Baseline cognitive abilities shape the effects of tDCS, tACS, and otDCS on object-location memory

Transcranial electrical stimulation (tES) can modulate neural dynamics, yet its effects on memory are heterogeneous. Individual differences in cognitive profiles, may well be one of the potential causes by setting boundary conditions on the extent and mode of the tES-induced modulation of network dynamics. In a sham-controlled, within-subject study (N = 42), we compared the effects of tDCS (1.5 mA), tACS ({+/-}1.0 mA at individual theta frequency, ITF), and otDCS (1.5 mA {+/-} 0.5 mA at ITF) over the left posterior parietal cortex on object-location (OL) associative memory, and examined whether six cognitive abilities (figural reasoning, semantic, visuospatial, processing speed, working memory, mnemonic binding) moderate stimulation outcomes. Associative memory recognition improved selectively under theta-otDCS, whereas tDCS and tACS showed no significant group-level effects. Yet all tES protocols exhibited considerable interindividual variability. Relative to cognitive abilities, processing speed moderated tES effects in line with neural efficiency predictions, yielding greater gains in cognitively faster individuals. In contrast, mnemonic binding and figural reasoning moderated benefits in a compensatory manner, with larger improvements in lower-ability individuals. Overall, the effects of tES on associative memory were specific to the tES protocol and outcome measure while being strongly shaped by cognitive profile via complementing magnification and compensation mechanisms.