Vision has a key role in navigation, but does spatial positioning affect the processing of visual information? In a new study, Saleem et al. show that, in mice, location-related activity can be detected early in visual processing, in the primary visual cortex (V1), suggesting that navigation influences vision.

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The authors recorded calcium signals in excitatory cells in V1 while the mice explored a virtual reality corridor by running on a treadmill. This corridor comprised two identical sections; each section included two different landmarks, so along the corridor, each landmark occurred twice and thus two repeating scenes were generated.

Predictably, some of the V1 neurons responded to the repeated scenes in a similar fashion. However, many V1 neurons showed differential responses to the repeated scenes, suggesting that the animal’s position in the corridor influences V1 activity.

The authors next examined whether the differences in V1 responses across sections were related to location-related activity in the hippocampus — a key region involved in navigation — so they allowed mice to explore the corridor while they simultaneously recorded from V1 and hippocampal area CA1 using electrode arrays. Notably, to determine an animal’s subjective position in the environment, the authors trained mice to lick for water when the animals had reached a specific region in the corridor (the reward zone).

As above, many V1 neurons showed stronger activity in one of the two sections of the corridor, and, predictably, CA1 neurons were preferentially activated in a given position in the corridor (their ‘place field’). Indeed, the position of the animal on the track could be decoded from the activity of either V1 or CA1 neurons using an independent Bayesian decoder. Thus, neurons in both brain regions encode location-specific signals.

Despite the training, animals made some errors by licking before or after the reward zone, and the authors found that there were correlated errors in activity in CA1 or V1. Interestingly, Bayesian decoding of licking-related activity in CA1 or V1, regardless of whether the licking occurred in the reward zone, placed the animals in this area. This suggests that the activity in V1 and CA1 encodes the subjective location of the animal.

This study reveals that early visual activity is influenced by signals for spatial location that are represented in the hippocampus. Moreover, these signals relate to where the animal perceives itself to be, as opposed to its actual location.