Brendon Omar Watson - US grants

DESCRIPTION (provided by applicant): The proposed studies are aimed at elucidating the cellular mechanisms within cortex that lead to the generation of UP states. UP states are a distinct type of synchronous activation of neuronal ensembles in mammalian brain in which groups of neurons are synchronously depolarized for hundreds of milliseconds and fire action potentials during that time. They have been associated with neural function such a sensory input and motor output. As importantly, the ensemble of neurons participating in an UP state appears to be stable, in that the same local group of cells fires in the same sequence on repeated occasions. The stereotyped spatiotemporal dynamics of these neural ensembles suggest that they may arise from underlying neuronal connectivity patterns that are critical for their organization and function. However, much remains to be learned about how these UP states are triggered or maintained. This application tests the hypothesis that neurons that are members of UP state ensembles are themselves critical for triggering and maintaining their own synchronous depolarization. We propose a series of stimulation and ablation studies to test this hypothesis. Given the possibility that these neural ensembles likely represent modular elements critical in cortical function, their disruption may lead to disorganization of neural activity as is observed in a number of neurological disorders including epilepsy.

? DESCRIPTION (provided by applicant): I am an M.D., Ph.D. psychiatrist currently doing research fellowship work as an Instructor in the Weill Cornell Department of Psychiatry. My doctoral work was in the study of neocortical microcircuit activity using two-photon calcium imaging. To gain tools to study neuronal activity in the naturally behaving animal I have devoted my fellowship to training with Dr. Gyorgy Buzsaki at New York University. With Dr. Buzsaki I have mastered many aspects of silicon probe recording in rats, but here I propose further training in optogenetics with Dr. Buzsaki's group in the context of a project studying the basic neuroscience of sleep. Sleep is crucial to normal brain function and also plays a role in many neuropsychiatric diseases including depression and seizure disorders. Perhaps indicative of a more precise role for sleep: decades of research show that learning is enhanced by post-learning sleep. By contrast, other work shows that sleep homeostatically downregulates neuronal and synaptic activity. How the homeostatic role for sleep and the memory consolidation role interact is not at all clear, especially given that they make differing predictins at the level of synapses: memory consolidation predicts synaptic strengthening over sleep, homeostasis predicts synaptic weakening. This proposal aims to synthesize the memory consolidation role for sleep and the homeostatic role. My outcomes will be measured using silicon probes and my interventions will involve learning paradigms and optogenetics. My first two Aims will assess how a novel object learning paradigm prior to sleep affects how the subsequent sleep modulates neural activity in the anterior cingulate cortex. Aim 1 will use silicon probes to assess the changes over sleep in single neuron firing and neuronal assembly behavior depending on whether neurons were subjected to a pre-sleep learning paradigm. Aim 2 will use optogenetics to specifically study synaptic changes over sleep depending on whether there was learning prior to sleep. Synapses have been theorized to be particularly crucial in both learning and homeostasis. I will use optogenetics to precisely probe synapses originating from distal neurons, with optogenetics giving the advantage of less contaminated and more precise and revelatory stimulation paradigms than traditional electrical stimuli. In Aim 3 I will ue direct optogenetic manipulation of spike rates in small subsets of neurons during waking, rather than learning, to determine more precisely how prior activity affects subsequent sleep modulation. This final experiment will take advantage of new combined optogenetic-silicon probe tools developed in the Buzsaki Lab. I will receive mentorship from Dr. Buzsaki and from Dr. Francis Lee and will take biostatistical and neuroscience theory courses to add to my training. I am optimistic that the projects, and training described in this application will provid the field with new knowledge and will prepare me well for independent research. Title: Role of waking activity in determining sleep-based modification of cortical circuits.

