Coordinator : Jocelyne Ventre Dominey
An electro-encephalography (EEG) system is used to record brain activity during cognitive tasks in human. The EEG signal is acquired at a sample rate of 2KHz ( low pass filter 400 Hz) from a 64 Ag-AgCl electrodes cap (Electro-Cap International, INC, Ohio, USA; Biosemi, ActiveTwo). The electrodes are referenced according to the 10-20 international system with electrodes used for signal referencing, for ocular movements recording and for artefact detection.
This EEG recording system is coupled to an eye movement sensor (Tobii Studio) for recording and analysis of eye gaze data in order to investigate ocular exploration of visual stimuli/scenes, and as a behavioural control, in conjunction with the Biosemi system.
The control of the stimuli presentation, the experiment monitoring and the data acquisition are provided by interactive software on PC computers (Eprime and Presentation for stimuli monitoring, Biosemi and Tobii software for collecting data).
This platform is currently used by 2 teams (Dominey and Proczyk) to study the evoked cortical activity during combined visual and language comprehension tasks and during decision making tasks in normal subjects.
A magnetic stimulator (Magstim, Rapid²) is used to investigate behavioural responses after localized and rapid perturbations of cortical activity. For this purpose, a stimulating figure-eight-shaped magnetic coil emitting strong, time varying magnetic fields is positioned on the scalp and oriented with respect to to the intended site of stimulation using a navigation software (Brainsight). This TMS technique, depending on the burst pattern and frequency of stimulation used can provide excitation or inhibition of the underlying nerve responses at different time scales.
Based on individuals MRI, Brainsight neuronavigation software allows the 3D curvilinear reconstruction of the brain and the scalp of the subject. In the experimental room, reflective markers placed on the head of the subject and the coil are detected by a camera and then head/coil relative positions are processed in Brainsight and superposed to reconstructed 3D brain and scalp. During the TMS session, the navigation of the coil relative to the head and the brain of the subject can thus be processed on line to be positioned as accurately as possible over the site to stimulate.
Currently in order to investigate the organisation of the human vestibular cortex, we investigate the effects of focalized stimulations in parietal and temporal cortices on vestibular responses in normal subjects. The paradigm uses a theta burst protocol (50 Hz, for 44sec- 600 pulses), at a stimulator intensity of 80% of the motor threshold. This type of stimulation induces temporary inhibition similar to a virtual lesion of the underlying cortex. This inhibitory effect has a duration of ~ ½ hour, and thus allows the study of vestibular function.