重复时间对大脑静息态功能磁共振成像比率低频振幅结果的影响

目的 探讨在磁共振静息态功能成像中,基于同时多层面采集(simultaneous multi-slice,SMS)技术,研究重复时间(TR)对大脑比率低频振幅(fALFF)测量结果的影响.方法 纳入8名健康志愿者为研究对象,分别采用4种不同TR(2000、1500、1100及700 ms)的SMS-EPI扫描序列,采集4组静息态下脑功能成像数据,经头动校正、空间标准化,采用半高全宽的4 mm高斯核平滑等预处理后,进行fALFF的计算并获得统计图,对测量结果进行组内单样本t检验及组间方差分析、配对样本t检验.结果 单样本t检验显示4种TR序列下fALFF统计图具有相似的分布模式,但经方差分析及配对样本t检验显示4组间fALFF值存在差异且差异具有统计学意义(P＜0.05,Alphasim校正).TR=2000 ms较TR=1100、700 ms在枕叶、后扣带回的fALFF值减低;TR=1500 ms较TR=1100、700 ms在枕叶、后扣带回及中央后回的fALFF值减低;仅TR=1500、1100 ms较TR=700 ms在扣带回处fALFF值增加;TR=2000 ms与TR=1500 ms差异无统计学意义.结论 静息态脑功能磁共振成像中,采用短TR能够获得更多脑区神经元的活动信息;另外,应用SMS-EPI序列采集图像不仅能显著降低TR获得高时间分辨率图像,而且图像采样点个数也会增加.     

Test-retest stability analysis of resting brain activity revealed by blood oxygen level-dependent functional MRI

Purpose:

To assess test–retest stability of four functional magnetic resonance imaging (fMRI)‐derived resting brain activity metrics: the seed‐region‐based functional connectivity (SRFC), independent component analysis (ICA)‐derived network‐based FC (NTFC), regional homogeneity (ReHo), and the amplitude of low frequency fluctuation (ALFF).

Methods:

Simulations were used to assess the sensitivity of SRFC, ReHo, and ALFF to noise interference. Repeat resting blood oxygen level‐dependent (BOLD) fMRI were acquired from 32 healthy subjects. The intraclass correlation coefficient (ICC) was used to assess the stability of the four metrics.

Results:

Random noise yielded small random SRFC, small but consistent ReHo and ALFF. A neighborhood size greater than 20 voxels should be used for calculating ReHo in order to reduce the noise interference. Both the anterior cingulate cortex (ACC) and posterior cingulate cortex (PCC)‐based SRFC were reproducible in more spatially extended regions than ICA NTFC. The two regional spontaneous brain activity (SBA) measures, ReHo and ALFF, showed test–retest reproducibility in almost the whole gray matter.

Conclusion:

SRFC, ReHo, and ALFF are robust to random noise interference. The neighborhood size for calculating ReHo should be larger than 20 voxels. ICC > 0.5 and cluster size > 11 should be used to assess the ICC maps for ACC/PCC SRFC, ReHo, and ALFF. BOLD fMRI‐based SBA can be reliably measured using ACC/PCC SRFC, ReHo, and ALFF after 2 months. J. Magn. Reson. Imaging 2012;36:344–354. ©2012 Wiley Periodicals, Inc.     

Excitotoxicity by kainate-induced seizure causes diacylglycerol kinase ζ to shuttle from the nucleus to the cytoplasm in hippocampal neurons

Little is known about how spontaneous brain activity during the resting state may be altered in posttraumatic stress disorder (PTSD) compared to traumatized individuals. In the current study, we used a measure of amplitude of low-frequency (0.01-0.08 Hz) fluctuation (ALFF) to investigate the regional baseline brain function of this disorder. Fifty-four medication-naive PTSD patients and seventy-two matched traumatized comparison subjects who experienced the Sichuan major earthquake participated in a functional magnetic resonance imaging (fMRI) scan. We analyzed the difference between the PTSD and comparison groups during a resting state using ALFF. PTSD patients showed decreased ALFF values in right lingual gyrus, cuneus, middle occipital gyrus, insula, and cerebellum, and increased ALFF values in right medial and middle frontal gyri, relative to traumatized individuals without PTSD. The ALFF value in the right medial frontal gyrus was positively correlated with severity of the disorder. Our findings show that abnormality of intrinsic brain activity exists under resting conditions in PTSD patients exposed to a major earthquake. Altered ALFF in predominantly right hemisphere cortical and subcortical regions and in cerebellum potentially contribute to the neural mechanisms underlying traumatic memory and symptoms in PTSD.     

