Amnesia, Transient Global

Amnesic stroke is an amnestic syndrome lasting less than 24 hours characterized by the occurrence of anterograde amnesia often associated with retrograde amnesia, the pathophysiology of which is still poorly understood at present. A recent study on a small sample size (N=29) highlighted an association between obstructive sleep apnea syndrome and amnesic stroke. Our study seeks to confirm or refute these results on a larger cohort (N=200-250). A better understanding of the pathophysiological processes involved would open up new therapeutic avenues.

There are few studies on the role played by emotions in transient global amnesia (TGA), in particular with regard to their impact on the functioning of memory. The study investigators wish to better understand the link between episodic memory, emotional state and psychogenic factors during TGA. It would be interesting to see if the patients suffering from TGA triggered by a psychological shock process emotional information differently from those whose TGA was triggered by an "organic" shock (physical effort, trauma, etc.). Finally, amnesic stroke is a good model for better understanding the function of the hippocampus, in particular of the CA1 region, in episodic memory.

The transient global amnesia (IA) is defined clinically as a temporary suspension and isolated from the ante and retrograde memory, totally regressing within 24 hours. The causes of AI remain unknown. The diagnosis of IA is based on consensus clinical criteria including the absence of associated location marks. In clinical practice, the MRI is often performed in conjunction with clinical examination because it ensures the absence of differential diagnoses, including stroke.
The visualization of MRI signal abnormalities related to AI directly dependent on the completion time of the review in relation to the onset of symptoms. Typically, no signal abnormality is visible in the hyperacute phase (ie D0-D1) while punctate appear hyperintense on diffusion sequences in hippocampal structures from J2 to J7 to disappear completely. It has been previously demonstrated that the use of higher values of b and / or a better spatial resolution significantly increases the sensitivity of the broadcasting sequence for the detection of these abnormalities hippocampal signal. At St. Joseph Hospital, Investigators explore the AI suspected patients with diffusion tensor sequence (DTI) on our high resolution 3T MRI.
Compared to the classical diffusion sequence, DTI is characterized by the use of a greater number of directions in which the diffusion gradients are applied. One advantage of this technique is to be able to perform tractography of white matter fibers. Thus the "connectome" is a new technique for post-processing of DTI images based tractography and to assess all the networks of nerve fibers in the brain. By this technique, the values of average diffusivity (MD) and fractional anisotropy (FA) can be measured along each of the studied nerve fibers. Group studies thus become feasible to compare quantitatively healthy subjects and patients groups in terms of structural differences within the connectome. The contribution of this technique was recently highlighted in patients with temporal lobe epilepsy.