Dieter Jaeger - US grants

DESCRIPTION (Adapted from applicant's abstract): This proposal aims to determine the functional significance of inhibition in cerebellar cortex. It is predicted from previous experiments and computer simulations that normal cerebellar function depends on a constant action of inhibitory input to Purkinje cells, which provide the only output from cerebellar cortex. The hypothesis that the computational algorithm taking place in cerebellum critically depends on the precise temporal and spatial pattern of this inhibition will be tested. A combined physiological and computer modeling approach will be used. In vitro whole cell recordings will be obtained to determine the time course and amplitude of single inhibitory inputs to Purkinje cells, and the relative contribution of inhibition to the soma and the dendrite. Realistic synaptic conductance patterns resulting from the input of many synapses will be generated with a computer model and will be applied to Purkinje cells in vitro with the dynamic current clamp technique. This manipulation is suitable to determine the accurate input-output function of Purkinje cells with respect to inhibition. Comparison of modeling and physiological results with the same input patterns will guide the predictions and analysis of the computation taking place in Purkinje cells. In vivo intracellular recordings in anesthetized rats will be used to determine the spatial pattern of inhibition of Purkinje cells with peripheral tactile stimuli that activate known receptive fields in the input layer of cerebellar cortex. The ultimate goal of this work is to produce a realistic computer model of network computation in cerebellum. Such modeling is vital in understanding the non-linear dynamics in the cerebellar neural network. Existing theories and models of cerebellar cortical function largely disregard the involvement of inhibition, without data to support this bias. The proposed work will test this assumption and will likely suggest a critical role for inhibition in cerebellar computation. New insights into the computational algorithm taking place in cerebellum are necessary to guide the understanding of the mechanisms underlying cerebellar movement disorders.

[unreadable] DESCRIPTION (provided by applicant): The objective of the proposed research is to understand the control of neural activity at the output stages of basal ganglia processing. This topic is highly relevant to our understanding of Parkinson's disease as changes in spike rate and pattern of basal ganglia output neurons are directly involved in the generation of dysfunctional neural activity in this disease. Furthermore, deep brain stimulation (DBS) interacts with the generation of spike patterns at this stage, and our work will address important biophysical mechanisms that may mediate the therapeutic effect of this treatment. We will focus our work on how the extensive dendrites of pallidal neurons contribute to signal processing. Recent evidence shows that dendrites make important contributions to signal integration through the activation of complex patterns of voltage-gated currents. The specific aims of this proposal address the contribution of distinct dendritic mechanisms to synaptic integration in pallidal neurons. In aim 1 we assess the presence of distinct physiological subtypes of neurons in globus pallidus (GP) and entopeduncular nucleus (EP), and their differential response to dendritic excitatory inputs. In aim 2 we determine the spatial and temporal processing of excitatory inputs in dendrites of GP and EP neurons, and how this processing is shaped by specific voltage-gated conductances. In aim 3 we examine how inhibitory and excitatory inputs interact in the control of output spiking. The overall experimental approach primarily relies on whole cell recordings from brain slices. Dendrites are visualized with fluorescent dyes and stimulated at varying distance from the cell body. An important component of the work is given by detailed biophysically realistic computer simulations of pallidal neruons to allow a complete examination of the dynamical interactions of input patterns with intrinsic membrane properties. By determining the details of input/ouput transformations at the single cell level we will be able to make important predictions to how alterations in this process can lead to changes in network processing. [unreadable] [unreadable]

[unreadable] DESCRIPTION (provided by applicant): This proposal aims to determine the functional significance of synaptic processing in the deep cerebellar nuclei (DCN), which provide the only output from cerebellum. Projection neurons in the DCN are controlled by excitatory input from the brainstem and the cerebral cortex, and by inhibitory input from cerebellar cortical Purkinje cells. The Purkinje cells themselves are controlled by the same excitatory inputs that are also received as collaterals by the DCN directly. This connectivity thus allows individual DCN projection neurons to compare the same signal before and after processing by the cerebellar cortex. The ensuing spike modulation of DCN neurons is believed to directly correspond to motor command signals aiding in movement coordination. We will combine intracellular and extracellular recordings in vivo and in vitro from the rat with computer modeling of this system to gain a better understanding of the important confluence of signals in the DCN. We will test the hypothesis that DCN output commands can be activated by excitatory inputs from outside the cerebellum. We will test the hypothesis that DCN output commands can also be generated by disinhibition due to pauses in spiking of groups of Purkinje cells. We will furthermore test the hypothesis that intrinsic active properties of DCN neurons make an important contribution to signal generation. Specifically we will determine whether DCN neurons may show bistability leading to a change in the time course of spike rate changes in the cerebellum. Rescaling the temporal properties of spike rate changes in the input to suit the control of muscle activity may be a fundamental function of the DCN. These studies are expected to generate important insights into cerebellar function and the mechanisms underlying cerebellar movement disorders. [unreadable] [unreadable]

