Transcranial Direct Current Stimulation of the Cerebellum to Modulate Cognition in Humans

Abstract

Source: Pope, P. A. Modulating Cognition Using Transcranial Direct Current Stimulation of the Cerebellum. J. Vis. Exp. (2015)

This video demonstrates the effects of cathodal tDCS on cognitive function by modulating neural activity in the cerebellum. It outlines the steps for administering tDCS, conducting cognitive tasks, and analyzing its impact on working memory.

Protocol

All procedures involving human participants have been performed in compliance with the institutional, national, and international guidelines for human welfare and have been reviewed by the local institutional review board.

1. Performing Cerebellar Transcranial Direct Current Stimulation (tDCS)

NOTE: tDCS is considered safe to use in humans. However, the researcher administering tDCS in this study was a first-aider. It is advisable that a first aider is at hand when performing tDCS to ensure that the participants' safety is not compromised if they feel unwell/faint during the procedure. Never leave a participant unattended when administering tDCS.

1. Pre-soak two sponge electrodes (surface area = 25 cm²) in a standard 0.9% NaCl saline solution until they are saturated.
2. To administer excitatory (anodal) stimulation over the right cerebellar cortex, place the red electrode 1 cm under and 4 cm to the right of the most prominent projection of the occipital bone (inion).
   NOTE: This lateral position on the scalp approximates the location of cerebellar lobule VII.
3. To complete the electrode montage, place the reference or cathodal electrode (blue) on the right shoulder over the deltoid muscle.
4. To administer inhibitory (cathodal) stimulation, repeat the above procedure and position the two sponge electrodes the other way round (i.e., place the blue electrode on the head and the red electrode on the shoulder).
5. To administer sham tDCS, deliver pseudo stimulation (e.g., 110 µA over 15 msec, every 550 msec) for 20 min instead of the stimulation current. Position the two electrodes the same as above, but counterbalance the position of the red and blue electrodes between participants in the sham group.
6. Secure the wet electrodes firmly to the head and upper arm with rubber straps or self-adherent wrap. Place some paper towel around the back of the participant’s neck to mop up dripping saline solution.
   NOTE: Check that the intended position of the electrodes has not moved after they have been secured. To ensure optimal electrode-skin interface, make sure the electrodes are placed flat on the scalp and not over the hair.
7. To onset and offset each stimulation intervention increase and decrease, respectively, the direct current (DC) in a ramp-like manner over 10 sec. Set the intensity of stimulation at 2 mA and deliver for 20 min using a reliable current-regulated DC stimulator (Table of Materials).
   NOTE: This intensity is similar to that used by others and is considered a safe level of exposure, well below the threshold for causing tissue damage.
8. Tell the participant to rest/relax during the stimulation period, and discourage them from using electronic devices, so to avoid introducing confounding variables that may potentially influence the outcome of the experiment.
   NOTE: It is common for participants to feel a mild itching sensation at one or both electrode sites (and/or a metallic taste in the mouth) when the stimulation current begins. Reassure participants that these sensations disappear after a few seconds – leaving tDCS unperceived.
9. Apply anodal, cathodal, or sham stimulation to three separate groups of participants in pseudo-random order (between-participants, unrelated samples). Ensure that the overall number, gender, and average age of participants are comparable between groups.

2. Following brain stimulation, perform the paced auditory serial addition task (PASAT) and the paced auditory serial subtraction task (PASST) in a counterbalance order, and the noun and verb reading tasks and the verb generation task in this order. Perform experiment one (calculation tasks) and experiment two (language tasks) in pseudo-random order. Do not provide practice on either task following brain stimulation.

NOTE: In other studies of cognition, real and sham stimulation have been applied to the same cohort (within-participants, related samples), separated by a wash-out duration of at least 5-7 days. However, differentiating sham and real stimulation is easier at higher current strengths. This could be problematic in a within-participants design, but not so in a between-participants design as described here.

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Headset	Beyerdynamic	DT234 Pro	Ensure the microphone does not move from the participants mouth in between testing.
DC stimulator	Magstim	DC Stimulator Plus	Electrode placement is a critical success factor for tDCS efficacy
Stimulus presentation and recording software	www.neurobs.com	Presentation (Version 14.2)	Maintain participant-specific stimulus presentation rate between sessions in experiment one