Multi-Session Transcranial Direct Current Stimulation Concurrent with Discrete Sequence Production Task in Young and Older Adults

The discrete sequence production (DSP) task is an explicit motor sequence learning task that can be used to measure chunking, or a grouping together of once discrete individual elements. The DSP task used here involves two, 6-item sequences presented at one time. Over many trials, participants learn the two, 6-item sequences and execute the sequences as 2 or more segments, or chunks. Right and left dorsolateral prefrontal cortex (DLPFC) have been demonstrated to be involved in early explicit sequence learning as well as early adaptation. Primary motor cortex (M1) has been shown to be involved in explicit sequence learning and retention. Further, pre-SMA has been shown to be involved in chunk loading in sequence learning. Here, we use transcranial direct current stimulation (tDCS), a non-invasive form of brain stimulation, in an effort to facilitate chunking in young and older adults in a modified version of the DSP task. Forty young (range 18-28 years) and 16 older (range 65-85 years), right-handed, adults completed a modified version of the DSP task while receiving anodal or sham tDCS to either right DLPFC, left DLPFC, M1, or pre-SMA over two sessions. Using a model developed by Acuna et al. (2014) to quantify chunking, preliminary results suggest that tDCS stimulation to pre-SMA facilitates at least one component of chunking in both young and older adults, whereas tDCS stimulation to m1 is more beneficial to only young adults. Specifically, the pause at the beginning of a chunk was significantly faster for young and older adults in the pre-SMA group relative to the sham group ( p = .037) providing further support for the notion that this region plays a role in chunk loading. There were no significant differences between m1, right, and left DLPFC groups relative to sham.