Date Presented 4/16/2015
A combined intervention of transcranial direct current stimulation and a working memory (WM) training protocol significantly enhanced performance on both trained and transfer WM tasks in healthy older adults. The continuation of this research includes tasks with greater ecological validity.
SIGNIFICANCE: Older adulthood is associated with cognitive changes. Although older adults have enhanced crystallized intelligence, other domains, such as working memory (WM), are susceptible to decline as early as our 20s. Decline in WM can have negative implications for continued and full participation in cognitively demanding instrumental activities living of daily living. Countering cognitive decline in healthy older adults is not novel. Substantial research has been devoted to WM training interventions, which can facilitate improvements on trained activities. Unfortunately, transfer, or improvement on untrained tasks, is infrequently obtained. It is conceivable that available training paradigms are not sufficient to strengthen neural activity. For this reason, interventions that could modulate underlying neural activity are appealing. One approach is noninvasive neurostimulation, such as transcranial direct current stimulation (tDCS); tDCS uses small amounts of electric current applied to the scalp to modulate the excitability of underlying neural populations. This approach has strong translational potential because it is safe and affordable.
INNOVATION: We describe our novel approach of using tDCS in combination with WM training with the goal of facilitating transfer to untrained tasks. This project extends the understanding and utility of tDCS and was designed to help meaningfully delay or counter WM decline in older adults. Findings from this project influence both neuroscience and rehabilitation science fields.
APPROACH: We hypothesized that pairing WM training with tDCS will facilitate transfer gains in healthy older adults. Transfer effects from training-only interventions are elusive. This intervention includes tDCS and training with the goal of effectively facilitating transfer to untrained tasks.
METHOD: We provided a tDCS and memory training intervention over 10 weekdays. We collected data representing baseline, daily, and follow-up (1 mo later) performance on trained and transfer tasks. These data were collected in a laboratory. In the extension of this research, we are also collecting data in participants’ homes. Seventy-two healthy older adults participated in this study. These adults were divided into one of four groups: an active prefrontal cortex (PFC) tDCS group, an active posterior parietal cortex (PPC) tDCS group, an active alternating (PFC/PPC) tDCS group, and a sham (i.e., placebo) tDCS group. All participants met safety criteria standards for tDCS research. We used standard measures of WM for both training and transfer tasks. In the continuation of this research, we included transfer measures with stronger ecological validity. We used a repeated measures analysis of variance (ANOVA) to compare improvements on trained and transfer tasks with a between-subjects factor of tDCS group.
RESULTS: Participants who received active tDCS, regardless of stimulation site, performed significantly better on both trained and transfer tasks at follow-up, indicated here with a benefit index (p < .05).
CONCLUSIONS: Unlike training-only studies, we facilitated gains on both trained and transfer tasks using tDCS and training. One limitation of this study is that the observed improvements were on laboratory-based measures of WM. In our current, ongoing research, we are testing for broader performance gains in cognitively demanding daily activities.
