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Effects of transcranial direct current stimulation (TDCS) on cortical activity: a computational modeling study

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2013-01
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Elsevier Inc.
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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.
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En este artículo se avanza en el conocimiento sobre los mecanismos por los cuales los campos aplicados externamente modulan la actividad de las neuronas. Se sabe que la estimulación de corriente directa transcraneal (tDCS) permite interactuar con ritmos endógenos cerebrales por lo que en este estudio se desarrolló un modelo computacional de masa neuronal que incluye subpoblaciones de células piramidales e interneuronas inhibidoras que median corrientes sinápticas con cinética lenta o rápida para investigar los efectos locales de la tDCS en un experimento in vivo. Se ajustaron los parámetros del modelo para reproducir potenciales evocados registrados en la corteza somatosensorial de conejos. Como resultado se consiguió simular los potenciales evocados en condiciones controles (sin tDCS), así como durante la aplicación de campos anodales y catodales. Este estudio reveló por primera vez que un mecanismo de inhibición de avance debe ser incluido en el modelo para una simulación precisa.
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Brain Stimulation, vol 6, nº 1, p. 25-39
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