Switching Memories ON and OFF

Mauro Costa-Mattioli Memory in ESSAYS ON SCIENCE AND SOCIETY series from Science:

Ireneo Funes, the fictional main character in Jorge Luis Borges’ short story “Funes el Memorioso,” could remember in vivid detail every day of his life after he was thrown from a wild horse at a ranch in Fray Bentos, Uruguay. He had acquired a prodigious ability to store new information without any practice. Unlike Funes [and real “autistic savants”, who could store information with a glance, most people learn new things only after many attempts.

Psychologists have identified two corresponding processes: short-term memory, which lasts from seconds to minutes; and long-term memory, which lasts for days, months, or even a lifetime. It is now well accepted that making long-lasting memories is dependent on the ability of brain cells (neurons) to synthesize new proteins. Indeed, animals treated with a drug that blocks the production of new proteins cannot form long-term memories, yet their short-term memory is preserved. But how are memories stored? It is hypothesized that information is stored in the brain as changes in strength of the connections (synapses) between neurons. Such changes in synaptic strength are observed when neuronal activity is recorded in the brain with microelectrodes: Relatively weak or infrequent stimulation elicits a short-lasting effect [early long-term potentiation (E-LTP)], whereas stronger or repeated stimulation elicits a sustained effect [late long-term potentiation (L-LTP)], lasting many hours instead of minutes. Similar to long-term memories, long-lasting changes in synaptic strength (L-LTP) are prevented by blocking protein synthesis.

If making new proteins is the rate-limiting step required to store new long-lasting memories, how is this process turned on? If one were able to identify the triggering mechanism and switch it on, then stimulation normally eliciting short-lasting changes should evoke long-lasting ones. Could an increase in the ability to make new proteins explain extraordinarily long-lasting memories?

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