BME PhD Defense Announcement for Shulan Xiao (K. Jayant, advisor) Everyone is invited to attend the public presentation beginning at 2:00pm. Title: Dendritic Mechanisms Underlying Multiplexing and Feature Selectivity in Cortical Layer 5 Pyramidal Neurons Date: February 6, 2025 Time: 2:00pm Location: MJIS 2001 and Zoom: https://purdue-edu.zoom.us/j/93930289877<https://nam04.safelinks.protection.outlook.com/?url=https%3A%2F%2Fpurdue-edu.zoom.us%2Fj%2F93930289877&data=05%7C02%7Cbmeroundtable-list%40ecn.purdue.edu%7C1479129fa1d642f56e0808dd3f207abf%7C4130bd397c53419cb1e58758d6d63f21%7C0%7C0%7C638736130898029039%7CUnknown%7CTWFpbGZsb3d8eyJFbXB0eU1hcGkiOnRydWUsIlYiOiIwLjAuMDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWFpbCIsIldUIjoyfQ%3D%3D%7C0%7C%7C%7C&sdata=bi6t5PvKVbm6Dcg%2BAd5qlCATsGuelkKacmdJRdT1eh0%3D&reserved=0> Committee: Dr. Krishna Jayant (Chair), Dr. Scott R. Pluta, Dr. Alexander A. Chubykin, Dr. Edward L. Bartlett, Dr. Fang Huang Abstract: Integrating bottom-up-driven sensory features with top-down contextual feedback is crucial for learning and executing sensorimotor cognitive tasks. The primary somatosensory cortex (S1) plays a central role in this integration by processing bottom-up feedforward inputs in its deep layers and feedback inputs in its superficial layers. Layer 5 pyramidal neurons (L5 PNs) are vital to this integration, as their extensive dendritic arborizations span both deep and superficial layers, while their axons project to various cortical and subcortical regions. This unique structure and connectivity allow L5 PNs to encode multiplexed sensory inputs and top-down feedback, effectively broadcasting the outcomes of this integration to downstream areas in the brain. However, the biophysical mechanisms underlying this integration at the subcellular level in individual L5 PNs have not been well understood. To investigate this cellular computation, I employed a combination of techniques, including holographic two-photon uncaging, electrophysiology, and both in vivo and ex vivo two-photon Ca²⁺ imaging, along with biophysical simulations. My findings showed that inputs from the basal dendrites, which represent feedforward sensory features, are multiplexed to create a "barcode" of somatic action potentials. This process involves the interaction between dendritic Na⁺ channels, NMDA receptors (NMDAR), and nonlinearities at the axo-somatic level. Moreover, this combined, basal-centric temporal-rate code dynamically integrates with feedback received through the apical dendritic arbors, and this integration depends on the specific subtype of pyramidal neurons. The study suggests that these integration profiles vary depending on the pyramidal tract subtype, allowing different integration outcomes to be directed toward distinct subcortical targets. In vivo results from animals engaged in a sensory discrimination task indicated that apical dendritic spikes—indicative of the translaminar integration of bottom-up and top-down inputs—evolve as the animals learn reward associations. These findings illuminate the synaptic and dendritic mechanisms that facilitate sensory feature multiplexing in L5 PNs and provide insights into how this integration dynamically changes during cognitive learning behaviors. -- Bmeroundtable-list mailing list Bmeroundtable-list@ecn.purdue.edu https://engineering.purdue.edu/ECN/mailman/listinfo/bmeroundtable-list