DIVERGENCE/CONVERGENCE IN RETINO/GENICULOALCORTICAL

Harvard University (Medical School), Boston MA

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Abstract

We will study the mechanisms by which visual information is transformed in the pathway from retina, to the lateral geniculate nucleus of the thalamus (LGN), and finally to layer 4 of primary visual cortex. The physiology of these three populations of neurons in the visual system have been extensively studied over the past forty years. Individual connections between these neurons have also been studied. Until recently, however, there has not been an explicit exploration of the interactions between multiple convergent inputs to single cells, or of the divergent projection from single cells to their multiple targets. The proposal is divided into three broad sections whose overarching goal is to understand the integration of multiple inputs to visual cortical neurons. In the first (A), we will study this problem directly by recording simultaneously in the LGN and layer 4 of visual cortex. In particular, we will concentrate on exploring synergistic interactions between near- synchronous inputs from convergent thalamic afferents. In the second section (B), we will study how the correlational structure of the thalamic inputs to visual cortex are determined by their retinal inputs. Preliminary results indicate that there is strong synchrony between groups of neurons in the thalamus. By recording simultaneously from neurons in the retina and LGN, we will study how synchrony in the LGN is caused by divergent input from the retina. Finally, in the third section (C), we will record simultaneously from all three levels in the pathway: retina, LGN, and visual cortex. This study will help us assess quantitatively the importance of the effects studied in (A) and (B) on the transmission of visual information from retina to cortex: single retinal ganglion cells diverge to synchronize to small pools of thalamic neurons, these synchronized neurons re-converge in a synergistic manner onto single cortical neurons. This basic research on information processing in the visual cortex should further our knowledge of general mechanisms of cortical function. Only by exploring the detailed interplay of multiple thalamic inputs to cortical neurons can we begin to understand functional disorders of this pathway, such as in certain forms of epilepsy.