Ah, Looks Familiar! Deja Vu and the Dentate Gyrus




Neuroscience_Neurology2.jpgThe human brain recognizes “patterns” as a natural way of looking at places and things. The feeling of deja vu is the result of such a pattern match; although we might not actually have been in a similar situation, the brain thinks it has, and produces a feeling of familiarity.

New research published online in Science reveals that specific neuronal pathways in the learning and memory center of our brain, the hippocampus, is crucial for rapidly “comparing” two scenarios based on visual cues, thus identifying similar contexts. In turn, this can lead to the feeling of familiarity we often get in odd places and circumstances, termed deja vu.

Surveys reveal that up to 70 percent of the population have experienced a deja vu at some point in their lives — and has also been described as a prominent symptom of temporal lobe epilepsy. It was the focal point in the novel by Marcel Proust, Remembrance of Things Past. The narrator recalls his past life through four moments of dega vu that involved complex experiences involving memories of smells and sounds from childhood, apart from visual memory.

The above-mentioned research project, carried out jointly by neuroscientists at MIT, UCLA, and Harvard, identified the signaling protein NMDA in the granule cells of the dentate gyrus in the hippocampus of mice. It is the key to rapid memory separation of two places, that serve as tools for discriminating two environments and thus crucial to learning. In some situations of similarity when the brain is not able to distinguish the two, it can also lead to the experiences of deja vu.

The Nobel laureate Prof. Susumu Tonegawa, in whose laboratory the study on mutant mice is being carried out, points out that the brain needs fine tuning in order to find out the unique cues which are crucial to distinguishing between familiar environments, to overcome the feeling of deja vu. The study is crucial for a better understanding of a host of disorders related to memory and learning, where the brain loses it ability to distinguish between similar environment, based on analysis of the unique features of each. It may also be impaired in some elderly patients with presumed changes in the hippocampus.

Deja vu then, could largely be due to a “confused” dentate gyrus.

Reference:

McHugh T J, Jones M W, Tonegawa S et al. Dentate Gyrus NMDA Receptors Mediate Rapid Pattern Separation in the Hippocampal Network. Science. 6 July 2007.

Sudip Ghosh, MD

Sudip Ghosh, MD, is a surgeon at the University of Manchester, UK and a medical writer.
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