Functional magnetic resonance imaging of working memory and response inhibition in children with mild traumatic brain injury

The current pilot study examined functional magnetic resonance imaging (fMRI) activation in children with mild traumatic brain injury (mTBI) during tasks of working memory and inhibitory control, both of which are vulnerable to impairment following mTBI. Thirteen children with symptomatic mTBI and a group of controls completed a version of the Tasks of Executive Control (TEC) during fMRI scanning. Both groups showed greater prefrontal activation in response to increased working memory load. Activation patterns did not differ between groups on the working memory aspects of the task, but children with mTBI showed greater activation in the posterior cerebellum with the addition of a demand for inhibitory control. Children with mTBI showed greater impairment on symptom report and "real world" measures of executive functioning, but not on traditional "paper and pencil" tasks. Likewise, cognitive testing did not correlate significantly with imaging results, whereas increased report of post-concussive symptoms were correlated with increased cerebellar activation. Overall, results provide some evidence for the utility of symptom report as an indicator of recovery and the hypothesis that children with mTBI may experience disrupted neural circuitry during recovery. Limitations of the study included a small sample size, wide age range, and lack of in-scanner accuracy data.     

Functional magnetic resonance imaging of mild traumatic brain injury

Functional magnetic resonance imaging (fMRI) offers great promise for elucidating the neuropathology associated with a single or repetitive mild traumatic brain injury (mTBI). The current review discusses the physiological underpinnings of the blood-oxygen level dependent response and how trauma affects the signal. Methodological challenges associated with fMRI data analyses are considered next, followed by a review of current mTBI findings. The majority of evoked studies have examined working memory and attentional functioning, with results suggesting a complex relationship between cognitive load/attentional demand and neuronal activation. Researchers have more recently investigated how brain trauma affects functional connectivity, and the benefits/drawbacks of evoked and functional connectivity studies are also discussed. The review concludes by discussing the major clinical challenges associated with fMRI studies of brain-injured patients, including patient heterogeneity and variations in scan-time post-injury. We conclude that the fMRI signal represents a complex filter through which researchers can measure the physiological correlates of concussive symptoms, an important goal for the burgeoning field of mTBI research.     

A functional magnetic resonance imaging investigation of episodic memory after traumatic brain injury

Traumatic brain injury often negatively impacts episodic memory; however, studies of the neural substrates of this impairment have been limited. In this study, both encoding and recognition of visually presented stimuli were examined with functional magnetic resonance imaging. Twelve adults with chronic complicated mild, moderate, and severe injuries were compared with a matched group of 12 controls. Behavioral task performance did not differentiate the groups. During neuroimaging, however, the group of individuals with traumatic brain injury exhibited increased activation, as well as increased bilaterality and dispersion as compared to controls. Findings are discussed in terms of increased resource recruitment.     

氢质子磁共振波谱成像技术在创伤性脑损伤后认知障碍中的应用

创伤性脑损伤(TBI)可引起一系列复杂的病理生理过程变化,这些变化包括脑内物质代谢异常,导致机体出现包括头痛、认知、运动和情感障碍等在内的长、短期症状,而认知障碍是阻碍TBI患者日常生活质量恢复和延缓其回归社会的重要因素。氢质子磁共振波谱成像技术(1H-MRS)可对急、慢性脑部损伤患者的脑组织代谢进行非侵入性检测,具有辅助诊断和预测长期功能预后的价值。该文将近年来1H-MRS在TBI后认知障碍中的应用进行总结和展望。[国际神经病学神经外科学杂志, 2021, 48(2):197-201]     

Brain activation during working memory after traumatic brain injury in children

Eight children with moderate to severe traumatic brain injury (TBI) and eight matched, uninjured control children underwent fMRI during an N-back task to test effects of TBI on working memory performance and brain activation. Two patterns in the TBI group were observed. Patients whose criterion performance was reached at lower memory loads than control children demonstrated less extensive frontal and extrafrontal brain activation than controls. Patients who performed the same, highest (3-back) memory load as controls demonstrated more frontal and extrafrontal activation than controls. Our findings of performance and brain activation changes in children after TBI await longitudinal investigation.     

Encoding and recognition after traumatic brain injury: neuropsychological and functional magnetic resonance imaging findings

Although impairment of episodic memory is common after traumatic brain injury (TBI), the complex nature of human memory suggests the need to study more than recall alone. For this reason, we are presenting an extension with additional analyses of persons reported in a previous publication ( Russell, Arenth, Scanlon, Kessler, & Ricker, 2011 ). We examined both the encoding and recognition components of an episodic memory paradigm containing both word and letter string blocks using functional magnetic resonance imaging (fMRI) and neuropsychological testing. This paradigm was completed by 12 persons with complicated mild, moderate, or severe TBI and 12 matched uninjured controls. Comparisons were made between groups and stimulus types. While task behavioral performance was not significantly different between groups, imaging results showed greater activation for the TBI group during the encoding portion of the task, while the control group exhibited more activation on the recognition portion. Observed areas of activation suggest that the TBI group may have used a less effective, but more automatic verbal strategy for encoding the nonpronounceable letter strings, while controls may have opted for more of a recognition-focused strategy. Group differences in California Verbal Learning Test-Second Edition (CVLT-II) performance supported these ideas, and further neuropsychological testing also suggested limitations in executive functioning in the TBI group that may have influenced performance. Implications for intervention are discussed.     

