Ron D. Frostig - US grants

The long term objective of the proposed research is to qualify and quantify the effects of learning on the functional organization of the adult cortex. We propose to reach this objective by undertaking studies which utilize the technique of in-vivo high-resolution optical imaging of intrinsic signals in conjunction with simultaneous, multiple, single- unit recording. The imaging technique will enable us to follow learning induced changes during and after learning from a global perspective while the unit recording will enable us to probe the cellular basis of learning induced changes from the functional network perspective. The study will be performed in the 'barrel cortex' division of the somatosensory cortex of rewarded and non-rewarded rats in order to quantify the changes induced by rewarded learning. While following and quantifying organizational changes over time we will seek evidence for the hypothesis that these changes originate within the cortex and that such changes involve 'unmasking' of existing changes. Successful completion of the proposed research will expand our understanding about the underlying mechanisms of neuronal organization and their possible modification by external factors. Understanding such mechanisms and their dynamics is important for both the healthy and the diseased brain.

9405146 Frostig One of the most informative ways to study the brain is to record from the brains of intact animals in a non-invasive way the electrical signals that brain cells use to communicate with each other. A new technique to do this is called optical imaging of intrinsic signals, in which signals from the illuminated surface of the brain are recorded with a digital CCD camera. One major impediment to getting good signals from the nerve cells is that the blood vessels on the surface of the brain disrupt the signals from the underlying brain tissue. Another obstacle in the development of the technique comes from the very large data set generated for each measurement (typically 120 images of a grid of 144 x 192 pixels, each pixels with 256 levels of light). This research focuses on ways to improve the digital signals recorded by the camera in studies of the part of the rat cortex that processes the tactile signals coming in from the rat's whiskers. It is a collaborative effort between biologists and mathematicians to develop new mathematical tools to separate the signals from the main blood vessels from those from the brain, so that the optical imaging of the intrinsic signals will have more faithful spatial resolution. A second goal of the project is to develop a more efficient way for the computer to handle the large data set so that the images can have better temporal resolution. The results of this study will have impact not only on neuroscience research, but also development of improved diagnostic tools in clinical neurology as well as impact on other types of image analysis. This multidisciplinary proposal was submitted to the Federal Interagency Coordinating Committee on the Human Brain Project and is being supported by three Programs within the National Science Foundation - Statistics and Probability, Computational Neuroscience, and Computational Biology.

Frostig 9507936 It has become clear just recently that the adult brain can reorganize its connections. One of the situations during which connections seem to change is when new behaviors are learned. With this award, Dr. Frostig will study how the brain's representation of different sound frequencies is altered as an animal is trained to discriminate certain frequencies. This will be done using new techniques to repeatedly image the activity levels of brain tissue in a non-invasive way. This work will provide new information on the time course of plastic changes in the brain, and will allow Dr. Frostig's group to study the relationship of specific behavioral capacities to specific changes in brain organization. ***

DESCRIPTION: The purpose of the proposed research is to describe the dynamic aspects of the functional organization of the adult cortex. Sensory deprivation is one of the main causes of functional reorganization of the adult cortex, but due to technical limitations little is known about the spatiotemporal aspects of such reorganization as well as the structural changes that underlie it. The major emphasis of this proposal is the quantification of the functional and structural reorganization in the adult cortex following a reversible deprivation and recovery of the original function. The study will be applied to several levels of cortical cortical organization: cortical columns, intra- and inter column interactions, single-neurons, and intracortical anatomical connections by the application of several techniques to the same animal. To quantify the functional changes within the same animal before, during, and after deprivation-induced reorganization and recovery of the original function, the unique advantages of optical imaging of intrinsic signals will be exploited since it enables the repeated visualization of activity patterns and the functional organization of the living cortex with the highest spatial resolution currently available (50 um) in a chronic preparation. Moreover, the high-resolution map of functional organization obtained by imaging can serve as a guide for precise localization of electrodes to record and analyze activity from the neurons recorded simultaneously in areas that exhibit functional reorganization. In addition, the anatomical changes underlying this form of functional reorganization will be studied by injecting anatomical tracers to areas that show reorganization as visualized by imaging. The target of the proposed research is the "barrel cortex" subdivision of the somatosensory cortex of the rat. This area has unique advantages for the proposed study since it has a precise structural and functional representation of each whisker on the rat's snout and the whiskers are unique in their ability to regrow after deprivation thus allowing to study the results of reversible deprivation paradigm. The main objective of this proposal is to study the recovery of the original function following permanent versus reversible deprivation of tactile input form the whiskers. The study also includes the investigation of the effects of the following on recovery of the original function: different periods of peripheral deprivation, the effects of different types of deprivation (reduction versus elimination), and the use of different, complementary deprivation paradigms. This research has relevance to our understanding of the structural and functional processes that accompany recovery of the cortical function following damage to the periphery, especially those related to facial and dental organs, since the trigeminal system carries both whisker as well as other facial and dental sensory information in the cortex.

