A primate model of human cortical analysis of auditory objects

PhD ThesisThe anatomical organization of the auditory cortex in old world monkeys is similar to that in humans. But how good are monkeys as a model of human cortical analysis of auditory objects? To address this question I explore two aspects of auditory objectprocessing: segregation and timbre. Auditory segregation concerns the ability of animals to extract an auditory object of relevance from a background of competing sounds. Timbre is an aspect of object identity distinct from pitch. In this work, I study these phenomena in rhesus macaques using behaviour and functional magnetic resonance imaging (fMRI). I specifically manipulate one dimension of timbre, spectral flux: the rate of change of spectral energy.I present this thesis in five chapters. Chapter 1 presents background on auditory processing, macaque auditory cortex, models of auditory segregation, and dimensions of timbre. Chapter 2 presents an introduction to fMRI, the design of the fMRI experiments and analysis of fMRI data, and macaque behavioural training techniques employed. Chapter 3 presents results from the fMRI and behavioural experiments on macaques using a stochastic figure-ground stimulus. Chapter 4 presents the results from the fMRI experiment in macaques using spectral flux stimulus. Chapter 5 concludes with a general discussion of the results from both the studies and some future directions for research.In summary, I show that there is a functional homology between macaques and humans in the cortical processing of auditory figure-ground segregation. However, there is no clear functional homology in the processing of spectral flux between these species. So I conclude that, despite clear similarities in the organization of the auditory cortex and processing of auditory object segregation, there are important differences in how complex cues associated with auditory object identity are processed in the macaque and human auditory brains.Wellcome Trust U

Influences of friction stir welding on the microstructure, mechanical and corrosion behaviour of AL-ZN-MG aluminium alloy 7039

This paper presents the influence of friction stir welding (FSW) on the microstructure, mechanical and corrosion behavior of precipitation hardening Al-Zn-Mg alloy AA7039. The microstructure of weld joints was investigated using an optical microscope. The grains in weld nugget zone (WNZ) and thermo-mechanically affected zone (TMAZ) of weld joints were finer than in the base metal and a reverse trend was observed for heat affected zone (HAZ). Mechanical properties of friction stir weld joints were determined by tensile and micro hardness test. The ultimate tensile strength of weld joints was found approximately equal to the base metal while yield strength and ductility of weld joints were found lower than in the base metal. HAZ of weld joints was more susceptible to corrosion than WNZ, TMAZ and base metal. The HAZ exibits the highest current density followed by the base metal

Latent coronary artery disease among smokers and smokeless tobacco users: a cross-sectional study

Background: Tobacco related mortality and morbidity and increase in developing country like India. WHO projected till 2020 India will accounts 15% of tobacco related mortality especially preventable causes of death e.g. cardiovascular disease. Active tobacco smoking is undoubtedly major risk factor for cardiovascular disease, but subjects use smokeless tobacco in dependence pattern is not extensively evaluated for cardiovascular risk factor. In India smokeless tobacco especially Khaini is major form of tobacco consumption. Scarcity of data on effects of smokeless tobacco in cardiovascular disease especially coronary artery disease major limiting factor for undermine the detailed evaluation of cardiovascular effects in smokeless tobacco dependence subjects. The aim of the study was to study the risk of coronary artery disease among smokeless tobacco dependence in comparison to tobacco dependence smokers.Methods: Cross-sectional assessments were done on 36 adults (>18 years), treatment-seeking patients with a ICD 10 diagnosis of Mental and behavioral disorders due to use of tobacco. Data was collected on socio-demographic characteristics, and after detailed clinical evaluation treadmill exercise test was done.Results: Mean age of tobacco dependence smokers 51.5±9.6 years vs 53.6±7.5 years. There were male predominant in study subjects and 38% subjects was treadmill test positive. Smokeless tobacco users had 35% positive treadmill test, and among Smokers 42% subjects was positive for treadmill test.Conclusions: Risk for latent coronary artery disease was similarly higher in smokers and smokeless tobacco dependence subjects

Intact mismatch negativity responses in clinical high-risk for psychosis and first-episode psychosis: evidence from source-reconstructed event-related fields and time-frequency data

Background: To examine whether Mismatch Negativity (MMN) Responses are impaired in participants at clinical high-risk for psychosis (CHR-P) and first episode psychosis (FEP) patients and whether MMN-deficits predict clinical outcomes in CHR-Ps. Methods: Magnetoencephalography (MEG) data were collected during a duration-deviant MMN-paradigm for a group of 116 CHR-P participants, 33 FEP patients, (15 antipsychotic-naïve), a psychosis-risk-negative group (CHR-N: n=38) with substance abuse and affective disorder and 49 healthy controls (HC). Analysis of group differences of source-reconstructed event-related fields as well as time-frequency and inter-trial-phase-coherence (ITPC) focused on bilateral Heschl’s gyri and superior temporal gyri. Results: Significant MMNm responses were found across participants in bilateral Heschl’s gyrus and superior temporal gyri. However, MMN-amplitude as well as time-frequency and ITPC-responses were intact in CHR-P and FEP-patients relative to HC. Furthermore, MMN-deficits were not related to persistent attenuated psychotic symptoms nor transitions to psychosis in CHR-Ps. Conclusions: Our data suggest that MMNm responses in MEG-data are not impaired in early-stage psychosis and may not predict clinical outcomes in CHR-P participants

Influences of friction stir welding on the microstructure, mechanical and corrosion behaviour of AL-ZN-MG aluminium alloy 7039

