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[Truncated abstract] The mammalian cochlea receives an efferent innervation which originates in the superior olive. Known collectively as the olivocochlear system, this efferent innervation can be divided into lateral and medial systems. While the function of the lateral efferent system in the cochlea is still unknown, previous studies have identified both excitatory and inhibitory changes in sound-evoked and spontaneous cochlear responses attributable to the lateral efferent system. One of the neurotransmitters in the lateral efferents is the catecholamine dopamine, which in the central nervous system is known to exert inhibitory and excitatory effects by activating different receptor subtypes. The first experiments in this thesis were designed to determine if activation or blockade of different dopamine receptor subtypes in the cochlea could lead to both excitatory and inhibitory changes in sound-evoked and spontaneous cochlear responses. Adult guinea pigs were anaesthetised (Nembutal and Hypnorm) and highly specific D1/5 (SKF 38393, SKF 81297, SCH 23390), D2 ((+) PHNO, L 741, 626) and D3 (PD 128907, U 99194A) receptor agonists and antagonists were perfused through the cochlea for 15 minutes. Sound-evoked (compound action potential, summating potential, cochlear microphonic) and spontaneous cochlear responses were recorded before and after perfusion. Remarkably, activating or blocking D1/5 or D2 receptor subtypes resulted in the suppression of CAP amplitudes. These findings are paradoxical as the agonist data suggest that the D1/5 and D2 receptor subtypes are inhibitory, but the antagonist perfusions suggest that these receptors are excitatory. We propose that the presence of an agonist induces a process of receptor desensitisation which would elicit changes akin to receptor antagonism. If this is indeed the case then our agonist findings are spurious and require further interpretation. ... The suppression of the cochlear microphonic suggests that dopamine recepto, Thesis (Ph.D.)--University of Western Australia, 2009

Summary: This dissertation examined the neural correlates of auditory perception, attention and expectation in three experiments. Experiment 1 analyzed neural correlates of auditory perception and expectation in an electroencephalography (EEG) experiment using a temporally perturbed metronome to establish an expectation for auditory events, then violate and reestablish that expectation. High frequency evoked (phase-locked) gamma band activity (GBA) was observed to follow the onset of tones whereas induced (nonphase- locked) GBA reached maximum power simultaneously with the occurrence oftone onset. Moreover, the latency of induced GBA was perturbed after an expectancy violation and relaxed back into synchrony as the expectation was reestablished. Experiment 2 was a methodological study to compare two functional magnetic resonance imaging (fMRJ) scanning techniques and assess their influence on auditory processing. Subjects passively listened to isochronous tone sequences at three rates while sparse or continuous scanning was employed. Sparse and continuous scanning was observed to yield comparable fMRI data, however, continuous scanner notse was observed to perturb known EEG evoked response potentials. Moreover, high frequency evoked activity, as identified by spectral analysis, was attenuated in the presence of continuous fMRl noise. Experiment 3 was conducted to study auditory expectancy and attention. First, subjects were tested behaviorally to determine their ability to tap the beat of ten highly syncopated patterns. Subjects were asked to return for one EEG and one fMRl session. In these sessions, they were instructed to attend to a syncopated pattern, mentally rehearse the pattern, and then reproduce the pattern. During the control condition, subjects heard the auditory patterns, however, they were instructed to study a list of words, remember the words during the retention interval, and then recall as many words as possible. Brain activity was localized to fro, 2006, Includes bibliography., Degree granted: Dissertation (Ph.D.)--Florida Atlantic University, 2006., Collection: FAU Electronic Theses and Dissertations Collection, Charles E. Schmidt College of Science

