Physiologic and anatomic investigation of a visual cortical area situated in the ventral bank of the anterior ectosylvian sulcus of the cat.

In this paper a cortical area is described that covers approximately the posterior two-thirds of the ventral bank of the anterior ectosylvian sulcus of the cat and is called anterior ectosylvian visual area (AEV). In cats anesthetized with a combination of N2O and barbiturate we explored this area by recording extracellularly the responses of AEV neurons to visual and electric stimulation as well as by injecting HRP into physiologically verified points. AEV neurons were found to be highly sensitive to small light stimuli moving rapidly in a particular direction through their large receptive fields. The properties of 74 neurons were quantitatively analyzed. Increasing the length of the stimulus within the receptive field to more than 2 deg strongly inhibited the responses, whereas increasing the speed of the stimulus movement up to 72-120 deg/s enhanced the neuronal responsiveness. Although the majority of neurons responded to a wide range of possible directions, one clearly preferred direction could usually be found for each neuron. There was predominance of preferred directions toward the contralateral hemifield. Anatomic and electrophysiologic connectivity studies showed that AEV receives its main afferent inputs from the lateral suprasylvian visual area (LS) and from the tecto-pulvinar complex. Although these studies suggested some topographical organization within the projection from LS to AEV, the large receptive fields in AEV, the great majority of which included the central area, did not reveal a clear retinotopic order. It is concluded that AEV is a specific visual area and that functionally the extrageniculate inputs predominate.