Population signals in the middle temporal (MT) area of marmoset visual cortex

Abstract

In primates, including humans, the perception of motion and the control of eye movements depend on the population activity of neurons in the middle temporal (MT) area of the visual cortex. Much is known about the responses of individual neurons in area MT, but it is unclear how neurons work together to provide motion analysis. In the work of this thesis, I use electrophysiological recordings from area MT of a New World monkey, the common marmoset (Callithrix jacchus), to provide knowledge of the spatial and temporal structure of spiking activity and local field potentials (LFP). I first establish that the functional properties of neurons in area MT of the marmoset are similar to those in the major primate model of visual processing, the macaque monkey. I then use multi-electrode arrays to examine co-variability in spiking activity and LFP during rest, and during presentation of visual stimuli. There are three main findings of this thesis. First, correlated variability is affected by the presentation of a visual stimulus, and its structure depends on whether the visual stimulus is a dot field or a grating. Second, correlated variability has local and global components; the local component is largely independent of the type of visual stimulus used, but the global component depends on whether the stimulus is a dot field or a grating. Third, the distinct structures of spiking co-variability observed during presentations of dot fields and gratings do not reflect distinct local mechanisms, but instead distinct global interactions between local mechanisms that are similarly employed during presentation of a stimulus. Together, these results suggest that visual processing in area MT involves stable neural circuitry that is local, and global neural circuitry that is dynamically modulated by a visual stimulus.