The influence of transcortical relationships on visual responses in rats

Visual responses of the 17/18 border of one hemisphere in anesthetized rats were studied while the opposite cortex was depressed. The depression of the opposite cortex was achieved by a cryoblockade of the homotopic area or by bleaching the unstimulated eye. In the first series of experiments field potentials were recorded, whereas in the second experimental series tests were carried out on single units. Bleaching the unstimulated eye produced mostly an enhancement of long latency potentials recorded in deeper layers. Cryoblockade of the contralateral cortex depressed the responses in a more uniform fashion. Most units typically presented a weaker evoked firing after cryoblockade. However, in some neurons the reaction to the treatment depended upon the nature of the stimulus and other units lost their orientation specificity. A single explanation such as a tonic excitatory transcortical influence is insufficient to account for these results.