DESCRIPTION (provided by applicant): This application addresses a core question in cerebellar function: How do the deep cerebellar nuclei (DCN) integrate the inhibitory signal from the cerebellar cortex with excitatory input from the rest of the brain to generate the ultimate output of the cerebellum? An interdisciplinary approach of computer modeling and multisite recordings in awake rodents is taken to determine the coding properties of the DCN with respect to the coordination of the rhythmic behaviors of breathing and whisking. These behaviors are represented through modulation of activity in the vermis of the cerebellar cortex and in the medial cerebellar nuclei. Anatomical tract tracing studies are part of the proposed work and will elucidate the exact spatial layout of cerebellar cortical connections of the area in the vermis representing these rhythmic movements to the DCN. Simultaneous recordings from both the vermis and a connected area in the DCN will show how the cerebellar cortical activity is reflected in the output from the DCN. Other influences that will be considered in shaping DCN output are excitatory input from other brain areas and the intrinsic dynamical properties of DCN neurons themselves. Biologically realistic computer simulations of DCN neurons present the ideal tool to integrate the experimental results in a working model of cerebellar output generation. These models will simulate the full morphological structure, ion channel composition, and synaptic inputs of DCN neurons, and will open the door for realistic network simulations of the cerebellum. The intellectual merit of this project lies in the innovative combination of in vivo techniques and modeling to address the question of synaptic integration at the level of a single neuron in a behaving animal. We know that neurons in vivo receive thousands of inputs per second, but what transfer function extracts useful information from this barrage to generate a single output spike train remains poorly understood. The proposed close interaction of multisite recordings to generate data specifically to educate and constrain a model is unique. A further important intellectual component of the problem to be addressed is how neural computation can use inhibition as main signal. This is clearly the case in the signal transfer from the cerebellar cortex to the DCN. The results could be paradigmatic for other connections in the brain mediated by inhibition, e.g. the striato-pallidal, and pallido-subthalamic connections in the basal ganglia. The broader impact of this work is several fold: 1) The computer model of DCN neurons will be disseminated through publicly accessible databases, most notably NeuronDB located at Yale University. This will enable cerebellar researchers and modelers worldwide to incorporate realistic DCN neurons into their models of cerebellar function. This model is expected to become the de facto standard of simulating DCN neuron dynamics. 2) The computer model will be used in training courses at Emory and internationally to teach biologically realistic synaptic integration to a diverse audience. The P.I. is routinely involved in such international training courses, for example the Latin American Course in Computational Neuroscience (LASCON, Brazil), and the Okinawa Course in Computational Neuroscience (OCNC, Japan). This model would be the first one that is specifically calibrated to replicate synaptic integration in behaving animals. 3) The proposed work introduces the coordination of rhythmic behaviors as a new model system to studying the function of the deep cerebellar nuclei. This is a very promising new paradigm and could lead to a new area of cerebellar investigation similar to the explosion of work using the eye blink reflex following the pioneering experiments of Richard Thompson.

