Spatiotemporal after-effects of transcranial direct current stimulation on sensory-evoked activity in rat S1: A pilot VSDI study

Cortical excitability of the human brain can be increased or decreased using brain stimulation techniques. One of the methods currently used for that purpose is weak transcranial direct current stimulation (tDCS). This portable, non-expensive and non-invasive technique has recently received new interest in the field and has given promising results mainly in clinical neuropsychiatric and stroke recovery studies [1-3]. However, the fundamental mechanisms underlying these changes in cortical excitability, as well as their after-effects on sensory processing remain mainly unknown. Concurrently with the comeback of this age-old technique, the voltagesensitive dye imaging (VSDI) method is a technological breakthrough since it offers the possibility to visualize in real-time the activity of large cortical neuronal populations with high spatiotemporal resolution [4-6]. Indeed, based on voltage-sensitive dyes that instantaneously change their fluorescence yield in proportion to membrane potential changes, VSDI allows the study of spatiotemporal dynamics of cortical processing at the mesoscopic level. Combining these two methodologies could help to reveal the neuromodulatory after-effects of tDCS on cortical population activity. This is indeed an issue of significant importance in this field [7], promising improvements in the therapeutic use of electrical stimulation.