Age-dependent non-linear neuroplastic effects of cathodal tDCS in the elderly population: a titration study

Abstract

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Transferability of cathodal tDCS effects from the primary motor to the dorsolateral prefrontal cortex: a multimodal TMS-EEG study

“…Moreover, the results of this study might not be one-to-one transferable to other cortical areas, other populations (Ghasemian-Shirvan et al, 2020;Ghasemian-Shirvan et al, 2022), as well as behavioral tDCS studies. Finally, the different effects obtained by prefrontal and motor cortex stimulation, as identified in this study, should be carefully evaluated in future studies, as it is not clear if these are due to biological differences between respective areas, or different current densities at the cortical level, due to anatomical differences.…”

No robust online effects of transcranial direct current stimulation on corticospinal excitability

“…and durations (15, 20 and 30 min) specifically for 2 mA of cathodal tDCS [27] and replicated again in pre-elderly but not elderly participants [28]; also when testing the intensity range of 0.5 to 2.0 mA for both anodal and cathodal tDCS, lower intensities (0.5, 1.0 mA) showed equal or even greater effects compared to higher intensities [19]; interestingly these non-linear MEP effects are contrasted by rather linear and polarity-specific relationships between intensity and BOLD response in a combined tDCS-fMRI study [29]. Given the complex relationships for offline effects [13], the lack of simple linear one between stimulation polarity/intensity and online corticospinal excitability may not come as a surprise, but online and offline effects follow different neurophysiological mechanisms [30] and different relationships between stimulation parameters and cortical excitability changes are well possible.…”

“…This procedure resulted in mean SIs (± SD) of 63.73 ± 10. 28 Note that the extension with the electrode cable connector (which helped to minimize coil-cortex distance and prevented retinal phosphenes from TMS-related induction of currents in the tDCS electrode leads; see tDCS methods for details) was insulated with tape to prevent it from being part of the stimulation interface. (C) Placement of the tailored electrodes on a subject's head (photos used with permission of the subject).…”

Non-invasive brain stimulation and neuroenhancement

“…The intervals between sessions may be key: for example, repetitive NIBS sessions play a distinct role. Spacing at intervals of several minutes (i.e., 3–30 min) have been explored to obtain greater and more durable changes in neuroplasticity responses than NIBS applied over more prolonged spacing periods (several hours or days), with the latter appearing to induce less stable, and rapidly reversible plasticity ( Ghasemian-Shirvan et al, 2022 , Goldsworthy et al, 2015 , Monte-Silva et al, 2013 ). It is assumed that long-term potentiation (LTP) and long-term depression (LTD) phenomena at the synaptic level are the physiological mechanisms for durable changes following NIBS ( Liebetanz et al, 2002 , Nitsche et al, 2003 , Sharma et al, 2022 , Rossini et al, 2019 ).…”