We will examine how the motor thalamus In mouse models of Parkinson's disease (PD) is involved in transmitting Parkinsonian activity patterns generated In the basal ganglia to the cerebral cortex. We will use simultaneous electrophysiological recordings from basal ganglia, thalamus, and cortex In anesthetized and awake mice to determine the presence of pathological activity patterns, and their relations between structures. One strength of the proposal consists of the use of in vivo intracellular thalamic recordings, which will allow us to examine the hypothesis that strong basal ganglia bursting activity observed In PD will trigger postlnhibitory rebound bursting In thalamus. Previous work suggests that such bursting in the basal ganglia Is one of the characteristics of pathological activity patterns in PD, but the transmission of this activity through thalamus to cortex remains unclear. We will carry out a detailed analysis of the specific mechanisms of synaptic integration in motor thalamus of the mouse In the brain slice preparation, where we test the control of action potential initiation by Parkinsonian patterns of Input. Finally, we will determine whether pharmacological compounds known to Interact with thalamic cellular properties (M1 and M4 muscarinic receptor agonists or antagonists or selective Cav3 calcium channel blockers) can be used to reduce the transmission of pathological activity from the basal ganglia through thalamus to cortex. This project Is tightly Integrated with the other projects of the overall Emory Udall Center grant application: We share the focus on thalamic processing with project 2, where It will be examined In primates rendered parkinsonian with MPTP. We share the VMAT2L0 mouse model of PD with project 3, where It will be used to determine possible neuroprotective treatment strategies. Our analysis of pathological electrical activity patterns In the VMAT2L0 mouse developed by Dr. Miller at Emory will aid in the validation of this model. We obtain the pharmacological compounds to be tested for specific effect on thalamic processing through our interactions with project 4. These compounds mentioned above are promising novel specific receptor agonists and antagonists as well as channel blockers that are not otherwise available.

Emory and Georgia Tech have steadily grown the number of faculty involved in computational neuroscience over the past 15 years. The research of these faculty stretch from cellular to systems and theoretical approaches. In 1997 the two Institutions formed a joint Department of Biomedical Engineering, further strengthening the highly collaborative atmosphere between researchers on both campuses. In addition both campuses have a strong track record both in undergraduate and graduate teaching. The proposed training program in computational neuroscience aims to capitalize on these strengths by formalizing an integrated approach to class work and research on both undergraduate and graduate levels. The strong NIH and NSF funded research programs of more than 15 principal investigators identified as computational neuroscientists range from detailed cellular computer simulations of neural dynamics to engineering approaches and the quantitative study of disease mechanisms underlying important disorders such as epilepsy and Parkinson's disease using computational methods. Therefore students will be exposed to multiple levels of approaches aimed ultimately at addressing medical questions. A highly qualified and diverse applicant pool for student fellowships under this program exists on both undergraduate and graduate levels, and will bring some applicants with a primarily background in the biological sciences to integrate computational approaches into their research, and vice versa brings more computational or theoretically oriented applicants in touch with biological experimental research. The program encompasses a cohort of 6 undergraduate and 6 graduate student fellows, who will absolve a rigorous curriculum in neurobiology and mathematical and computational methods through a core sequence of required classes as well as individually chosen electives. Undergraduate fellows will be funded for a period of two years in their junior and senior years, during which they will undertake specialized class work and research in a computational neuroscience lab. Undergraduate trainees will be primarily recruited from the Emory Neuroscience and Behavioral Biology and the Georgia Tech Biomedical Engineering majors, who bring a biological and quantitative strength to the program, respectively. Over 200 students join these majors annually, and we will only take applicants with a GPA of 3.5 or better and expressing an interest in future research graduate training. The graduate students in this program will be recruited from the applicant pools for the Neuroscience and Biomedical Engineering programs, which together receive more than 120 highly qualified applications each year. A special track for fellows in computational neuroscience will be announced on the program websites, that will also link to an extensive independent website describing this program. Graduate students will be funded for the first two years of their education, and then obtain individual training grants or be funded by research grants.