[Truncated abstract] The cochlea presumably possesses a number of regulatory mechanisms to maintain cochlear sensitivity in the face of disturbances to its function. Evidence for such mechanisms can be found in the time-course of the recovery of CAP thresholds during experimental manipulations, and in observations of slow oscillations in cochlear micromechanics following exposure to low-frequency tones (the “bounce phenomenon”) and other perturbations. To increase our understanding of these oscillatory processes within the cochlea, and OHCs in particular, investigations into cochlear regulation were carried out using a combination of mathematical modelling of the ionic and mechanical interactions likely to exist within the OHCs, and electrophysiological experiments conducted in guinea pigs. The electrophysiological experiments consisted of electrocochleographic recordings and, in some cases, measurement of otoacoustic emissions, during a variety of experimental perturbations, including the application of force to the cochlear wall, exposure to very-low-frequency tones, injection of direct current into scala tympani, and intracochlear perfusions of artificial perilymph containing altered concentrations of potassium, sodium, and sucrose. To obtain a panoramic view of cochlear regulation under these conditions, software was written to enable the interleaved and near-simultaneous measurement of multiple indicators of cochlear function, including the compound action potential (CAP) threshold, amplitude and waveshape at multiple frequencies, the OHC transfer curves derived from low-frequency cochlear microphonic (CM) waveforms, distortion-product otoacoustic emissions (DPOAEs), the spectrum of the round-window neural noise (SNN), and the endocochlear potential (EP). ... The mathematical model we have developed provided a physiologically-plausible and internally-consistent explanation for the time-courses of the cochlear changes observed during a number of diff, Thesis (M.Clin.Audiol./Ph.D.)--University of Western Australia, 2005

Summary: The experiments in this dissertation were designed to produce a systematic characterization of the neuroelectric and neuromagnetic correlates of isochronous tone stimulation and simple rhythmic movements over a broad range of rates. The goal was to determine how the cortical representation of rhythm changes with rate, which would provide insight into known rate-dependent differences in perceptual and coordinative abilities. Fundamental transitions in the composition of the auditory and motor responses were hypothesized to occur within the parameter ranges studied here, including the attenuation of major response components and a shift from discrete transient activity at low rates to continuous steady-state activity at high rates. The auditory responses were studied in separate electroencephalography (EEG) and magnetoencephalography (MEG) experiments with stimulation rates ranging from 0.5 to 8Hz. In both studies, a transition from a transient to a continuous steady-state representation of the tone sequence occurred near 2Hz. In addition, an N1m component of the transient responses disappeared at rates near 8Hz, which may indicate the border beyond which tones are no longer distinct since the response is known to be an index of novelty in the auditory environment. Moreover, in a result important for understanding how evoked activity interacts with activity already present in the cortex, the phase of ongoing 40Hz rhythms is shown to affect the amplitude of the auditory evoked 40Hz response. Rhythmic finger movement was studied using a continuation paradigm in two EEG and MEG experiments at movement rates from 0.5 to 2.5Hz. Major findings included the disappearance of activity associated with movement planning and initiation at rates above 1Hz, suggesting a transition into a steady-state motor response in which there is less direct control of individual movements by the cortex. In addition, the neural correlates of synchronization and continuation were compare, Thesis (Ph.D.)--Florida Atlantic University, 2003.

Summary: The P300 component of the auditory event-related potential waveform was investigated in control children and two groups of HIV-infected children (asymptomatic and symptomatic), aged five to seven, under combinations of two interstimulus interval (ISI) rates (1 and 2 sec) and two target probability rates (.2 and.5). No group differences were found under the different combinations of ISI and target probability, for either P3a amplitude and latency, or P3b amplitude and latency. Although the present study was not able to distinguish between-groups by manipulating the target presentation rate, there were several within-group effects on P3a latency that were dependant upon the specific clinical or control group. The general findings for the study were that as the target presentation rates increased, P3a latencies increased., Thesis (M.A.)--Florida Atlantic University, 1997.

Summary: The P300 component of the auditory event-related potential waveform was investigated in two groups of HIV positive children (symptomatic and asymptomatic) who were compared to HIV negative relatives. Results demonstrated the expected increased latencies of the P3b component in the symptomatic group, but no P3a latency differences. Amplitude measures of P3a and P3b showed no group differences. However, the symptomatic children had relatively larger P3a amplitudes whereas the asymptomatic children had a larger P3b. Difference measures (P3b minus P3a) revealed a significant difference across groups. Discussion focuses on three interrelated issues: (1) the cognitive mechanisms which could account for the current findings, (2) the relevance of a symptomatic/asymptomatic distinction and a P3a/P3b distinction for the purposes of clinical research, and (3) the clinical implications of these findings., Collection: FAU Electronic Theses and Dissertations Collection, Thesis (M.A.)--Florida Atlantic University, 1996., Charles E. Schmidt College of Science

