Event

Optical technologies have been transformative for our current understanding of structure and function of neuronal circuits underlying behavior and are in many cases the limiting factors for pushing our understanding of the brain forward. I will discuss two different areas of research in our lab in this context.

In systems neuroscience it is generally accepted that knowledge of structural connectivity in neuronal circuits is necessary for understanding information representation and processing in local circuits. However, structural connectivity alone it is not sufficient to predict how input stimuli are mapped onto activity patterns of neuronal populations and how the collective dynamics of all neurons in the network leads to behavior. I will discuss two different functional imaging modalities developed in our lab that have allowed us to capture whole-brain neuronal dynamics at high speed and near single cell resolution.

Using the technique of light sculpting in combination with genetically encoded calcium indicators we have demonstrated near-simultaneous recording of activity of up to 70% of all head neurons in C. elegans [1]. Variants of this technique also allow to capture large scale neuronal populations dynamics in other model organisms including rodents. Using light-field microscopy in combination with 3D deconvolution [2] we have also demonstrated intrinsically simultaneous volumetric Ca-imaging in the entire brain of larval zebrafish during sensory stimulation. We are able to track the activity of 5000 neurons distributed throughout the brain at 20Hz volume rate. These tools combined with high speed optogentic control of neuronal circuits [3, 4], advanced statistics tools and mathematical modeling and will be crucial to move from an anatomical wiring map towards a dynamic map of neuronal circuits.

In vision science despite of investigations for over seventy years, the absolute limits of human vision have remained unclear. Rod cells have been shown to respond to individual photons, yet whether this information is processed by the brain and is accessible on the behavioral level has remained a fundamental open question.

We have recently been able to show that humans can report a single photon incident on the eye with a probability significantly above chance [5]. This was achieved by combining a two-alterative forced choice psychophysics procedure with quantum light source; a tool that allowed us to eliminate the irreducible variability of photon numbers in previous experiments. Furthermore, we found that the probability for reporting a single photon is modulated by the presence of an earlier photon. Our results and other applications of this tool may open up fundamentally new avenues for investigating yet undiscovered retinal pathways using quantum technologies.

References:

1. Schrodel, T., et al., Brain-wide 3D imaging of neuronal activity in Caenorhabditis elegans with sculpted light. Nature Methods, 2013. 10(10): p. 1013

2. Prevedel, R., et al., Simultaneuos whole-animal 3D-imaging of neuronal activity using light-field microscopy. Nature Methods, 2014 (in press)

3. Andrasfalvy, B., et al., Two-photon Single Cell Optogenetic Control of Neuronal Activity by Sculpted Light. PNAS, 2010. 107.

4. Losonczy, A., et al., Network mechanisms of theta related neuronal activity in hippocampal CA1 pyramidal neurons. Nature Neuroscience, 2010. 13(8): p. 967-72.

5. Tinsley, J. et al. Direct Detection of a Single Photon by Humans, Nature Communications, 2016 7, 12172