The brain's code seems to be in constant flux. Neuroscientists are baffled

Neuroscience has long assumed that specific neurons respond consistently to specific stimuli, enabling stable behavior. Tracking individual mouse neurons over time revealed that this baseline stability does not hold. Many cells changed their firing patterns over days and weeks, so neurons active in a particular location became weak responders later. In experiments in the parietal cortex, neurons fired predictably within a day in response to the mouse’s position in a virtual maze. Over weeks, even with the same navigation task, activity patterns reorganized: some neurons stopped responding to previously effective stimuli and others began responding. Across groups of neurons, activity patterns stayed more consistent, suggesting that single-cell roles may be less important than coordinated population dynamics.

"It is a dogma in neuroscience that certain brain cells respond in the same way to the same thing. Specific neurons always fire, for example, when we see particular shapes and colours; other neurons activate to swing an arm or wiggle a nose. The brain needs this stability, the theory goes, to respond to the outside world in a consistent way."

"To Driscoll's surprise, the baseline kept moving. Over the course of several days, many of the cells' responses had shifted noticeably. Neurons that had fired when a mouse was in a specific location on day one were barely responding in the same spot after a few weeks. "It absolutely defied all of our expectations," recalls Driscoll, who is now at the Allen Institute in Seattle, Washington."

"Over a single day, neurons in the parietal cortex, a hub for processing sensory information, fired predictably in response to specific things, such as the position of the mouse in a virtual maze. But over the course of a few weeks, even though the task of navigating the maze remained the same, these activity patterns underwent major reorganization. Some of the neurons stopped firing in response to stimuli that had previously activated them; others did the reverse."

"In groups of cells, however, patterns of neuronal activity remained more consistent over time. The results suggested that individual neurons might not have fixed roles, and that the response of single cells might be less important than the activity of whole populations."

Read at Nature