Author: Dr. Lucía Del Valle, PhD candidate in Medical Sciences at the University of Chile.
When to stimulate?
Optimal timing for tDCS application: new evidence to decide between before, during, or after
Is it better to stimulate before, during, or after the task?
One of the most common questions when using transcranial direct current stimulation (tDCS) is: when is the best time to apply it?
Although many guidelines suggest doing it before the intervention (offline mode), recent evidence reveals that the answer depends on the type of task one seeks to enhance: cognitive, motor, or psychotherapeutic.
tDCS during cognitive training improves learning
An experimental study conducted on healthy adults compared the use of anodal tDCS in the left dorsolateral prefrontal cortex before and during a working memory task.
The result was clear: stimulation applied during the task (online mode) improved skill acquisition more within the session and the following day, compared to prior stimulation.
This finding suggests that, at least in cognitive domains, the simultaneous activation of specific neural networks during stimulation may be key to enhancing plasticity.
And in motor tasks? No consensus
A cross-over, randomized investigation in healthy adults showed that anodal tDCS applied before motor training increased corticospinal excitability (measured by motor evoked potentials), while stimulation during or after had no such effect.
However, a more recent study with 90 participants compared the three application times (before, during, and after) in a sequential motor task and found no significant difference in motor skill acquisition in tests 1 or 24 hours later.
These data prompt a reconsideration of the usefulness of a single tDCS session as a motor learning enhancer and reinforce the idea that the effect depends on the type of task, the training design, and the number of sessions.
In psychotherapy, stimulation is synchronized with the session
In protocols that combine tDCS with cognitive behavioral therapy, stimulation is usually applied simultaneously with the psychotherapeutic session. The logic is to stimulate precisely when the cognitive circuits to be reinforced are activated. Although the evidence on additional efficacy is still debated, studies agree that this modality is safe, well-tolerated, and feasible.
References
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