Neural Circuit Of Audiovisual Integration And The Impairment In Patients With Affective Disorder

During daily life,integrating multimodal information(like speech or emotional inform)into a unified and stabilized perception is a fundamental human capacity,which is called multisensory integration.Such integration of multiple sensory inputs often relies on auditory and visual channel.The abnormal activity of specific neural circuits during audiovisual speech and emotion processing in a variety of mental diseases has been extensively investigated in previous studies.However,there remains several problems in previous studies: Firstly,Mc Gurk effect is often regarded as the measurement of audiovisual integration ability.Despite being a remarkable phenomenon,the illusory percept does not occur with the same degree of susceptibility.But how does this difference manifest itself in the audiovisual integration loop;Secondly,unimodal emotional processing in patients with affective disorder has been widely revealed.But,unimodality experiments cannot adequately simulate the natural settings of emotion perception in real life.It is necessary to investigate the neural mechanism during multisensory emotion processing in patients by using audiovisual emotional stimuli;Thirdly,although patients have abnormalities in audiovisual emotional integration in few experimental studies using multi-channel emotional stimuli,the neural basis of potentially negative biased emotional processing of multimodal inputs remains unclear.Therefore,combined with functional magnetic resonance imaging(f MRI)technology and brain activation and network analysis,dissertation aims to explore the neural mechanism of audiovisual integration in patients with affective disorder.The f MRI experiment associated with audiovisual speech and emotion integration has been designed.The functional specificity of regions in the audiovisual loop was explored.The mechanism of audiovisual integration and the dynamic network transformation of brain function in patients with affective disorder were investigated.The research content mainly includes the following four aspects:To verify whether the neural mechanism of Mc Gurk effect characterizing the ability of audiovisual integration in mental illness,the audiovisual integration experiment which associated with Mc Gurk effect was designed.Firstly,a behavioral experiment was implemented to examine the Mc Gurk susceptibility.To probe the possible involvement of specific neural circuits in individual differences in multisensory speech perception,functional magnetic resonance imaging(f MRI)was performed to measure the brain activity in response to non-Mc Gurk audiovisual syllables.The result showed that there are significant differential activations of the auditory and visual regions and the left superior temporal sulcus(STS),as well as multiple motor areas between strong and weak Mc Gurk perceivers.The individual engagement of the STS and motor areas could specifically predict the behavioral Mc Gurk susceptibility,contrary to the sensory regions.These findings suggest that the distinct multimodal integration in STS as well as coordinated phonemic modulatory processes in motor circuits may serve as a neural substrate for interindividual differences in multisensory speech perception.To study the information integration and exchange between the auditory and visual modal during emotion perception in patients with mental diseases,an audiovisual emotional f MRI task was designed in patients with major epression disorder(MDD).All the participants were asked to distinguish the laughing or crying sound while being exposed to faces with different emotional valences as background during f MRI scanning.Patients revealed a significantly decreased activation in the subcortical limbic affective network,orbital medial frontal and lateral prefrontal cortex in both congruent and incongruent conditions.A more widely widespread deactivation in inferior frontal areas and striatum in response to incongruent emotional stimulus pairs was found in MDD,which was not prominent in congruent condition.This result suggests that patients were associated with conflict monitoring dysregulation when they were solving incongruent emotional stimuli from different channels.To explore the negative biased emotional perception of mental diseases,the f MRI experiment was designed for depression patients using audiovisual emotional stimuli.This study combined general linear model and psychophysiological interaction analyses to identify abnormal local functional activity and integrative processes during audiovisual emotional processing in MDD patients.At the local neural level,MDD patients showed increased bias activity in the ventromedial prefrontal cortex(vm PFC)while listening to negative auditory stimuli and concurrently processing visual facial expressions,along with decreased dorsolateral prefrontal cortex(dl PFC)activity in both the positive and negative visual facial conditions.At the network level,MDD exhibited significantly decreased connectivity in areas involved in automatic emotional processes and voluntary control systems during perception of negative stimuli,including the vm PFC,dl PFC,insula,as well as the subcortical regions of posterior cingulate cortex and striatum.These findings demonstrated that negative bias effects in patients may be facilitated by the excessive ventral bottom-up negative emotional influences along with incapability in dorsal prefrontal top-down control system.Aiming at the brain state transformation characteristic of primary sensorimotor related brain neural activity in psychiatric diseases,this study adopted the brain signal variability(BSV)to study the dynamic intrinsic signatures of generalized anxiety disorder(GAD).The result showed that patients with GAD exhibited decreased BSV in widespread regions including the visual network,sensorimotor network,frontoparietal network,limbic system,and thalamus,indicating an inflexible brain state transfer pattern in these systems.Furthermore,the correlation between BSV and trait anxiety score was prone to be positive in patients with GAD but negative in HCs.The opposite relationships between BSV and anxiety level in the two groups indicate that the brain with moderate anxiety level may stay in the most stable rather than in the flexible state.The decreased BSV in patients with GAD similar to that in other mental disorders but with a nonlinear relationship between BSV and anxiety level indicating a novel neurodynamic mechanism of the anxious brain.In summary,as the important parts of audiovisual circuit,the STS was associated with the integration between different sensory channel,while the motor cortex was related to the phonemic modulatory processes.The activation of these regions could affect the individual ability of multisensory speech perception.In patients with mood disorders the audiovisual emotional integration of abnormal circuitry mainly contains the limbic affective network,medial frontal cortex,inferior frontal gyrus,striatum,and lateral frontal regions.The negative activity of the medial frontal network and the decreased control ability of the lateral frontal lobe may lead to the abnormal negative bias of the patients.In addition,abnormal neural activiti of audiovisual circuit still exist in spontaneous activities of patients with affective disorder,not only in task activation.