Polarity- and valence-dependent effects of prefrontal transcranial direct current stimulation on heart rate variability and salivary cortisol

Abstract

Recent evidence has supported the notion that the hypothalamic-pituitary-adrenal (HPA) and the sympatho-adreno-medullary (SAM) systems are modulated by cortical structures such as the prefrontal cortex. This top-down modulation may play a major role in the neuroendocrine changes associated with stressful events. We aimed to investigate further this hypothesis by modulating directly prefrontal cortex excitability using transcranial direct current stimulation (tDCS) -a non-invasive, neuromodulatory tool that induces polaritydependent changes in cortical excitability -and measuring effects on salivary cortisol and heart rate variability as proxies of the HPA and SAM systems. Twenty healthy participants with no clinical and neuropsychiatric conditions were randomized to receive bifrontal tDCS (left anodal/right cathodal or left cathodal/right anodal) or sham stimulation, in a withinsubject design. During each stimulation session, after a resting period, subjects were shown images with neutral or negative valence. Our findings showed that excitability enhancing left anodal tDCS induced a decrease in cortisol levels. This effect is more pronounced during emotional negative stimuli. Moreover, vagal activity was higher during left anodal tDCS and emotional negative stimuli, as compared to sham stimulation and neutral images. We also observed an association between higher mood scores, higher vagal activation and lower cortisol levels for anodal stimulation. Subjective mood and anxiety evaluation revealed no specific changes after stimulation. Our findings suggest that tDCS induced transient, polarity specific modulatory top-down effects with anodal tDCS leading to a down-regulation of HPA and SAM systems. Further research using tDCS and neuroendocrine markers should explore the mechanisms of stress regulation in healthy and clinical samples.3

Beyond the silence: Bilateral somatosensory stimulation enhances skilled movement quality and neural density in intact behaving rats

“…Some features of this plasticity mediated by enhanced tDCSdependent synaptic potentiation have been previously reported in which anodal tDCS elicited a short lasting synaptic potentiation [64]. An alternative possible mechanism for functional online effects of tDCS includes enhanced psychomotor activity by alleviating the effects of stress and depression [69,70]. While stress is known to reduce skilled reaching performance, administration of antidepressants was shown to enhance skilled reaching success [71,72].…”

Nonlinear effects of respiration on the crosstalk between cardiovascular and cerebrovascular control systems

“…Despite this promising scenario and modelling work suggesting its feasibility in humans, just a handful of studies have investigated the application of tDCS for the modulation of cardiovascular human functions [125], with current literature showing very conflicting results [143,144]. Most of the studies involved the delivery of tDCS using a classic bipolar, cephalic electrode montage (i.e.…”

Effects of acute transcranial direct current stimulation in hot and cold working memory tasks in healthy and depressed subjects

“…It is also possible that subjective (self-report) mood evaluation is not sensible enough, at least in healthy volunteers, to index tDCS effects. For instance, in a previous study we observed [6] that tDCS did not change mood in healthy individuals, although cortisol levels and heart rate variability changed in a polarity-and valence-specific manner. Nonetheless, in the present study we did not examine the acute effects of tDCS on HDRS scores -future studies in depression could examine whether tDCS has fast antidepressant effects as observed for other novel therapies, such as ketamine.…”