Unexpected Brain Strategy Links Two Events Separated by Time
Arthur T Knackerbracket has found the following story:
The brain is a master of forming patterns, even when it involves events occurring at different times. Take the phenomenon of trace fear conditioning-scientists can get an animal to notice the relationship between a neutral stimulus and an aversive stimulus separated by a temporal chasm (the trace) of a few or even tens of seconds. While it's a well-established protocol in neuroscience and psychology labs, the mechanism for how the brain bridges the time gap between two related stimuli in order to associate them is "one of the most enigmatic and highly investigated" questions, says Columbia University neuroscientist Attila Losonczy.
If the first stimulus is finished, the information about its presence and identity "should be somehow maintained through some neuronal mechanism," he explains, so it can be associated with the second stimulus coming later.
Losonczy and his colleagues have recently investigated how this might occur in a study published May 8 in Neuron. They measured the neural activity in the hippocampal CA1 region of the brain-known to be crucial for the formation of memories-of mice exposed to trace fear conditioning. The team found that associating the two events separated by time involved the activation of a subset of neurons that fired sparsely every time mice received the first stimulus and during the time gap that followed. The pattern emerged only after mice had learned to associate both stimuli.
The study highlights "the important question of how we link memories across time," says Denise Cai, a neuroscientist at the Icahn School of Medicine at Mount Sinai who was not involved in the work. Studying the basic mechanisms of temporal association is critical for understanding how it goes wrong in disorders such as post-traumatic stress disorder (PTSD) or Alzheimer's disease, she says.
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