ROLE OF INTRINSIC SYNAPTIC CIRCUITRY IN COLLICULAR SENSORIMOTOR INTEGRATION

The superficial gray layer of the superior colliculus contains a map t hat represents the visual field, whereas the underlying intermediate g ray layer contains a vector map of the saccades that shift the directi on of gaze, These two maps are aligned so that a particular region of the visual field is represented directly above the neurons that orient the highest acuity area of the retina toward that region. Although it has been proposed that the transmission of information from the visuo sensory to the motor map plays an important role in the generation of visually guided saccades, experiments have failed to demonstrate any f unctional linkage between the two layers, We examined synaptic transmi ssion between these layers irt vitro by stimulating the superficial la yer while using whole-cell patch-clamp methods to measure the response s of intermediate layer neurons. Stimulation of superficial layer neur ons evoked excitatory postsynaptic currents in premotor cells. This sy naptic input was columnar in organization, indicating that the connect ions between the layers link corresponding regions of the visuosensory and motor maps. Excitatory postsynaptic currents were large enough to evoke action potentials and often occurred in clusters similar in dur ation to the bursts of action potentials that premotor cells use to co mmand saccades. Our results indicate the presence of functional connec tions between the superficial and intermediate layers and show that su ch connections could play a significant role in the generation of visu ally guided saccades.