Our long-range research interest is to understand adult sensory cortical plasticity. To this end, we found that application of neurotrophins to the adult somatosensory sensory cortex resulted in rapid (minutes) and dramatic changes in both amplitude and areal extent of evoked sensory response to tactile stimulation. These results suggest a surprising new role for neurotrophins in mediating rapid adult cortical plasticity. The proposed experiments will examine the role and mechanism by which the neurotrophin nerve growth factor (NGF) induces such rapid cortical plasticity. We will test the hypothesis that NGF is part of a cortex-to-basal forebrain cholinergic system (BFCS) feedback mechanism that can induce very rapid cortical plasticity. Specifically, NGF may be released by activated cortical neurons that, in turn, enhance the cholinergic release from terminals located on BFCS projections in the cortex. If supported, such a hypothesis would provide a mechanism that would explain how the cortex could self-regulate its own plasticity. For example, such self-regulation of plasticity may provide a means for the cortex to enhance rapidly the effects of sensory input that has important behavioral value. Indeed, the BFCS has been implicated in enhancing the behavioral importance of a sensory stimulus by inducing cortical plasticity. Experiments are designed to prove that cortex-to-BFCS feedback system, via the action of NGF on the BF CS projections in the cortex, is both necessary and sufficient to elicit rapid cortical plasticity. Our research strategy is to identify the NGF/ACh projections to the somatosensory cortex, to stimulate that system and then to eliminate its function. The results of the proposed experiments will be quantified by using in vivo high-resolution imaging of cortical activity. If our hypothesis is verified, it will add a fundamental insight to the cellular and molecular mechanisms by which the adult cortex can regulate its own plasticity and to the nature of cortical plasticity in general. As cortical plasticity is implicated in many fundamental processes of the brain in general and the cortex in particular, ranging from recovery after injury and sensory deprivation to learning and memory, there is a growing need to better understand the mechanisms underlying such plasticity.

[unreadable] DESCRIPTION (provided by applicant): Our long-range research interest is to understand the functional organization of the adult sensory cortex and its plasticity. The target of our research is the somatosensory cortex of the adult rat, especially the subdivision that processes information from the whiskers known as Postero Medial Barrel Sub Field (PMBSF). We have demonstrated that the size of a whisker functional representation (WFR) in the PMBSF is large and consequently overlap extensively with the WFRs of other whiskers. We have also demonstrated that the size of the WFR in the cortex is mutable following changes in the patterns of sensory input. For example, after removal of all its neighboring whiskers, a spared (remaining) WFR could expand dramatically. However, when such whisker-deprived rats were removed from their home cages and given brief opportunity to explore a novel environment, an unexpected strong contraction of the spared whisker's WFR was found. The degree of contraction of the spared whisker WFR became more pronounced with increasing amount of time actually spent exploring the environment with the remaining whiskers. We propose to extend these findings from whisker-deprived rats to non-deprived rats. Our general hypothesis is that solitary confinement of the laboratory rat to the typical small and bare cage is an inadvertent form of sensory deprivation that lead to abnormally expanded sensory representation in the cortex. If correct, conditions that promote natural, innate behavior in rats such as tunnel digging, navigation, foraging and social interactions - by transferring rats from their home cage to a new kind of an 'enriched environment' (EE) - can refine cortical functional organization by inducing a contraction of cortical representations and consequently reducing their overlap, a refinement verified by our preliminary results. Using functional imaging, single unit recordings and anatomical techniques we propose to characterize functional and anatomical aspects of such plasticity, its time course, and its effects on neuronal activity patterns and receptive field characteristics within PMBSF. We also propose to study whether exposure to an EE endows the cortex with some immunity to the deprivation effects of the standard cage. Successful completion of our proposal should have major implications for both basic and clinical research because they question the relevance of caged, laboratory rat brain to serve as a model for the brain of humans in their natural environments. In addition, such findings could have important implications for treatment of adult perceptual/motor disorders. [unreadable] [unreadable]

