Patrick O. Kanold - US grants

Subplate (SP) neurons are among the earliest generated neurons of the cerebral cortex, and are present only during the time when cortical organization is highly susceptible to altered neural activity (the critical period). SP neurons have been implicated in visual cortical development because their removal before the critical period leads to disruption of thalamocortical connections and ocular dominance columns in visual cortex. SP removal also increases cortical expression of activity-regulated genes (such as BDNF, trbK and GAD). By controlling cortical activity levels, SP neurons may play a role in cortical development and the critical period. The basic physiology of the subplate and its influence on the cortical circuitry is unknown. The proposed research will investigate in vitro the developmental role of the SP. We will test the hypothesis that SP neurons control or modulate the balance of excitation and inhibition of developing cortex and by that manner influence the critical period. This work will investigate the cortical targets of SP innervation and how the SP modulates thalamocortical activity. Since SP ablation disrupts cortical development and affects cortical gene expression, studies proposed here will test if synaptic efficacy and plasticity are altered. Because inhibition has been shown to be crucial for development, we will also examine if SP ablation affects the maturation cortical inhibition. These studies should further our understanding of SP physiology, and also elucidate how the subplate influences cortical excitability. Thus, this study will provide crucial insight into the function of this transient neuronal population during development and its possible role in regulating the onset and duration of the critical period.

DESCRIPTION (provided by applicant): The perception of speech and language requires normal functioning of the primary auditory cortex. Many disorders lead to speech and language disorders and it is likely that some affect the wiring and function of the auditory cortex. Thus to understand how these deficits develop and to devise novel treatment approaches one has to understand the function of the auditory cortex. The auditory cortex contains millions of neurons and one challenge has been to identify what sound stimulus every neuron is responsive to and how neurons of different response properties are organized in the auditory cortex. Our studies will uncover how auditory cortex is organized and how complex sound stimuli such as speech stimuli are represented in auditory cortex. By using advanced imaging technology we will be able to account fully for the activity of all neurons in a cortical region and thus will be able to better understand the functional circuitry that processes auditory inputs. By studying these circuits over the developmental period and during plasticity tasks we will be able to learn how the circuitry of auditory cortex is changing and maturing. This is crucially important information, since early deficits in peripheral auditory processing can lead to altered wiring of cortical circuits. To be able to correct these potentially miswired circuits we have to understand which circuits are present during development and how they process the sensory information. Our proposed experiments lay the fundamental groundwork for a better understanding of auditory cortex by studying for the first time the large-scale organization and plasticity of auditory cortex with single cell resolution. PUBLIC HEALTH RELEVANCE: The perception of speech and language are of crucial important for human communication. Many disorders lead to speech and language disorders and it is likely that some affect the wiring and function of the auditory cortex. Our proposed experiments lay the fundamental groundwork for a better understanding of auditory cortex by studying for the first time the large-scale organization and plasticity of auditory cortex with single cell resolution.

DESCRIPTION (provided by applicant): The perception of speech and language requires normal functioning of the auditory cortex. Abnormal brain function, due to alterations in wiring, i thought to be responsible for many disorders such as cerebral palsy, schizophrenia, autism, and tinnitus. Correction of these disorders would seem to require the ability to rewire the brain. The young brain can adjust its connectivity depending on external inputs especially during early critical periods. For example early experience with speech is required for the normal development of the brain, and abnormal experience prevents normal development. Replacement of sensory experience after the critical period does not lead to successful functional recovery. We are investigating the ability of the young cortex to establish and adjust its wiring in response to experience. We characterizing circuits throughout development, and identify and manipulate key neuronal populations that regulate development and plasticity. Our work focuses on the auditory cortex a region crucial for human language communication. The developing cerebral cortex contains an enigmatic population of neurons called subplate neurons. Remarkably, these neurons are largely absent in adults highlighting their specialized role in development. However, despite their importance, detailed knowledge about subplate neurons and their role(s) are sparse. We hypothesize that subplate neurons provide both a substrate to establish a template of intra-cortical organization and that early spontaneous activity and sensory experience shape the functional and synaptic organization of subplate. To address these fundamentally important issues we propose a series of in vivo and in vitro experiments in mouse auditory cortex using a combination of electrophysiological and imaging techniques. 1) What is the functional organization of the distinct subcircuits within subplate? 2) What is the role of subplate and early sensory activity in patterning of intra-cortical circuits? 3 What is the role of subplate and early sensory activity in sculpting the functional organization of auditory cortex? Collectively these experiments will provide the fundamental framework of understanding development and plasticity of auditory cortex by elucidating the function of a previously ignored central component of auditory cortex development.

