he is supposed to press a button twice, or once when they are perceived to be identical. The correct reactions to unequal and equal stimuli are appraised as a correct identification and a correct negative; erroneous reactions are appraised as signal missing and as a false alarm, respectively. In six

V. P. Serbskii All-Union Scientific-Research Institute of General and Forensic Psychiatry, Ministry of Public Health of the USSR, Moscow. Translated from Zhurnal Nevropatologii i Psikhiatrii imeni S. S. Korsakova, Vol. 88, No. i, pp. 110-113, January, 1988. Original article submitted February 26, 1987. 0097-0549/89/1802- 0155512.50

9 1989 Plenum Publishing Corporation

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Fig. i. The index of the criterion of decision-making with polarization of the frontal cortex of healthy individuals (I) and schizophrenic patients (II). a) The dynamics of the criterion in a subgroup with a small number of signal missings; b) with a large number. Here and in Fig. 2: i) Background; 2) cathode; 3) anode.

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experiments the reactions of the subjects were, according to the instructions, the reverse of the usual, i.e., in perceiving the flashes as different, it was necessary to press the button once; if equal, twice. In this case, one press in response to a flash of equal brightness is appraised as a false alarm, and two presses in response to a flash of unequal brightness, as signal missing. On the basis of an analysis of the data in the literature [2, 5], a current density from 50 to 200 ~ / c m 2 , which does not exceed that allowable in physiotherapeutic procedures, was chosen for polarization. Neither subjective sensations nor negative consequences of polarization were noted in connection with the action of the polarizing current. Silver cup electrodes were employed for the application of the current. A polarizing electrode was placed in the occipital area along the sagittal suture 2.5 cm above the thalamus in the case of the polarization of the occipital cortex, and 7 cm rostral to the vertex and 4-6 cm lateral to the sagittal suture (to the right or to the left) with polarization of the frontal cortex. The second polarizing electrode was placed on the mastoid. The switching on and the switching off of the polarization were effected continuously over the course of i-3 sec. The experiment consisted of three series: prior to polarization, and with cathodal or anodal polarizations following one another of the occipital or frontal cortex. A five-minute pause preceded each series, in the course of which the chamber was illuminated. The series began 1 min following the darkening of the chamber. The purpose of this procedure was the equalization of the series of an experiment with respect to the characteristics of dark adaptation. In order to obtain additional information on the subjective sphere of perception, the subject, besides responding regarding the results of the perception, "labelled" the situation by means of a special button when he was not sure of the correctness of the perception. The investigation showed that, as in the investigation of healthy subjects [7], with polarization of the occipital cortex, cathodal polarization of the visual cortex led reliably (p < 0.01) to an increase in differential sensitivity (approximately by a factor of 3), while anodal polarization led to a decrease (approximately by a factor of 1.5). In this case the index of the criterion did not undergo substantial changes. The index of the criterion did not undergo reversal in 89% (p < 0.01) of schizophrenic patients, as compared with healthy individuals, during the polarization of the frontal cortex. It can be seen from Fig. 1 that such a reversal was not observed either in the subgroup with a small number of misses or in the subgroup with a small number of false alarms. The only thing that can be noted here is that this is a shift in the index of the criterion over the course of the experiment in the direction of an increase in its initial value. The above-described regularity did not extend to the paranoid form of schizophrenia, for which, during the polarization of the frontal cortex, dynamics of the index of the psychophysical criterion similar to those recorded in healthy individuals were characteristic. It is interesting that schizophrenic patients, as contrasted with healthy individuals, as a rule made more errors of the signal missing type than errors of the false alarm

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Fig. 2. The IS during polarization of the frontal cortex in healthy individuals (I) and schizophrenic patients (II).