Beware detrending: Optimal preprocessing pipeline for low‐frequency fluctuation analysis

Resting‐state functional magnetic resonance imaging (rs‐fMRI) offers the possibility to assess brain function independent of explicit tasks and individual performance. This absence of explicit stimuli in rs‐fMRI makes analyses more susceptible to nonneural signal fluctuations than task‐based fMRI. Data preprocessing is a critical procedure to minimise contamination by artefacts related to motion and physiology. We herein investigate the effects of different preprocessing strategies on the amplitude of low‐frequency fluctuations (ALFFs) and its fractional counterpart, fractional ALFF (fALFF). Sixteen artefact reduction schemes based on nuisance regression are applied to data from 82 subjects acquired at 1.5 T, 30 subjects at 3 T, and 23 subjects at 7 T, respectively. In addition, we examine test–retest variance and effects of bias correction. In total, 569 data sets are included in this study. Our results show that full artefact reduction reduced test–retest variance by up to 50%. Polynomial detrending of rs‐fMRI data has a positive effect on group‐level t‐values for ALFF but, importantly, a negative effect for fALFF. We show that the normalisation process intrinsic to fALFF calculation causes the observed reduction and introduce a novel measure for low‐frequency fluctuations denoted as high‐frequency ALFF (hfALFF). We demonstrate that hfALFF values are not affected by the negative detrending effects seen in fALFF data. Still, highest grey matter (GM) group‐level t‐values were obtained for fALFF data without detrending, even when compared to an exploratory detrending approach based on autocorrelation measures. From our results, we recommend the use of full nuisance regression including polynomial detrending in ALFF data, but to refrain from using polynomial detrending in fALFF data. Such optimised preprocessing increases GM group‐level t‐values by up to 60%.     

Age‐related and individual variations in altered prefrontal and cerebellar connectivity associated with the tendency of developing internet addiction

Internet addiction refers to problematic patterns of internet use that continually alter the neural organization and brain networks that control impulsive behaviors and inhibitory functions. Individuals with elevated tendencies to develop internet addiction represent the transition between healthy and clinical conditions and may progress to behavioral addictive disorders. In this network neuroscience study, we used resting‐state functional magnetic resonance imaging (rs‐fMRI) to examine how and whether individual variations in the tendency of developing internet addiction rewire functional connectivity and diminish the amplitude of spontaneous low‐frequency fluctuations in healthy brains. The influence of neurocognitive aging (aged over 60 years) on executive‐cerebellar networks responsible for internet addictive behavior was also investigated. Our results revealed that individuals with an elevated tendency of developing internet addiction had disrupted executive‐cerebellar networks but increased occipital‐putamen connectivity, probably resulting from addiction‐sensitive cognitive control processes and bottom‐up sensory plasticity. Neurocognitive aging alleviated the effects of reduced mechanisms of prefrontal and cerebellar connectivity, suggesting age‐related modulation of addiction‐associated brain networks in response to compulsive internet use. Our findings highlight age‐related and individual differences in altered functional connectivity and the brain networks of individuals at a high risk of developing internet addictive disorders. These results offer novel network‐based preclinical markers of internet addictive behaviors for individuals of different ages.     

