Matthew J. McGinley, Ph.D. - US grants

[unreadable] DESCRIPTION (provided by applicant): The broad goal of the proposed project is to understand the fundamental mechanisms of cortical processing in the olfactory system and their role in seizure initiation. The work will specifically address three synaptic pathways in olfactory cortex which may contribute to epileptogenesis. Whole-cell patch-clamp of cortical pyramidal cells in anterior olfactory nucleus (AON) and piriform cortex will be used to study the response to stimulation of input from the olfactory bulb. Paired recordings will be used to study the interactions of cells within and between the cortical regions being studied (including important inhibitory inputs) and immunochemistry and confocal imaging to compliment electrophysiological results. Two types of principal neurons in the olfactory bulb project to the olfactory cortex: tufted and mitral cells. Tufted cells project to AON and ventrorostral anterior piriform cortex (aPCvr), while mitral cells project to the entirety of olfactory cortex. While tufted and mitral cells carry different information about the olfactory world, the physiological response and functional significance of this is not known. We will separate the response, in cortex, to these two types of inputs. The aPCvr is reciprocally connected to an underlying cortex which is highly susceptible to the initiation of tonic-clonic seizures, leading to the hypothesis that tufted cell input plays a special role in the initiation of seizures in piriform cortex. The aPCvr receives feedforward input from the AON. Critically, AON feedforward excitation terminates directly adjacent to the cell bodies of pyramidal cells in anterior piriform, while olfactory bulb terminals are on the distal apical dendrites. Therefore it appears that AON input, but not olfactory bulb input, may be the driving input to this epileptogenic brain region. Recordings of piriform cortical pyramidal cells during stimulation of their AON inputs will allow detailed study of this previously unexplored synaptic connection. Axo-axonic cartridge endings of chandelier cells, and cholecystokinin positive basket cell bodies and endings are absent from aPCvr. I will study the synaptic influence of these inhibitory neurons in piriform cortex. Relevance of Research to Public Health The cortex of the olfactory system is known to be an important site for the initiation of some types of epileptic seizures. Study of the sensory input to and synaptic connections between cells in this region will help understand the mechanisms that underlie seizure initiation. A long-term commitment to the development of better treatments for epilepsy depends critically on an understanding of underlying circuitry. [unreadable] [unreadable] [unreadable]

Project Summary The primary complaint of patients with hearing loss is the strain required to understand speech in noisy environments. This excessive `listening effort' results in stress, fatigue, and cognitive impairment. A major challenge in mitigating these effects is to identify good measures of the problem. The task-evoked pupil response is an objective and non-invasive measure of listening effort that is well established in hearing research, and increasingly used in studies of hearing loss, hearing aids, and cochlear implants. However, we have little knowledge of the physiological processes tracked by the pupil or the mechanisms of related effects on sound processing. This proposal will determine which neuromodulator(s) are released in association with task-related pupillary measures (Aim 1) and examine the impact of this pupil-indexed modulation on sound processing in auditory cortex (ACtx) of mice (Aim 2). A third aim will assess how hearing loss alters task-related pupil activity for future mechanistic study. Experiments in Aim1 will address the question: What do task-evoked pupillary responses tell us about neuromodulator release in auditory processing? The hypothesis is that ACh and NE release in ACtx are tracked by distinct components of pupillary dynamics during behavior. To test this, I will correlate pupillary measures associated with behavioral responses in a psychometric tone-in-noise detection task, to activity in cortical axons using two-photon calcium imaging. Experiments in Aim 2 will determine mechanisms of the influence of pupil-indexed neuromodulator release on auditory cortical processing. I hypothesize that NE and ACh differentially modulate aspects of spontaneous and sound-driven auditory cortical activity. To test this, I will monitor the pupil while recording membrane potentials or extracellular unit activity in ACtx. I will then optogenetically silence NE/ACh axons or locally block families of NE/ACh receptors in ACtx to dissect the influence of these modulators and their receptors on sound processing. Finally, experiments in Aim 3 will examine changes in the pupillary dynamics in mice resulting from hearing loss induced by acute noise trauma. The hypothesis is that mice with hearing loss exhibit changes in their pupil responses that are similar to those seen in humans. These altered pupillary responses after hearing loss will provide a model system for future mechanistic study of increased listening effort with hearing loss associated with pupillometric readouts. Overall, this proposal will reveal cholinergic and noradrenergic modulatory mechanisms in auditory cortex related to pupil-indexed listening effort. The results will be of interest to scientists and clinicians who: use pupillometry; study neuromodulation; are concerned with listening effort; study the processing of sounds in noisy environments; or study or treat hearing loss. In addition, this proposal will lay a technological and methodological foundation for future mechanistic study of diverse behavioral modulations of auditory processing in mouse models of normal and impaired hearing, including mechanistic dissection of increased listening effort associated with hearing loss.

