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

 The transient global amnesia is a transient, massive and pure memory disorder. Its
 pathophysiology is poorly known, but the disease process involves the Papez circuitry, and
 more specifically the medial part of the temporal lobes (hippocampi). It involves 3-8 per
 100,000 people per year. The age of patients affected is between 50 and 70 years. Structural
 MRI can confirm the diagnosis by revealing a focal and selective lesion located on the CA1
 region of the hippocampus better observed between 48h and 72h after onset of the episode.

 Main purpose:

 The main aim of this study is to identify neuronal functional impairment in a group of
 patients vs. a group of healthy subjects during the acute phase of transient global amnesia
 (TGA) using resting state fMRI imaging.

 Secondary purpose:

 -  Show correlations between functional activity observed in resting state fMRI at the
 acute phase and cognitive performance in the patient group.

 -  Describe the evolution of functional impairment in resting state fMRI between the acute
 phase (visit 1) and post-acute phases (visit 2 and 3) in the patient group compared to
 the control group subjects.

 Study design:

 Monocentric, pilot, prospective, controlled study including consecutive patients admitted to
 the emergency department of the CHU of Toulouse for transient global amnesia. investigators
 will compare two independent groups: patients and controls We expect three months between the
 signing of consent and the end of the study. The total duration of the study will not exceed
 27 months.

 Arm number or label and arm type: This study is exploratory. investigators will compare two
 independent groups: patients and controls

 Interventions:

 After signing the informed consent each patient TGA will receive a neuropsychological
 assessment, a topographic MRI and an evaluation in resting state fMRI during three successive
 visits:

 -  During the acute phase within 24 hours

 -  In 72 hours

 -  In 3 months

 Number of subjects:

 It's difficult to estimate the number of subjects required to show a difference in resting
 state between the two groups during the acute phase of TGA. No study of that type in the
 literature is available to estimate the sample size to be recruited. In this pilot study we
 will recruit 22 subjects in each group.

 Expected benefits:

 The transient global amnesia is a model for exploring memory because this disorder is
 massive, pure and temporary. Better understand the Neural Network substrates underlying this
 alteration could help to better understand memory disorders in other diseases (Korsakoff
 syndrome, thalamic stroke, dissociative amnesia, Alzheimer's disease). Such discovery could
 lead to clinical trials of functional brain stimulation as recently developed in other
 neurological disorders in which functional impairment has been shown. (TMS, TDCS)

 Statistical analysis:

 The SPM8 software will be used to generate activation map using fMRI images. The obtained
 maps will be compared between groups using t test imbedded in the same software. Correlation
 maps between cognitive performance and activation will be also calculated. Intra group
 comparison across time will then be assessed.
Inclusion Criteria:

 Patient group

 Clinical criteria of definition of transient global amnesia:

 Acute disorder of anterograde memory observed by a witness. Respect of the other cognitive
 functions. No exclusion criteria for this diagnosis (see exclusion criteria section).

 Hippocampal lesion in DWI MRI performed at 72h Clinical resolution of memory disorder
 within 24 hours

 Control group No cognitive complaint No history of transient amnesia

 Both groups Age between 40 and 80 years old

 Exclusion Criteria:

 Patient group Disturbance of consciousness or loss of identity Argument in favor of seizure
 disorders Presence of a neurological deficit focused

 Both groups Recent head trauma Acute intoxication ethyl Taking drugs influencing memory
 processing Severe hypoglycemia Psychiatric disorder altering capacity for judgment
 Progressive neurological disorder with cognitive alteration Indication against MRI French
 language level insufficient to be appropriately involved in neuropsychological assessment,
 Administrative issues: unable to give informed about information, not covered by a social
 security system, refusal to sign the consent, patient under curators.

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