Stimulus-dependent interaction between the visual areas 17 and 18 of the 2 hemispheres of the ferret (Mustela putorius).

To study how the visual areas of the 2 hemispheres interact in processing visual stimuli we have recorded local field potentials in the callosally connected parts of areas 17 and 18 of the ferret during the presentation of 3 kinds of stimuli: 2.5 degrees squares flashed for 50 ms randomly in the visual field (S1), 4 full-field gratings differing in orientation by 45 degrees and identical in the 2 hemifields (S2) and gratings as above but whose orientation and/or direction of motion differed by 90 degrees in the 2 hemifields (S3). The gratings remained stationary for 0.5 s and then moved in 1 of the 2 directions perpendicular to their orientation for 3 s. We compared the responses in baseline conditions with those obtained whereas the contralateral visual areas were inactivated by cooling. Cooling did not affect the responses to S1 but it modified those to S2 and to S3 generally increasing early components of the response while decreasing later components. These findings indicate that interhemispheric processing is restricted to visual stimuli which achieve spatial summation and that it involves complex inhibitory and facilitatory effects, possibly carried out by interhemispheric pathways of different conduction velocity.