Effects of transcranial Direct Current Stimulation (tDCS) on cortical activity: A computational modeling study

Abstract

Although it is well-admitted that transcranial Direct Current Stimulation (tDCS) allows for interacting with brain endogenous rhythms, the exact mechanisms by which externally-applied fields modulate the activity of neurons remain elusive. In this study a novel computational model (a neural mass model including subpopulations of pyramidal cells and inhibitory interneurons mediating synaptic currents with either slow or fast kinetics) of the cerebral cortex was elaborated to investigate the local effects of tDCS on neuronal populations based on an in-vivo experimental study. Model parameters were adjusted to reproduce evoked potentials (EPs) recorded from the somatosensory cortex of the rabbit in response to air-puffs applied on the whiskers. EPs were simulated under control condition (no tDCS) as well as under anodal and cathodal tDCS fields. Results first revealed that a feed-forward inhibition mechanism must be included in the model for accurate simulation of actual EPs (peaks and latencies).Interestingly, results revealed that externally-applied fields are also likely to affect interneurons.Indeed, when interneurons get polarized then the characteristics of simulated EPs become closer to those of real EPs. In particular, under anodal tDCS condition, more realistic EPs could be obtained when pyramidal cells were depolarized and, simultaneously, slow (resp. fast) interneurons became de-(resp. hyper-) polarized. Geometrical characteristics of interneurons might provide some explanations for this effect.

Understanding the nonlinear physiological and behavioral effects of tDCS through computational neurostimulation

“…We here simulate the effects of tDCS by simply adding an additional current to the pyramidal cells and inhibitory interneurons, based on values from simulations reproducing tDCS-induced changes in sensory-evoked potentials in vivo (Molaee- Ardekani et al, 2013) and current understanding of the mechanism of action of tDCS (Bikson et al, 2004;Bindman et al, 1964;Funke, 2013;Nitsche and Paulus, 2011;Radman et al, 2009;Rahman et al, 2013). Specifically, depolarizing (anodal) stimulation was simulated by adding depolarizing current into each pyramidal cell and hyperpolarizing current into each interneuron, while hyperpolarizing (cathodal) current was simulated by adding hyperpolarizing current into pyramidal cells and depolarizing current into interneurons.…”

Noninvasive Neuromodulation in Poststroke Gait Disorders

“…114 Moreover, modeling and MRI studies indicate that anodal polarization may also affect excitability in inhibitory interneurons. 115,116 The behavioral consequences of NIBS could, therefore, be strictly related to the emergent properties of the stimulated networks, also considering the fact that an increase in excitability does not necessarily mean an increase in processing efficacy and vice versa. 112 …”

Computational modeling of neurostimulation in brain diseases

“…It was assumed that the perturbation is linearly related to the stimulus amplitude and direction dependent (relative to the stimulus field). Interestingly, Molaee-Ardekani et al (2013) found that only when including an effect of the stimulation field on interneuron populations, the model produced a better prediction of experimental measurements. Finally, at the population level, the modeling of the TCS stimulation can be combined with the FEM approach, where MRI-derived head models inform the positioning of neural populations, and a realistic electric field is simulated .…”

“…Extrapolating from the detailed models in network models point neurons have been used, where only 1 Introduction pyramidal neurons are affected by the stimulation due to their geometry (Reato et al, 2010). On the neural population level, a similar extrapolation has been used, where the stimulus was modeled as a perturbation on the mean membrane potential of populations (Ali et al, 2013;Dutta and Nitsche, 2013;Molaee-Ardekani et al, 2013). It was assumed that the perturbation is linearly related to the stimulus amplitude and direction dependent (relative to the stimulus field).…”