Abstract While altered broad-scale brain dynamics are a key brain signature of major depressive disorder (MDD) and despite the plethora of powerful neuroscientific tools available in rodents, we actually do not currently have the capacity to assess these broad-scale neocortical dynamics in rodents with synaptic-timescale temporal and single neuron resolution. This is a key gap in the capacity of neuroscientists to study MDD-related biology via rodent models including the sustained threat model. Electrophysiologic and optogenetic approaches would be ideal to study how neocortical dynamics are orchestrated at baseline and are perturbed in disease, since many mechanisms may be synaptic in nature and both methods can operate at synaptic-timescales. We are a team of neuroscientists and mechanical engineers and we aim to develop a system to allow implantation of previously- impractical complex combinations of electrodes and optic fibers to record and manipulate the rat brain. The basis of our approach is a 3-dimensionally printed (3D printed) replacement for the dorsal rat skull ? an ?Interface Plate? - which we have already successfully attached to two rats with good survival. Unlike a natural skull the Interface Plate is custom designed and fabricated and so can be adapted to guide and secure many devices to the animal using a novel surgical approach including pre-surgical assembly. We aim to optimize our design for the Interface Plate to enable two experiments that will be novel and crucial to studies of sustained threat-related disturbances in neocortical dynamics. The first aim will use our 3D printed positioning and guide system to place 128 electrodes broadly across the entire dorsal neocortex. This will enable the first ever mapping of electrical activity at sub-millisecond resolution across the entire dorsal neocortex enabling us to capture events ranging from synaptic transmission to oscillations to neuromodulation, behavior and brain state transitions. We will additionally place electrodes at both superficial and deep layers to gather data about relative roles of these evolutionarily-conserved anatomical layers. In a second aim we will adapt our Interface Plate to enable recording in neocortex while simultaneously recording and optogenetically stimulating regions that play key roles in coordinating neocortex including the dorsal hippocampus, the medial dorsal nucleus of the thalamus (MDN) and the thalamic reticular nucleus (TRN). In this aim, 8 (and later 32) electrodes will be implanted in cortex for recording while into dorsal hippocampal CA1, MDN and TRN we will implant silicon probes with 64 recording channels and a coupled optic fiber. This will facilitate experiments examining and testing the roles of non- neocortical structures in coordinating the cortex both in and out of sustained threat conditions. The experiments enabled here will provide fundamental new data regarding the neocortex in health and disease. This work will also lead to the creation of a customizable and flexible new tool which we will make openly available to enable complex experiments in freely behaving animals for anyone in the neuroscience community.

ABSTRACT: Chronic psychological stress triggers and exacerbates major depressive disorder (MDD) and many other psychiatric conditions ? causing changes in sleep, eating habits, addictive behaviors, activity levels, circadian rhythms, mood and other domains. The rodent stress response shares many behavioral and physiologic alterations with that of humans. Chronic stress also has broad effects on the brain. But major gaps exist in our knowledge in regard to the integrated behavior and physiology as well as the corresponding brain circuit changes with chronic stress. Prior work has found many behavioral and physiologic phenotypes of stress, but we lack a cohesive sense of how these variables co-evolve over time. Our first aim is to delineate this co-evolution of stress response elements in stressed versus unstressed mice. We will accomplish this by examining mice under a chronic unpredictable stress (CUS) paradigm versus controls in our new naturalistic observation system the ?Digital Homecage?. This system allows us to monitor over 50 behavioral measures simultaneously over weeks. Mice will live in these homecages for 8 weeks: 2 weeks baseline, 4 weeks CUS and 2 weeks of recovery. An exploratory element of that aim is to use machine learning to determine a coherent mouse stress biomarker for future quantitative studies. Our next goal is to determine electrophysiologic signatures of chronic stress. It is known that chronic stress alters brain circuit synaptic structure and neuromodulatory balance. It is known that the behavior is controlled by the electrophysiologic state of brain networks and that those networks operate both locally within regions and via coordinated multi-regional transmission. Therefore, we aim to study changes in electrophysiology both within and across regions. We focus on the medial prefrontal cortex, the ventral hippocampus and infralimbic medial prefrontal cortex given their strong involvement in chronic stress. We will implant tetrode arrays into these regions and will record over 8 weeks as above. In Aim 2, we will determine the effects of chronic stress on within-region spiking tendencies including spike rate variability and excitatory- inhibitory balance. In a second part of this aim we will use machine learning applied to a wider variety of within- region dynamical measures to determine a potentially more complete set of differences between CUS and control mice. In our final Aim, we will assess cross-regional coordination between these 3 regions. We will test the hypothesis that pairwise coupling between regions will be altered in a manner consistent with MDD by measuring coupling using both spiking and LFP. Again, we will then use machine learning methods on our large dataset to detect further inter-regional dynamics un-revealed in our hypothesis-driven testing. This mixture of behavior and electrophysiology is done to generate new understanding about chronic stress. We also have a long-term vision of creating large dataset for future analysis, a fully-refined Digital Homecage system for future studies, with an eye towards developing interventions based on natural electrophysiologic circuit function.