Single trial analysis of auditory fMRI data
Zhu, Xi 1984-
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This research is concerned with functional magnetic resonance imaging (fMRI) of the brain during auditory information processing. The main focus is the exploration of the brain areas involved in sensory gating, i.e., the ability of the central nervous system (CNS) to inhibit or modulate its sensitivity to incoming irrelevant sensory auditory input, as measured using a paired auditory stimulus paradigm. It is well-known that the brain’s responses are variable from trial-to-trial. This calls into question the current practice of using a single, representative response function (canonical HRF) to model fMRI data. Therefore, a correlation-based method was developed to deal with the variability of the HRF in response to repeated presentation of identical auditory stimuli. The goal of the analysis technique is to identify ‘active’ trials among all single trials. We verified that this correlation-based method can find significant differences between brain areas and brain states in actual fMRI data. Second, we determined if the cluster-based method can improve conventional fMRI analysis by exploring the brain regions involved in processing single stimuli using both methods. Data was collected from 14 healthy subjects listening to auditory tones. Our results indicated that by focusing on ‘active’ trials only, as determined by the clustering method, we obtained better statistical maps and that the sensitivity of the fMRI data analysis was increased through the identification of activated areas. The results indicated that the superior temporal gyrus (STG), inferior frontal gyrus (IFG), dorsolateral prefrontal cortex (DLPFC), and thalamus (THA) were involved in auditory information processing and sensory gating in general. While the conventional analysis could not find any regions involved in gating, the correlation-based method confirmed the involvement of bilateral STG, right THA and left DLPFC in sensory gating. Specifically, the right THA relays the sensory signal to the STG, with the bilateral STG involved in the first stage of auditory processing and the left DLPFC involved in the inhibitory circuit of sensory gating processing. Our findings suggest that the correlation-based single trial analysis method provides quantitative assessment of the neuronal origins of the sensory gating. It also improves the current fMRI analysis technique.