Music depends on the perception and production of complex temporal patterns, or rhythms, as a vital part of its power to communicate. These experiments investigated the neuroanatomical substrate of rhythm perception and production in patients with focal cerebral lesions, and in neuroimaging studies with normals. The hypotheses focused on the role of the primary and secondary auditory cortex, as well as the cerebellum and other motor-related areas. / Experiment I. To estimate the extent of removals in the region of auditory cortex in neurosurgical patients, a 3D probabilistic map of Heschl's gyrus (HG) was developed from magnetic resonance imaging (NW scans of normals. The map was coregistered with patent MRIs, revealing that most removals involved only anterior secondary auditory cortical regions, with relatively little encroachment onto primary auditory cortex. Additionally, this experiment compared the volumes of HG between hemispheres and found a consistent L > R asymmetry in the volume of cortical white matter, which could contribute directly to the preferential left-hemisphere processing of speech. / Experiment II. Using a paradigm contrasting reproduction of auditory and visual rhythms, four groups of patients were tested: those with right or left anterior temporal-lobe removals (RT-a, LT-a) and those with similar removals which also included HG (RT-A, LT-A). RT-A patients were impaired on auditory but not visual rhythms, particularly when accurate reproduction of stimulus durations was required. In contrast, LT-a, RT-a and LT-a patients were not impaired. These results demonstrated a role for the right anterior secondary auditory cortical regions in the retention of auditory temporal information. / Experiment III. The rhythm reproduction paradigm was adapted for a positron emission tomography (PET) activation study in normals. These data confirmed the participation of secondary auditory regions in the retention of auditory temporal information. They also demonstrated a supra-modal contribution of the lateral cerebellar cortices, vermis and basal ganglia to the task, pointing to a distributed system of neural structures involved in the production of a timed motor response from external stimuli. / The results are discussed in relation to possible interhemispheric differences in auditory temporal processing as well as the role of the cerebellum in motor and perceptual timing.

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Autor Markéta Popelová Název práce Software tool for modelling coding and processing of information in auditory cortex of mice Abstrakt Porozumění zpracovávání a kódování informací ve sluchové k·ře (AC) je stále ne- dostatečné. Z několika r·zných d·vod· by bylo užitečné mít výpočetní model AC, například z d·vodu vysvětlení, či ujasnění procesu kódování informací v AC. Prv- ním cílem této práce bylo vytvořit softwarový nástroj (simulátor SUSNOMAC), zaměřený na modelování AC. Druhým cílem bylo navrhnout výpočetní model AC s následujícími vlastnostmi: Izhikevich·v model neuronu, dlouhodobá plasticita ve formě Spike-timing-dependent plasticity (STDP), šestivrstvá architektura, pa- rametrizované typy neuron·, hustota neuron· a pravděpodobnost vzniku synapsí. Navržený model byl testován v desítkách experiment·, s r·znými sadami para- metr· a v r·zných velikostech (až 100 000 neuron· s takřka 21 milióny synapsí). Experimenty byly analyzovány a jejich výsledky srovnány s pozorováním skutečné AC. V práci popisujeme a analyzujeme několik zajímavých pozorování o aktivitě modelované sítě a vzniku tonotopického uspořádání AC. 1

Thesis (Ph.D.)--University of Melbourne, Dept. of Otolaryngology, 2005. / Typescript. Author's name on spine: B.Y. Cahyono. Includes bibliographical references (p. 185-220).

