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VisualCircuits Report Summary

Project ID: 631909
Funded under: FP7-PEOPLE
Country: Belgium

Periodic Report Summary 1 - VISUALCIRCUITS (Dissecting the retinal inputs to behaviorally relevant computations in the central brain)

A key function of the visual system is to extract behaviourally relevant features about the visual scene from the barrage of incoming photons. This process begins in the retina, however despite our detailed knowledge of how information is organized within the visual system, it remains unknown how information sent by the retina to the brain is used to guide behavior. In order to provide mechanistic understanding the goal of this proposal is to delineate the inputs, originating in the retina, to specific behavioural computations in central brain regions. The specific objectives set out in this proposal were: To characterize the distribution of feature maps within the superior colliculus; To dissect the retinal input to specific computations within the superior colliculus; and to determine the retinal contribution to orientating and avoidance behaviours.
Towards this end we have done the following work since the beginning of the project. In the initial stages we were setting up equipment and writing software. This included the building of three experimental rigs that could record neural activity. The first was a two-photon microscope that allowed us to perform both targeted patch-clamp recordings, as well as calcium imaging from the retina. The second was a two-photon microscope that allowed us to perform two-photon calcium imaging of neural activity in the intact animal. The third was an electrophysiological rig that allowed us to perform in vivo ¬patch-clamp recordings and multi-electrode probe recordings. In addition, we have established a viral production facility to produce both AAV and rabies viruses necessary for circuit tracing. Finally, we have built a floating ball apparatus to perform head-fixed behavioral experiments during either two-photon calcium, or electrophysiological experiments.
This work has resulted in the following results. Our main result to date has been the characterization of the relationship between orientation and direction selective neurons of the superior colliculus. We found that directionally selective neurons have a perpendicular orientation to neighbouring orientation selective neuron. This work builds on recent state of the art finding showing that orientation selective neurons exist in vertically organized patches of similarly orientation selective neurons and that these patch are organized in concentric rings around the centre of vision (Feinberg and Meister, 2014; Ahmadlou and Heimel 2014). We are currently finalizing the experiments for this work and expect to submit a paper by the end of the year. This piece of work has been carried out by the first PhD student to join the lab using two-photon calcium imaging and helps fulfill our first objective of characterizing the distribution of feature maps within the superior colliculus.
We are currently building up a data set addressing objectives two, dissecting the retinal input to the superior colliculus. To date we have established the protocols for producing rabies viruses and perform two-photon calcium imaging in the retina necessary to carry out these experiments. There is now a postdoctoral fellow and PhD student devoted to this set of experiments. With regards to objective three, determining the retinal contribution to behavior, we have collected preliminary data on two fronts. First, two MSc students have demonstrated that in head fixed animals we are able to evoke the same visually guided orientating and avoidance behaviors as in freely moving mice. Second, in collaboration with the laboratory of Lieve Moons at the KU Leuven, we have demonstrated our ability to evoke orientating and avoidance behaviors using direct optogenetic stimulation of the superior colliculus.
The expected results of this collective set of work is to demonstrated two principals of how the retina contributes to behavior via the superior colliculus. First, demonstrate that different distribution of receptive field properties in different parts of the visual field match the evoked behaviors that occur when visual stimuli are presented there. Second, dissect the underlying circuitry that exists linking the retina and central brain areas underlying these computations. This work backs will provide mechanistic understanding of a recent set of experiments demonstrating that in both rodents and primates the location of visual stimuli in the visual field has a profound consequence on how the information is processed by the brain and used to guide behavior.

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Life Sciences
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