Soterix 1x1 TACS Lab Report

¬Note: This is instruction manual on how to perform tACS using the Soterix medical’s stimulator that we have in cognition lab. I have used examples from the current tACS project to demonstrate some ideas.

Introduction

Transcranial alternating current stimulation (tACS) is non-invasive technique for rhythmic brain stimulation. In this, a small amount of alternating current is directly delivered to the brain, through skull. The transcranial current directly influences cortical activity, thus entrains neural oscillations. tACS is a relatively new brain stimulation technique, currently it is used only for investigative purposes, and not for clinical. tACS effects on cognitive processes are categorized as: a) online effects: the effects observed

The soterix 1X1 tES is capable of having only 1 active electrode, and maximum of 4 return electrodes. By default, tES device and HD-Explore take anode as the active electrode. However, we can choose either anode or cathode as the active electrode, depending on the requirements of experiment. The active electrode should be positioned at location in 10-20 electrode system, which corresponds to the region of interest. Through literature survey we found that P4 and P3 respectively correspond to right and left PPC. Refer to trans-cranial technologies’ cortical function reference to find the position of brain regions (Appendix 1). In HD-Explore mark the active electrode at the stimulation location and mark return electrodes at surrounding around it to form a 4X1 rectangular montage. Such rectangular montage of electrodes ensures focal delivery of current, though at the cost of reduced current intensity. Proceed to step 3, verify all the entered parameters and explore the electric field distribution.

HD-Explore allows us to see coronal, sagittal and axial views of the simulated fields in brain. Adjust the slices to position the pointer at the MNI co-ordinates of the region of interest. MNI co-ordinates for various brain regions can be checked in Appendix 2.

Operating tACS

Connect the CSIN-X2 input cable (figure 3) to the anode and cathode positions respectively, at the back panel of 1X1 tES (figure 1), and connect the

When turned on, the amplitude of current is maintained zero throughout the set stimulation duration, except for a 30 second ramp up and ramp down to the peak intensity, before start and at the end of stimulation duration. We used auto-sham feature for sham session of our experiment. Even when auto-sham is turned off it takes around 30 seconds for the device to reach peak value of the current, and then the timer for the set stimulation duration starts. Please note, even when the stimulation duration ends, it takes around 30 seconds for the device to fully stop current flow. A led above the 'start' button remains lit at all times the device is