Amnesia is combined in the plural: retrograde, anterograde, infantile, traumatic… The brutality of one of them, called the amnesic ictus is particularly impressive: during which the affected person no longer knows the date, the time , where she is… And the crisis lasts from a few minutes to a few hours.
If the stroke fascinates neurologists so much, it is because it offers a unique opportunity to learn more about how memory works and the networks involved in memorization.
"By the acute, massive, characteristic and isolated character of the mnesic disorder, it represents a privileged model for the study of memory disorders",
confirms Dr. Rigal, neurologist at the CHU Purpan in Toulouse.
A few years ago, a clinical research study was conducted under the responsibility of Pr Jérémie Pariente (neurology, CHU Toulouse) to learn more about this disorder.
All people suspected of having an amnesic stroke in Haute-Garonne benefited from a specific multidisciplinary assessment between November 2013 and July 2015, with neuropsychological tests followed by research MRI examinations during the stroke, then, three days later and finally three months later: a fine example of clinical research.
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“When the stroke occurs, the imaging (MRI) is normal.
It is only when the symptoms disappear that imaging finds very discreet and transient abnormalities, probably testifying to suffering, but not commensurate with what is usually seen in a vascular accident.
Then everything goes back to normal,”
says researcher Patrice Péran.
Causes still mysterious
What does the presence of this discreet anomaly mean and why is its appearance delayed in relation to the occurrence of symptoms on the MRI?
“Perhaps structural MRI is not a sensitive enough instrument to detect other abnormalities earlier.
This is why our team thought about the interest of supplementing the “classic” MRI which allows us to see the structures of the brain, with a research MRI which allows us to see the brain functioning.
The use of these functional imaging techniques allows us to know at a precise moment the functional relationships between the cerebral structures involved in memory and the hippocampus.
This research work made it possible to show that there was a significant dysfunction, extending well beyond the hippocampus, as if the latter were temporarily disconnected from the other areas of the memory network.
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However, the intimate causes of amnesic stroke remain mysterious.
It can be triggered by physical exertion, emotional stress or certain painful medical procedures but some have been observed after immersion in cold/hot water, sexual intercourse or acute pain.
“Understanding memory is a major challenge that goes far beyond the amnesic stroke
,” conclude Dr Rigal and Patrice Péran.