June 4, 2014
Memory is a funny thing. More than once, I’ve been telling a story with my mother or sister in the same room, only to get interrupted halfway through by a wave of the hand and an insistent interjection: “No, that was you outside in the sprinklers. I was in the car watching the neighbor’s dog.” Most scientists agree that memory is largely reconstructive, and even intense “flash-bulb” memories that we feel are burned into the back of our head forever (where were you when the World Trade Center was attacked?) might not be as accurate as we adamantly insist.
Recently, researchers at the University of California in San Diego discovered an intriguing method through which the hippocampus can be manipulated to repress and restore memories in mice. By using a previously-established technique called long-term potentiation (LTP), which involves running electrical currents through the hippocampus, scientists were able to elicit a fear response in genetically altered rats whose brains had been altered to produce a light-sensitive protein. They activated this protein and then followed that with a shock to create neurochemical changes that would cause the rats to fear the special light pulses that the scientists were using.
The second step of the process was to stimulate the same cluster of neurons, but with a different series of stimuli known to weaken the synaptic connections (called long-term depression, or LTD). After subjecting the rats to LTD, they no longer reacted to the light pulses that had previously caused them fear. Re-subjecting them to LTP, however, returned them to their original fearful state. The scientists were able to modulate back and forth with ease, erasing and creating the fear-response at will. According to their research, this seemed to suggest that the LTP and LTD effects were “erasing” and “restoring” the memory of the electroshock conditioning.
While this is certainly intriguing, I’m keenly interested in the rapidity with which this study compares Pavlovian instinct to memory. While one could argue that such conditioning is tied to memory (the rats remember that the light causes pain; thus they are afraid), I wonder if it might be too large of a jump to label this “memory loss” as most people would understand it. Memory is far more than an instinctual recall; it is also the active recollection of an event or series of events not necessarily tied to an immediately present catalyst. While this test certainly seems to show a capacity to repress the instinctual connection between light and pain, we have no way of testing whether or not these rats have lost their capacity to recall the connection while not under the effects of the relevant stimulus, though I doubt that’s even testable.
That said, it’s probably about as close as we’re going to get without messing around with other people’s brains … and that’s kind of a grey area. Still, it’s progress, and there is a good chance that finding this connection between LTP, LTD, and memory will give us more insight into Alzheimer’s research.
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