The Neural Control of Visually Guided Eye Movements
C. Cortical Mechanisms of Visually Guided Saccadic Eye Movements

To further assess the effects of bicuculline in these two areas, we examined the monkey's ability to make visual discriminations. This is shown in Figure 26. A brightness discrimination was used as previously described, with one target centered within the visual or motor field of the neurons injected. The degree of luminance difference between the target and comparison stimuli was systematically varied. Injection of bicuculline into V1 produced a major deficit in V1 but had no effect in the FEF.

It appears therefore that the role of GABAergic neurons in V1 and the FEF is quite different. In V1, inhibitory circuits are essential for processing information about the nature of visual stimuli. Release from inhibition does not result in increased neuronal activity in the cortico-tectal cells that reside in layer 5 of V1 that under normal conditions play a role in initiating saccades through the superior colliculus. By contrast, in the FEF, release from inhibition as the result of the bicuculline injection results in an increase in the signals sent downstream for eye-movement generation without affecting the ability to discriminate the visual stimuli.