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Neurons in the visual cortex change their responses over time

Neural activity in the brain is expected to change over days while learning or experiencing. Although it is quite surprising that the neural activity still changes across days even if there are no learning or experience changes, it suggests a new study.

The study by the Washington University in St. Louis reveals that neurons in the visual cortex change their responses to the same stimulus over time.

Scientists explored sensory information processing in the brain by using novel data analysis. The analysis helps them address questions of dynamics and computation in neural circuits of the brain’s visual cortex.

They showed mice a single, short movie clip on a loop. When mice watched the movie, scientists recorded activity in several hundred neurons in the primary visual cortex. They used a two-photon calcium imaging technique.

The same task was performed repeatedly for up to seven weeks. Then, using new computational approaches, scientists parsed the data from mice and analyzed changes in neuronal population activity over time.

They found that single-neuron responses to natural movies are unstable across weeks. It means individual neurons did not respond the same way to the visual stimuli — what was happening on the screen at the same moment in the film — when the mouse watched the film one week compared with another week.

In this study, scientists also have demonstrated a way to decode the response to the visual stimuli across weeks if they factored in the population activity of all of the neurons tracked for a given mouse.

Ji Xia, a recent Ph.D. graduate of the laboratory of Ralf Wessel, said, “But even with those studies already in print, many scientists are not prepared to deal with the possibility of drift in other areas of the brain.”

“People still don’t expect this kind of drift to be coming from the primary visual cortex. The general belief is that those primary sensory cortices should be very reliable because they are expected to encode the information from the sensory stimuli faithfully.”

Journal Reference:
  1. Xia, J., Marks, T.D., Goard, M.J. et al. Stable representation of a naturalistic movie emerges from episodic activity with gain variability. Nat Commun 12, 5170 (2021). DOI: 10.1038/s41467-021-25437-2

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