In a nutshell: A switch in how some brain cells respond to visual scenes is caused by changes in the whole network, rather than in the cells themselves.

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One of the major brain regions responsible for making sense of what we see is called the primary visual cortex, or V1. There are two types of cells in V1: simple and complex. Simple cells have a simple receptive field – that is, they become active only in response to stimuli in specific areas within our field of vision. Complex cells have a much more complex receptive field, responding to visual stimuli in many different locations.

In some situations, however, complex cells can behave like simple cells. This can happen when we look at a scene with low contrast between different elements, like when driving in snow with low visibility.

To understand this shift in brain cell behaviour, Brain Function CoE investigators Molis Yunzab, Hamish Meffin, Shaun Cloherty and Michael Ibbotson, along with a team of collaborators, studied V1 responses in mice.

The researchers measured the activity of individual cells within the brain while a mouse viewed a screen showing different patterns. The contrast of the patterns was varied to see how this affected the response of simple and complex cells in V1.

The researchers found that the switch from complex cells to simple cells when viewing low-contrast patterns is not a result of specific changes within individual brain cells. Instead, the switch is due to a change in the whole network of brain cells, which is caused by the altered visual inputs. This result shows that the activity signature of V1 complex cells – in other words, whether they behave like simple or complex cells – is not completely fixed but depends to some degree on the activity of the whole network.

This discovery could help researchers to build more accurate models of brain networks, which can be used to study how the brain works.

Next steps:
The researchers hope to learn more about the brain cells involved in the environment-dependent network changes. This information will help them to link the cells’ function and location in the brain with the network’s activities.

Yunzab, M., Choi, V., Meffin, H., Cloherty, S.L., Priebe, N.J., & Ibbotson, M.R. (2019). Synaptic basis for contrast-dependent shifts in functional identity in mouse V1. eNeuro, 6(2), ENEURO.0480-18.2019. doi: 10.1523/ENEURO.0480-18.2019

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