DESCRIPTION (provided by applicant): Emory and Georgia Tech have steadily grown the number of faculty involved in computational neuroscience over the past 15 years. The research of these faculty stretch from cellular to systems and theoretical approaches. In 1997 the two Institutions formed a joint Department of Biomedical Engineering, further strengthening the highly collaborative atmosphere between researchers on both campuses. In addition both campuses have a strong track record both in undergraduate and graduate teaching. The proposed training program in computational neuroscience aims to capitalize on these strengths by formalizing an integrated approach to class work and research on both undergraduate and graduate levels. The strong NIH and NSF funded research programs of more than 15 principal investigators identified as computational neuroscientists range from detailed cellular computer simulations of neural dynamics to engineering approaches and the quantitative study of disease mechanisms underlying important disorders such as epilepsy and Parkinson's disease using computational methods. Therefore students will be exposed to multiple levels of approaches aimed ultimately at addressing medical questions. A highly qualified and diverse applicant pool for student fellowships under this program exists on both undergraduate and graduate levels, and will bring some applicants with a primarily background in the biological sciences to integrate computational approaches into their research, and vice versa brings more computational or theoretically oriented applicants in touch with biological experimental research. The program encompasses a cohort of 6 undergraduate and 6 graduate student fellows, who will absolve a rigorous curriculum in neurobiology and mathematical and computational methods through a core sequence of required classes as well as individually chosen electives. Undergraduate fellows will be funded for a period of two years in their junior and senior years, during which they will undertake specialized class work and research in a computational neuroscience lab. Undergraduate trainees will be primarily recruited from the Emory Neuroscience and Behavioral Biology and the Georgia Tech Biomedical Engineering majors, who bring a biological and quantitative strength to the program, respectively. Over 200 students join these majors annually, and we will only take applicants with a GPA of 3.5 or better and expressing an interest in future research graduate training. The graduate students in this program will be recruited from the applicant pools for the Neuroscience and Biomedical Engineering programs, which together receive more than 120 highly qualified applications each year. A special track for fellows in computational neuroscience will be announced on the program websites that will also link to an extensive independent website describing this program. Graduate students will be funded for the first two years of their education, and then obtain individual training grants or be funded by research grants. PHS 398/2590 (Rev. 06/09) Page Continuation Format Page

DESCRIPTION (provided by applicant): The cerebellum is a large hindbrain structure involved in many aspects of motor control as well as cognitive aspects of behavior. Dysfunction of the cerebellum has been identified to be the primary cause in important motor disorders, notably ataxias, and some forms of dystonia. Nevertheless, at a fundamental level we do not understand how the cerebellum operates. This is in part due to a lack of the appropriate experimental techniques that can manipulate different subunits of the cerebellar network to study its function. Genetic mouse lines are starting to help in isolating specific cerebellar functional involvement in disease, and the present study is using mice to link to this research. The specific innovation of the present proposal consists of using a newly developed optogenetic approach that allows the insertion of channelrhodopsin-2 (ChR2) gene into specific areas or cell types of the brain. ChR2 is a photosensitive ion channel that results in a depolarizing current into neurons expressing it when exposed to blue-wavelength light. We will express ChR2 in the inferior olive of adult mice through adeno-associated viral vector injections, and then study the olivary input to the cerebellum with light stimulation of olivary axons in the cerebellum. This presents an important advance in our ability to dissect cerebellar circuits, as previously electrical stimulation only allowed mixed activation of various fiber pathways. Most importantly, the deep cerebellar nuclei (DCN), which provide the final output from the cerebellum, receive excitatory input from olivary axons, but this functional significance of this pathway has never been isolated. In contrast, Purkinje cells in the cerebellar cortex receive olivary input in the form of climbing fibers, which have been extensively studied as each individual input is extremely strong and can easily be identified as a climbing fiber response. We will determine the effect of olivary input to the DCN using both brain slice recordings and recordings from animals with an intact cerebellar network. The slice recordings will allow us to determine the detailed synaptic properties of the olivary connection to DCN neurons for the first time. The recordings from intact animals will shed light on the impact of this connection in the intact network and whether the same olivary axons exciting a DCN neuron will also lead to a delayed inhibition of the same neuron via Purkinje cell climbing fiber activation. Overall our optogenetic studies address the actions of an important cerebellar input pathway, which hitherto could not be studied with classical techniques. We expect that significant excitatory effects on the DCN balancing inhibitory action of Purkinje cell input will be found. This knowledge will lay the basis for future studies examining the involvement of the olivary input pathway in cerebellar disease states in mouse mutants of ataxia and dystonia. PUBLIC HEALTH RELEVANCE: The cerebellum is the source of debilitating motor disorders, most notably cerebellar ataxias and some forms of dystonia. To better understand and treat these diseases we will study excitatory input to the deep cerebellar nuclei with optogenetic methods allowing a detailed analysis of this pathway for the first time. This analysis will help us to examine changes in cerebellar activity in mouse mutants causing cerebellar disease in future studies. PHS 398/2590 (Rev. 06/09) Page Continuation Format Page