This research investigated the effects of age, sex, male vs female voice, and unfamiliar vs familiar voice upon the infants body movements. The sample consisted of 40 middle-class infants, balanced according to sex, at four age levels -- 3, 6, 9, 12 months. Four tape-recorded stimulus conditions -- mother's voice, father's voice, female stranger’s voice, and male stranger's voice -- were presented to each infant. The body movements of the infants were recorded at one frame per second by an 8mm. camera. Analyses of variance were performed to determine any differences among the four stimulus conditions and control periods. The 12-month-old infants showed more activity to the father's voice than to the male stranger's voice or to the mother's voice. These subjects also showed more activity to the female stranger's voice than to the male stranger's voice. Female subjects were more active than male subjects to the unfamiliar voices on Trial 1. On Trial 2 females showed greater activity than males to the familiar voice. Females exhibited greater activity than males overall. Males showed greater activity than females to the cessation of the female voice and to the initiation of their father's voice. Results were discussed in terms of the infant's development as affected by sex of the infant and the cross-over effect found by Friedlander (1970).

The purpose of the present investigation was to examine the two major theoretical explanations for subject-initiated timeout responding during a successive discrimination. Stimulus change theorists suggest that the perceptible changes in the stimulus configuration as a consequence of timeout responding serve to reinforce that responding. Escape theorists maintain that timeout responses are emitted in order to eliminate specific stimuli that have acquired aversive characteristics. Different consequences for a timeout response, varying in the amount of visual and auditory stimulus change, were arranged for six groups comprised of three pigeons each. Two tones of differing frequencies were used as stimuli in the separate components of the multiple discrimination schedule. In the S+ component, pecks on a key were required in order to obtain reinforcement; in the S- component, responses on a foot treadle were required for reinforcement. The timeout key was introduced once the auditory discrimination was well established. Timeout responses were first recorded during a baseline phase. Experimental manipulations included an extinction phase which involved eliminating reinforcement for treadle responding. This procedure was used in an attempt to increase the aversiveness of the S-. A second procedure to enhance the aversiveness of the S- was the application of shock contingent upon treadle pressing during S-. The final procedure sought to extinguish timeout responding by the elimination of its consequences. Timeout responses during baseline, treadle extinction, shock, and timeout extinction were compared. Key-peck response rates were also examined.

Sensory gating is a mechanism by which irrelevant sensory information is filtered in the brain, enabling efficient information processing. The auditory conditioning-test paradigm, an index of sensory gating, measures the reduction in the auditory-evoked response (AER) produced by a test stimulus following an initial conditioning stimulus. Schizophrenic patients demonstrate a lack of attenuation of the test response measured in the P50 component of the cortical auditory-evoked potential. The N2/N40 auditory-evoked potential recorded from rat hippocampus is considered homologous to the human P50 wave. Altered glutamatergic neurotransmission and the endocannabinoid system have been implicated in the pathogenesis of schizophrenia with structural and functional abnormalities in the hippocampus and the medial prefrontal cortex (mPFC). The current study examined sensory gating using auditory conditioning-test paradigm in the dentate gyrus (DG) and the CA3 region of the hippocampus and in the medial prefrontal cortex (mPFC) before and after administration of N-Methyl- D-Aspartate (NMDA) receptor antagonist phencyclidine (PCP; 1 mg/kg, i.p) or the cannabinoid agonist WIN55,212-2 (1.2mg/kg, i.p). Electrophysiological recordings were conducted in Lister hooded rats, under isoflurane anaesthesia, during the presentation of paired auditory stimuli. Extracellular action potential spikes and local field potentials (LFPs) were recorded simultaneously using multi-electrode arrays and the effects of acute administration of PCP (1 mg/kg, i.p) or WIN55,212-2 (1.2mg/kg, i.p) was determined. Gating of the N2 wave was assessed by measuring the ratio of the Test to Conditioning response amplitude (T/C ratio); T/C ratio ≤ 50% was indicative of gating. Robust auditory-evoked potentials were recorded from the hippocampal CA3 and DG regions and the mPFC; some rats demonstrated auditory gating while others failed to. In rats that demonstrated gating of N2, mPFC showed higher T/C ratios and shor