The neuropsychology of visuospatial attention : effects of transcranial Direct Current Stimulation

Details

Supervisors

Grade, Stéphane ; Edwards, Martin

Faculty

Faculté de psychologie, logopédie, sexologie et des sciences de la famille

Degree label

Master [120] en sciences psychologiques

Abstract

Since several decades, we know from neuropsychology that damage to the parietal areas of the brain causes reduced visuospatial attention. However, little is known regarding processes underlying this function. In this research, we used a transcranial Direct Current Stimulation (tDCS) to modulate brain activity in the parietal lobe, known as the main site of visuospatial attention. We tested eighteen subjects on three visuospatial attention tasks: the landmark task, the proximity task and the temporal order judgment task. The main aim of this study was to test if a dual tDCS can modulate participants’ performances on this three tasks using a 1,5mA intensity of 20min and two active electrodes. Moreover, we want to challenge two main theories which suggests a competition between both hemispheres. It is a question of Heilman’s theory and Kinsbourne’s theory. The first author proposes that the right hemisphere has the main role concerning visuospatial attention taking care essentially of the left hemifield but also of a little part of the right side of the visual field whereas the left hemisphere only deals with the right hemifield. The latter author, as for him, suggests an inhibitory process between both hemispheres, i.e. the right hemisphere takes care of the contralateral hemifield and prevent the left hemisphere to deal with it thanks to this process, and vice versa. We conducted an experiment with three different conditions: the anodal condition (with the anode over the right parietal cortex and the cathode over the left one), the cathodal condition (with the reverse montage) and the sham condition. Each subjects came through these conditions during three different meetings. Three dependent variables were measured: reaction times, response types and accuracy. Results showed performances in line with our prediction, especially regarding Kinsbourne’s theory and the temporal order judgment task. An effect of the cathode was observed which cancel the inhibitory process of the hemisphere on which the cathode was put. These results are in line with Kinsbourne’s theory. Furthermore, it seemed that a bigger effect was found when the cathode was under the right hemisphere which is also in line with Heilman’s theory. Therefore, we can proposed a mix model in which both theories are in play. There is an inhibitory process but also a main role of the right hemisphere.