Modulation of GABA and resting state functional connectivity by transcranial direct current stimulation

Abstract

We previously demonstrated that network level functional connectivity in the human brain could be related to levels of inhibition in a major network node at baseline (Stagg et al., 2014). In this study, we build upon this finding to directly investigate the effects of perturbing M1 GABA and resting state functional connectivity using transcranial direct current stimulation (tDCS), a neuromodulatory approach that has previously been demonstrated to modulate both metrics. FMRI data and GABA levels, as assessed by Magnetic Resonance Spectroscopy, were measured before and after 20 min of 1 mA anodal or sham tDCS. In line with previous studies, baseline GABA levels were negatively correlated with the strength of functional connectivity within the resting motor network. However, although we confirm the previously reported findings that anodal tDCS reduces GABA concentration and increases functional connectivity in the stimulated motor cortex; these changes are not correlated, suggesting they may be driven by distinct underlying mechanisms.DOI: http://dx.doi.org/10.7554/eLife.08789.001

Non-Invasive Brain Stimulation in Dementia: A Complex Network Story

“…Antonenko et al [29] reported a reduction of GABA concentrations following atDCS together with a decreased FC in the sensorimotor cortex in elderly. This pattern is different from that observed in young adults [30, 31, 39]. Stratification of the elderly sample into younger (< 63 age) and older (> 63 age) revealed a differential effect of atDCS-induced GABA modulation and network coupling: in younger, lower GABA correlated with higher sensorimotor strength (i.e., the same pattern observed in young adults), while in older the correlation was reversed [29].…”

“…The majority of these studies investigated neurometabolite changes in the motor cortex in young adults, reporting a consistent reduction of GABA after atDCS [31, 70, 75, 76], except for Tremblay et al [77]. The above finding was generally coupled with increased FC over the motor network [31, 39], indicating that these connectivity changes may be driven by a decrease in the inhibitory neurotransmitter.…”

“…The above finding was generally coupled with increased FC over the motor network [31, 39], indicating that these connectivity changes may be driven by a decrease in the inhibitory neurotransmitter. Indeed, Stagg et al [76] estimated a decrease of around 12% of GABA levels in the motor cortex following motor atDCS and an inverse correlation with motor network FC [39].…”

“…Increased functional connectivity (FC) was found both in regions proximal to the electrode [30, 34, 38] and in distal regions belonging to the sensorimotor network [31, 36, 39]. Similarly, studies using graph theory, an approach taking into account network topology and synchronization between brain hubs [64], suggested a network-specific enhancement of connectivity following atDCS [32, 33, 35, 37].…”

Transcranial Direct Current Stimulation Targeting Primary Motor Versus Dorsolateral Prefrontal Cortices: Proof-of-Concept Study Investigating Functional Connectivity of Thalamocortical Networks Specific to Sensory-Affective Information Processing

“…During tDCS, however, the equipment was restored; the subject table was pulled out of the scanner while the participant lay supine and electrodes were reconnected to the tDCS device. Active tDCS was delivered for 20 min at 1 mA intensity with ramp-up/ramp-down periods of 10 sec, as described in earlier studies (Bachtiar et al, 2015;Stagg et al, 2013). For sham, the stimulator provides stimulation at the beginning and at the end to mimic the somatosensory artifact of active tDCS.…”