No modulation of object-location memory through high-definition transcranial direct current stimulation of the right temporoparietal lobe

Abstract Background: Object-location memory (OLM) has been shown to be mediated by the right temporoparietal lobe, with structural plasticity in lateral and medial parietal areas induced by learning. Objective: We investigated whether high-definition transcranial direct current stimulation (HD-tDCS) of the right temporoparietal lobe has immediate and sustained effects on OLM performance. Methods: Fifty-two participants performed a two-day OLM training, requiring to remember the positions of the second objects in pairs of pictures. HD-tDCS (2 mA, 20 min) was applied during first training. Training gains were additionally assessed on the subsequent day. Performance levels were compared between an anodal and a sham group. Baseline structural and microstructural parameters were extracted and electric fields induced on individual brain surfaces were estimated. The study was preregistered (https://osf.io/h5x6j). Results: Participants showed training gains over time with no difference between anodal and sham groups on either training day. Neither individual electric field magnitudes, nor volume or microstructure in the stimulation target and related right-hemispheric memory-relevant structures were associated with training gains. Neuropsychological data showed no correlation with visual-spatial memory scores. Further exploratory analyses revealed associations with volume and microstructure of left-hemispheric areas and pathways (such as the hippocampus and the cingulum bundle) and with verbal learning memory scores. Conclusion: Focal stimulation of the right temporoparietal lobe did not enhance training gains of the OLM task. This group-level finding was confirmed by non-existent associations of individual benefits with electric fields or regional (micro)structural parameters in the stimulation target. The null effect may be explained by choosing a “wrong” target for the modulation of performance in this particular task rather than by inter-individual variability in responsiveness. Our study shows that the integration of neuropsychological, behavioral, and neuronal measures, can provide more specific insights into underlying brain plasticity modulation, further promoting the understanding of null effects. Research Category and Technology and Methods Basic Research: 9. Transcranial Direct Current Stimulation (tDCS) Keywords: non-invasive brain stimulation, visuo-spatial memory, diffusion tensor imaging, electric field simulations