Abstract TMP39: The neural and behavioral basis of Transcranial Direct Current Stimulation

Abstract

Non-invasive brain-stimulation has been reported to modulate cortical excitability, synaptic plasticity, and interhemispheric interactions of homotop brain regions. All of these processes could play a role in facilitating stroke recovery. Modulation in cortical excitability covaries with changes in regional cerebral blood flow. Our aim was to determine whether varying parameters of transcranially applied direct current stimulation would modulate regional cerebral blood flow and behavioral measures such as motor sequence learning in a differential effect. Twelve right-handed subjects participated in all behavioral and imaging studies. We used three different dose levels (Sham, 2mA and 4mA corresponding current densities: 0mA/cm2, 0.156mA/cm2, and 0.318mA/cm2) and two different electrode montages (unihemispheric or bihemispheric) to examine tDCS effects on a finger sequence learning task and on regional cerebral blood flow (using Arterial Spin Labeling as a Blood Flow MR sequence) using an MR compatible NeuroConn DCMC stimulator. An anodal electrode (diameter of 4 cm) was placed over the right motor region (C4) while the cathodal electrode (diameter of 5 cm) was either placed over the left supraorbital region (unihemispheric montage) or over the left motor region (C3; bihemispheric montage). Each stimulation was of 10 min duration (ON condition) and preceded by 6 minutes of no stimulation and followed by 8 minutes of no stimulation (OFF conditions). A significant difference (p<0.05) in cerebral blood flow between ON and OFF conditions was seen for the group in a region of interest including the perirolandic region on the right (under the anodal electrode) showing an increase in rCBF between sham, 2mA and 4mA. There were trends for stronger bihemispheric blood flow changes for the bihemispheric montage than the unihemispheric montage. In the finger sequence learning task, subjects learned to type a randomly chosen sequence of 7 numbers with digits 2-5 of each hand as accurately and as fast as possible, before and immediately after a 10 minute stimulation phase. Higher numbers of correct finger sequence were seen in the higher current conditions for the unihemispheric condition. Results were more mixed for the bihemispheric montages.