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Thesis (M. Phil.)--University of Hong Kong, 1999. / Includes bibliographical references (leaves 87-100).

Thesis (Ph. D.)--Oklahoma State University, 2005. / Vita. Includes bibliographical references (p.132-145).

Thesis (M.S.)--University of Wisconsin--Madison, 1981. / Typescript. eContent provider-neutral record in process. Description based on print version record.

In this thesis the in vitro release of immunoreactive CCK₈ (iCCK₈) from rat central nervous system preparations and the regulation of this release have been studied. Rat brain was dissected into the following regions; hypothalamus, cerebral cortex, striatum and thalamus, according to the method of Brownstein, Arimura, Sato et. al. (1975). CCK₈ was found to be distributed throughout these regions (range of 9 - 300 pmoles), with the highest concentration in cortex (300 pmol). In addition, low levels (range 9 - 30 pmoles) of CCK₈ were found in spinal cord, brain stem and cerebellum, in agreement with other workers. Immunohistochemical techniques have demonstrated CCK-like immunoreactivity in nerve cell bodies and fibres throughout brain, particularly in the cortex. Subcellular fractionation of rat brain was used to study the subcellular localisation of CCK. Tissue was homogenised to shear off nerve terminals (synaptosomes) which were purified and used to study the release of the peptide from hypothalamic and extrahypothalamic nerve endings.

The primary somatosensory cortex (SI) and primary motor cortex (M1) receive somatosensory afferent input to influence motor hand circuitry and control. Much of the literature has investigated this relationship extensively using animal models. In contrast, much of these relationships and neural mechanisms are still not well understood in humans. The present work investigated homosynaptic and hetersynaptic protocol’s modulatory effects on SI and M1 sensorimotor circuitry. Experiment 1 used the homosynaptic protocol continuous theta-burst stimulation (cTBS) over SI and M1 and measured motor evoked potentials (MEP) and short-latency afferent inhibition (SAI). CTBS over M1 suppressed MEPs and did not alter SAI. In contrast, cTBS over SI facilitated MEPs and decreased median and digital nerve evoked SAI. Experiment 2 used the heterosynaptic protocol rapid-rate paired associative stimulation (rPAS) on SI and M1. SAI and MEPs were measured to investigate the sensorimotor changes following rPAS. Results indicated minimal decreases in SAI but increases in MEPs following SI rPAS. However, M1 rPAS lead to significant reductions in SAI and increased MEPs. The findings from this thesis highlight the selective modulation of sensorimotor circuitry through the use of various stimulation protocols. / Thesis / Master of Science in Kinesiology

Eight experiments are described exploring the consequences of training eye-movements. Training is related to Findlay & Walker’s (1999) model of saccade generation, and consists of strategies for visual search and stimulus discrimination. These two components are separated in an effort to link training to the hypothesised Move and Fixate centres, respectively, within Findlay & Walker’s framework. Training directed towards the Move centre thus consistently improved visual search, and in Experiments 1-4 it was also shown that training directed towards the Fixate centre could further improve performance (in terms of target response discrimination) in an additive way over Move Training alone. Experiments 5-7 investigated the idea that training which promotes activity in the Move centre, independently, may actually be detrimental. This hypothesis draws upon the reciprocal inhibitory relationship between the Move and Fixate centres described by Findlay & Walker: training people where to look may increase activity in the Move centre and consequently hinder information processing during fixational eye movements, owing to an associated diminution of activity in the Fixate centre. Partial support for this conclusion was found. When training encouraged saccades away from a task-relevant centrally located stimulus, towards a visible saccade target in the periphery, there was evidence of premature disengagement when fixating, causing sub-optimal processing of the central stimulus in the first instance (Exp. 5). However, this effect was sensitive to changes in task (Exps. 6 & 7). This may explain why Move training did not encumber performance in a driving task (Exp. 8). Nevertheless, the findings reported herein have implications for training eye-movements in applied settings, because they suggest combined eye movement training directed towards the Move and Fixate centres in concert may produce cumulative performance gains, and offset detection failures associated with a sole emphasis on visual scanning.

The auditory system needs to be able to analyse complex acoustic waveforms. Many ecologically relevant sounds, for example speech and animal calls, vary over time. This thesis investigates how the auditory system processes sounds that occur sequentially. The focus is on how the responses of neurons in the primary auditory cortex ‘adapt’ when there are two or more tones. When two sounds are presented in quick succession, the neural response to the second sound can decrease relative to when it is presented alone. Previous two-tone experiments have not determined whether the frequency tuning of cortical suppression was determined by the receptive field of the neuron or the exact relationship between the frequencies of the two tones. In the first experiment, it is shown that forward suppression does depend on the relationship between the two tones. This confirmed that cortical forward suppression is ‘frequency specific’ at the shortest possible timescale. Sequences of interleaved tones with two different frequencies have been used to investigate the perceptual grouping of sequential sounds. A neural correlate of this auditory streaming has been demonstrated in awake monkeys, birds and bats. The second experiment investigates the responses of neurons in the primary auditory cortex of anaesthetised guinea pigs to alternating tone sequences. The responses are generally consistent with awake recordings, though adaptation was more rapid and at fast rates, responses were often poorly synchronised to the tones. In the third experiment, the way in which responses to tone sequences build up is investigated by varying the number of tones that are presented before a probe tone. The suppression that is observed is again strongest when the frequency of the two tones is similar. However, the frequencies to which a neuron preferentially responds remain irrespective of the frequency and number of preceding tones. This implies that through frequency specific adaptation neurons become more selective to their preferred stimuli in the presence of a preceding stimulus.

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