Could déjà vu be explained by grid cells?
—Robyn Ganeles, San Francisco
Neuroscientist Edvard I. Moser of the Norwegian University of Science and Technology responds:
This is a great question, because grid cells, which are involved in processing spatial information about our surroundings, are located in a brain region that is part of a larger memory system thought to be responsible for the feeling of familiarity. After considering their function in detail, however, I think it seems more likely that a different system of neurons, place cells, plays a stronger role in providing us with the sense that a new locale is familiar—a feeling called “déjà visité.”
In any environment, the brain must keep track of the distinct locations within the surrounding area (say, at the kitchen table versus in front of the refrigerator). It also must note how these different locales relate to one another (the table is three feet to the right of the fridge, for instance). Place cells are involved in the former type of processing; each place cell corresponds to a specific location in an environment and fires when you pass through that spot.
In contrast, grid cells work in a network to produce a kind of internal coordinate system, noting information about distance and direction. These neurons do not correspond to a specific location but become active across several regularly spaced points in any setting. The geometric arrangement of these cells, relative to one another and to the external setting, ultimately helps us form a mental map of a certain environment.
Grid cells are located in the entorhinal cortex, a brain region that processes information before sending it to the hippocampus, the area where place cells are located. Because we know that place cells have a unique firing pattern for nearly every experience, it is likely that the hippocampus, and not primarily the entorhinal cortex, decides whether a location is novel or being revisited. When a strange place is experienced as familiar, it may be because the activated ensemble of place cells at that location happens to be similar to a pattern of activity that was elicited by a previous locale.
Do the typical sleep schedules of elderly people have a physiological benefit, or do they simply reflect generational trends?
—Shannon Atkinson, Raleigh, N.C.
Michael V. Vitiello, professor of psychiatry and behavioral sciences at the University of Washington, replies:
It is unlikely that the “typical sleep schedules of elderly people” either reflect generational trends or convey any physiological benefit. There is no evidence to support the idea that the typical sleep schedules of older adults in developed countries—marked by earlier sleep and rise times, less total sleep and more nighttime wakefulness—are cohort effects (that is, result from having grown up or lived during a specific time period). The few studies that have looked at how sleep patterns change as people age show slow and progressive changes in sleep patterns across the human life span. If there were specific cohort or generational differences, this pattern of regular, progressive change would be much less predictable.
Given that the sleep patterns of older adults appear long after these individuals are capable of reproduction, they probably do not confer any physiological benefit. It is much more likely that they reflect biological and social changes that occur as people age. Biological changes include alterations in the body’s underlying circadian rhythm, which helps to regulate the timing and depth of sleep, and age-related reductions in the homeostatic sleep drive, the metabolic process that causes the inclination to sleep after a period of wakefulness.
Other factors likely to influence the quality and timing of sleep in older adults include the increased prevalence of illnesses, such as osteoarthritis, that can directly disrupt sleep, and the presence of primary sleep disorders, such as obstructive sleep apnea or restless legs syndrome. Various behaviors and environmental factors can also disrupt sleep. Many of these variables, such as irregular sleep schedules, staying in bed too long, and bedding or a bedroom that is not conducive to sleep, can be adjusted for improved slumber.
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6 Comments
Add CommentI wonder how that can be related into the theory that feelings of deja vu are ripples in the space-time continuum because the past has been changed in a small way.
Reply | Report Abuse | Link to thisDeva vu happens because you actually see the future each night when you sleep.
Reply | Report Abuse | Link to thisIt is somewhat like a Carrot Top act. The mind uses any image, anything, or anyone to be pulled out of the "trunk" to be used to convey the "feeling" of that moment. It is hard to believe, but the future has already happened somewhere. Each night we dream and we leave our bodies to "peek" into the coming days. When you walk into a room and it feels like you have been there, think about recent dreams, and see if you can match the "feeling" or details you could not already be aware of.
Here is a personal experience. In a dream I traveled to another country and watched a friend write me a letter.
When I received it later, they described an event that happened while they were writing the letter. An event I saw while "out of my body", and was surprised and not surprised when I read in detail what I had seen.
"They" say the universe is a holagram.
I can see how one could move about this in the dream state.
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Edited by chrixthornton at 04/21/2008 4:36 PM
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Edited by chrixthornton at 04/21/2008 4:38 PM
And what about blind people? Do they experience a similar phenomenon concerning the sense of hearing? On the other hand, all of us happened to recognize a tune we could not have listened for previously.
Reply | Report Abuse | Link to thisWith regard to the deja vu phenomenon, the question is this: What energic factors, directed at what object representations, are operating in the unconscious to induce a localized ego regression as a defensive operation, resulting in the highly unique and specific sense of familiarity that characterizes the current reality situation?
Reply | Report Abuse | Link to thisRegarding sleep patterns - I would argue that just because a human is beyond reproductive age does not mean that their actions create no impact on the survival of their progeny - grandparents, and I am thinking of Hrdy speaking of grandmothers specifically, can impact the survival of their grandchildren, and thus altered sleeping patterns amongst oldsters Could, arguably, have a physiological benefit.
Reply | Report Abuse | Link to thisScientists seem determine to dismiss Deja Vu as just a "feeling" of having been here before, but I have proven to myself that it is more than that. I used to get Deja Vu experiences quite frequently. One evening while listing to a live talk show I had a Deja Vu experience and knew exactly what the announcer was going to say, so I said it out loud BEFORE the announcer so I could hear myself say it relative to the announcer thus proving it's not just a case of the brain getting the signal via multiple routes or other such explanations. The fact that I could hear my own voice saying what the announcer was going to say, verbatim, for about a minute, proved that.
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