Déjà vu is a fascinating, mystifying experience in which we, in a spontaneous and very elusive way, recognize that a situation is very familiar while we are concurrently aware that this sense of familiarity is inappropriate or that this “recollection” is in fact false. Occasional occurrences of déjà vu are reported by 60-80% of healthy individuals, implying that the psychic phenomenon is very widespread. Despite the fact that there is a large amount of hypotheses suggesting various explanations for common déjà vu, nobody had brought specific proof of the real principle of this phenomenon so far.
“One hundred and thirteen healthy subjects underwent a structural examination of their brain by means of magnetic resonance and subsequently by using a new sensitive method for an automatic analysis of brain morphology (Source-Based Morphometry) the size of individual brain regions was compared among the individuals who have never experienced déjà vu and those who have experienced it. Except for the presence of the examined phenomenon, both groups of individuals were fully comparable”, Milan Brázdil, the main author of the research and the Leader of the programme, Brain and Mind Research, from CEITEC, describes the procedure in the research. The performed analysis showed small, but statistically significant differences in the amount of grey matter in some regions of the brain, with a maximum of findings in the differences in hippocampal regions – small structures within the medial temporal lobes, in which memory and recollections originate. It was these structures that were significantly smaller in individuals with the occurrence of déjà vu than in individuals who have not experienced déjà vu. The scientists have also discovered that the more often the examined individuals experience déjà vu, the smaller the aforementioned brain structures are.
“When we stimulate the hippocampus we are able to induce déjà vu in neurological patients. By finding the structural differences in hippocampus in healthy individuals who do and do not experience déjà vu, we have unambiguously proved that déjà vu is directly linked to the function of these brain structures. We think that it is probably a certain small “error in the system” caused by higher excitability of hippocampuses. It is the consequence of changes in the most sensitive brain regions which probably occurred in the course of the development of the neural system”, adds Brázdil. The hippocampus is exceptionally vulnerable to various influences of external environment, pathological (e.g. inflammation, ischemia, seizures), as well as physiological (e.g. psychosocial stress or sleep deprivation) mainly in early childhood. All these factors, together with genetic influences, as also shown in the current piece just being published in one of the most prestigious journals, Nature Genetics, and in which a colleague from the CEITEC team, Richard Barteček, participated, can lead to a smaller hippocampus size and to its increased neuronal excitability. Common accidental stimulation of nerve cells in weakened hippocampuses can probably become small “errors in the system” – false recollections – déjà vu.
The scientists do not yet know what triggers déjà vu. The idea that there are similar processes taking place during this experience, as with temporal-lobe epilepsy, has been subject to discussion for a long time. An aura of déjà vu character in the beginning of an epileptic seizure has been reported by up to 30% of patients with this disease. “Similar to déjà vu in healthy individuals and in epileptics, this experience lasts only shortly and is unambiguously caused by a seizure stimulation of hippocampuses. That is why we were looking for similar links with healthy people too,” comments Tomáš Kašpárek, the co-author of the research and a member of the programme Brain and Mind Research from CEITEC.
The research results have been published by an international journal Cortex (Impact Factor 7.25). The discovery is expected to stimulate further research and to be an impetus for scientists from around the world to further engage in it. The authors have already been invited to report on the results of the study at several international conferences and workplaces. Scientists from Brno have cooperated on the research with their colleagues from the University of Exeter, United Kingdom. Scientists at Masaryk University have been researching the phenomenon of déjà vu for about 5 years; they have been working under the Central European Institute of Technology CEITEC mantle since June 2011. They will continue their research under CEITEC, thanks to a European subsidy which the CEITEC project acquired with its approval last June; they are getting financial and material support and, in 2014, they are moving to newly built modern CEITEC laboratories.
