Research On FMRI-based Brain Entropy

Entropy indicates system irregularity and the capacity for information processing.The human brain is one of the most complex systems in the world,and using brain entropy(BEN)to assess brain complexity may provide more physical characters to increase our understanding of brain activity.In the past,BEN has been evaluated using EEG data,which the lack sufficient spatial resolution,we recently proposed an fMRIbased method,then normal BEN distribution patterns were identified,and others studies have found alters of BEN in aging and brain diseases that indicate the possibility of BEN as a newly-developing biomarker.Acceptance of BEN is relatively low in the clinical or basic cognitive neuroscience due to its relatively novelty.The deep-seated reason is that the relationship between BEN and the well-known methods is not clear,whether BEN is reversible,whether it can reflect the effects of neuromodulation or treatment is also unknown.Following the frontier topic-BEN,this research mainly solves two pivotal problems.In the first part,we study the associations between BEN and cerebral blood flow(CBF),fractional amplitude of low-frequency fluctuations(fALFF)at resting state brain,in order to provide more evidence for BEN as a new indicator of activity;in the second part,we investigated the effects of high-frequency repetitive transcranial magnetic stimulation(rTMS)on the left lateral dorsolateral prefrontal(DLPFC)on BEN to verify the sensitivity of BEN and provide evidence for BEN as a potential for biomarkers.Part 1 Associations of Brain Entropy to Cerebral Blood Flow andfractional Amplitude of Low-Frequency Fluctuations in the Resting BrainEntropy is a fundamental trait of human brain.Using fMRI-based BEN mapping,interesting findings have been increasingly revealed in normal brain and neuropsychiatric disorders.As BEN is still relatively new,an often-raised question is how much new information can this measure tell about the brain compared to other more established brain activity measures.The study aimed to address that question by examining the relationship between BEN and CBF and the fALFF,two widely used resting state brain state measures.fMRI data acquired from a large cohort of normal subjects were used to calculate the three metrics;inter-modality associations were assessed at each voxel through the Pearson correlation analysis.A moderate to high positive BEN-CBF and BEN-fALFF correlations were found in orbito-frontal cortex(OFC)and posterior inferior temporal cortex(ITC);Strong negative BEN-fALFF correlations were found in visual cortex(VC),anterior ITC,striatum,motor network,precuneus,and lateral parietal cortex.Positive CBF-fALFF correlations were found in medial OFC(MOFC),medial prefrontal cortex(MPFC),left angular gyrus,and left precuneus.Significant gender effects were observed for all three metrics and their correlations.Our data clearly demonstrated that BEN provides unique information that cannot be revealed by CBF and fALFF.Part 2 The impact of rTMS on BENRecent research has identified shown interesting entropy distribution patterns in normal brain and its changes due to aging and brain disorders.A question of great scientific and clinical importance is but it remains unknown for whether BEN can be modulated using non-invasive neuromodulations.The purpose of this study was to address this open question using high-frequency rTMS.BEN was calculated from resting state fMRI acquired before and after applying 20 Hz rTMS or SHAM(control)stimulation.As compared to SHAM,20 Hz rTMS reduced BEN in medial orbito-frontal cortex and subgenial anterior cingulate cortex(MOFC/sgACC),suggesting meaning a reduced information processing therein,probably as a result of the enhanced top-down regulation by the left DLPFC rTMS.No significant changes were observed to the functional connectivity(FC)between the left DLPFC(the target site)target site to the rest of the brain,suggesting that rTMS may not affect FC though it might use FC to transfer its effects or the ad hoc information.Our data proved that rTMS can modulate BEN and BEN can be used to monitor rTMS effects.