DESCRIPTION (provided by applicant): Our long-range research interest is to understand the functional organization of sensory cortex, its plasticity and their relationship to behavior. The target of our research is the somatosensory cortex of the rat, especially the subdivision that processes information from the facial whiskers known as Postero Medial Barrel Sub Field (PMBSF). Using chronic functional imaging and single unit recordings we have demonstrated that in the adult rat the size of a whisker functional representation (WFR) in the PMBSF is large and consequently overlaps extensively with the WFRs of other whiskers. Surprisingly, we found that this description of the WFRs is valid only in rats that live in a standard cage (SC). If rats are allowed out of the cage and thus are able to express innate behaviors that are not typically expressed in the SC, such as whisker-dependent navigation, the WFRs contract and weaken and thus minimize their overlap, but if the rat stays in its SC the WFRSs expand and strengthen. The contraction of WFRs was found both in adult deprived rats that experienced a removal of all whiskers except one (spared whisker) and were allowed a few minutes of navigation outside the cage, or in normal, non deprived adult rats that were spending a month in a naturalistic habitat (NH) - a new type of housing environment that imitates the rat's natural environment by enabling rats to engage in innate behaviors such as exploration, tunnel digging, subterranean navigation, foraging and social interactions. Because the cortex is especially sensitive to environmental influences during development, we propose to investigate the hypothesis that the ability to express innate behaviors since birth by being raised in the NH, may have anatomical, functional and behavioral consequences that would refine the cortex to be better optimized for whisker discrimination abilities compared to SC-raised rats. To test the hypothesis, we propose to compare the anatomy, neurophysiology and whisker-dependent discrimination behavior of NH-raised rats vs. SC-raised rats. Successful completion of the proposal would highlight the importance of expressing innate behaviors during development for the optimal maturation of cortical structure, function that is associated with this behavior. Such findings could have implications for the optimal treatment of developmental abnormalities of behavior in humans, and regeneration after injury or disease. Further, such results would help in reassessment of the appropriateness of SC-raised rats to serve as models for the normal human brain.

DESCRIPTION (provided by applicant): Our research interests focus on the topographical mapping of sensory epithelia in sensory cortex and their plasticity. We are particularly interested in delineating the spatial extent of cortical activation (e.g., the spatial spread of all the responding neurons) to small (point) stimulation because it is fundamental to our understanding of cortical maps. Functional imaging methods are advantageous for characterizing the spatial extent because of their ability to provide quick, high spatial resolution assessment of activity from large cortical regions. However, one limitation of most of the functional imaging methods is that they rely on hemodynamic events that follow brain activation and therefore provide only an indirect means for assessing the spatial extent of the underlying neuronal evoked activation and thus imagers lack the means to assess the spread of neuronal activation using imaging. Because there is no direct way to verify the spatial extent of the underlying neuronal activation area in humans, imagers typically apply conservative thresholds for analysis that typically emphasize peak, or near peak activation areas. Such practice, however, may lead to a biased and possibly distorted view of cortical function because it may underestimate the real size of cortical activation. To address these issues, it is proposed to directly relate the spread of neuronal activation to the spread imaged by functional imaging of the same cortical area with the same stimulation. The point stimulation is either a whisker or a pure tone, and the spread of cortical activation is imaged by intrinsic signal optical imaging in the adult rat somatosensory and auditory cortex, respectively. Imaging results will be directly compared to post-imaging neuronal recording using electrode arrays within the imaged cortex. Imaging and neuronal results, in turn, will also be superimposed on the anatomical maps of the same areas to highlight cortical structure-function relationship related to the spread of activity. Because functional imaging methods can detect both suprathreshold (action potentials) and subthreshold (local field potentials), the spread of both types of neuronal activations will be recorded and compared with imaging results. Once the rules of mapping neuronal spread to imaging spread are quantified, it will enable unbiased, direct, imaging-based description of the entire somatosensory and auditory cortices using such rules.