无灶性癫痫患者静息态fMRI与注意功能的相关性研究

目的采用静息态功能磁共振成像的低频振幅技术,探讨无灶性癫痫患者低频振幅与注意功能之间可能存在的关系。方法对16例无灶性癫痫患者和16名正常志愿者进行静息态fMRI数据采集及注意功能行为学测试,采用REST软件计算显示无灶性癫痫患者相对于正常人ALFF增高和减弱的区域,对上述的16例无灶性癫痫患者和16例正常对照进行气球叉掉测试,数字符号转换测试及stroop测试检测其注意功能,观察无灶性癫痫患者静息态fMRI与注意功能之间可能存在的联系。结果①无灶性癫痫组和正常对照组相比,ALFF增强的脑区分布在右侧颞叶(15,-90,21)、内侧额叶(0,24,-24)、腹侧前扣带回(-12,30,27)及右侧小脑半球(-51,-57,-4);②无灶性癫痫组和正常对照组相比ALFF减弱的脑区分布在左侧小脑半球及相邻后缘枕叶(-48,-15,39)、后扣带回(60,-21,33)及楔前叶(-6,-54,66);③无灶性癫痫患者的三项注意功能测试反应时间均较正常对照组延长(P<0.01)。Stroop测试结果表明无灶性癫痫组与对照组相比冲突条件下较一致、中性条件下的错误率显著增加。结论无灶性癫痫患者静息状态下表现出异常的脑功能活动方式。长期异常放电对患者的注意功能有明显损害,其中持续注意能力下降,可能与无灶性癫痫患者的颞叶及额叶的病变相关;选择注意能力下降,可能与腹侧前扣带回的损伤密切相关。     

Measuring abnormal intrinsic brain activities in patients with retinal detachment using amplitude of low-frequency fluctuation: a resting-state fMRI study

Objective: The targets of this study were to access the alternations of spontaneous brain activity in RD patients by amplitude of low-frequency fluctuation (ALFF) method and to explore their relationships with clinical behavioral performance.

Methods: A total of 20 patients with RD (6 males and 14 females), and 20 healthy controls (HCs) (6 males and 14 females) were recruited, and were matched in sex and age. All participants finished the functional magnetic resonance imaging (fMRI) scanning. We applied the ALFF method to detect the spontaneous brain activity. Receiver operating characteristic (ROC) curve was applied to distinguish RD Patients from HCs.

Results: RD patients showed decreased ALFF values in the right occipital lobe and right medial frontal gyrus and increased ALFF values in the right frontal superior orbital and left inferior temporal gyrus when compared with HCs. In RD patients, we did not find any relationship between the mean ALFF values and the clinical behavioral performances.

Conclusion: The RD patients exhibited abnormal spontaneous brain activity in vision and vision related brain regions, which might explore potential pathological mechanism of acute vision loss in RD patients.     

Altered resting‐state activity in seasonal affective disorder

At present, our knowledge about seasonal affective disorder (SAD) is based mainly up on clinical symptoms, epidemiology, behavioral characteristics and light therapy. Recently developed measures of resting‐state functional brain activity might provide neurobiological markers of brain disorders. Studying functional brain activity in SAD could enhance our understanding of its nature and possible treatment strategies. Functional network connectivity (measured using ICA‐dual regression), and amplitude of low‐frequency fluctuations (ALFF) were measured in 45 antidepressant‐free patients (39.78 ± 10.64, 30 ♀, 15 ♂) diagnosed with SAD and compared with age‐, gender‐ and ethnicity‐matched healthy controls (HCs) using resting‐state functional magnetic resonance imaging. After correcting for Type 1 error at high model orders (inter‐RSN correction), SAD patients showed significantly increased functional connectivity in 11 of the 47 identified RSNs. Increased functional connectivity involved RSNs such as visual, sensorimotor, and attentional networks. Moreover, our results revealed that SAD patients compared with HCs showed significant higher ALFF in the visual and right sensorimotor cortex. Abnormally altered functional activity detected in SAD supports previously reported attentional and psychomotor symptoms in patients suffering from SAD. Further studies, particularly under task conditions, are needed in order to specifically investigate cognitive deficits in SAD. Hum Brain Mapp 35:161–172, 2014. © 2012 Wiley Periodicals, Inc.