Main PhD Research (2017-PRESENT)

Functional role of cortex in sensory-guided behaviors

@Columbia University

Lorente de Nó (1933)

Thesis Project (Bruno Lab)

I joined Dr. Randy Bruno’s lab to understand the functional role of cortical layers in sensory-guided behaviors. The human brain contains more cortical neurons than any other species on earth, a characteristic that is thought to underlie our advanced cognitive abilities. The neocortex, comprised of multiple distinct layers, processes sensory input from the periphery, makes decisions, and executes actions. Despite extensive investigation of cortical anatomy and physiology, how individual cortical layer contributes to sensory guided behaviors remains unknown.

To that end, I developed tactile, whisker-dependent behaviors in mice and demonstrated that texture discrimination, but not object detection, requires the computational power of the cortex. Through targeted optogenetic inhibition of cortical layers, I revealed that both the deep and superficial layers are critical for texture discrimination. This is the first demonstration of cortical layers’ function in a sensory-guided behavior and suggests that even basic cortical computations require coordinated transformation of sensory information across all layers.

Park, J.M., Hong, Y.K.*, Rodgers, C.C.*, Dahan, J.B., Schmidt, E.R.E., & Bruno, R.M. (2020). Deep and superficial layers of the primary somatosensory cortex are critical for whisker-based texture discrimination in mice. bioRxiv 2020.08.12.245381. *co-second authors. Under review at eLife.

Park, J., Rodgers, C., Hong, Y. K., Dahan, J., & Bruno, R. (2019). Primary somatosensory cortex is essential for texture discrimination but not object detection in mice. IBRO Reports.

I am currently using high-speed videography to monitor the interaction of whiskers with the surfaces as mice perform the texture discrimination task. Using both conventional whisker tracking algorithms and newer neural network techniques, I am analyzing features such as whisker contact force, angle, vibrational frequencies, and other candidate cues. This will allow me to use decoding models to assess which features best identify texture identity and mouse's choice.

Concurrently, I am investigating the neural representation of these whisker events in barrel cortex. I am using laminar arrays to record individual neurons across all cortical layers simultaneously. These recordings will allow me to build encoder models, which allow us to assess the degree to which various sensory and motor variables may contribute to a neuron’s activity. Regressing out multiple variables’ contributions in this manner will allow me to investigate the nature of encoding in distinct cell types, such as excitatory vs inhibitory (regular- vs fast-spiking) cells, and cortical layers.

Awards:

Young Investigator Training Program Award, 2019 – International Brain Research Organization

US-Korea Conference Travel Award, 2018, 2019 – Korean-American Scientists and Engineers Association

Graduate Student Organization Travel Scholarship, 2019 – Columbia University

Kavli Institute Travel Award, 2018 – The Kavli Institute for Brain Science

AKN Pre-doctoral Award, 2018 – Association of Korean Neuroscientists

US-Korea Conference Excellent Poster Award, 2018 – Korean-American Scientists and Engineers Association

Collaboration 1 (Dr. Ewoud Schmidt, Polleux Lab)

My texture discrimination paradigm was further utilized in a collaboration to demonstrate that when we express a human cortical gene (SRGAP2C) in a mouse’s brain to increase cortical circuit connectivity, we also improve behavioral performance on our cortex-dependent task.

Schmidt, E.R.E., Zhao H.T., Park, J.M., Dipoppa, M., Monsalve-Mercado, M.M., Dahan, J.B., Rodgers, C.C., Lejeune, A., Hillman, E.M.C., Miller, K.D., Bruno, R.M., & Polleux, F. (2021). A human-specific modifier of cortical connectivity and circuit function. Nature.

Collaboration 2 (Dr. Chris Rodgers, Bruno Lab)

In a more complicated shape discrimination task, we demonstrated that this behavior requires multiple whiskers, is cortex-dependent, and that task-specific neural representations were aligned with behavioral requirements.

Rodgers, C.C., Nogueira, R., Pil, C., Greeman, E.A., Park, J.M., Hong, Y.K., Fusi, S., Bruno, R.M. (2021). Sensorimotor strategies and neuronal representations for shape discrimination. Neuron.

Collaboration 3 (Drs. Michael Goldberg & Eric Kandel)

We are interested in the role of proprioception in the establishment of long-term spatial memory in mice. Place cells in the hippocampus report spatial locations independent of the animals' direction of gaze, implying that by the time visuospatial information reaches the hippocampus, it has been transformed into an accurate supraretinal representation. We suspect that the dysgranular zone (DZ) of the neocortex, a proprioceptive area between primary motor and somatosensory areas, may be required to establish accurate representation of remembered space. We are combining chronic lesions with chemogenetic inactivation methods to demonstrate that proprioception is necessary for long-term visuospatial memory and the establishment of place cells in the hippocampus.

Funding:

F99 NIA Fellowship, 2021-2023 - National Institute on Aging

NSF GRFP Fellowship, 2018-2021 – National Science Foundation

Ruth L. Kirschstein NRSA Institutional Training Grant (T32), 2016-2018 – National Institutes of Health