Different Brain States are Differentially Responsive to Ultrasonic Stimulation

Thesis (Master's)--University of Washington, 2018University of Washington Abstract Different Brain States are Differentially Responsive to Ultrasonic Stimulation Devon Griggs Chair of Supervisory Committee: Pierre Mourad Division of Engineering & Mathematics It is well known that direct, non-invasive, spatially specific ultrasonic stimulation of the brain can activate neural responses, however it is less studied how the brain’s state itself affects the responses. This thesis explores the differential responses to different brain states in mice, particularly the anesthetized brain state as induced by isoflurane and the sedated, awake-like brain state as induced by medetomidine. The electrocorticographic (ECoG) technique was utilized to record responses in the visual cortex (V1), the somatosensory cortex, and the auditory cortex when a flash of light was cast on the retina of the eye and when a burst of pulsed ultrasound was focused on V1. It was found that the responses due to these two stimulation techniques of the same brain state were largely similar. For example, under isoflurane, each stimulation generated slow waves; under medetomidine, they did not. This preliminary result serves to confirm the effects of different brain states regardless of stimulation technique. Differences were discovered, too. For example, it was also found that direct visual stimulation generated stronger neural responses than did ultrasonic stimulation for both brain states. All results presented here are preliminary due to the small sample size but will guide future studies. Taken together, these preliminary results pave the way to further investigation of the similarities and differences of direct ultrasonic stimulation of the cortex and indirect neural stimulation of the cortex via light cast on the retina of the eye, as well as other sensory input such as sound and pinching, when applied to mice experiencing various brain states