Project Summary . Attending to a speaker in a noisy environment, such as a cocktail party, can be an effortless and pleasantly immersive experience for individuals with normal hearing and cognitive function. However, for individuals with hearing loss, this ?listening effort? is their primary complaint, and can be a severe source of stress and fatigue that impacts their quality of life and employment. Unlike an audiogram, which can be measured objectively, listening effort is a high-level cognitive process, and challenging to measure. Pupillometry, measuring the size of the pupil of the eye, has proven extremely useful as a physiological readout of listening effort. However, we have very little understanding about the neural interactions underlie mental effort, and therefore do not know what the pupil tells us, specifically, about these circuits. Experiments are needed that behaviorally engage listening effort while probing the underlying neural circuits mechanisms, and determining which circuit interactions are read out by pupil dilation. Our laboratory has recently developed a behavioral approach to study the attentional component of listening effort (attentional effort), in mice. Mice report detection of temporal coherence in ongoing noise by licking for sugar reward. We parametrically vary the difficulty on each trial, and manipulate listening effort by changing reward volume in blocks of trials. We find that mice expend more attentional effort during high-reward blocks, resulting in better detection of temporal coherence during blocks. In parallel work, we have extensively characterized the physiological correlates in the auditory system of several pupillometry metrics during a simpler auditory detection behavior. Furthermore, human and animal work consistently show that frontal cortex structures that combine task performance and motivational information are active during attentional effort. These results lead to the following central hypothesis: differences in cortical coding between states of low and high reward, result from changes in modulation on fast and slow time scales, together with auditory-frontal interactions that enhance coding of high-value sounds and provide feedback signals that improve subsequent performance, and that these circuits are upregulated after hearing loss. We will test this hypothesis by electrically recording from neurons in the auditory cortex and assaying their coding of sounds, while two-photon imaging or optopgenetically manipulating inputs from neuromodulatory systems or frontal cortex, and doing pupillometry during our listening effort task. Our results will reveal the contributions of neuromodulatory and frontal cortex inputs to auditory cortex to shifts in listening effort allocated to temporal coherence detection, and will directly relate multiple pupil metrics and statistical modeling approaches to these circuit mechanisms.

Project Abstract Understanding how neuronal computations build up a perception of the external world is fundamental to our understanding of how the brain works. This is particularly relevant to sensory systems, where heterogenous inputs representing distinct sensory features must be re-assembled to generate a perception. How individual neurons in early stages of sensory circuits process parallel inputs, and how these circuit elements later contribute to cortical computations that bind the inputs together is completely unknown. Studies have demonstrated that the timing, position and strength of a given input along the dendrite of a given neuron is a critical strategy used by the brain to encode sensory features. However, how such dendritic integrations of inputs in single neurons contribute to an animal's overall perception is not understood. To re-assemble diverse features from the same initial stimulus, the brain needs to determine which features occurred at the same time. Currently, little is known about how or where this timing information might be encoded. The auditory system offers an ideal system to tackle this question based on its tractability to interdisciplinary methods and its known ability to encode even miniscule differences in timing. Specifically, we will take advantage of a unique cell type in the auditory cochlear nucleus, called octopus cells, as a model to investigate the question of how small cell classes contribute to behavioral and perceptual circuits. Octopus cells are prominent in all mammalian species and are well known to encode temporal inputs with submillisecond precision through integration of primary sensory inputs along their large and extensive dendrites. We propose to carry out a multi- lab, integrated analysis of the molecular and biophysical properties of octopus cells and to track how these single cell computations are transformed along the auditory pathway to contribute to an animal's final auditory percept and hence behavior. Using the mouse as a model system, we will apply new sequencing methods together with high resolution brain imaging and single cell reconstructions to create a comprehensive wiring diagram of octopus cells and their auditory inputs. By generating mouse strains for selective access to octopus cells, we will be ideally positioned to investigate the in vitro and in vivo physiology of octopus cells and therefore bridge experimental and computational models for how timing information is encoded at the single cell level. Lastly, we will study how timing information propagates to higher auditory centers by recording from large populations of neurons in the midbrain, thalamus, and cortex and then assessing the functional relevance of temporal coding for auditory behavior. By leveraging molecular, biophysical, electrophysiological, behavioral, and computational approaches toward the study of this model cell type, these studies will allow us to extract general principles of single cell computations and their effects on systems-level circuit function, with broad implications for understanding how parallel streams of information are integrated to generate sensory perception.