Research

Previous work

Visual maps formation:

Efficient sensory processing requires correct alignment of neural maps throughout the brain. In the superficial layers of the superior colliculus in the midbrain, projections from retinal ganglion cells and V1 cortex must be aligned to form a visuotopic map, but the basic principle and underlying mechanism are elusive and still incomplete. In a new mouse model, over-expression of ephrin-A3 in a subset of retinal ganglion cells disrupts the cortico-collicular map alignment onto the retino-collicular map, creating a visuotopic mismatch. In vivo inactivation of retinal ephrin-A3 over-expression restores a wild-type corticocollicular map. Theoretical analyses using an original algorithm models the stochastic nature of maps formation and alignment, and recapitulates our observations. More recently we have extended our findings and confirmed our approach with another mouse model, the Isl2EphA3KI. Our results identify a basic principle for the alignment of converging maps and the associated mechanism, validated by a theoretical model.

Modulation and organization of the mouse superior colliculus

To detect relevant visual information, the upper superficial layer of the SC (sSC) is enriched with cells tuned to motion direction. Recent studies suggest a stereotypical organization of these cells, reporting the existence of columns or biases in the representation of certain motion direction across the visual field. Furthermore, behavioral state, such as locomotion, has been shown to strongly affect visual responses in other visual areas. The need for consistent responses for threats suggests a robust and unbiased encoding of visual information in the SC, which would translate into a stable tuning across behavioral states and uniform representation of motion directions across the visual space.

By performing two-photon calcium imaging of head-fixed male and female mice running on a treadmill, we find that only a minority of neurons in the most superficial lamina of the SC display significant changes during locomotion. The overall change in the SC is small, whereas V1 responses almost double during locomotion. We also assessed the spatial organization of motion sensitive neurons based on their direction-preference. While a higher proportion of cells seems to prefer temporal motion, individual analysis revealed that there is no consistent organization across animals, nor a direct relationship between distance and direction preference.

Ongoing Research

My long-term goal is to characterize visual information integration and how internal states shape visual responses. To achieve this, I study the visual layers of the superior colliculus (sSC), in which distinct visual streams converge. My previous work suggests that the collicular pathway carries a copy of visual information unaffected by internal states, used as a reference in cortical visual areas. To test this hypothesis, my work now focuses on the major output of the sSC, the wide-field vertical cells (WFV), which project to the pulvinar. I am currently characterizing their response properties and modulation using two-photon calcium imaging and chemogenetics in mice. In parallel, I am characterizing the sSC visual responses in tree shrews, a highly visual animal closely related to primates to perform comparative studies. This approach will help us understand the parallel processing of vision and unravel the contribution of the sSC to behavior throughout evolution.

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