DESCRIPTION (provided by applicant): Proper integration of multiple senses is critical for providing a coherent perception of the environment. Cross-modal relay of sensory information is not only critical for multisensory integration, but provide substrates for cross-modal compensation when losing a sensory modality. For example, in blind individuals cross-modal compensation is observed as enhanced functionality in the remaining senses as well as recruitment of visual areas by Braille reading. While cross-modal plasticity is largely beneficial to blind individuals, it poses a challenge when attempting to recover function by clinical interventions. For instance, the success of recovering hearing by cochlear implants is reported to inversely correlate with the extent of cross-modal sensory compensation. It is likely that recovery of vision will encounter similar obstacles. Most studies of cross-modal plasticity focuses on systems level analyses, hence cellular and circuit level mechanistic understanding is quite limited. We previously reported that depriving rodents of vision by dark-rearing not only alters synaptic transmission in primary visual cortex (V1), but also produces opposite changes in primary auditory cortex (A1). In particular, we observed an increase in excitatory synaptic transmission in the superficial layers of V1, but a decrease in excitatory synaptic transmission in the superficial layers of A1 following dark-rearing. While our data suggest that visual deprivation can globally alter excitatory synaptic transmission across different primary sensory cortices, it is unclear how these changes affect cortical function. In this proposal, we will test the hypothesis that visual deprivation-induced decrease in excitatory synaptic transmission alters the receptive field properties of A1 neurons. We will test our hypothesis by combining in vitro whole-cell recordings to assess specific circuit properties of layer 2/3 neurons in A1, and in vivo single unit recordings of these neurons from awake mice. Specifically, we will determine whether visual deprivation alters the functional circuitry (Aim 1) and the receptive field properties (Aim 2) of layer 2/3 neurons in A1. Furthermore, we will investigate whether the cross-modal synaptic changes are responsible for altering receptive field properties in A1 (Aim 3). Results from our project will provide a cellular and circuit level mechanistic understanding of how loss of vision affects the functionality of A1 neurons. In addition, it will provide evidence that cross-modal changes occur in primary sensory cortices. PUBLIC HEALTH RELEVANCE: Blind individuals display enhance functionality in the remaining senses, such as better sound localization and discrimination. We will examine how loss of vision affects the function of primary auditory cortex, an area of the brain involved in sound processing. Results from our work will benefit the development of therapeutics for recovering vision, as extensive sensory compensation is known to impede the recovery of the lost sense.

DESCRIPTION (provided by applicant): Recent studies highlight that each primary sensory cortex does not work in isolation, but have some degree of interaction, which is not only critical for multisensory integration, but also important for sensory compensation in the event of losing a sensory modality. In blind individuals, there are several reports of cross- modal compensation that allow enhancement of the remaining senses. While cross-modal plasticity is largely beneficial to blind individuals, it hinders the recovery of function by clinical interventions. For example, the success of recovering speech recognition following cochlear implants is reported to inversely correlate with the extent of cross-modal plasticity. It is likely that similar obstacls will be met when trying to restore vision in blind. While there are many studies on cross-modal plasticity, most analyses are done at the level of systems neuroscience. Therefore, there is scarce information as to what types of changes happen at the cellular and circuit level. We previously showed that depriving rodents of vision increases the excitatory synaptic transmission in primary visual cortex (V1), in line with homeostatic adaptation. Importantly, we also found that visual deprivation reduces the excitatory synaptic transmission in the superficial layers of primary auditory cortex (A1). These results suggest that losing vision can cross-modally alter synaptic function in other primary sensory cortices, but how these cellular level changes alter the neuronal and circuit function of A1 is unknown. In the current proposal, we will test our hypothesis that visual deprivation-induced synaptic plasticity alters the functional circuitry and the neuronal receptive field properties in A1. To do this, we will determine whether visual deprivation alters the synaptic strength (Aim 1-1) and spatial extent (Aim 1-2) of specific excitatory and inhibitory circuitry of A1. To examine the in vivo consequences, we will examine whether visual deprivation alters the receptive field properties of neurons (Aim 2-1) and the population encoding in A1 (Aim 2-2). Results from our study will provide a comprehensive mechanistic understanding of how visual deprivation changes the functionality of A1. Functional connectivity across different brain regions is not restricted to sensory cortices. Therefore, our findings can be generalized to elucidate how neurons globally adjust to insults to other parts of the brain, such as would occur during neural injury, stroke and neurodegeneration.

