Public defence in Neuroscience and Biomedical Engineering, M.Sc. Nataliia Martyniuk

Title of the thesis: Resolving functional connections between visually guided behavior and the retinal signals in dim light

Thesis defender: Nataliia Martyniuk
Opponent: Associate Professor Soile Nymark, Tampere University, Finland
Custos: Adjunct Professor Petri Ala-Laurila, Aalto University School of Science

All visual information sent from the eye to the brain is encoded in spike trains by retinal ganglion cells (RGCs), yet how signals from different RGC types are used to guide visually driven behavior remains largely unclear. This doctoral thesis investigates how retinal ganglion cell activity is linked to behavior at the sensitivity limit of vision and how small populations of neurons encode visual information.

The purpose of the study was to determine which retinal ganglion cell types support visually guided behavior under extremely dim light conditions and to understand the neural mechanisms that shape information coding in small neuronal populations. The research combines electrophysiological recordings, behavioral experiments with freely swimming mice, computational modeling, and advanced imaging methods.

The results show that ON and OFF alpha retinal ganglion cells are among the most sensitive output neurons in the mouse retina. These cells respond differently to light: ON alpha cells increase their firing in response to light increments, whereas OFF alpha cells decrease their firing. Behavioral experiments demonstrated that detection of dim light increments relies primarily on ON alpha RGCs, whereas detection of dim light decrements, or “quantal shadows,” depends on the OFF alpha RGCs.

In addition, the thesis introduces a new experimental approach combining four-electrode patch clamp recordings with two-photon imaging, enabling simultaneous measurement of synaptic inputs, spike outputs, and dendritic morphology from a small population of retinal neurons. Using this method, the study shows that dendritic organization plays an important role in shaping correlated activity in neural populations and provides experimental evidence that higher-order noise correlations can be explained by pairwise correlations in excitatory input currents.

The findings contribute to a better understanding of how neural circuits encode sensory information and how the brain reads out signals from populations of neurons to guide behavior. These results are relevant for neuroscience research on sensory processing, neural population coding, and the fundamental limits of visual perception.

Keywords: visual sensitivity, scotopic vision, physical limits, vision, retina, retinal circuit visual sensitivity, visual threshold, visually guided behavior, photon detection, decrement, ON pathway, OFF pathway, ON and OFF retinal ganglion cells, multi-electrode patch clamp, two-photon imaging, population coding, noise correlations, dendritic morphology

Thesis available for public display 7 days prior to the defence at Aalto University's public display page. 

Contact information: nataliia.martyniuk@aalto.fi