DESCRIPTION (provided by applicant): We request funding to establish a voltage-sensitive dye (VSD) imaging setup in the Department of Biology at Emory University. This setup will greatly enhance the research capability of the neuroscience faculty in the Department with active NIH funding (Drs. Jaeger, Calabrese, Liu and Prinz). The P.I. (Dr. Jaeger) has a long track record in the research of basal ganglia and cerebellar networks. To extend this analysis to the level of cortical activity modulation due to basal ganglia and cerebellar feedback loops would be innovative, impactful, and timely. VSD imaging of mouse cortical activity in vivo will be a crucial tool to determine the temporal and spatial effects of basal ganglia and cerebellar activation on cortical activity. Similarly, the research of Dr. Liu is concerned with cortical actiity patterns, albeit the activation following social ultrasound signaling in mice on auditory circuits. VSD imaging would allow this work to progress towards a better understanding of spatial and temporal signal flow beyond primary auditory cortex. For both Dr Jaeger and Dr. Liu this technology would be particularly timely to implement soon, as the development of optogenetic stimulation techniques and genetic voltage-sensitive indicators will allow us to address important questions with an expected high impact in novel findings. The work of Drs. Calabrese and Prinz explores the function of invertebrate pattern generation circuits in the leech heartbeat circuit and crab/lobster stomatogastric ganglion, respectively. However, similarly to the question of spatial dynamics of cortical dynamics, these ganglia consist of a spatial network in the respective ganglia with complex activity patterns that can be fruitfully surveyed by voltage-sensitive dye imaging techniques. The equipment we request will allow us to flexibly conduct experiments on the spatial scale required in rodents in vivo (10x10 mm area of interest) and invertebrate ganglia (1x1 mm area of interest) by mounting a state of the art dual CMOS camera system either on an in vivo imaging setup or on an Olympus BX50 microscope. Both setups will share manipulators and amplifiers for simultaneous electrophysiological recordings. A substantial amount of the basic equipment (Olympus BX50 microscope, vibration isolation table, recording amplifiers) needed for this setup will be contributed by the major investigators, and a dedicated room is made available by the Dept. of Biology. The core item requested is the dual camera CMOS system, along with the necessary optical equipment (beam splitter, software, etc), and auxiliary hardware. The expectation from obtaining this setup is that innovative and timely methods will be available to the established research programs of the major investigators, and allow the development of junior faculty as well. The health impact is also highly relevant, in that the research by the Jaeger lab is directly applied to establishing Parkinson's disease mechanisms, work in the Liu lab is relevant to the study of autism, and work in the Calabrese and Prinz labs demonstrate fundamental mechanisms of neuromodulation and homeostasis that underlie understanding of how pathological brain activity may arise as a maladaptation of normal dynamics.

? DESCRIPTION (provided by applicant): To address the core question underlying the Obama Brain Initiative to better understand the function of complex brain circuits, we propose a multi-scale recording and data analysis project to study the dynamical interactions between sensory cortex, motor cortex, and the basal ganglia in the process of motor planning and execution. The multi-scale approach will involve simultaneous recordings at the cellular, network, and systems level in head-fixed behaving mice trained to perform a rewarded locomotor task. Sensory stimuli delivered to the whiskers will denote GO or STOP cues, and resulting brain processes initiating or suppressing movement will be analyzed. At the cellular level, in vivo whole cell recordings employing autopatcher technology will yield detailed information on the membrane potential trajectory of individual neurons in the sensory and motor cortex in this task. At the network level multiple single unit and local field potential (LFP) recordings will allow the assessment of local population dynamics across multiple layers of cortex and for thalamo-cortical interactions. At the systems level, voltage imaging of the cortical surface using novel transgenic voltage sensing proteins will allow the study of spatio-temporal dynamics of macroscopic activity patterns with a frequency resolution of up to 200 Hz. Recording data simultaneously will allow for a multi-scale analysis of the relations between cellular and network dynamics. For example, the relationship between fluctuations in the field potential and the membrane dynamics of single neurons will be analyzed and is expected to yield important insights into population coding. Similarly, the relation between activity maps obtained with imaging and oscillatory network activity revealed by LFP recordings of cortex is expected to result in important insights into the organization of motor planning. Our work will pay specific attention to the role of beta band (12-35 Hz) oscillations in the control of the observed behavior, because beta oscillations have been implicated convincingly both in cortical sensory processes as well as motor control. Further, beta oscillations are pathologically overexpressed in the basal ganglia of Parkinson's patients and 6OHDA lessoned rodent animal models of Parkinsonism with a likely source in motor cortex. Thus, our guiding hypothesis is that beta oscillations provide an important scaffold to the communication between brain areas in the process of motor planning and execution. To test the causal relation between beta oscillations and motor processing we will artificially induce beta band activity with ontogenetic stimulation of basal ganglia efferent, sensory cortex, or motor cortex and analyze resulting changes in behavior and brain dynamics in stimulated and non-stimulated areas. Overall, these studies will raise the level of systems neurophysiology of motor processing in the behaving rodent to a new level, and are expected to provide fundamental insights into the organization of brain activity across multiple scales. These insights will be invaluable in studies of pathological brain dynamics in neurological disorders affecting the basal ganglia such as Parkinson's disease, Huntington's disease and OCD.

