The Temporal-spatial Features Of Brain Imaging Signals In Patients With Autism Spectrum Disorder

Autism spectrum disorder(ASD)could severely affect the social and cognitive abilities of patients,thus it is necessary to understand its neural mechanisms.Compared to traditional research tools which are based questionnaires and behavioral observation,modern neuroimaging techniques provide objective measures in order to detect underlying neural mechanisms and diagnose this disease.However,in our opinions,previous studies focused on the neural mechanisms of ASD at least have the following limitations:(1)the test-retest reliability of used measures may be poor;(2)the spatial information and temporal information of brain imaging signals were investigated in isolation;(3)existing technologies may provide biased estimation;(4)lack of comparison of results from different neuroimaging techniques.In order to solve these limitations,the f MRI/f NIRS technique which could measure the slow hemodynamics information and the EEG technique which could detect the fast electrophysiological activity were applied to investigate the temporal-spatial features of brain activities in the following three levels: the dynamical behavior of instantaneous amplitudes of nodes,the spatial organization of nodes within certain brain networks,the dynamical behavior of switching between large-scale neural networks.During the investigation of the first level temporal-spatial features of brain activities(i.e.,the dynamical behavior of instantaneous amplitudes of nodes),we studied the test-retest reliability of detrended fluctuation analysis(DFA)which could assess the long-range temporal correlations(LRTCs)of neuronal oscillations of certain brain regions firstly(Experiment 1A),which indicated that DFA has moderate reliability.Then,DFA was used to investigate the dynamical behavior of instantaneous amplitudes of signals of ASD patients collected from different neuroimaging techniques(Experiment 2A,Experiment 3A and Experiment 4A).The DFA on resting-state f MRI signals found that compared to the typical developing(TD)group,the DFA exponents of signals from four prefrontal regions within default mode network(DMN)were significantly lower in ASD group.The DFA on f NIRS signals found that:(1)the DFA exponent of f NIRS signals were attenuated in children with ASD;(2)the DFA exponent of f NIRS signals increased with age in TD children,whereas the DFA exponent of f NIRS signals decreased with age in ASD children;(3)the DFA exponent of f NIRS signals was negatively correlated with autistic symptom severity.The DFA on resting-state EEG signals found that the DFA exponents of neural activities of regions within DMN,mirror neuron system(MNS)and salience network(SN)were significantly lower in ASD patients.The results from all these three neuroimaging signals suggest that the autistic brain is associated with highly volatile,random and irregular states of neuronal oscillations.During the investigation of the second level temporal-spatial features of brain activities(i.e.,the spatial organization of nodes),firstly we studied the test-retest reliability of spatial complexity techniques which could assess the spatial organization pattern within certain large-scale brain networks.It revealed that the reliability of unbiased,normalized entropy based normalized spatial complexity was moderate and was not lower than the traditionally omega complexity.Then,normalized spatial complexity was used to investigate the spatial organization of nodes of signals collected from different neuroimaging techniques(Experiment 2B,Experiment 3B and Experiment 4B).The resting-state f MRI signals analysis found that(1)compared to TD group,the spatial complexity of DMN was significantly higher in ASD group,which suggested that the internal information exchange within DMN was aberrant in ASD patients;(2)compared to TD group,the contribution of anterior medial prefrontal cortex in reducing the spatial complexity of DMN was significantly reduced in ASD group,which may lead to lower efficiency in self-related information processing,and finally affect their abilities in social cognition and communication.The f NIRS signals analysis found that compared to TD group,the regional spatial complexity of bilateral prefrontal cortices was significantly higher in ASD group.Moreover,the contribution of bilateral prefrontal cortices in reducing the global spatial complexity was smaller in ASD group.These results suggested that in children with ASD,the efficiency of information communication was poor,and the link between prefrontal cortices and other regions was also aberrant.The resting-state EEG signals analysis revealed that in ASD groups,the contribution of MNS related regions in reducing whole-brain spatial complexity was lower,whereas the contribution of visual processing areas was higher,which may result in lower efficiency in processing social information,and higher efficiency in visual processing.Taken together,the results from f MRI/f NIRS/EEG signals suggested that the spatial organization of brain regions is aberrant in patients with ASD.During the investigation of the third level temporal-spatial features of brain activities(i.e.,the dynamical behavior of switching between large-scale neural networks),the EEG microstate analysis was conducted on the resting-state EEG signals(Experiment 4C).We found that the patients with ASD spent less time in processing verb information and self-related representation,whereas spent more time in visual processing.The activities in ventral attention network were also aberrant.In the above studies,we investigated the test-retest reliability of brain imaging techniques,and our understanding of ASD related mechanisms was broadened.We found the following results.Firstly,autistic brain is associated with highly volatile,random and irregular states of neuronal oscillations,which is mainly occurred in autistic symptom related brain areas.Secondly,the information communication efficiency between autistic symptom related brain areas and other areas is much lower in ASD group.Moreover,certain areas which play crucial roles in social information processing are less important in spatial organization of cortical regions.Lastly,the temporal dynamics of large-scale brain networks is abnormal in patients with ASD.