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An important question in sensory neuroscience is what coding strategies and mechanisms are used by the brain to detect and discriminate among behaviorally relevant stimuli. To address the noisy response properties of individual neurons, sensory systems often utilize broadly tuned neurons with overlapping receptive fields at the system's periphery, resulting in homogeneous responses among neighboring populations of neurons. It has been hypothesized that progressive response heterogeneity in ascending sensory pathways is evidence of an efficient encoding strategy that minimizes the redundancy of the peripheral neural code and maximizes information throughput for higher level processing. This hypothesis has been partly supported by the documentation of neural heterogeneity in various cortical structures. This dissertation examines whether selective and sensitive responses to behaviorally relevant stimuli contribute to a heterogeneous and efficient encoding in the auditory midbrain. Prior to this study, no compelling experimental framework existed to address this question. Stimulus design methodologies for neuroethological experiments were largely based on token vocalizations or simple approximations of vocalization components. This dissertation describes a novel state-space signal modeling methodology which makes possible the independent manipulation of the frequency, amplitude, duration, and harmonic structure of vocalization stimuli. This methodology was used to analyze four mouse vocalizations and create a suite of perturbed variants of each of these vocalizations. Responses of neurons in the mouse inferrior colliculus (IC) to the natural vocalizations and their perturbations were characterized using measures of both spike rate and spike timing. In order to compare these responses to those of peripheral auditory neurons, a data-driven model was developed and fit to each IC neuron based on the neuron's pure tone responses. These models were then used to approximate how peripheral auditory neurons would respond to our suite of vocalization stimuli. Using information theoretic measures, this dissertation argues that selectivity and sensitivity by individual neurons results in heterogeneous population responses in the IC and contributes to the efficient encoding of behaviorally relevant vocalizations.

The brain is a complex system that seamlessly solves intricate problems with unprecedented efficiency. Part of the brain’s task is gathering sensory information from its environment, processing and representing it in a highly efficient manner. One of the key mechanisms used by sensory pathways is to process information by its context, disregarding redundancies and selectively focusing on novelty (deviance/change detection). A quantitative measure for how well the brain can detect novel stimuli is measured with the oddball paradigm and the mismatch negativity component (MMN). Deficits in context modulation and reduced MMN components are associated with mental disorders such as schizophrenia. Typically, oddball studies are done with coarse recording methods like EEG and MEG, and the network response dynamics underlying novelty detection is still unclear. In this work we used two-photon calcium imaging in awake mice listening to acoustic oddball stimuli, and recorded from large populations of neurons in primary and secondary auditory cortex (AC). We analyzed single cell and population representations of contextual information and found robust context modulation across all recorded AC regions. Responses to redundant stimuli were strongly suppressed while those to novel stimuli amplified. Furthermore, responses to identical stimuli in deviant, neutral, or redundant contexts were encoded by distinct populations of neurons, indicating an even stronger context encoding than seen in average population activity. Finally, we found that stimulus complexity also has an effect on where and to what extent context information is most robustly expressed. A2 was the most engaged in context processing for simple tones, while for complex frequency gratings A1 was doing novelty detection to the largest extent. My results provide a circuit basis for novelty detection in the auditory cortex, as a stepping stone to understand how processing of sensory stimuli is carried out by the brain.

Vocal communication sounds are an important class of signals due to their role in social interaction, reproduction, and survival. The higher-order mechanisms by which our auditory system detects and discriminates these sounds to generate perception is still poorly understood. The auditory cortex is thought to play an important role in this process, and our current work provides new evidence that the auditory cortex changes its neural representation of sounds that are acquired in natural social contexts. We use a mouse ultrasonic communication system between pups and adult females to elucidate this. We record single neurons in the auditory cortex of awake mice, and assess the cortical differences between animals that either do (mothers) or do not (naïve virgins) recognize the pup ultrasounds as behaviorally relevant. We then evaluate the role that pup experience and the maternal physiological state play in this cortical plasticity. Finally, we develop a model to predict the responses to pup vocalizations as a way to segregate the diversity of cortical neuronal responses in the hope of more clearly assessing their roles in processing acoustic features. Our results demonstrate the detailed nature by which the core auditory cortex processes natural vocalizations, showing how it changes to represent behavioral relevance.

