Examination of the temporal-spatial dynamics of working memory training-induced neuroplasticity

Efficient working memory (WM) performance involves the dynamic coordination of neural activity on a milli-second time-scale. However, the correspondence between the timing and spatial localization of changes in neural activity following targeted WM training has not been well-established. To address this, we used an event-related potential (ERP) source localization approach to identify the patterns of cortical activity changes that are induced by WM training along both the temporal and spatial dimensions. Healthy adult participants completed approximately 20 sessions of training on either a WM training protocol (visual-letter n-back task), or a control training protocol (visual-letter search task). ERP measures were obtained before and after training (pretest and posttest) for a letter 3-back task. A beamformer source localization method was applied to the ERP data in the N2 (approximately 200-350 msec post-stimulus) and P3 (approximately 300-600 msec post-stimulus) component time windows to identify the cortical activity associated with WM training at distinct stages of information processing. Pretest-to-posttest cortical activity changes that corresponded with WM training gains were observed within the N2 time window, but not the P3 time window. Within the WM training group, training-related enhancement of N2 source activity in bilateral medial orbitofrontal cortex, left rostral anterior cingulate, and right posterior cingulate cortex was significantly associated with behavioral performance improvements on the trained task and untrained tasks of WM. The findings suggest that medial orbitofrontal and cingulate enhancement within 200-350 msec after stimulus onset represents a target for WM training and an important inflection point along the spatial-temporal dimensions of cortical activity for the enhancement of WM performance.