Allison Doupe - US grants

[unreadable] DESCRIPTION (provided by applicant): Basal ganglia-cortical (BG) circuits are critically involved in normal motor behavior (especially sequenced behavior) and learning, in motivation and reward, and in numerous neuropsychiatric disorders, including schizophrenia, drug addictions, and Parkinson's disease. Despite the importance of these pathways, much remains to be learned about their function, in part because of the complexity in many animals both of the circuits and of the behaviors they control. Songbirds provide a potentially powerful small animal model for providing insights into mechanisms of BG action, because their relatively simple learned vocal behavior, song, is mediated by a discrete set of brain areas that includes a specialized BG circuit. It is well-established that this 'anterior forebrain pathway' (AFP) is critical for vocal learning and adult vocal plasticity, and it has been suggested that it contributes motor variability necessary for motor exploration and/or adaptive signals to guide song learning. However, most in vivo neurophysiological studies of the AFP have focused on its pallial output nucleus 'LMAN'. Thus, relatively little is known about other components of the circuit in behaving birds and about whether and how neural firing during singing changes as it traverses the loop. In this proposal we aim to test the hypothesis that there is a gradual transformation of the encoding of song- related activity through the AFP that is likely to be critical both to adult plasticity and to song learning. We will accomplish this by first recording from multiple cell types in the striato-pallidal portion of the AFP, Area X, as well as from LMAN, in awake, behaving adult zebra finches during singing, and analyzing how the activity in these two regions co-varies, and how it relates to song (Aim 1). We will then manipulate activity in Area X, either with pharmacological inhibition or with lesions, and assess the effects on LMAN firing and on song (Aim 2). This will test ideas from Aim 1 about processing through the circuit, and should also shed light on why disruptions of Area X and LMAN have strikingly different effects on song plasticity. Finally, we will analyze Area X and LMAN firing in young birds in the process of sensorimotor learning, when song still varies in its sequence and syllable stability (Aim 3). By studying these circuits before learning is complete and then following the neural changes as song is crystallized, we should gain further insights into how activity evolves in this circuit and how it relates to the accuracy and stability of song. This will also provide tests of the hypotheses that signals in the AFP contribute variability and/or instruction. Analyses of our simple circuit have the potential to elucidate very general rules about how BG circuits function, both normally and in the many diseases in which these structures are involved. [unreadable] [unreadable] [unreadable]

The long-term goal of this research is to understand the neural basis of learning and memory, especially how the brain learns complex motor behaviors, guided by sensory information. Vocal learning in songbirds provides a useful model system for this purpose, with special relevance to human speech learning. Songbirds learn to produce a copy of a previously memorized tutor song during a period of "sensorimotoi" learning, in which they use auditory feedback of their own voice to refine their vocal output until it matches the memorized song. The work proposed here focusses on a particular part of the system of brain areas devoted to song learning and production, a specialized cortical-basal ganglia circuit known as the anterior forebrain pathway (AFP), because it plays a crucial but illunderstood role both in song learning and in adult vocal plasticity. Moreover, cortical-basal ganglia circuits, which are well conserved evolutionarily, are thought to function in motor and reinforcement learning in many vertebrates, and to be one critical site of dysfunction in a number of neuropsychiatric disorders. Because the songbird AFP is a discrete cortical-basal ganglia circuit controlling a specific behavior, it may prove a particularly tractable system for elucidating the very general functions of such pathways. both normally and in disease. The AFP develops song-selective auditory responses that could participate in the auditory evaluation of song during learning, and shows motor-related activity during singing, but how these sensory and motor responses relate to each other is not clear. Activity in this circuit is also extremely variable from trial to trial, raising the question of how it could reliably encode information or guide song. With simultaneous recordings from multiple neurons in the output nucleus of the AFP, LMAN, during both singing and song playback, the first aim will test the hypothesis that the AFP encodes relevant song- and singing-related information in the form of a distributed, "population" code. A further hypothesis is that specific patterns of AFP neural activity are critical for normal song development, perhaps guiding the formation of connections in the vocal motor nucleus RA. This will be tested with simultaneous recordings of neurons in both LMAN and RA, so that the covariance of their activity and how it relates to vocal output can be analyzed. LMAN-RA interactions will be studied first in normal birds at different stages of learning, and then after experimental disruptions of the pattern of activity in the AFP, in ways that will shed light both on normal synaptic processing within this circuit as well as on how it influences the song motor pathway.

DESCRIPTION (provided by applicant): Midbrain dopamine (DA) neurons and the cortico-basal ganglia circuits they innervate are critically involved in normal motor behavior and learning, in motivation and reward, and in numerous neuropsychiatric disorders, including drug addictions and Parkinson's disease (PD). Despite the importance of DA, much about its mechanism of action remains to be discovered, in part because of the complexity both of the behaviors and of the circuits studied in many animals. Songbirds can provide a useful small animal model for providing insights into DA function, because their speech-like learned behavior, the song, is subserved by a discrete set of brain regions that include a specialized basal ganglia-cortical circuit, complete with midbrain DA inputs. This 'anterior forebrain pathway'(AFP) is critical for vocal learning and adult vocal plasticity, and like mammalian basal ganglia circuits, is modulated by context. In particular, prior work from this lab has revealed that social context potently modulates this sensorimotor circuit: males singing to females ('directed singing') show a marked decrease in the rate and variability of AFP neuronal firing and consequently in the variability of song, compared to birds singing alone ('undirected'song). This proposal hypothesizes that this social modulation of neural and song variability is a result of DA action, and that it represents a tractable example of DA's general function in gating and selecting inputs and increasing signal-to-noise in the brain in response to important external cues. This will be tested in three general ways. First, in vivo microdialysis will be used to ask whether DA is released into the AFP of male finches in response to the 'directed'social context. Then DA signaling will be disrupted in the AFP in vivo, either acutely, by infusing DA antagonists, or chronically, with a neurotoxin used in models of PD, to test whether this alters 1) the normal neurophysiological differences between directed and undirected firing in the AFP, and 2) song production. The prediction is that decreases in DA will transform the stereotyped activity and behavior in the social setting first towards the more variable undirected activity and song, and then beyond, towards abnormalities reminiscent of DA diseases. Experiments in this simple system with its highly quantifiable activity and motor output should shed general light on the function of DA in the modulation of behavior and behavioral variability, with implications both for intact animals and learning as well as for neuropsychiatric diseases.

