Ultrasound Stimulation for Altered Level of Consciousness

Participants assigned to the MRS arm will also complete five visits, with a different brain region targeted at each visit. Each visit will include a pre-LIFUP baseline MRS acquisition, an excitatory LIFUP condition, a post-excitatory non-LIFUP MRS acquisition, an inhibitory LIFUP condition, and a post-inhibitory non-LIFUP MRS acquisition. Each MRS acquisition period will last approximately 13 minutes and will include approximately 5 minutes of glutamate plus glutamine measurement and 8 minutes of gamma-aminobutyric acid (GABA) measurement. The order of the excitatory and inhibitory LIFUP conditions will be randomized across participants.

Participants assigned to the fMRI arm will complete five visits, with a different brain region targeted at each visit. Each visit will include seven consecutive 10-minute scanning periods: one pre-LIFUP baseline fMRI scan, five fMRI scans conducted during LIFUP using five predefined combinations of duty cycle and pulse repetition frequency, and one post-LIFUP baseline fMRI scan. The five stimulation parameter combinations will be labeled Combination 1 through Combination 5. The order of the five parameter combinations will be randomized within each visit. The total planned scanning time for these seven periods is approximately 70 minutes, excluding structural imaging, participant positioning, transducer placement, safety checks, and other required study procedures.

Participants assigned to the glymphatic MRI arm will complete up to five visits, with a different prespecified brain region targeted at each visit. Tissue-to-fluid water exchange, velocity spectrum imaging, and cerebral perfusion using arterial spin labeling will be assessed before, during, and after LIFUP. The planned imaging periods total approximately 1.5 hours per visit, excluding participant positioning, structural imaging, transducer placement, safety checks, and other required study procedures.