Squint Affects Synchronization of Oscillatory Responses in Cat Visual Cortex

As shown previously, neurons in various areas of the cat's visual cortex respond to appropriate visual stimuli with oscillatory activity in the frequency range of 30 – 70 Hz. It has been suggested that synchronization of such responses serves to define assemblies of coherently active cells which represent individual visual objects. In this study, we have investigated this putative binding mechanism in the visual cortex of strabismic cats. We used six adult cats in which divergent squint had been induced surgically at the age of 3 weeks. Multiunit activity was recorded from area 17 with arrays of four or five closely spaced microelectrodes. Subsequently, auto‐ and cross‐correlation functions were computed for all spike trains. To quantify the oscillatory nature of the responses and the strength of synchronization between spatially remote sites, damped sine wave functions were fitted to the correlograms. Analysis of responses obtained from 202 recording sites showed that the vast majority of cells had become monocular. Auto‐correlation analysis revealed that the proportion of oscillatory firing patterns was similar to that observed in normal cats. However, cross‐correlation analysis of 153 response pairs demonstrated that synchronization was reduced significantly between cells dominated by different eyes while it was as frequent and strong as in normal cats between cells dominated by the same eye. These findings indicate that strabismus not only causes a reorganization of afferent inputs but also affects intracortical interactions. Since strabismic cats lack tangential intracortical connections between territories connected to different eyes and are unable to combine signals conveyed by the two eyes these results support the notion that response synchronization is achieved by cortico‐cortical connections and serves as a mechanism for feature binding.