? DESCRIPTION (provided by applicant): The cortex is a laminated structure that is thought to underlie sequential information processing. Sensory input enters layer 4 (L4) from which activity quickly spreads to superficial layers 2/3 (L2/3) and deep layers 5/6 (L5/6) and other cortical areas eventually leading to appropriate motor responses. Sensory responses themselves depend on ongoing, i.e. spontaneous cortical activity, usually in the form of reverberating activit from within or distant cortical regions, as well as the state and behavioral context of the animal. Receptive field properties of neurons can rapidly and adaptively be reshaped when an animal is engaged in a behavioral task, indicating that encoding of stimuli is dependent on task- or context-dependent state. Responses also depend on ongoing cortical dynamics in a lamina-dependent fashion and differ between the awake and anesthetized state. The intricate neuronal interplay between behavioral context, ongoing activity, and sensory stimulus underlying cortical representations is unknown. Specifically, we do not know how neuronal circuits shape these emergent dynamics within and between laminae, and we do not know which neurons encode which aspect of a sensory stimulus. One shortcoming of all prior studies of sensory processing is that only a few neurons are sampled, and thus information about the interactions between neurons, and between neuron and global brain state is lacking. Here we address these challenges by developing new in vivo 2-photon imaging technology that allows rapid imaging and stimulation in multiple focal planes and new computational and information theoretic techniques to extract network dynamics at the single neuron and population level. These measures go beyond paired measures and take synergistic interactions between neurons into account. We use these new techniques to investigate the 3D single cell and population activity patterns in the auditory cortex in mice. We investigate the influence of single neurons relative to the synergistic influence of specific groups of neurons (the crowd) on network dynamics and ultimately behavior of the animal.

Within sensory structures, even the simplest stimulus engages thousands of neurons that have widely varying stimulus selectivity and are spatially distributed in sensory brain maps. This organization raises the essential question of the rules governing the integration of the activity of such a large dispersed population of neurons to produce uniform percepts and reliable behaviors. Do behavioral responses to a sensory stimulus rely on a weighted sum of all active neurons that represent it, or a weighted sum of particular subpopulations of neurons (for example, defined by genetic identity, stimulus selectivity, location, or projection targets)? Moreover, how are neurons in different regions of an active population weighted? While these issues have been computationally investigated using a variety of decoding approaches, the causal link between population activity and behavior has been lacking. This project will provide such links by using patterned stimulation of targeted and characterized neuronal populations with in vivo holographic stimulation to bias and drive behavioral responses. The proposed experiments will determine how the spatial relationships between neurons relate to their relative impact on behavior, and assess how this spatial weighting is affected by changes in stimulus intensity, signal-to-noise ratio, and stimulus complexity. Comparisons between sensory systems will reveal which rules are general, and which are related to particular sensory demands. Because sensory neurons are broadly tuned, every stimulus activates neurons with different stimulus preferences. The experiments will test whether neurons that share a particular stimulus preference have cooperative effects and how this weighting is affected by variation in signal-to-noise ratio. Finally, because neurons in each brain area have different identities that reflect their different functional contributions, the project will test if behavioral roles vary between neurons across cortical layers, genetic identities, or projection targets. Collectively, these experiments will provide new and previously unattainable information about the encoding and readout of stimuli as well as how those results generalize to more natural sensory stimuli.

PROJECT SUMMARY To understand neuropsychiatric disorders behavioral phenotypes, have to be linked to altered brain function and brain circuits. However, most neuropsychiatric disorders show a range of phenotypes and high variability making the association with neurological correlates difficult. Development of animal models of neuropsychiatric disorders such as autism, have been facilitated by gene discovery through linkage analysis. Pharmacological treatments also model aspects of these disorders in rodents. However, comprehensive behavioral and physiological analysis is very time consuming. Moreover, common behavioral and physiological testing is performed in specialized apparatuses requiring handling of the rodents which in turn can affect their performance and lead to experimenter and environment induced variability. This it is difficult to observe multiple measures such as behavioral and neural activity in the same animal without perturbation and can capture developmental trajectories of disease progression and/or therapeutic intervention. We here aim to solve this problem by developing a new, flexible platform in which mice can be continually assessed within their home cage environments with a barrage of behavioral tests as well as neurophysiological measures (brain functional imaging) and optogenetic intervention. Our system will include autonomous monitoring and control of brain activity within these home cages in the context of stimuli used to assess auditory sensory processing. The combination of the home cage environments with auditory learning paradigms provides a single platform for both training, assessment, and potential therapeutic manipulation. Our strategy will employ a collaborative effort to build home cages for up to 10 mice/cage, which can be housed continually for up to a 1-year period. Over this time, the animals will initiate self-directed trials of brain imaging, as well as auditory processing assessments. A core feature of our system is the usage of relatively small footprint open source, Linux-based computer tools employing single board Raspberry Pi and Arduino computers. These systems will work together to enable the flexible home cage training and assessment system. The first goals are to refine the hardware and software to enable cross-laboratory collaboration and then wider dissemination of these tools to the broader neuroscience community. We will test the home cages on specific lines of mice which have previously been shown to model autistic-like behaviors and uncover co-variation of behavioral, cognitive, and physiological deficits within and across the various models.

