The ability to remember something like a grocery list or telephone number even under bombardment from loud noises, incoming text messages or other distractions requires an intricate shape-shifting act in the brain.
A Singaporean team has found that the neuronal response patterns responsible for retaining short-term memories reorganize into a different configuration in the face of distracting stimuli — a process dubbed ‘code-morphing’.
“This code-morphing capability may be an important factor underlying cognitive flexibility,” says Camilo Libedinsky, a neuroscientist at the A*STAR Institute of Molecular and Cell Biology who co-led the research.
The team’s findings may help computer scientists develop more brain-like neural network algorithms for artificial intelligence, or help biomedical researchers better understand diseases such as Parkinson’s, schizophrenia and dementia, all of which involve memory deficits.
The brain’s center for short-term memory storage sits behind the forehead in the lateral prefrontal cortex. The neurons there were once thought to be unaffected by disruptions, but Libedinsky’s team has shown otherwise.
Working with Shih-Cheng Yen, an electrical engineer at the National University of Singapore, Libedinsky and colleagues trained two long-tailed macaques to perform a simple visual task. Using drops of juice as a reward, the monkeys were shown a grid on a screen and trained to remember the location of a red square that flashed briefly, without getting thrown off by the subsequent flash of a green square.
Each monkey had a suite of electrodes implanted in the brain, both in the prefrontal cortex and in the frontal eye field, a nearby region involved in controlling visual attention and eye movements. This allowed the researchers to track neuronal activity as the monkeys performed the memory test.
The team found that neurons in the prefrontal cortex became activated following the initial stimulus, maintaining the memory of the location, but this activity — the ‘code’ used by the brain to remember the red square’s location — morphed after the monkeys saw the green square, creating a different code held by the same group of neurons, all without losing any information or impacting the memory in any way.
This was not the case in the frontal eye field, however. There was no evidence of code-morphing ability in this visual part of the brain. This told the researchers that there was something special about short-term memory retention in the prefrontal cortex. They traced this cognitive capacity to a unique set of neurons with the ability to multitask.
“These results will be of interest to researchers in a number of fields,” says Aishwarya Parthasarathy, a postdoctoral research fellow at A-STAR and the study’s first author, noting that all areas of memory-related research — cognitive neuroscience, artificial intelligence and neuropsychiatry — could benefit from the discovery.The A*STAR-affiliated researchers contributing to this research are from the Institute of Molecular and Cell Biology. For more information about the team’s research, please visit the Libedinsky lab webpage.
Parthasarathy, A., Herikstad, R., Bong, J. H., Medina, F. S., Libedinsky, C. & Yen, S. C. Mixed selectivity morphs population codes in prefrontal cortex. Nature Neuroscience 20, 1770–1779 (2017). | Article