In fuelling imagination, memory helps us plan for what lies ahead.
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It is perhaps one of the most vexing aspects of life once you’ve hit middle age; it is often easier to recall the phone number you had 20 years ago than the password you made up yesterday. Those of us familiar with a failing short-term memory might console ourselves with the metaphor of an overstuffed library – that our brain is loaded up with so much information there’s little space for much more. The less reassuring reality is that it’s more likely to do with our shrinking hippocampus – and an inevitable consequence of getting on.
There are two broad theories on why we seem to be able to remember events of long ago more easily than what we had for breakfast, both of which revolve around the hippocampus. Memories are processed and stored in different parts of the brain – a memory of a smell in one part, emotional memories in another, recollections of sound in others. The hippocampus acts as a kind of conductor, selecting and drawing the different fragments together into one (mostly) cohesive memory.
The “consolidation theory” argues that although the hippocampus is integral to putting down new memories, it’s not necessary in the recollection of older ones. Donna Rose Addis, who heads the Memory Lab in the University of Auckland’s psychology department, explains: “It’s the idea that the hippocampus provides a kind of scaffolding. When the memory is still new, the hippocampus provides the scaffolding to put it all back together. But after a while the cement dries, and the cortex can take it over.” Which is why, according to the theory, older memories are more resistant to hippocampal damage, whether from Alzheimer’s, from brain injury or from getting older.
Addis, however, is more in favour of (and has done studies to support) the “multiple-trace theory”. According to this, the hippocampus is always involved in the recollection of detailed memories – from any time in our lives. The reason memories from long ago are more easily remembered than recent ones is that, over time and through repeated recollection and rehearsal, they have become a different kind of memory.
“It has become a string of words, a narrative. And you can still know what happened without your brain having to pull together what you were seeing and what you were feeling and what you could smell at that time. It’s more like telling a folk tale.” As Addis notes, even a fit and healthy hippocampus can get things wrong, by leaving out important details and drawing in false ones. This is a characteristic of the human brain – or, if you prefer, the human mind – that our criminal courts might pay more attention to when calling on witness testimonies.
Because it is easily inclined to error, our memory system has often been framed as somewhat faulty. But Addis argues that the system works to our benefit, because it allows space for the imagination – we can combine different details from our memory to create something new. Imagination isn’t only that which helps us create great works of art, or solve the mysteries of the universe, she says. It allows us to learn from the past in order to navigate the future.
“You have to be able to access details from your memory in order to mentally recreate detailed simulations of future experiences. And if you are able to simulate future events in detail, you are better able to cope with situations when they arrive. You can mentally troubleshoot for future obstacles. One of the most intriguing findings I’ve had is that when you look at neural activity, you see more activity in the hippocampus when people imagine than when they remember. We’ve always thought of the hippocampus as a memory structure, but we’ve now shown that it is being more activated by the imagination.”
In other words, memory doesn’t just define who we are and where we have come from, but helps prepare us for the future. Unsurprisingly, the memory – and the hippocampus – are things we’d all prefer to hang onto. There is plenty of evidence that exercise improves hippocampal function, that it stimulates the growth of new neurons. We can also exercise our hippocampus through a few mental processes. Addis recommends practising the art of remembering. She also suggests that when we lay down new memories we consciously build different associations around that memory, and construct a more elaborate context for it. Make that hippocampus work. “The more details you have for a memory, the more ways you have to get into it.”
STEM CELLS FOR SIGHT
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Human embryonic stem cells have been used to treat macular degeneration in two patients, according to the Lancet. The first published account of the use of such stem cells in humans involved one elderly patient and one young patient, who had severe vision loss from different forms of macular degeneration. For both women, the transplants appeared to be safe after four months, and both had some improvement in vision.
BORN TO RUN?
The skeletal structure of the feet and ankles of human sprinters is different from that of non-sprinters, according to Pennsylvania State University researchers who used MRI scans to scrutinise the feet of 16 males, half of them sprinters and half of them not. The Achilles tendon lever arms of the sprinters were 12% shorter than those of non-sprinters, the combined length of the bones in their big toes around 6.2% longer and the length of their first metatarsal 4.3% longer.
HEAD CASE
Repeatedly hitting the soccer ball with the head may lead to abnormalities in the white matter similar to those who have suffered traumatic brain injury, according to researchers reporting at the recent annual meeting of the Radiological Society in North America. In the study of 38 amateur soccer players, those who headed the ball more than 1320 times a year (an average of 3.6 times a day) had microscopic injuries in the white matter – that area of the brain that transmits signals between different parts of the grey matter – while those who didn’t head the ball so often didn’t.