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type (72% of the subjects); however, patients with the paranoid form of the illness differed from patients with the other forms of the illness with respect to this index as well. Among the patients with the paranoid form of schizophrenia, the subgroups with a larger or a smaller number of signal missings were identical. The level of doubts regarding the correctness of perception in schizophrenia was extremely low as contrasted with healthy subjects. It was equal to zero in 72.8%, or did not exceed 10%, and this feature of perception was also observed in the patients with the paranoid form of schizophrenia. In order to test whether the large number of signal missings, sometimes exceeding the number of correct responses, was the result of an "economizing" reaction (one press of the button instead of two presses when evaluating the flashes as unequal in brightness), in a study with six schizophrenic patients the pre-experiment instructions called for a one-time press of the button in case of a perception of the flashes as unequal in brightness. In these conditions five subjects as before made more errors of the signal missing type than errors of the false alarm type; one subject, as in the case of the usual instructions, more often pressed the button once, i.e., made a larger error of the false alarm type. According to contemporary data, the occipital cortex is associated with the regulation of sensitivity [7], while the frontal cortex is associated with the realization of the activity and the selectivity of perception, which are reflected also in the parameters of biopotentials [4, 8-10]. This makes it possible to distinguish two components which differ in functional significance in the regulatory mechanisms of perception, namely an active and a passive. Passive regulation is reflected in spontaneous fluctuations in the sensitivity of the analyzer or in a relative instability of the decision criterion [3], and to a large extent is manifested in the background fluctuations of the potential of the occipital and frontal cortex, as per [7]. Active regulation is manifested indirectly in directed shifts in the functional status of the brain, first and foremost of the frontal divisions of the cortex [i], exerting a marked influence on other cortical areas, including the projection areas. These facts provide grounds for linking the specific effects, which depend on the direction of the current and on the set of the subject in response to a significant signal, of the polarization of the frontal cortex, with the active regulatory component of perception, and that of the occipital cortex, with the passive component. Considering the psychophysiological features of the disturbances in the formation of the subjective image in schizophrenia, it is possible to draw the conclusion that the component of passive regulation of the function of perception is preserved in schizophrenia, since the effects of the polarization of the occipital cortex are similar in healthy individuals and schizophrenic patients. Thus, a "breakdown" of the active component of the regulatory mechanisms of perception, in the realization of which, as was shown previously [7], the frontal region of the cortex of the cerebral hemispheres plays an important role, underlies the disturbances of perception which are characteristic for schizophrenia. Although during polarization the functional state of the frontal cortex is in fact altered, the changes in the motivational sphere of perception which are characteristic for healthy individuals do not take place, since in schizophrenia an adequate psychological set, which is one of the important psychophysiological correlates of the activity of perception and which is mediated by the functions of the frontal cortex, is not formed toward a significant signal. Thus a quite simple method can be suggested for use following the appropriate 137

practical testing as a supplement to the existing diagnostic techniques. The method does not require the complicated apparatus typically employed for the analysis of brain biopotentials. It is sufficient to suggest that the examinee differentiate two kinds of signals (for example, 60-100 pairs of light flashes, as in the present study), to distinguish the signals in the perception of which he has erred less frequently (for healthy subjects, as was demonstrated previously [7], such stimuli are significant), and then to calculate the index of significance (IS). The latter is defined as the logarithm of the ratio of probabilities of the correct identification of significant and insignificant stimuli. The results of such a calculation for healthy individuals and schizophrenic patients are presented in Fig. 2, from which it can be seen that in healthy individuals the dynamics of the IS during polarization in the case of the successive series "background", "cathode", "anode" may be described by the IS 0 + IS+ + ISr where IS 0 is the initial value of IS; IS+ is a decrease in its numerical value relative to the initial, or as a rule, the reversal of the sign of the IS; ISr is an increase in numerical value relative to the initial, or in the case of the use of the anode following the cathode, a repeat reversal of the IS. In the calculation of the IS during polarization, the same stimuli as in the determination of the IS 0 were taken as the index signal. Taking due account of the definition of the positive, a negative value of the IS during the action of the cathode indicates that in this case perception is accomplished with the support of another signal, i.e., indicates a reversal of psychological set. This regularity is not observed in schizophrenia, and the term IS itself as applied to schizophrenia is, thus, quite conditional, since it has not been possible in the patients examined to distinguish significant signals either by physiological or psychological indices [6]. As regards the negative value of the IS, calculated in accordance with the formal definition accepted in psychophysics of different stimuli as signals, it reflects not the great significance of equal flashes, but passivity in the accomplishment of the task of differentiating signals, not a set toward the discrimination of equal stimuli, but a deficit in the activity of perception. The possible objection, that the absence of the dynamics of the IS in schizophrenia is the result of the use of neuroleptics, is disposed of by the fact that in patients with the paranoid form of schizophrenia who have received the same treatment the dynamics of the IS are similar to those in healthy individuals. Thus, the investigation of the function of perception using the polarization of the frontal and occipital cortex in a situation of the discrimination of visual stimuli has made it possible to identify disturbances in the regulatory mechanisms of perception which are specific to schizophrenia. These disturbances consist in the dysfunction of the active component of the regulation of perception, which is mediated in healthy individuals by the frontal region of the cortex, and which determines the superior perception of signals which are subjectively regarded as more significant. LITERATURE CITED I. 2. 3. 4. 5. 6. 7. 8. 9. I0.

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A. G. Asmolov, Activity and Purpose [in Russian], Moscow (1979). A. M. Gutman, The Biophysics of the Extracellular Currents of the Brain [in Russian], Moscow (1980). Yu. M. Zabrodin, The Efficiency of Operator Activity [in Russian], Moscow (1982), pp. 3-29. A. M. Ivanitskii, V. B. Sterlets, and I. A. Korsakov, Information Processes of the Brain and Mental Activity [in Russian], Moscow (1984). Lo A. Komarova and L. A. Blagovidova, Manual of Physical Treatment Methods [in Russian], Leningrad (1983). I. A. Korsakov, Zh. Nevropatol. Psikhiatr., No. 12, 83-88 (1982). I. A. Korsakov, The Electrophysiology of Learning [in Russian], Moscow (1985). A. R. Luria, Principles of Neuropsychology [in Russian], Moscow (1973). Yu. F. Polyakov, The Pathology of Cognitive Activity in Schizophrenia [in Russian], Moscow (1974). E. T. Sokolova, Motivation and Perception in the Norm and in Pathology [in Russian], Moscow (1976).