martedì 7 agosto 2012

Come passa il tempo ...

MEDICAL MYTHS| 10 July 2012

Does life speed up as you get older ?

Why you get the sinking feeling that weeks, months and years are passing you by faster than ever.
If you are like me, you’ll be astonished to discover it’s already halfway through the year. And before you know it, Thanksgiving or Christmas will be upon you yet again.
When I was a child it all seemed so different. I thought it was the dumbest, most obvious thing for my relatives to point out how much I’d grown since they last saw me. Now I spend my time constantly surprised at the way the months and years fly by, I finally understand what they meant. The school summer holidays used to stretch on forever. Now summer is gone in the blink of an eye. How can it be almost seven years since Hurricane Katrina, and twenty-six since the explosion at Chernobyl, when I remember so clearly hearing those news stories?
I know I’m not alone. The sensation that life is speeding up is a commonly reported aspect of ageing. Experiments have suggested that our ability to assess the passing of time does alter with age. If you ask a twenty-year-old and a seventy-year-old person to guess when a minute has passed without counting, the younger person does it more accurately, while time appears to be going slightly faster for the older person.
American biologist Robert B. Sothern has spent forty-five years seeing if he encounters a similar effect as he ages. Five times a day he records his temperature, blood pressure, heart rate and estimation of the passing of a minute. He never misses a day, even when he’s on holiday. His main research interest is in whether the timing of medical treatments can affect their efficacy, a theory about which most researchers remain sceptical, but his diligent self-study does tell us something extraordinary about time perception. As he has become older his time estimation has become less accurate and time seems to be gradually speeding up.
This is not as straightforward as it seems. The way we assess time remains something of a mystery. Nowhere in the brain has anyone been able to find a single area dedicated to time perception. We do have a body clock that rules our 24-hour sleep/wake cycle, however, this only governs our circadian rhythms and plays no role in estimating seconds, minutes, or even the years passing.
But different medical conditions indicate that at least four different parts of the brain could have a role in time perception. Children with Tourette’s Syndrome, for example, who need to use the pre-frontal cortex just behind the forehead to help them control their tics, are better at estimating intervals of just over a second than other children. Meanwhile, studies in which children with ADHD are given time estimation tasks shows time passes very slowly for them. This backs up other findings suggesting time perception is linked to the dopamine system in the brain. So for these children sitting still for five minutes could feel like far longer.
Breaking routines
That said, the idea that time feels as though it’s going faster in middle age appears to be a myth. In fact, it depends on the time-frame you are considering. In time perception studies, adults in mid-life report that the hours and days pass at what feels like a normal speed; it is the years that flash by.
As I have discussed in my book Time Warped: Unlocking the mysteries of Time Perception, I believe this is because we constantly assess time in two ways. We look at it prospectively, asking ourselves how fast time passing right now. And then we also gauge it retrospectively – has fast did yesterday or last week go by?
Usually these two perceptions match up and time feels smooth, but sometimes they get out of sync. Ageing is an example of this.  The days still feel as though they pass at an average speed, but we’re surprised when markers of time indicated how many months and years have passed or at how quickly birthdays come round yet again. Part of the reason is that as we get older life inevitably brings fewer fresh experiences, and more routines. Because we use the number of new memories we form to gauge how much time has passed, an average week that doesn’t loom large in the memory gives the illusion that time is shrinking.
There is a remedy. If you want the weekend to go slowly, don’t spend time resting and watching TV. Instead fill it with new experiences and by Sunday night you will look back and the weekend will seem long.
That said, we do have to ask ourselves whether we really want to slow time down. If you look at the circumstances where evidence tells us that time goes slowly, they include having a very high temperaturefeeling rejected and experiencing depression.
So, as surprising or frustrating as it might seem, perhaps if life does seem to be rushing by it is a sign that things are going well.
If you want to test your own time perception, there are some games you can play on Claudia's website
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You can hear more Medical Myths on Health Check on the BBC World Service.
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