Yan, JunXiong, Colin2018-01-192018-01-192017-12-18Xiong, C. (2017) Thalamocortical forward modulation in the auditory cortex (Doctoral thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca.http://hdl.handle.net/1880/106288Auditory masking is a psychoacoustic phenomenon with strong physiological correlates in the central auditory system such as in the primary auditory cortex. The caveat of conventional two-tone paradigms in testing the neurophysiology of forward masking (i.e., forward suppression) is that tones are processed at every auditory center, meaning the recorded activities do not represent the pure characteristics of the recorded site. Thus, there is a great need for a specialized protocol to tease out and uncover the pure suppression characteristics at each site, particularly the thalamocortical system - the primary sensory input to the auditory cortex. This study implemented an in vivo thalamocortical model in C57 mice along with common electrophysiological techniques to examine the pure role of the thalamocortical system in cortical forward modulation; focal electrical stimulation (ES) of the ventral division of the medial geniculate body (MGBv, ESMGBv) substituted for one or both tones of the conventional two-tone stimulus paradigm. With this ameliorative approach, I demonstrated that ESMGBv facilitated succeeding ESMGBv while suppressing succeeding tones. This suggests that the default state of the thalamocortical system is facilitation while maintaining the capability of forward suppression through heterosynaptic thalamocortical inputs. Forward suppression of tones by ESMGBv was comparatively weaker than forward suppression of ESMGBv by tone stimulus. The period of complete suppression in the cortex for all stimuli was approximately 100 ms. Furthermore, the thalamocortical forward suppression spectral areas were found to be mirrored images of the receptive fields of recorded cortical neurons. Together, these data suggest that thalamocortical forward facilitation and suppression in the recorded cortical neurons can be accomplished without the involvement of complex cortical circuitry. This idea is further supported by the finding that cortical GABAA inhibition was not required for the thalamocortical forward suppression. Additionally, it was shown that two-tone stimulus resulted in complete MGBv suppression for approximately 75 ms. This means that the thalamus provides the cortex with a 75 ms “silent window” during which cortical mechanisms, such as GABAA inhibition, are not necessary for forward suppression. Following careful investigation of literature, a novel "single-cell” model appears to account for thalamocortical forward modulation.  enIn consideration of Library and Archives Canada making my thesis available to interested persons, I, Colin Xiong hereby grant a non-exclusive license, for the full term of copyright protection, to Library and Archives Canada: to preserve, perform, produce, reproduce, translate theses and dissertations in any format, and to make available in print or online by telecommunication to the public for non-commercial purposes. I undertake to submit my thesis, through my university, to Library and Archives Canada. Any abstract submitted with the thesis will be considered to form part of the thesis. I represent and promise that my thesis is my original work, does not infringe any rights of others, and that I have the right to make the grant conferred by this non-exclusive license. If third party copyrighted material was included in my thesis for which, under the terms of the Copyright Act, written permission from the copyright owners is required I have obtained such permission from the copyright owners to do the acts mentioned in paragraph (a) above for the full term of copyright protection. I retain copyright ownership and moral rights in my thesis, and may deal with the copyright in my thesis, in any way consistent with rights granted by me to Library and Archives Canada in this non-exclusive licence. I further promise to inform any person to whom I may hereafter assign or license my copyright in my thesis of the rights granted by me to Library and Archives Canada in this non-exclusive licence.single-unit model of thalamocortical forward modulationauditory temporal processingin vivo electrophysiologyauditory forward maskingthalamocortical systemEducation--Sciencesdoctoral thesis10.11575/PRISM/5369