Why We Feel a Sense of Déjà Vu

by VR Sreeraman on  June 9, 2007 at 12:44 PM General Health News   - G J E 4
Why We Feel a Sense of Déjà Vu
A recent research has identified a neuronal mechanism that our brains may use to rapidly distinguish similar, yet separate places and experiences.

The study, conducted by University of Bristol neuroscientists working with colleagues at the Massachusetts Institute of Technology (MIT), could lead to treatments for memory-related disorders, as well as for the perplexity and uncertainty that plague elderly individuals who have trouble distinguishing between separate but similar places and experiences.

Forming memories of places and contexts in which episodes happen engages a part of the brain called the hippocampus. The laboratory of Nobel Laureate, Susumu Tonegawa, Picower Professor of Biology and Neuroscience at MIT, has been exploring how each of the three hippocampal subregions-the dentate gyrus, CA1 and CA3- add distinctively to diverse aspects of learning and memory.

In the current study, co-authors Matthew Jones, Research Councils UK (RCUK) Academic Fellow in the Department of Physiology at the University of Bristol and Dr Thomas McHugh, a Picower Institute research scientist, have revealed that the learning in the dentate gyrus is critical in quickly recognizing and amplifying the small differences that make each place exceptional.

"We constantly make split-second decisions about how best to behave at a given place and time. To achieve this, our nervous system must employ highly efficient ways of rapidly recognising and learning important changes in our environment," Dr Jones said.

"This paper demonstrates that a particular protein signalling molecule (the NMDA receptor) in a particular network of brain neurons (the dentate granule cells of the hippocampus) is essential for these rapid discrimination processes, hopefully paving the way for therapies targeting learning and behavioural disorders," he added.

Professor Tonegawa, a frequent world traveler, describing his own special experience of finding the airport in a new city uncannily familiar, added: "This occurs because of the similarity of the modules-gates, chairs, ticket counters-that define the context of an airport. It is only by seeking out unique cues that the specific airport can be identified."

Researchers believe that a set of neurons called 'place cells' fire to supply a somewhat blueprint for any new space we come across. The next time we see the space, those same neurons fire. Thus we know when we've been somewhere before and don't have to relearn our way around recognizable turf. But similar spaces may set off overlapping neuronal blueprints, leaving room for uncertainty if the neurons are not fine-tuned.

In this study, the researchers used a line of genetically altered mice to pin down how the dentate gyrus contributes to the kind of pattern separation involved in identifying new and old spaces. While the mice behaved normally in most situations, they became confused when required to distinguish between different spaces. This may model the difficulties in forming distinct memories for similar but distinct places and experiences that afflicts some elderly individuals.

Source: ANI

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