Orientador: Ana Cláudia Figueiredo Frizzo / Resumo: Introdução: O Zica vírus tornou-se uma epidemia no Brasil a partir do início de 2015, tendo os primeiros casos de microcefalia com suspeita de causa pelo Zica Virus confirmados nos estados do Rio Grande do Norte e Pernambuco. Desde então, pesquisas evidenciam a necessidade de maiores investigações acerca da fisiologia dos indivíduos afetados pela doença, sintomas e prognósticos a fim de aprimorar o tratamento das crianças com a chamada “síndrome congênita do zica vírus”. Desta forma, para estudar e minimizar os impactos que uma possível alteração no córtex auditivo possa acarretar no desenvolvimento comunicativo destas crianças, este estudo tem como objetivo principal descrever os valores do potencial cortical auditivo de crianças que provavelmente foram infectadas pela síndrome congênita do Zica vírus. Métodos: Trata-se de um estudo multicêntrico, transversal descritivo, o qual foi desenvolvido no Setor de Audiologia do Centro de Estudos da Educação e da Saúde (CEES), da Universidade Estadual Paulista (UNESP), e na Universidade Estadual de Ciências da Saúde de Alagoas – UNCISAL, Laboratório de Audiologia do Centro Especializado em Reabilitação (CER III), com aprovação no comitê de ética CAAE nº 68684117.8.1001.5406. Participaram do estudo 30 crianças, de ambos os gêneros, de seis a 38 meses de vida, compondo o grupo estudo, com microcefalia e provável síndrome congênita do zica vírus e grupo controle, nos quais foram realizados exames de potencial evocado auditivo cortical e... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Introduction: The Zika virus became an epidemic in Brazil from the beginning of 2015, with the first cases of microcephaly with suspected cause by Zika Virus confirmed in the states of Rio Grande do Norte and Pernambuco. Since then, research has shown the need for further research into the physiology of individuals affected by the disease, symptoms and prognosis in order to improve the treatment of children with the so-called congenital zygote virus syndrome. Thus, in order to study and minimize the impacts that a possible alteration in the auditory cortex may have on the communicative development of these children, this study has as main objective to describe the cortical auditory potential values of children who were probably infected by the congenital syndrome of Zika virus. Methods: This is a multicenter, cross-sectional descriptive study, which was developed in the Audiology Sector of the Center for Education and Health Studies (CEES), Universidade Estadual Paulista (UNESP), and at the State University of Health Sciences of Alagoas - UNCISAL, Audiology Laboratory of the Specialized Center for Rehabilitation (CER III), with approval in the ethics committee CAAE nº 68684117.8.1001.5406. The study consisted of 30 children of both genders, from six to 38 months of age, making up the study group, with microcephaly and probable congenital syndrome of the virus zika and control group, in which cortical auditory evoked potential tests were performed in children with development.... (Complete abstract click electronic access below) / Mestre

Past decades of auditory research have identified several acoustic features that influence perceptual organization of sound, in particular, the frequency of tones and the rate of presentation. One class of stimuli that have been intensively studied are sequences of tones that alternate in frequency. They are typically presented in patterns of repeating doublets ABAB… or repeating triplets ABA-ABA-... where the symbol “-” stands for a gap of silence between triplets repeats. The duration of each tone or silence is typically tens to hundreds of milliseconds, and listeners hearing the sequence perceive either one auditory object ("stream integration") or two separate auditory objects (“stream segregation”). Animal studies have characterized single- and multi- unit neural activity and event-related local field potentials while systematically varying frequency separation between tones (ΔF) or the presentation rate (PR). They found that the B tone responses in doublets were differentially suppressed with increasing PR and that the B tones responses in triplets decreased with larger ΔF. However, the neural mechanisms underlying these animal data have yet to be explained. In this study, we built an integrate-and-fire network model of the primary auditory cortex (AC) that accurately reproduced the experimental results. Then, we extended the model to account for basic spectro-temporal features of electrocorticography (ECoG) recordings from the posteriomedial part of the Heschl's gyrus (HGPM; cortical area equivalent to the AC of monkeys), obtained from humans listening to sequences of triplets ABA-. Finally, we constructed a firing rate reduced model of the proposed integrate-and-fire network and analyzed its dynamics as function of parameters. A large network of voltage-dependent leaky integrate-and-fire neurons (3600 excitatory, 900 inhibitory) was constructed to simulate neural activity from layers 3/4 of AC during streaming of tone triplets. Parameters describing synaptic and membrane properties were based on experimental data from early studies of AC. Network structure assumed spatially-dependent probability of connections and tonotopic organization. Subpopulations of neurons were tuned to different frequencies along the tonotopic map. In-silico recordings were performed during the presentation of long sequences of triplets and/or doublets. The network’s output was derived with two types of measurements in mind: spiking activity of individual neurons and/or local populations of neurons, and local field potentials. The network spiking neural activity reproduced reliably data reports, including dependence of responses to the B tone in triplets ABA- on stimulus parameter ΔF. Approximations of average evoked potentials (AEPs) from ECoG signals recorded at four depth contacts placed over human HGPM during auditory streaming of triplets were also obtained.