Project Summary To survive, organisms must both accurately represent stimuli in the outside world, and use that representation to generate beneficial behavioral actions. Historically, these two processes ? the mapping from stimuli to neural responses, and the mapping from neural activity to behavior ? have largely been treated separately. Of the two, the former has received the most attention. Often referred to as the ?neural coding problem,? its goal is to determine which features of neural activity carry information about external stimuli. This approach has led to many empirical and theoretical proposals about the spatial and temporal features of neural population activity, or ?neural codes,? that represent sensory information. However, there is still no consensus about the neural code for most sensory stimuli in most areas of the nervous system. The lack of consensus arises in part because, while it is established that certain features of neural population responses carry information about specific stimuli, it is unclear whether the brain uses (?reads?) the information in these features to form sensory perceptions. We have developed a theoretical framework, based on the intersection of coding and readout, to approach this problem. Experimentally informing this framework requires manipulating patterns of neuronal activity based on, and at the same spatiotemporal scale as, their natural firing patterns during sensory perception. This work must be done in behaving animals because it is essential to know which neural codes guide behavioral decisions. In the first phase of this project (funded by the BRAIN Initiative), we developed the technology necessary for realizing this goal. In the present proposal, we will extend our patterned neuronal stimulation technology and apply it to answer long-standing questions about neural coding and readout in the visual, olfactory, and auditory systems. We will pioneer the capacity to determine which neurons within a network are encoding behaviorally relevant information, and also to determine the extent to which temporal patterns of those neurons? activity are being used to guide behavior. Finally, we will study these neural coding principles across changes in behavioral state and during learning to determine how internal context and past experience shape coding and readout. The contributions of the proposed work will be three-fold. First, we will provide the neuroscience community with the tools needed to test theories of how neural populations encode and decode information throughout the brain. Second, we will reveal fundamental principles of spatiotemporal neural coding and readout in the visual, olfactory, and auditory systems of behaving animals. And third, our unifying theoretical framework for cracking neural codes will allow the broader neuroscience community to resolve ongoing debates regarding neural coding that have been previously stalemated by considering only half of the coding/readout problem.

Project Summary It is well documented that the ability of the brain to undergo plasticity becomes limited in adults. In particular, sensory experience-dependent plasticity of cortical circuits is rather confined to a limited time during development, termed the critical period. Recovery and refinement of sensory processing is therefore difficult in adults. For example, the success rate of speech recognition in artificial cochlear implant patients becomes quite low, if the surgery is done later in life. Hence discovery of mechanisms that can recover adult cortical plasticity is of essence to benefit recovery of hearing or for treating abnormal auditory processing as occurs with tinnitus. We found that temporary visual deprivation is quite effective at producing large-scale plasticity in the adult primary auditory cortex (A1) of mice. Such changes occurred as potentiation of feedforward excitatory synapses from the primary auditory thalamus (MGBv) to layer 4 (L4) as well as L4 to L2/3. This was accompanied by weakening of synapses arising from lateral intracortical sources to L2/3 of A1. In parallel, we also observed refinement of cortical circuits of A1 L4 and L2/3. Collectively, these changes suggest that A1 circuit adapts to allow better processing of bottom-up auditory inputs, which is consistent with our published observation of refinement of A1 L4 neuronal receptive field and lowering of detection threshold in visually deprived mice. In this application, we aim to determine the mechanisms involved in driving adult A1 plasticity with visual deprivation, and whether visual deprivation improves auditory behavior in adults. Based on our observation that visual deprivation induced potentiation of thalamocortical (TC) inputs to A1 L4 requires audition, but no due to changes in the auditory environment, we surmise that there is central adaptation in circuits mediating auditory signals going through the thalamus and the cortex. In particular, we hypothesize that short-term visual deprivation promotes A1 plasticity in adults by regulating inhibitory circuits at the level of thalamus and cortex (Aim 1). The circuit and synaptic adaptation seen in A1 following vision loss accompanied refinement of A1 L4 neural function, and is predicted to enhance auditory function. We will examine how short- term visual deprivation alters auditory behavioral tasks in adults, and investigate whether this is due to changes in A1 neuronal responses and population encoding during auditory tasks using in vivo 2-photon imaging (Aim 2). Results from our proposed study will provide mechanistic understanding on how short-term visual deprivation enables plasticity of adult A1 via regulation of thalamic and cortical circuits, and will provide means to enhance auditory processing in the adult brain that could benefit development of treatment options for enhancing or recovering auditory function as would be needed for better prognosis of artificial cochlear implants. Furthermore, our results can be generalized to provide insights into how cortical circuits adapt to losing major inputs as it may happen during injury, stroke, and neuronal degeneration.