Since the first demonstrations in 1985 of cortical magnetic stimulations in humans, Transcranial Magnetic Stimulation (TMS) has been widely developed in a therapeutic aim as well as in cognitive neuroscience research. In 2008, CerCo acquired a TMS machine for human experimentations. At the moment, it is used as part of studies on oscillatory mechanisms of cortical activity and to tackle high cognitive functions like visual attention and memory.
CerCo has a Magstim Rapid2 TMS machine of 3.5 Tesla, producing a biphasic current, and 2 figure-of-eight stimulation coils (70mm). When the coil is pressed against subjects’ head it produces a magnetic field which modulates neural activity, affecting local field potentials. The TMS pulse has a very good spatial resolution (1-2cm) and temporal resolution (the pulse lasts less than 1ms and the neuronal effect is totally abolished in 1s). During TMS experiments, ElectroEncephalography (EEG) could be simultaneously recorded. Matlab and EEGLAB are the software used for the analysis of the behavioral and EEG data
The inactivation of brain structures by cooling is used to assess the functional impact of the deafferented region and its connectivity. It can be easily coupled with electrophysiological recordings and behaviour. This technique has many advantages compared to the more traditional approach with cortical lesions. It prevents the postlesional plasticity, hence directly addressing the role of the deactivated zone and not the reorganisation of the circuits consecutive to the lesion itself. It is fully reversible in a few minutes and the duration and spread of the inactivation can be controlled by the experimenter. Since the cooling probe can be permanently implanted (even within sulci), it allows the animal subject to be its own control ; it also allows to investigate several questions in one animal (because of the reversibility, new tasks can be learned by a given implanted animal). Hence it fully complies with the 3R ethical rule. Several probes can be used in one subject, allowing for double dissociation studies. Finally, we aim at using this technique in fMRI. A cooling probe is a hypodermic stainless tube forming a loop of a few mm size. The inactivation is carried out while circulating cooled fluid in the tube and the temperature, monitored by a thermocouple at the base of the loop, is regulated by the speed of the pump. During cooling, the cortical temperature follows a gradient and the effects of cooling are mainly localised to 1 or 2 mm around the probe.
Mise à jour 25/02/2011