EEG-fMRI Fusion And Its Application In Auditory Research

EEG and fMRI are common neuroimaging tools.EEG instruments detect neural activity with electrodes attaching on the scalp while fMRI bases on blood oxygen level dependent(BOLD)to detect neural activity.When local neural activity increases,the BOLD activity increases and that's the principle of fMRI to image neural activity.Both EEG and FMRI have their merits and demerits.EEG has high temporal resolution while the source localization of EEG is essentially an ill-posed problem.On the contrary,the mm-scale space resolution of fMRI allows localization of both superficial and deep sources of activity,although,its temporal resolution is poor because of the slow nature of the BOLD response and the low sampling rate required for the acquisition of the whole-brain fMRI data.Combining EEG and fMRI can potentially provide a more sensitive measure of neuronal activity based on the complementarity between their temporal and spatial resolutions;the origin of their sources;and the potential capability of fMRI to locate EEG generators,while avoiding the EEG inverse problem.However,how to fuse EEG and fMRI is indeed a challenge.The state of the brain inevitably ebb and flow over time.Even to the same stimulus,the brain can response different and this phenomenon is called cross-trial variability.Cross-trial variability is a bridge which connect the EEG and fMRI because this variability can be detected both by EEG and fMRI.Taking advantage of EEG and fMRI may generate a method with both high temporal and high spatial resolution.In this paper,we chose appropriate feature according to the situation to fuse EEG and fMRI and used this method to study three topics in auditory field.The topics are as follows:1).The dynamic process of pure tone processing.Pure tone refers to single frequency tone,the sounds in nature are consist of pure tones with different frequencies.Pure tone is the most basic and simplest sound and often used as stimulus in auditory research.So far,although there are a lot of research about processing of pure tone,however,its dynamic processing process is still unclear.In this paper,we used EEG-fMRI fusion method to study the process of pure tone processing.We found that neural responses responding to pure tone perception are spatially along the auditory pathway and temporally divided into three stages:(1)the early stage(around 30 ms),wherein activation occurs in the midbrain,which constitutes a part of the low level auditory pathway;(2)the middle stage(100~200 ms),wherein correlates were found in areas associated with the posterodorsal auditory pathway,including the primary auditory cortex and the motor cortex;(3)the late stage(around 400 ms),wherein correlation was found in the motor cortex.This indicates that trial-by-trial variation in neural activity in the P1,N1,P2,and N4 components reflects the sequential engagement of low-and high-level parts of the auditory pathway for pure tone processing.Our results demonstrate that during simple pure tone listening tasks,regions associated with the auditory pathway transiently correlate with trial-to-trial variability of the EEG amplitude,and they do so on a millisecond timescale with a distinct temporal ordering.2).Neuronal entrainment to beat and meter.Rhythm perception refers to the mental interpretation of rhythm by a listener.Musical rhythm perception typically involves two steps: beat extraction and metrical structure assignment(meter perception).The entrainment theories propose that different neuronal oscillations entrain to different levels of metrical structure in the rhythm(e.g.,beat and meter)and thereby form a representation of the rhythm in the mind.Thus,neuronal populations that entrain to beat and meter should theoretically be different.However,although entrainment theories have been supported by many studies,the neuronal populations that entrain to beat and meter remain largely unknown.In this study,we used a paradigm to induce neuronal entrainment to beat and meter and obtained images of the neuronal populations with an electroencephalogram functional magnetic resonance imaging(EEG-fMRI)fusion method.We observed that some neuronal populations,including the bilateral putamen,bilateral caudate,left thalamus,and supplementary motor area(SMA),entrain to both beat and meter.We also observed that the bilateral putamen entrains more to meter and the SMA entrains more to beat.Our results suggest that the bilateral putamen plays an important role in meter perception.3).The generation process of auditory mismatch negativity.The MMN is a change-specific component of the event-related brain potential(ERP).This component is elicited when a repeating stimulus(termed the standard stimulus)is occasionally exchanged by a different stimulus(termed the deviant stimulus).The MMN is a negative difference waveform with a frontocentral scalp distribution peaking between 100 and 200 ms.Although research on the mismatch negativity(MMN)has been ongoing for 40 years,the generation process of the MMN remains largely unknown.In this study,we used a single-trial EEG-fMRI coupling method which can analyse neural activity with both high temporal and high spatial resolution and thus assess the generation process of the MMN.We elicited the MMN with an auditory oddball paradigm while recording simultaneous EEG and fMRI.We divided the MMN into five equal-durational phases.Utilizing the single-trial variability of the MMN,we analysed the neural generators of the five phases,thereby determining the spatiotemporal generation process of the MMN.We found two distinct bottom-up prediction error propagations: first from the auditory cortex to the motor areas and then from the auditory cortex to the inferior frontal gyrus(IFG).Our results support the regularity-violation hypothesis of MMN generation.Above all,we used across-trial EEG-fMRI to study three difficult topics in auditory field which are hard to study due to the limitation of EEG or fMRI.Our method worked well and achieved good results.The successful usage of EEG-fMRI in auditory research proved that this method can analysis neural activity with both high temporal and high spatial resolution,indicating the great application and promotion value of this method.