Emory and Georgia Tech have steadily grown the number of faculty involved in computational neuroscience over the past 15 years. The research of these faculty stretch from cellular to systems and theoretical approaches. In 1997 the two Institutions formed a joint Department of Biomedical Engineering, further strengthening the highly collaborative atmosphere between researchers on both campuses. In addition both campuses have a strong track record both in undergraduate and graduate teaching. The proposed training program in computational neuroscience aims to capitalize on these strengths by formalizing an integrated approach to class work and research on both undergraduate and graduate levels. The strong NIH and NSF funded research programs of more than 15 principal investigators identified as computational neuroscientists range from detailed cellular computer simulations of neural dynamics to engineering approaches and the quantitative study of disease mechanisms underlying important disorders such as epilepsy and Parkinson's disease using computational methods. Therefore students will be exposed to multiple levels of approaches aimed ultimately at addressing medical questions. A highly qualified and diverse applicant pool for student fellowships under this program exists on both undergraduate and graduate levels, and will bring some applicants with a primarily background in the biological sciences to integrate computational approaches into their research, and vice versa brings more computational or theoretically oriented applicants in touch with biological experimental research. The program encompasses a cohort of 6 undergraduate and 6 graduate student fellows, who will absolve a rigorous curriculum in neurobiology and mathematical and computational methods through a core sequence of required classes as well as individually chosen electives. Undergraduate fellows will be funded for a period of two years in their junior and senior years, during which they will undertake specialized class work and research in a computational neuroscience lab. Undergraduate trainees will be primarily recruited from the Emory Neuroscience and Behavioral Biology and the Georgia Tech Biomedical Engineering majors, who bring a biological and quantitative strength to the program, respectively. Over 200 students join these majors annually, and we will only take applicants with a GPA of 3.5 or better and expressing an interest in future research graduate training. The graduate students in this program will be recruited from the applicant pools for the Neuroscience and Biomedical Engineering programs, which together receive more than 120 highly qualified applications each year. A special track for fellows in computational neuroscience will be announced on the program websites, that will also link to an extensive independent website describing this program. Graduate students will be funded for the first two years of their education, and then obtain individual training grants or be funded by research grants.

