Inside our brains, a
cashew-shaped structure called the hippocampus stores the sensory and emotional
information that makes up memories, whether they be positive or negative ones.
No two memories are exactly alike, and likewise, each memory we have is stored
inside a unique combination of brain cells that contain all the environmental
and emotional information associated with that memory. The hippocampus itself,
although small, comprises many different subregions all working in tandem to
recall the elements of a specific memory. Now, researchers have shown just how
pliable memory is if you know which regions of the hippocampus to stimulate, which
could someday enable personalized treatment for people haunted by particularly
troubling memories. In their study, researchers show how traumatic memories (such
as those at the root of disorders like PTSD) can become so emotionally loaded.
By artificially activating memory cells in the bottom part of the brain's
hippocampus, negative memories can become even more debilitating. In contrast,
stimulating memory cells in the top part of the hippocampus can strip bad memories
of their emotional oomph, making them less traumatic to remember.
Using a technique called
optogenetics, they mapped out which cells in the hippocampus were being
activated when male mice made new memories of positive, neutral, and negative
experiences. A positive experience, for example, could be exposure to a female
mouse. In contrast, a negative experience could be receiving a startling but
mild electrical zap to the feet. Then, identifying which cells were part of the
memory-making process, they were able to artificially trigger those specific
memories again later, using laser light to activate the memory cells. Their
studies reveal just how different the roles of the top and bottom parts of the
hippocampus are. Activating the top of the hippocampus seems to function like
effective exposure therapy, deadening the trauma of reliving bad memories. But
activating the bottom part of the hippocampus can impart lasting fear and
anxiety-related behavioral changes, hinting that this part of the brain could
be overactive when memories become so emotionally charged that they are
debilitating. That distinction, suggests suppressing overactivity in the bottom
part of the hippocampus could potentially be used to treat PTSD and anxiety
disorders. It could also be the key to enhancing cognitive skills.
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