Laminar optical tomography of the hemodynamic response in the lumbar spinal cord of rats.

Intrinsic optical imaging (IOI) has emerged as a very powerful tool to assess neuronal function in small animals. Although it has been used extensively in the brain, its application to the spinal cord is rare. The inability of intrinsic optical techniques to resolve different depths and embedded gray matter hampers their capacity to distinguish larger vasculature contributions of hemodynamic signals originating from motoneuron and interneuron activation. Laminar optical tomography (LOT) is a recently-developed method that fills the gap left between IOI and diffuse optical imaging. With distinct source-detector separations, light that propagates deeper into tissues can be distinguished from light originating from the surface, providing depth sensitivity. In this work, LOT is investigated for the first time to image spinal cord activation with simultaneous IOI of the cortex in rats. Such proof of concept provides a powerful imaging modality to study spinal cord activation and disruption after injury.