TDCS and memory function among individuals with or without elevated ADHD symptoms

We determined whether transcranial direct current stimulation (tDCS) improved memory function via strengthened executive control among university students with or without elevated scores on a measure of adult attention deficit-hyperactivity disorder (ADHD). The prediction that volunteers receiving left DLPFC anodal/right frontopolar cathodal stimulation would demonstrate improved executive control/memory function (determined by performance on California Verbal Learning Test-CVLT and Rey Complex Figure Test-RCFT) following a single tDCS session (2 mA, 20 minutes) relative to participants in a sham-tDCS group was tested. Unexpectedly, individuals receiving genuine tDCS (n = 27) did not obtain significantly higher scores on measures of executive control and immediate/delayed recall relative to sham group participants (n = 26). Group differences on almost all RCFT/CVLT variables did not approach significance or were not in expected direction. Separate analyses by gender revealed that males receiving active tDCS (n = 17) obtained significantly higher scores on CVLT short- and long-delay recall relative to males in the sham-tDCS group (n = 13). On most CVLT variables, males in the active-tDCS group obtained higher scores relative to sham group members (non-significant differences). Group differences on RCFT were not significant. Active-tDCS (n = 10) and sham-tDCS (n = 13) groups among females did not differ significantly on CVLT and RCFT. Males with elevated scores (above sample mean) on ADHD scale receiving active-tDCS obtained higher scores on most CVLT variables relative to males in sham group. Group differences on CVLT short- and long-delay free and cued recall were statistically significant. Groups did not differ significantly on RCFT. Among males with lower ADHD scale scores (equal to or below sample mean), active- and sham-tDCS group differences on CVLT/RCFT were not significant. Among females with elevated or lower ADHD scores, active- and sham-tDCS group differences on CVLT/RCFT did not approach significance or were not in expected direction.