Date of Award
Doctor of Philosophy
Neuroimaging approaches have identified multiple brain sites that are activated in music perception, including the posterior part of the superior temporal gyrus and adjacent perisylvian areas. Yet, to what extent brain signals represent the time course of specific acoustic features in natural auditory stimuli and the detailed spatial and temporal relationship of neural signals that support auditory function are largely unknown. In the two studies documented in this Dissertation, a novel neuroimaging framework is applied to electrophysiological signals recorded from the surface of the brains (electrocorticography (ECoG)) of 8-10 human epileptic subjects while they were listening to a continuous piece of music. This framework allows clinicians and researchers to identify those ECoG features related to the processing of a continuous piece of music and to investigate their spatial, temporal, and causal relationships. The results presented here demonstrate robust stimulus-related modulations in the alpha (8-12 Hz) and high gamma (70-110 Hz) bands at neuroanatomical locations implicated in auditory processing. Specifically, stimulus-related ECoG modulations in the alpha band were identified in areas adjacent to primary auditory cortex, which are known to receive afferent auditory projections from the thalamus. In contrast, stimulus-related ECoG modulations in the high gamma band were identified not only in areas close to primary auditory cortex, but also in other perisylvian areas known to be involved in higher-order auditory processing, and in an unexpected and distinct area in superior premotor cortex. Moreover, ECoG activity in the high gamma band recorded from these cortical areas were observed to be highly correlated with the sound intensity of music. Across all implicated areas, modulations in the high gamma band preceded those in the alpha band by 280 ms, and activity in the high gamma band causally predicted alpha activity, but not vice versa (Granger causality, p < 1e-8). Additionally, detailed analyses using Granger causality identified causal relationships of high gamma activity between distinct locations in early auditory pathways within STG and posterior STG, between posterior STG and inferior frontal cortex, and between STG and the newly identified location in premotor cortex. Evidence suggests that these relationships reflect direct cortico-cortical connections rather than common driving input from subcortical structures such as the thalamus. In summary, analyses showed that ECoG signals encode information about the sound intensity of music, and define the spatial and temporal relationships between music-related brain activity in the alpha and high gamma bands. They provide experimental evidence supporting current theories about the putative mechanisms of alpha and gamma activity, i.e., reflections of thalamo-cortical interactions and local cortical neural activity, respectively. These results are also in agreement with existing functional models of auditory processing and highlight a previously largely unrecognized role of superior premotor cortex in music processing. Results documented in this study make a strong case for the use of ECoG to map brain activity and brain networks related to cognitive, sensory, and motor functions.
Received from ProQuest
Cristhian Mauricio Potes
Potes, Cristhian Mauricio, "Development and Validation of a Novel Framework to Map Brain Function" (2013). Open Access Theses & Dissertations. 1705.