DESCRIPTION (provided by applicant): While great advances have been made in understanding the mechanisms of learning in the single synapse or cell, a large gap remains between this understanding and our knowledge of learning at the behavioral level. We know that the activity of large-scale neuronal circuits gives rise to behavior, yet we have little knowledge of what changes in those circuits during learning or how sensory feedback drives these changes. The biggest impediment to answering these questions is the inability to quantitatively measure large-scale circuit properties (e.g. connectivity between brain areas) or to precisely manipulate the activity patterns across these circuits. Optogenetics offers the potential to bridge this gap by allowing the direct control of neural activation in targeted cell types on the millisecond timescale. The development of these tools is progressing most rapidly in mouse, due to the relative ease of genetic manipulations in that species. In contrast, behavioral and circuit-level studies of learning are most practical and have been most successful in "non-genetic" species. Within our team, we have expertise in studying both the behavioral and neural bases of learning in rat, songbird, and nonhuman primate. We propose to develop the optogenetic tools and experimental techniques required to study the circuit-level mechanisms of learning in these species and to apply these to two specific scientific aims: Aim 1: Determine the functional connectivity of learning-related circuitry and how it is altered by experience. It is widely presumed that learning relies on the ability of instructive signals to drive functional modifications of connectivity in the circuits that underlie behavior. However, the tools for measuring functional connectivity in vivo have been limited. We will overcome this limitation using temporally and/or spatially precise optical activation of neurons within a circuit. Functional connectivity will be measured by recording optical-stimulation-triggered changes in activity in downstream neurons. We will assess how functional connectivity is dynamically altered by learning and by factors that may contribute crucially to learning. Connectivity changes will serve as a mechanistic index of the nature and sites of the plasticity that give rise to behavioral change. Aim 2: Test the causal contributions of patterned activity to learning in vivo. Prior research has generated specific and testable hypotheses about how and where patterned activity drives learning. Yet support for these hypotheses has derived primarily from correlative observations of activity during learning rather than causal tests of the proposed mechanisms. We will use optogenetics to causally test the contributions of patterned activity to learning. We will test the sufficiency of instructive signals by imposing precisely controlled patterns of activity at defined loci in a circuit and test their necessity by eliminating the putative signals for learning. PROJECT NARRATIVE This project is aimed at revolutionizing the study of the mechanisms of learning within large neural circuits in the brain by directly measuring large-scale properties of these circuits and precisely manipulating circuit activity. To accomplish this, we will make use of, and continue to develop, advanced new techniques that permit the control of specific population of neurons using optical stimulation (light). The knowledge and tools that we gain from these studies are likely to find broad application in the search for treatments of neurological disorders.

DESCRIPTION (provided by applicant): Processing and perception of communication sounds such as speech are enormously important to humans, and hearing is a critical component of both. Yet we know surprisingly little about how the brain transforms auditory signals to accomplish these complex tasks. Our long-term objective is to further the development of a unified framework for understanding high-level auditory processing and how it changes, for good or ill, with experience and learning. To this end, we propose to study a stage in a central auditory circuit where there is a remarkable change from simple, primary-like response properties to complex vocalization-sensitivity, in the auditory forebrain of songbirds. These animals provide an excellent model for extracting general principles of higher-level sound processing, because they learn auditory tasks of similar difficulty to humans, and possess a hierarchical network of auditory areas that sub serve these tasks, including the avian equivalent of primary auditory cortex, field L, and several secondary areas that are the likely equivalent of belt cortex. Moreover, we have access to a rich set of auditory stimuli of behavioral relevance, songs. We recently found that within field L there is a strikingly orderly organization of receptiv fields, along spectral and temporal axes. We will ask whether and how this organization propagates to the next level, by mapping the response selectivity of these secondary areas to batteries of songs, using an information theory-based technique called maximally informative dimensions (MID). We will also record responses to songs learned earlier (from father, mate) to examine the additional hypothesis that sound memories learned early in life have a special representation in such areas. In parallel, we will test the anatomical and physiological contribution of the inputs from field L to these secondary areas, by selectively labeling or turnin off subsets of these inputs. Finally, armed with the knowledge of these circuits' organization, we will ask whether and how their receptive field organization and song representations change after birds learn a behavioral discrimination task that strongly focuses their attention on either spectral or temporal aspects of song, two key parameters mapped in field L, and critical both in normal and impaired auditory processing. PUBLIC HEALTH RELEVANCE: Hearing dysfunction is implicated in many disabilities including specific language impairments, dyslexia, and autism. A basic understanding of high-level auditory processing of complex sounds, as well as the ways in which this changes with experience, will provide a solid foundation for exploring symptoms and causes of altered hearing and perception, and may suggest new treatment strategies.