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1. The amplitude of the negative component of EP in the cat parastriate cortex to binocular flashes is about 10% greater in the left hemisphere than in the right. 2. During simultaneous and equal superficial polarization of symmetrical points of the parastriate cortex by a dc anode two dominant foci are formed. In their time course they pass through the following stages: parallel development, alternate predominance of one of them, gradual weakening of the focus on the right side and, finally, preservation only of the dominant focus on the left side with complete suppression of that on the right. 3. The time course described above is accompanied by initial involvement of shorter callosal pathways by the left-sided dominant focus for the realization of summational-reciprocal interhemispheric relations, whereas the right-sided dominant focus, because of the limited capacity of the corpus callosum for these purposes, utilizes an extracallosal commissural system. 4. In the after-period facilitatory interhemispheric influences of the dominant focus on the right side are interrupted first, followed by the depressing influences. As a result only the dominant focus on the left side remains, and is fully capable of realizing its minimal initial advantages.

Anodic polarization of the parastriate area in the right hemisphere causes in symmetric regions of cat's visual cortex dynamic changes in EPs, interhemispheric functional asymmetry and interhemispheric relations, depending on the intensity of photic stimulation. The sequence of phases of interhemispheric callosal relations and characteristics of interaction between callosal and extracallosal influences were traced in different periods of polarization excitation. It was found that interhemispheric callosal and extracallosal influences lead either to stabilization of initial EP levels and interhemispheric asymmetry or to their change depending on conditions of photostimulation and on the stage in the formation of polarization site.

Interhemispheric relations of symmetrical regions of the fields 18 and 17 in the cat's cortex were studied during bilateral simultaneous polarization of the parastriate cortex. The formation of two dominant sites was shown as well as their "fight", with subsequent retention of the left side alone and suppression of the right one. The interhemispheric relations between the dominant sites during their formation, were of a summation reciprocal type; the interhemispheric influences for the left-side dominant were of callosal nature, whereas for the right-side one they were extracallosal. The "fight" between two dominants resulted in first partial and then complete disturbance of the extracallosal mechanism, whereas the callosal one persisted. This dynamics of the dominants interaction was accompanied by extracallosal mutually depressing inhemispheric influences in the field 17. The obtained data show the role of the functional interhemispheric asymmetry of the surface cortical layers in the hemisphere dominance during interaction of the polarization dominants.

In 40 anesthetized cats, evoked potentials following light flashes during unilateral polarization of the secondary cortical visual area with DC anode (2-10 mcA) were studied in symmetrical centers of the 17th and 18th fields. Four phases of interhemisphere interrelationships between the 18th field's symmetrical centers were shown: 1 -- extracallosal phase of synergic depression; 2 -- callosal phase of dominant interrelationships; 3 -- callosal phase of synergic depression; 4 -- callosal-extracallosal phase of dominant interrelationships. In symmetrical centers of the 17th field, the only 1 extracallosal phase of synergic depression was observed during which the transcallosal modulation of nervous processes occurred. The data obtained are interpreted from the standpoint of the role of dominanta in interhemisphere interrelationships.