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Wednesday, Aug. 8, 2007
MEMORIES ARE MADE OF . . .
How is it our time seems to speed up?
By ROWAN HOOPER
"I never think of the future; I find it comes soon enough."
That was one of Albert Einstein's semi-mystical sound bites, offered when he'd grown from being a radical, brilliant mathematical genius into a white-haired old man with a beguiling penchant for philosophy.
He was still a genius, but he no longer set the agenda for mathematics and physics.
It's worth starting this month's column with this quote from Einstein, I thought, as it's August already, and it seems this year has dashed by. Older readers, I hope, are nodding their heads in agreement. At this rate, before we know it we'll be reflecting on a year gone by. My future self is right now reflecting on a life gone by.
But why does time seem to speed up as we get older? Is it just an illusion, made to seem real because of the changing proportion of our lives that we are experiencing? As we age, each day, each month, each year is a smaller proportion of our entire life, so it just seems to pass quicker. This probably does account for some of the feeling of time speeding up. And think about an important event in your life: It probably seems to have happened more recently (unless it happened yesterday) than it really did. We underestimate how much time has passed.
Memories are formed differently in the brains of children and adults. The first time you do something — be it ride in a plane or fall in love — it is scored more deeply in your memory than the next time. Children do lots of things for the first time, and when you are older you've seen it all before.
The ability to remember factual information — who, what, where, when — emerges gradually during childhood. It is not well developed in early years, which is probably why most people have no memories prior to the age of 3 or 4. But luckily this ability kicks in, for without it we'd have trouble learning anything.
Now a simple experiment has compared how memories are formed in children and in adults, and the results give certain compensation to those of us who are past the first flush of youth: Mature brains remember things in a more detailed, richer way.
Forty-nine healthy volunteers ranging in age from 8 to 24 were tested recently on their recognition of 250 common scenes, such as a kitchen, shown to them as they lay in a functional magnetic resonance imaging (MRI) scanner. Their brain responses were recorded by researchers at the Massachusetts Institute of Technology as the volunteers tried to commit each picture to memory. Shortly after the volunteers left the scanner, they were shown 500 scenes and asked if they had seen each one before, and if so, how vividly did they recall the scene.
After gathering the results, researcher Noa Ofen went back to the brain-activation patterns recorded by MRI. In both children and adults, several areas in the prefrontal cortex (PFC) and the medial temporal lobe (MTL) of the brain showed higher activation at the time when subjects studied a scene they remembered. No age-related differences showed up in the activation patterns of the MTL regions in children and adults, but differences did appear in the PFC when looking at pictures that were correctly recognized.
Now here's the point. Those age-related differences related to the quality of the volunteers' memories. The older the volunteers, the more frequently their correct answers were enriched with contextual detail. Going back to the brain scans, Ofen found that the enriched memories also correlated with more intense activation in a specific region of the prefrontal cortex. In other words, the older brains remembered things better, more deeply.
"We found no change with age for memories without context. All the maturation is in memories with context," Ofen says. "Our findings suggest that as we mature, we are able to create more contextually rich memories, and that ability evolves with a more mature prefrontal cortex."
Over at Yale University, neuroscientists looked at how brain activity was boosted by giving mice more mental exercise, as well as physical exercise.
Young, middle-aged and old mice were kept in cages where they could exercise on running wheels, cages where they could play with toys, cages with both, or cages with neither. After living for four weeks like this, their brain power was tested by getting the mice to navigate through a maze, a common test of learning and memory. Spatial memory is supported in part by the hippocampus, a brain region among the first to be affected both by normal aging and Alzheimer's disease. Thus, spatial memory is a good indicator of hippocampal health in both mice and humans.
For all of the experimental mice, spatial memory worsened with age. For middle-aged mice with exercise and a complex environment — cages with toys to play with — their brain ability was boosted only when combined in the same cage. For old mice, however, any enriched environment on its own helped. That is, either an exercise wheel, or a complex environment, or both. All boosted the ability of the mice to solve the maze.
The results suggest that as we get old and maybe less able to exercise, brain stimulation can help to compensate for a failing memory.
The future does come soon enough, as Einstein said. Here's something from Japan's greatest haiku poet, Basho. I don't know how old Basho was when he wrote this, but I like it because it's somehow more mature and reflective, and it seems a fitting and rich point for a maturing brain to finish on:
Gray hairs being plucked,
and from below my pillow
a cricket singing
The second volume of Natural Selections columns translated into Japanese is published by Shinchosha. The title is "Hito wa Ima mo Shinka Shiteru (The Evolving Human: How New Biology Explains Your Journey Through Life)"; Price ¥1,500.