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Thesis (Ph. D.)--University of Hong Kong, 2001. / Includes bibliographical references (leaves 118-130).

Thesis (Ph. D.)--University of Queensland, 2002. / Includes bibliographical references.

published_or_final_version / Human Performance / Doctoral / Doctor of Philosophy

Motor learning is widely investigated in the literature on sports and rehabilitation sciences. In recent years, researchers have begun to apply general motor learning principles to voice motor learning. This study investigated the effects of relative frequency (100% feedback versus 50% feedback versus 0% feedback) of augmented vibration feedback on the acquisition of resonant voice in a motor learning task. Thirty adults and 30 children with normal voice were randomly assigned to three groups of different relative frequencies of feedback: 100%, 50% and 0% feedback. During resonant voice training, participants were taught how to read aloud nasal nonsense consonant vowel (CV) syllables and short phrases with resonant voice. Vibration feedback using piezoelectric accelerometers placed at the nasal bridge was provided for participants. Participants in the 100% feedback group received vibration feedback after the production of every training stimulus. Participants in the 50% feedback group received vibration feedback after the production of every two training stimuli. Participants in the 0% feedback group received no vibration feedback during the training sessions. Motor learning and generalization were assessed using accelerometric vibrations detected at baseline (before training), during training, retention and transfer (one week after completing the training). With respect to the adult participants, vibration feedback presented at frequencies of 100%, 50% and even at 0% was effective in facilitating the acquisition of resonant voice. Generalization of resonant voice production to untrained short phrases was also evidenced. No significant time (time phase) by group (different relative frequency of feedback) interaction effect was shown on three groups of relative frequencies of feedback on learning or generalization in the adult group. With respect to the child participants, significant time effect was observed in most of the trained stimuli and untrained stimuli. Significant time (time phase) by group (different relative frequency of feedback) interaction effect was noted across three relative frequencies of feedback groups. The results demonstrated that the greatest increment in accelerometric vibrations occurred in the 100% feedback group, followed by 50% feedback group. The group which received 0% feedback had the least improvement on acquiring resonant voice. The present study demonstrated that there were learning differences in acquiring resonant voice between adults and children. Adults did not require as much feedback during the acquisition of resonant voice when compared to children. Children required more feedback than adults in order to facilitate their learning. The differences in learning of this voice task between adults and children may shed light on later voice motor learning studies. The provision of relative frequency of feedback may need to be adjusted when working with different age groups in both populations. / published_or_final_version / Speech and Hearing Sciences / Master / Master of Philosophy

Motor coordination and motor learning processes are vital for animal survival. Both functions require the participation of cerebellar Purkinje neurons, which are the integrating center as they receive both excitatory and inhibitory inputs from various neurons and send out the sole inhibitory output of cerebellar cortex. Secretin, a classical peptide hormone, has been shown previously as a retrograde factor to up-regulate GABAergic inhibitory transmission on basket-Purkinje cell synapses in rats. In behavioral perspectives, there have been studies reporting changes of motor function, anxiety level, spatial memory and social interactions after application or deprivation of secretin. Based on current knowledge, secretin is hypothesized to modulate mouse motor coordination and motor learning behaviors through its effects on Purkinje neurons. To test this hypothesis, a Purkinje cell-specific secretin gene knockout moue model (Pur-Sct-/-) has been developed using Cre-Loxp recombination technique. Using immunohistochemical staining and in situ hybridization, secretin expression has been shown to be specifically eliminated in Purkinje neurons. Pur-Sct-/- mice had intact general motor ability and anxiety level in an open field. Neuromuscular strength of Pur-Sct-/-mice was impaired compared to wild type littermates in wire hanging test. Motor coordination ability was compromised as shown by vertical climbing and rotarod tasks. Further tests using repeated training on rotarod suggested impaired motor learning ability. All these behavioral changes have also been observed in secretin-null (Sct-/-) and secretin receptor-null (Sctr-/-) mice, suggesting that normal motor control and motor learning depend on integrity of secretin-secretin receptor axis in cerebellum. Postnatal neural developmental study revealed later occurrence of two motor reflexes –righting and negative geotaxis –in Pur-Sct-/-juveniles. Motor deficits in rotarod tasks persisted across mice aging from month 2 to month 9 while wire hanging impairments occurred early in Pur-Sct-/-. Secretin thus may also play a role in early postnatal cerebellar development and neural protection in mature cerebellum. To investigate the underlying mechanism, Purkinje neurons were voltage-clamped for current recording. Secretin potentiated both spontaneous and miniature inhibitory postsynaptic currents (sIPSC and mIPSC) in wild type Purkinje cells. InPur-Sct-/- and Sctr-/- mice, basal levels of sIPSC and mIPSC were significantly decreased, suggesting a role of endogenous secretin in maintaining cerebellar inhibitory transmission. The exogenous application of secretin restored IPSC in Pur-Sct-/- but not in Sctr-/- mice to comparable wild type levels, indicating the specific binding of Purkinje-derived secretin and secretin receptor underlyingthis inhibitory potentiation. In summary, secretin released in Purkinje neurons has significant role in maintaining normal motor coordination and motor learning functions. Secretin also participates in the facilitation of inhibitory transmission on interneuron-Purkinje synapses. This inhibitory potentiation is likely to coordinate motor behaviors, although further in vivo studies are required for substantiation. This study has demonstrated the function of secretin in modulating mouse motor coordination and motor learning behaviors, and in Purkinje neuron inhibitory transmission, suggesting its potential usage in drug development against cerebellar-related motor disorders. / published_or_final_version / Biological Sciences / Doctoral / Doctor of Philosophy

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