Transient Global Amnesia (TGA). Exploratory Study of the Default Mode Network During the Acute Phase

The transient global amnesia, in which the memory disorder is massive, transient and pure, offers a unique model for exploring episodic memory. Topographic MRI can reveal a focal and selective lesion located on the CA1 region of the hippocampus better visible between 48h and 72h after onset of the episode. There is therefore a real dissociation between structural lesions witch are minimal or non-existent and the massive memory disorder. This suggests that functional impairment goes far beyond the structural damage in this condition. To our knowledge, no study has been performed to identify this functional impairment using resting state fMRI. Thus, investigators wish to study the neural networks involved in memory impairment during the acute phase of transient global amnesia using resting state imaging. This technique appears to be modern and adapted to these patients population. Investigators hypothesize that despite limited structural lesions, a large functional network is impaired compared to that observed in a group of healthy subjects. investigators believe that the alteration of the functional network will explain the depth of memory impairment observed. The main aim of this study will be to identify functional impairment in the patient group vs. control group during the acute phase of transient global amnesia (TGA) using resting state imaging. Patients potentially eligible will be informed during their arrival to the emergency unit. If the patient is eligible and would like to participate, information will be given. For the patients willing to participate, inclusion and exclusion criteria will be verified. Two imaging exams (topographic MRI and resting state fMRI) and neuropsychological assessment will be performed during three visits.