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Aim Applications of transcranial direct current stimulation (tDCS) aim at targeting specific cognitive domains. Optimization of tDCS protocols is therefore crucial. It has been suggested to combine tDCS with a cognitive task aiming at the networks related to the targeted cognitive domain. The present study investigates (1) the timing of tDCS in relation to the target task (working memory). (2) Specificity of DLPFC-stimulation on executive functions. Methods A total of 80 subjects aged 18–30 participated in the study; eight were excluded for IQ above 130 (40 female; age M  = 22.0, SD = 3.2; IQ M  = 107.2, SD = 11.1). Twenty-four hours after baseline examination (T0), participants were randomly allocated to one of four different conditions of tDCS timing: Verum stimulation (1) before, (2) during and (3) after performing an adaptive n-back task (T1) as well as (4) sham stimulation during the n-back task. 1.5 mA anodal tDCS was delivered through the Starstim system for 17 min (Neuroelectrics, Barcelona, Spain). The size of the circular active electrode (left DLPFC) was 8 cm 2 and of the reference electrode 25 cm 2 (contralateral mastoid). Cognitive examination covered attention, executive functions (working memory, cognitive flexibility, inhibitory control), verbal and non-verbal memory, and visuo-spatial functioning. Repeated measurement ANOVA was performed to compare each verum condition to sham stimulation. Results Concerning executive functions, participants in the conditions ‘before’ and ‘after’ didn’t improve as much as the sham group at T1 in a Go-NoGo task (median reaction time). Regarding memory, participants in the condition ‘before’ didn’t improve as much as the sham group at T1 in non-verbal delayed recall (Rey-Osterrieth Complex Figure Test). Participants in the ‘during’ condition improved at T1 compared to the sham group in verbal delayed recall (Rey Auditory Verbal Learning Test). Discussion These preliminary results show that anodal tDCS over the left DLPFC can selectively modulate single functions from executive functions and memory. (1) Stimulation before and after an executive target task showed similar negative effects on inhibitory control, while stimulation during the target task did not show any effect on executive functioning. Yet, we only saw changes in one out of seven conducted executive tasks. Therefore, we cannot conclude a preferred timing of stimulation in relation to a working memory task aiming at the networks of executive functions through DLPFC stimulation. Interestingly, the only positive effects on cognition were seen with stimulation during the target task. (2) Stimulation during the target task had a positive impact on delayed recall in verbal memory, which is known to be hippocampus-dependent. Together with the negative effect on non-verbal delayed recall in the ‘before’ condition, these results indicate a wider, impact of tDCS on cognition, possibly related to electrode montage and subsequently activated brain networks. [ABSTRACT FROM AUTHOR]