Browsing by Author "Lim, Wesley"

Filter results by typing the first few letters
Now showing 1 - 2 of 2
  • Thumbnail Image
    ItemOpen Access
    Effects of online repetitive transcranial magnetic stimulation (rTMS) on cognitive processing: A meta-analysis and recommendations for future studies.
    (Neuroscience and biobehavioral reviews, 2019-12) Beynel, Lysianne; Appelbaum, Lawrence G; Luber, Bruce; Crowell, Courtney A; Hilbig, Susan A; Lim, Wesley; Nguyen, Duy; Chrapliwy, Nicolas A; Davis, Simon W; Cabeza, Roberto; Lisanby, Sarah H; Deng, Zhi-De
    Online repetitive transcranial magnetic stimulation (rTMS), applied while subjects are performing a task, is widely used to disrupt brain regions underlying cognition. However, online rTMS has also induced "paradoxical enhancement". Given the rapid proliferation of this approach, it is crucial to develop a better understanding of how online stimulation influences cognition, and the optimal parameters to achieve desired effects. To accomplish this goal, a quantitative meta-analysis was performed with random-effects models fitted to reaction time (RT) and accuracy data. The final dataset included 126 studies published between 1998 and 2016, with 244 total effects for reaction times, and 202 for accuracy. Meta-analytically, rTMS at 10 Hz and 20 Hz disrupted accuracy for attention, executive, language, memory, motor, and perception domains, while no effects were found with 1 Hz or 5 Hz. Stimulation applied at and 10 and 20 Hz slowed down RTs in attention and perception tasks. No performance enhancement was found. Meta-regression analysis showed that fMRI-guided targeting and short inter-trial intervals are associated with increased disruptive effects with rTMS.
  • Thumbnail Image
    ItemOpen Access
    Site-Specific Effects of Online rTMS during a Working Memory Task in Healthy Older Adults.
    (Brain sciences, 2020-04-27) Beynel, Lysianne; Davis, Simon W; Crowell, Courtney A; Dannhauer, Moritz; Lim, Wesley; Palmer, Hannah; Hilbig, Susan A; Brito, Alexandra; Hile, Connor; Luber, Bruce; Lisanby, Sarah H; Peterchev, Angel V; Cabeza, Roberto; Appelbaum, Lawrence G
    The process of manipulating information within working memory is central to many cognitive functions, but also declines rapidly in old age. Improving this process could markedly enhance the health-span in older adults. The current pre-registered, randomized and placebo-controlled study tested the potential of online repetitive transcranial magnetic stimulation (rTMS) applied at 5 Hz over the left lateral parietal cortex to enhance working memory manipulation in healthy elderly adults. rTMS was applied, while participants performed a delayed-response alphabetization task with two individually titrated levels of difficulty. Coil placement and stimulation amplitude were calculated from fMRI activation maps combined with electric field modeling on an individual-subject basis in order to standardize dosing at the targeted cortical location. Contrary to the a priori hypothesis, active rTMS significantly decreased accuracy relative to sham, and only in the hardest difficulty level. When compared to the results from our previous study, in which rTMS was applied over the left prefrontal cortex, we found equivalent effect sizes but opposite directionality suggesting a site-specific effect of rTMS. These results demonstrate engagement of cortical working memory processing using a novel TMS targeting approach, while also providing prescriptions for future studies seeking to enhance memory through rTMS.