The right inferior frontal gyrus as pivotal node and effective regulator of the basal ganglia-thalamocortical response inhibition circuit

Background:The involvement of specific basal ganglia-thalamocortical circuits in response inhibition has been extensively mapped in animal models.However,the pivotal nodes and directed causal regulation within this inhibitory circuit in humans remains con-troversial.Objective:The main aim of the present study was to determine the causal information flow and critical nodes in the basal ganglia-thalamocortical inhibitory circuits and also to examine whether these are modulated by biological factors(i.e.sex)and behavioral performance.Methods:Here,we capitalize on the recent progress in robust and biologically plausible directed causal modeling(DCM-PEB)and a large response inhibition dataset(n=250)acquired with concomitant functional magnetic resonance imaging to determine key nodes,their causal regulation and modulation via biological variables(sex)and inhibitory performance in the inhibitory circuit encompassing the right inferior frontal gyrus(rIFG),caudate nucleus(rCau),globus pallidum(rGP),and thalamus(rThal).Results:The entire neural circuit exhibited high intrinsic connectivity and response inhibition critically increased causal projections from the rIFG to both rCau and rThal.Direct comparison further demonstrated that response inhibition induced an increasing rIFG inflow and increased the causal regulation of this region over the rCau and rThal.In addition,sex and performance influenced the functional architecture of the regulatory circuits such that women displayed increased rThal self-inhibition and decreased rThal to GP modulation,while better inhibitory performance was associated with stronger rThal to rIFG communication.Furthermore,control analyses did not reveal a similar key communication in a left lateralized model.Conclusions:Together,these findings indicate a pivotal role of the rIFG as input and causal regulator of subcortical response inhibition nodes.

Correlation between LIFG and Autonomic Activation during Stressful Tasks:A Functional Near-infrared Spectroscopy (fNIRS) Study

It remains unclear whether language tasks in one＇s first （L1） or second （L2） language can cause stress responses and whether frontal, autonomic and behavioral responses to stressful tasks are correlated. In this study, we studied 22 Chinese subjects whose L2 was English and measured the cerebral blood oxygenation in their frontal lobe by using functional near-infrared spectroscopy （fNIRS） as par- ticipants engaged in a mental arithmetic task （MAT） and verbal fluency tasks （VFTs） in L1 （Chinese） and L2 （English）. To examine the activated cortical areas, we estimated the channel location based on Montreal Neurological Institute （MNI） standard brain space by using a-probabilistic estimation method. We evaluated heart rate （HR） changes to analyze autonomic nervous system （ANS） functioning. We found that the MAT and VFTs induced greater increases in HR than did the control （Ctrl） task. Further- more, subjects developed greater increases in HR in the MAT and VFTt~ than they did in the VFTL1. Compared with the Ctrl task, the MAT and both VFTLland VFTL2 produced robust and widespread bi- lateral activation of the frontal cortex. Interestingly, partial correlation analysis indicated that the activity in the left inferior frontal gyrus （LIFG） [Brodmarm＇s area （BA） 47] was consistently correlated with the increases in HR across the three tasks （MAT, VFTL2, and VFTL1）, after controlling for the performance data. The present results suggested that a VFT in L2 may be more stressful than in L1. The LIFG may affect the activation of the sympathetic system induced by stressful tasks, includin~ MATs and VFTs.

Cerebral activation during unilateral clenching in patients with temporomandibular joint synovitis and biting pain： an functional magnetic resonance imaging study

Background Functional magnetic resonance is a non-invasive method that can examine brain activity and has been widely used in various fields including jaw movement and pain processing. Temporomandibular disorder （TMD） is one of the most frequent facial pain problems. The objective of this study was to investigate the brain activities using functional magnetic resonance imaging （fMRI） during unilateral maximal voluntary clenching tasks in the TMD synovitis patients with biting pain.Methods Fourteen TMD synovitis patients with unilateral biting pain and 14 controls were included in the study.Contralateral biting pain was defined as right molar clenching causing left temporomandibular joint （TMJ） pain. Ipsilateral biting pain was defined as right molar clenching causing right TMJ pain. Symptom Check List-90 （SCL-90） was administered to the patients and controls. Independent sample t-test was used to compare the SCL-90 subscales between the two groups. Unilateral clenching tasks were performed by the patients and controls. Imaging data were analyzed using SPM99.Results Patients were divided into contralateral TMD biting pain group （n=8） and ipsilateral TMD biting pain group （n=6）. The SCL-90 subscales were significantly different between the two groups for somatization, depression, anxiety,phobic anxiety, and paranoid ideation. Group analysis of the controls demonstrated brain activations in the inferior frontal gyrus, precentral gyrus, middle frontal gyrus, superior temporal gyrus, and insular. The areas of activation were different between right and left clenching task. In TMJ synovitis patients with contralateral or ipsilateral biting pain, the group analysis showed activations in the inferior frontal gyrus, superior temporal gyrus, medium frontal gyrus, precentral gyrus,and anterior cingulate cortex.Conclusions The inferior frontal gyrus and precentral gyrus play essential roles during the unilateral clenching task.Activation of anterior cingulate cortex in the synovitis patients with biting pain was associated with higher levels of psychological distress.

Regional homogeneity and functional connectivity in resting-state brain activity in tinnitus patients

Objective:Subjective tinnitus is characterized by the perception of sound in the absence of any external auditory stimuli.This perceived sound may be related to altered intrinsic neural activity generated along the central auditory pathway.This retrospective study was designed to investigate regional homogeneity and functional connectivity in the resting-state brain activity of patients with tinnitus.Methods:We recruited tinnitus patients with normal hearing or mild hearing loss(n=17)and age-matched healthy controls(n=20),and examined regional homogeneity and functional connectivity in resting-state brain activity using resting-state functional magnetic resonance imaging data.The present study protocol was approved by the Institutional Review Board on Experimental Ethics at Sun Yat-sen University,China(approval No.SYSEC-KY-KS-2019-083).Results:Compared with normal controls,patients with tinnitus had significantly decreased regional homogeneity in the anterior lobe of the cerebellum and increased homogeneity in the inferior frontal gyrus(P<0.05 corrected at a cluster-level).In addition,tinnitus patients showed enhanced functional connectivity between the inferior frontal gyrus and the ventral striatum and midbrain,as well as increased connectivity between the cerebellum and ventromedial prefrontal cortex(P<0.05 corrected at a cluster-level).We also found decreased connectivity between the cerebellum and the anterior insula compared with controls(P<0.05 corrected at a cluster-level).Conclusion:Abnormal connectivity in non-auditory brain structures,particularly those related to emotion processing,may be associated with tinnitus persistence.