Cristopher M. Niell
Visual Processing in the Brain
How do we make sense of visual world around us? Our brain takes a pattern of photons hitting the retina, and continually creates a coherent representation of what we see (detecting objects and landmarks) rather than just perceiving an array of pixels. This allows us to perform a range of visual tasks such recognizing a friend’s face, finding your way to the grocery store, and catching a frisbee. However, how these computational feats are achieved by the neural circuitry of the visual system is largely unknown. Furthermore, this circuitry is wired up by a range of cellular processes such as axon and dendrite growth, synapse formation, and activity-dependent plasticity, and thus these developmental mechanisms effectively determine how we see the world.
Our research is focused on understanding how neural circuits performs the image processing that allows us to perform visual tasks, and how these circuits are assembled during development. We use a combination of in vivo recording techniques, including high-density extracellular recording and two-photon imaging, along with molecular genetic tools to dissect neural circuits, such as cell-type specific markers, optogenetic activation and inactivation, tracing of neural pathways, and in vivo imaging of dendritic and synaptic structure and dynamics. Furthermore, we have implemented behavioral tasks for mice to perform quantitative pyschophysics to measure the animal’s perception, and we use theoretical models to understand general computational principles being implemented by a neural circuit.
The mouse can provide a powerful model system for understanding visual processing and development, due to the powerful genetic tools that are available for dissecting neural circuits. Despite the fact that mice do in fact have relatively low resolution vision, our in vivo recordings have demonstrated that mouse primary visual cortex shows nearly all the hallmarks of cortical processing that have long been studied in other species. In addition to revealing the range of visual features that neurons in mouse V1 encode, and how these properties differ throughout the cell types and layers of the cortex, these findings support certain universal aspects of cortical image processing. Our subsequent studies have demonstrated that the visual representation in cortex varies depending on the behavioral state of the animal, and elucidated the relative role of innate guidance molecules and correlated neural activity in the establishment of topographic maps of the visual world in cortex.
In future studies we aim to extend this work to investigate how higher visual functions, such as object recognition, working memory, and spatial navigation, are implemented by the visual cortex and its interaction with other brain regions. We are also studying how dendritic growth and synapse formation/plasticity mechanisms give rise to the distinct cell-type specific receptive field properties found in visual cortex.