Project Summary ? Project 1 In this project we are studying how the communication between brain structures is changed in a mouse model of Parkinson's disease, compared to normal control mice. In particular, an important output pathway of the ba- sal ganglia is directed towards the motor cortex. This pathway passes through the ventral motor thalamus be- fore it reaches cortex. The main hypothesis of this research is that processing of basal ganglia signals in motor thalamus is altered in the parkinsonian state. We will address this hypothesis in three specific aims that exam- ine changes in the cellular and signal processing properties of neurons in the motor thalamus in the parkin- sonian condition, using the 6-hydroxydopamine lesion model of dopamine depletion in mice. In aim 1 we will analyze in a brain slice preparation which properties of thalamic neurons and synaptic inputs are changed in the parkinsonian condition using electrophysiological intracellular recordings. In aim 2 we will examine with electrophysiological recordings from neurons in the motor thalamus of awake behaving mice whether electrical activity patterns in parkinsonian mice differ from those in control animals during motor behavior. We will also use optogenetic stimulation techniques to trace specific signals along the basal ganglia-thalamocortical route. These stimulation techniques will also be studied with respect to their potential use as counteracting pathologi- cal patterns of activity seen in the parkinsonian animals. Finally, in aim 3, we will synthesize the results from aims 1 and aim 2 by building a detailed computer model of how neurons in the motor thalamus of parkinsonian mice process input from the basal ganglia and how this differs from the normal condition. We will test the validi- ty of this model with accompanying brain slice experiments, in which real neurons are subjected to the same synaptic input patterns that are used in the computer simulations. This allows for a direct comparison between spiking activity patterns generated by the computer model and those seen in recordings. This research will result in new insights concerning the mechanisms that lead to the expression of patho- logical neural activity patterns in the parkinsonian state. In particular little is known about the involvement of the motor thalamus in the pathophysiology of parkinsonism, and our results will make a substantial contribution to filling this knowledge gap. Further, our research results are expected to inform us about potential new tech- niques of optical deep brain stimulation with a positive effect on thalamic signal integration that could amelio- rate parkinsonian signs and symptoms. Our computer model will be made publicly available and will allow oth- er researchers to improve brain network models of how different pharmacological and deep brain stimulation interventions affect basal ganglia-thalamocortical circuitry and provide therapeutic function. This project is high- ly synergistic with project 2, which address parkinsonian pathology in the same circuit in a non-human primate system closer to the human disorder, while our rodent studies can provide more mechanistic detail. The ana- tomical studies in project 3 in turn will allow a close comparison of rodent and primate circuitry.

Project Summary/Abstract The overall goal of this project is to determine how output from the basal ganglia influences cerebral cortical activity in the processes of decision making, motor planning, and movement execution. The studies will employ mice as the best suited species in order to bring modern optogenetic and genetically encoded sensor technologies to bear on this critical gap in our understanding of brain function. In aim 1 we address the impact of basal ganglia output on network activity in cortex across sensory and motor areas. To this end will use genetically encoded calcium sensors selectively expressed in thalamic neurons receiving input from the basal ganglia (BGT) to record the pattern of activation of these thalamic axons in cortex with wide-field imaging. We will further image the resulting activation or inhibition of these thalamic terminals in cortex upon optogenetic manipulations of basal ganglia output activity in quietly awake mice and mice performing a forced choice left/right licking task. In a second study under aim 1 we will use genetically encoded voltage sensors to image the postsynaptic activation of specific cortical cell types upon optogenetic basal ganglia output manipulations. The expected outcome of these studies is that we will have characterized the impact of basal ganglia modulated thalamic activity on cortical network activation. In aim 2 we will address the question of how these network effects are mechanistically achieved at the cellular and subcellular level. We hypothesize that the input of BGT, which is primarily restricted to superficial cortical layers, will result in the activation of non-linear dendritic properties of pyramidal cell dendrites such as calcium or NMDA spikes. To address this hypothesis we will use simultaneous 2-photon calcium imaging in thalamic terminals and cortical dendrites in the context of our behavioral task. In a second study we will use whole cell recordings in behaving mice in conjunction with optogenetic basal ganglia output manipulations to determine the balance of excitatory and inhibitory effects converging on pyramidal cells as a consequence of basal ganglia activity. Finally, in aim 3 of our proposed research we will use detailed biophysical neural modeling to construct a thalamo-cortical network model that can replicate the observed physiological responses to basal ganglia output manipulations. On the subcellular level, we will use this model to determine the specific synaptic input strengths and voltage-gated ion channel types in pyramidal neuron dendrites that are required to explain observed responses. On the network level we will use the model to search through a large number of optogenetic basal ganglia output manipulations to identify candidate stimulus patterns that indicate specific mechanisms at work. We will then employ these patterns in our recordings to test model predictions and come to a better understanding of network interactions resulting from basal ganglia activity. Overall, we expect that our work will result in a much improved mechanistic understanding of basal ganglia thalamo-cortical signal transmission, and how dysfunction of this pathway contributes to symptoms in basal ganglia disorders such as Parkinson?s disease.