Relationships between image structure and gamma oscillations and synchronization in visual cortex of cats

The relationships between visual object configurations and interneuronal spike synchronization and gamma oscillations are examined in the present investigation. Cells were initially stimulated with moving, optimally oriented, single 20 degrees -long bars of light, centred on the compound receptive field of a pool of cortical neurons. When this kind of stimulus evoked intrinsic gamma oscillations and/or synchronization, we gradually fractured the original target. In addition, colinearity was ruptured by forming L- and T-shaped configurations. All fractures and discontinuities were introduced well outside the excitatory receptive field. Multiunit activity in the visual cortex (areas 17 and 18) was recorded in anaesthetized cats. Recording sites were separated by 0.4-1.2 mm. The data analysis indicates that gamma oscillations follow a rule by which unfractured bars yielded the highest S/N ratios. Synchronization strength, as revealed by the central peak in cross-correlograms, also seemed to depend upon stimulus configuration. However, the magnitude of the central peak failed to follow a consistent trend. For instance, the greatest magnitude of the central peak occurred for both colinear and orthogonal types of target. Our results support the notion that both gamma oscillations and neuronal synchronization are stimulus-dependent.