The effect of transcranial direct current stimulation on the short-term spatial memory in healthy volunteers

Introduction. Transcranial direct current stimulation (tDCS) is a method of non-invasive brain stimulation. The application of a weak, subthreshold direct current on the cerebral cortex leads to a change in cortical neuron activity, which continues for a certain amount of time after exposure. The main mechanism of this effect is subthreshold changes in the membrane potential, while the after-effect phenomenon is associated with the influence of tDCS on synaptic plasticity.

Study objective. To examine the effect of tDCS of the posterior parietal cortex on certain types of spatial memory with the electrodes positioned P3– P4+ and P3+ P4–.

Materials and methods. The study included 18 healthy volunteers (10 men and 8 women) aged 18–23 years. The experiment used stimulation points P3 and P4 according to the 10–20 international electrode positioning system. Stimulation was performed using a direct current of 0.7 mA for 20 min. The study participants underwent three stimulation sessions (P3– P4+, P3+ P4–, P30 P40) in a randomized order with an interval of 3 days between them. After each session, the state of their short-term spatial memory was assessed using the Spatial Memory (categorical spatial memory) and Spatial Span (coordinate spatial memory) tests by Cambridge Brain Sciences, as well as the subjective effect of tDCS.

Results. There were no statistically significant differences in the results of neuropsychological tests between ‘active’ stimulation (P3– P4+ and P3+ P4–) and sham stimulation. The lack of effect may be due to the use of insufficient current (0.7 mA) or other factors (duty cycle, electrode location, stimulation time, etc.). No adverse effects of stimulation were reported.

Conclusion. tDCS with 0.7 mA current does not affect spatial memory in healthy people when using P3– P4+ and P3+ P4– electrode mountings.