FMRI Detection of Antidromic Excitation in Both White and Gray Matter of Spinal Cord after Optogenetic Cortical Stimulation

Motivation: To detect BOLD signals in spinal cord produced by neural excitation in brain Goal(s): To demonstrate functional connectivity between brain and spinal cord and antidromic signal effects following stimulation of neurons in cortex. Approach: A light-sensitive cation channel, introduced into the S2 region of squirrel monkeys by an adeno-associated virus, was excited via laser light. Images of evoked BOLD responses were recorded in brain and cervical spine at 9.4T. Results: BOLD signals were detected in S2 and in multiple connected regions. Robust, focal BOLD signals were also detected in spinal gray and white matters in response to light stimulation. Impact: This is a first demonstration of antidromic excitation of spinal cord produced by excitation of the brain, and of functional MRI responses to "top down" neural signaling in both gray and white matter in the cord.