Local EPI distortion induced by blue light delivery in the naïve brain: implications for optogenetic fMRI studies

Abstract

Previously, it has been reported that blue light delivery in the naïve brain resulted in pseudo positive and negative fMRI responses, which were attributed to NMR frequency shifts, and T1 and T2* changes. EPI is known to be susceptible to NMR frequency shifting, field inhomogeneity and T2* changes. However, the effects of blue light delivery in the naïve brain and EPI distortion have not been examined. The aim of this study was to investigate the local EPI distortion induced by laser stimulation in the naïve posterior thalamus. Our results showed that the pseudo negative fMRI response was at the fiber tip, while the pseudo positive fMRI response was adjacent to the pseudo negative fMRI response along the phase encoding direction. This study brings attention to EPI distortion as a possible confounder which must be taken into account when optogenetic fMRI experiments are designed.