Analysis of Cortical and Thalamic Contributors to The Functional Organization of Primate Primary Visual Cortex (V1)

Abstract

The primate visual system is highly interconnected and hierarchically organized. Three separate pathways, originating in the layers of the lateral geniculate nucleus (LGN), carry retinal information to primary visual cortex (V1) which, in turn, sends information into the ventral and dorsal streams. These higher areas also send massive feedback to V1. The contribution of these feedforward and feedback inputs to the functional organization of V1 remains unclear. The broad aim of this thesis is to address this question. The specific aims were as follows: 1) To obtain a more complete picture of V1 functional maps by characterizing the distribution of temporal frequency selectivity in bush baby V1. 2) To tease out the contributions of magno- (M) and parvocellular (P) feedforward LGN inputs to the functional organization of V1. 3) To investigate the functional role of feedback from middle temporal area (MT) to V1. As part of the latter aim, the retinotopic organization of MT was investigated. We first demonstrated that, unlike spatial frequency and orientation, temporal frequency selectivity is not organized into domains but is distributed uniformly across V1. Inactivating either P or M channels reduced activity in V1. Blocking the P input left the map of orientation preference unchanged but altered spatial frequency map. M block resulted in greater reduction in activity than P block, suggesting that in bush baby, the M pathway may play a major role in the function of V1. Next, we found that MT has both a local and global retinotopic organization in owl monkeys. The cardinal axes of visual space are represented anisotropically. As part of a collaborative effort, we also showed that MT depends on V1 for its main drive. Additionally, we showed that feedback from MT influences the overall activity and the temporal frequency responses in V1. This thesis provided new information about the organization of primate V1 by showing that functional maps in V1 depend on contributions of both feedforward LGN channels and feedback from MT.