This paper presents the influence of friction stir welding (FSW) on the microstructure, mechanical and corrosion behavior of precipitation hardening Al-Zn-Mg alloy AA7039. The microstructure of weld joints was investigated using an optical microscope. The grains in weld nugget zone (WNZ) and thermo-mechanically affected zone (TMAZ) of weld joints were finer than in the base metal and a reverse trend was observed for heat affected zone (HAZ). Mechanical properties of friction stir weld joints were determined by tensile and micro hardness test. The ultimate tensile strength of weld joints was found approximately equal to the base metal while yield strength and ductility of weld joints were found lower than in the base metal. HAZ of weld joints was more susceptible to corrosion than WNZ, TMAZ and base metal. The HAZ exibits the highest current density followed by the base metal

EEG Responses to auditory figure-ground perception

Speech-in-noise difficulty is commonly reported among hearing-impaired individuals. Recent work has established generic behavioural measures of sound segregation and grouping that are related to speech-in-noise processing but do not require language. In this study, we assessed potential clinical electroencephalographic (EEG) measures of central auditory grouping (stochastic figure-ground test) and speech-in-noise perception (speech-in-babble test) with and without relevant tasks. Auditory targets were presented within background noise (16 talker-babble or randomly generated pure-tones) in 50% of the trials and composed either a figure (pure-tone frequency chords repeating over time) or speech (English names), while the rest of the trials only had background noise. EEG was recorded while participants were presented with the target stimuli (figure or speech) under different attentional states (relevant task or visual-distractor task). EEG time-domain analysis demonstrated enhanced negative responses during detection of both types of auditory targets within the time window 150-350 ms but only figure detection produced significantly enhanced responses under the distracted condition. Further single-channel analysis showed that simple vertex-to-mastoid acquisition defines a very similar response to more complex arrays based on multiple channels. Evoked-potentials to the generic figure-ground task therefore represent a potential clinical measure of grouping relevant to real-world listening that can be assessed irrespective of language knowledge and expertise even without a relevant task

Dynamics underlying auditory‐object‐boundary detection in primary auditory cortex

Auditory object analysis requires the fundamental perceptual process of detecting boundaries between auditory objects. However, the dynamics underlying the identification of discontinuities at object boundaries are not well understood. Here, we employed a synthetic stimulus composed of frequency modulated ramps known as "acoustic textures", where boundaries were created by changing the underlying spectro-temporal statistics. We collected magnetoencephalographic (MEG) data from human volunteers and observed a slow (<1 Hz) post boundary drift in the neuro-magnetic signal. The response evoking this drift signal was source localized close to Heschl's Gyrus (HG) bilaterally, which is in agreement with a previous fMRI study that found HG to be involved in the detection of similar auditory object boundaries. Time-frequency analysis demonstrated suppression in alpha and beta bands that occurred after the drift signal

In vitro characterization of gamma oscillations in the hippocampal formation of the domestic chick

Avian and mammalian brains have evolved independently from each other for about 300 million years. During that time, the hippocampal formation (HF) has diverged in morphology and cytoarchitecture, but seems to have conserved much of its function. It is therefore an open question how seemingly different neural organizations can generate the same function. A prominent feature of the mammalian hippocampus is that it generates different neural oscillations, including the gamma rhythm, which plays an important role in memory processing. In this study, we investigate whether the avian hippocampus also generates gamma oscillations, and whether similar pharmacological mechanisms are involved in this function. We investigated the existence of gamma oscillations in avian HF using in vitro electrophysiology in P0–P12 domestic chick (Gallus gallus domesticus) HF brain slices. Persistent gamma frequency oscillations were induced by the bath application of the cholinergic agonist carbachol, but not by kainate, a glutamate receptor agonist. Similar to other species, carbachol-evoked gamma oscillations were sensitive to GABAA, AMPA/kainate and muscarinic (M1) receptor antagonism. Therefore, similar to mammalian species, muscarinic receptor-activated avian HF gamma oscillations may arise via a pyramidal-interneuron gamma (PING)-based mechanism. Gamma oscillations are most prominent in the ventromedial area of the hippocampal slices, and gamma power is reduced more laterally and dorsally in the HF. We conclude that similar micro-circuitry may exist in the avian and mammalian hippocampal formation, and this is likely to relate to the shared function of the two structures

The representation of time windows in primate auditory cortex

Whether human and nonhuman primates process the temporal dimension of sound similarly remains an open question. We examined the brain basis for the processing of acoustic time windows in rhesus macaques using stimuli simulating the spectrotemporal complexity of vocalizations. We conducted functional magnetic resonance imaging in awake macaques to identify the functional anatomy of response patterns to different time windows. We then contrasted it against the responses to identical stimuli used previously in humans. Despite a similar overall pattern, ranging from the processing of shorter time windows in core areas to longer time windows in lateral belt and parabelt areas, monkeys exhibited lower sensitivity to longer time windows than humans. This difference in neuronal sensitivity might be explained by a specialization of the human brain for processing longer time windows in speech

Auditory figure-ground analysis in rostral belt and parabelt of the macaque monkey

Abstract Segregating the key features of the natural world within crowded visual or sound scenes is a critical aspect of everyday perception. The neurobiological bases for auditory figure-ground segregation are poorly understood. We demonstrate that macaques perceive an acoustic figure-ground stimulus with comparable performance to humans using a neural system that involves high-level auditory cortex, localised to the rostral belt and parabelt