Physical exercise improves long-term memory no less than transcranial direct current stimulation

Question – It has been shown that electrical brain stimulation, in particular transcranial direct current stimulation (tDCS), can improve memory performance. Physical exercise has also been shown to be able to improve different aspects of cognition. The aim of this study was to investigate which of these methods is more effective in improvement of long-term memory. Those tDCS and physical exercise protocols were chosen that have been shown to be effective in improvement of long-term memory: tDCS during memorisation (targeting encoding phase) and physical exercise after memorisation (targeting consolidation phase). We expected to see improvement following application of both methods. No prediction was made on which method is more effective.

Methods – Participants (n = 24) took part in three experimental sessions. They were asked to memorise a set of images (‘encoding’) for a later old/new recognition task (‘recognition’). In one of the sessions participants were asked to cycle for 30 minutes on an exercise bike following encoding. In the other two sessions they received either 15 minutes (‘active’ stimulation) or 16 seconds (‘sham’ stimulation) of 1.5 mA anodal tDCS applied over the left dorsolateral prefrontal cortex (left-DLPFC). Performance of the participants in the recognition phase was recorded for analysis.

Results – Both physical exercise and active stimulation led to significant improvement of long-term memory performance compared to sham stimulation (paired sample t-test p < 0.01 and p < 0.05, respectively). Physical exercise, however, led to stronger improvement (cohen’s d effect size physical exercise > active tDCS).

Conclusions – These results show that only 30 minutes of physical exercise can significantly improve long-term memory performance. Furthermore, this duration of physical exercise during consolidation was more effective than 15 minutes of tDCS during encoding. Considering that tentatively physical exercise lead to less adverse side effects as compared to electrical brain stimulation, physical exercise can be considered potentially a more effective method of cognitive enhancement, in particular in healthy participants.