Image representation in primary visual cortex depends critically on the spatiotemporal pattern of activation of distributed visual cortical networks. Such activation relies on distribution of contrasts in the visual scene but also in part in the scaffolding of horizontal connections in supragranular layers 2-3 that connect cortical columns of similar orientation. For individual visual cortical cells their spatially well defined receptive field (RF) is not sufficient to explain their visual responses to visual scenes. Indeed, the context of visual stimuli falling outside of the RF is a critical component of the cell response. Such effects have been called contextual effects, they depend on the relative properties between the visual stimulus inside and outside of the RF and can be facilitatory, inhibitory or they can modulate the gain (the slope of the input-output function) of the neuron. A fundamental impediment to understanding the underlying mechanisms of contextual stimuli is the ability of manipulating inhibition at the mesoscale of the cortical column. Here, in Aim 1 we propose to implement in the cat optogenetic approaches that allow to manipulate inhibition with great temporal sensitivity. We will use a strategy developed recently based on the selective expression of the DLX homeobox gene enhancer mDlx in cortical GABAergic interneurons of all vertebrate species. We will procure (from the Penn Vector Core) and inject AAV vectors containing depolarizing (ChR2) and hyperpolarizing (ArchT) opsins under the control of mDLx. We will verify selective expression with electrophysiology and inmunohistochemistry and will calibrate the effect of blue and green light on the responses to visual stimuli and current injection of regular and fast spiking neurons recorded intracellularly in vivo. Work in Aim 1 will be done with the help of Dr. John Wolfe from the Veterinary School which is an expert in viral approaches for gene therapy.
In Aim 2 we will obtain preliminary data on the role of GABAergic inhibition in surround suppression and gain modulation caused by contextual stimuli. In addition to strong preliminary data for a future R01 application this project will implement an approach that will allow addressing over 50 year old questions in a highly visual animal.
Making meaningful representations of the visual scene relies heavily on specific patterns of connectivity between cortical columns of similar orientation in primary visual cortex. However, the role of inhibition is unknown due to the lack of tools to explore it. Here, we propose to implement such tools. Understanding the role of local inhibition in critical not only for normal vision but also for major psychiatric illnesses such as schizophrenia.