Temporal Interference Methods for Non-invasive Deep Brain Stimulation, Study 1.3

Through the grant's duration, the investigators hypothesize that temporal interference (TI) electrical neurostimulation will be well tolerated and effective at focally manipulating deep brain activity as measured by functional MRI (fMRI) BOLD signals. The investigators will investigate whether TI stimulation can increase BOLD activity in targeted deep brain regions including the nucleus accumbens (NAcc) and dorsal anterior cingulate cortex (dACC), and whether this stimulation can influence cognitive functions controlled by these regions. TI works by applying alternating currents of slightly different frequencies through multiple electrode pairs, creating an interference pattern that can stimulate deep brain regions without significantly affecting superficial cortical areas. This method is similar to traditional transcranial direct current stimulation (tDCS), however TI can stimulate deeper brain structures that tDCS cannot reach effectively. The study is broken up into two main aims with multiple sub-studies. In Aim 1, the investigators will characterize the effects of TI on fMRI BOLD signals, test different beat frequencies, and compare TI effects in the nucleus accumbens versus dorsal anterior cingulate cortex. In Aim 2, the investigators will apply TI to the dorsal anterior cingulate cortex to test causal theories about its role in cognitive control, conflict monitoring, risk avoidance, and foraging behavior using established cognitive tasks while subjects undergo fMRI scanning.

Study 1.3 (Aim 1, Study 1.3) will test whether TI can focally modulate activity in the dorsal anterior cingulate cortex, around MNI coordinates 0, 30, 30, as measured by fMRI BOLD signal. Healthy subjects (n=30) will complete a single study visit during which they will undergo fMRI while receiving TI stimulation through carbon fiber electrodes attached to the scalp with conductive gel. Electrode placement may vary by participant to optimize dACC targeting using individualized finite element modeling.

Participants will receive active and sham TI stimulation at a selected beat frequency potentially including 5 Hz, 30 Hz, 40 Hz, or another frequency in the 1-100 Hz range. Stimulation will follow an on/off sequence of 2 minutes on, 2 minutes off, 2 minutes on, and 2 minutes off, with 30-second ramp up and ramp down periods beginning at the start of each 2-minute stimulation period. Study 1.3 will also examine whether increased stimulation intensity improves modulation of BOLD activity in the dACC. Stimulation may be delivered up to ±5 mA per channel, corresponding to 10 mA peak-to-peak, with the second stimulation channel linearly scaled based on individualized modeling to maintain optimal targeting. Active and sham stimulation blocks will be counterbalanced across subjects.