DESCRIPTION (provided by applicant): For the last 30 years, there has been a growing recognition that adult plasticity is a fundamental mechanism underlying a host of brain processes ranging from recovery after injury to learning and memory and involves multiple levels of the brain including synapses, neurons, neuronal circuits, representational maps, and even supporting metabolic and vascular systems. Enhancement of neuronal plasticity as a means of treatment of neurological disorders and injuries has not been fully utilized, although such treatments are an attractive alternative to more conventional treatments because they have few, if any, side effects. Could plasticity be exploited for protection from brain injury? We propose the hypothesis that one type of plasticity, neurovascular plasticity, could be exploited to completely protect the cortex from ischemic injury. The proposed multifaceted study is designed for detailed quantification to further answer specific hypotheses related to protection by neurovascular plasticity and its underlying mechanisms at the functional, metabolic, histological, vascular, and behavioral levels in both adult and old rats. PUBLIC HEALTH RELEVANCE: The brain, and especially the cortex, is plastic (i.e., mutable) as demonstrated for many brain processes ranging from recovery from injury to learning and memory. Could plasticity be further exploited to protect it from brain injury? Based on new findings from our laboratory, we propose the hypothesis that one type of plasticity, neurovascular plasticity, could indeed be exploited to completely protect the ischemic injury (stroke) in adult and old rats.

The majority of current neurovascular research involves monitoring neurovascular parameters from animals housed in a standard cage, which is clearly not an environment that mimics the human condition. Indeed, previous findings from our lab regarding large scale plasticity in sensory cortex of rats demonstrated that activity-dependent plasticity of whiskers cortical representations in uncaged rats shows opposite direction and magnitude compared to activity-dependent plasticity in caged rodents. These findings suggest that the large- scale plasticity seen in uncaged rats should also be accompanied by large scale supportive neurovascular plasticity. We propose to study such cortical neurovascular plasticity by using our ?naturalistic habitat?. The naturalistic habitat is an environment which mimics the natural world of rats within the confines of a vivarium by promoting free movement, burrowing, foraging and continuous interactions with conspecifics, which led to major plasticity of cortical maps. To study how transfer to the naturalistic habitat for one and six months modifies the neurovascular system, we propose to employ a battery of vascular imaging and neuronal recording techniques within the same rat and compare the findings with rats that stayed for the same period in standard cages. Based on our previous plasticity results, our hypothesis is that rats that stay in the naturalistic habitat will have a much more efficient neurovascular system compared to the standard cage rats, and that longer duration in the naturalistic habitat will entail a progressively more efficient system. In addition, in order to further improve our animal model, we propose to divide our proposed studies into two major parts. In the first part all imaging and recording studies will be performed in anesthetized rats. In the second part all proposed studies will be performed on awake, head fixed rats. This design will achieve (1) further optimizing our rat model to the human condition, and (2) ability to study the effects of anesthesia on our neurovascular model. Successful completion of our combined aims could have major implications for the appropriateness of caged animals as a model of healthy human neurovascular system and therefore successful completion of our proposal could lead to a more optimal animal model that, in turn, could lead to better success of future translational neurovascular research in healthy rodent models and in rodent models of pathological neurovascular diseases.