工作记忆与脑的功能磁共振成像

工作记忆是临时信息编码、保持和提取的过程 ,是学习记忆研究的热点之一。功能磁共振作为一种新型无损伤技术 ,为研究工作记忆提供了一个新的途径。本文对功能磁共振的原理、实验设计和目前工作记忆功能磁共振检查的研究进展进行综述。     

工作记忆与脑的功能磁共振成像

工作记忆是临时信息编码、保持和提取的过程,是学习记忆研究的热点之一.功能磁共振作为一种新型无损伤技术,为研究工作记忆提供了一个新的途径.本文对功能磁共振的原理、实验设计和目前工作记忆功能磁共振检查的研究进展进行综述.     

轻度创伤性脑损伤后脑组织微环境变化:多模态磁共振成像研究

目的探讨弥散张量成像(DTI)联合磁共振波谱(MRS)及磁敏感加权成像(SWI)的功能磁共振成像方法,在评估轻度创伤性脑损伤(mTBI)脑组织代谢及微结构变化的应用价值,为临床制定相应的治疗方案提供影像学参考。方法纳入21例mTBI患者和16例健康志愿者,mTBI患者在伤后4～72 h内接受T1WI、T2WI、FLAIR、DTI、MRS及SWI序列扫描,通过各序列图像及参数值评估mTBI患者伤侧脑组织和对照组内囊前肢、内囊后肢、胼胝体膝部、胼胝体压部、扣带回、半卵圆中心、额叶白质及视辐射的差异。结果两组FA值比较,仅胼胝体压部差异有统计学意义(P0.01)。mTBI组胼胝体膝部NAA/Cr值低于对照组,差异有统计学意义(P0.01)。mTBI组内囊后肢和胼胝体膝部Cho/Cr值均高于对照组,差异均有统计学意义(P0.05或0.01)。结论 FA值及NAA、Cho、Cr值能测定mTBI后脑组织水分子扩散及代谢情况,DTI联合MRS及SWI可以作为一项客观指标,定量评估mTBI患者的病情及预后。     

MR序列优化组合在创伤性脑损伤的诊断价值

目的分析MR诊断创伤性脑损伤(TBI)的价值,探讨TBI患者MR一站式诊断的可行性。方法对260例TBI病例进行MR序列组合扫描,包括小角度激发快速梯度回波序列(FLASH)、流动衰减反转恢复序列(FLAIR)、自旋回波(SE)T1WI、快速自旋回波(TSE)T2WI,比较MR序列组合和CT对各种类型TBI诊断的差异。结果脑实质内出血61例,MR显示61例,CT显示53例;硬膜下出血55例,MR显示55例,CT显示49例;硬膜外出血45例,MR显示45例,CT显示40例;脑挫(裂)伤35例,MR显示35例,CT显示25例;蛛网膜下腔出血35例,MR显示31例,CT显示33例;弥漫性轴索损伤29例,MR显示29例,CT显示5例。MR序列组合准确显示病变256例,CT为209例,两者差异有极显著统计学意义(P0.01),MR序列组合总体诊断敏感性高于CT。结论 MR序列组合(FLASH\FLAIR\T1WI\T2WI)诊断创伤性脑损伤明显优于CT,可列为TBI常规检查方法,实行TBI一站式诊断。     

功能磁共振成像研究睡眠剥夺36小时对健康男性工作记忆的影响

目的 利用功能磁共振成像(functional magnetic resonance imaging,fMRI)技术研究睡眠剥夺36 h对健康男性工作记忆的影响及可能机制.方法 10名健康男性受试者连续36 h睡眠剥夺,睡眠剥夺前后分别接受工作记忆任务测试,同时进行fMRI扫描.fMRI扫描采用2项工作记忆任务,收集获得的行为学结果和fMRI图像,用SPM2软件进行图像分析.比较睡眠剥夺前后工作记忆任务测试及fMRI扫描结果.结果 剥夺后LTR任务的反应时间为(866±102)ms,比剥夺前[(754±91)ms]明显延长(t=2.59,P<0.01),准确率为84.78%±8.71%,比剥夺前(95.31%±3.56%)明显降低(t=3.52,P<0.01);剥夺后PLUS任务的反应时间为(848±94)ms,比剥夺前[(756±79),ms]明显延长(t=2.37,P<0.05),准确率为84.22%±9.66%,比剥夺前(95.70%±4.72%)明显降低(t=3.38,P<0.01);剥夺前在额顶叶、前扣带回和丘脑等工作记忆相关性脑区被激活.PLUS任务较LTR任务激活脑区范围更广,强度更显著.剥夺后顶叶激活降低,前额叶和丘脑的激活增强.结论 睡眠剥夺能够导致工作记忆能力受损.fMRI显示睡眠剥夺后完成工作记忆任务时,在相应脑区顶叶激活降低,前额叶和丘脑激活增强,这可能是睡眠剥夺导致认知功能损害的机制之一.     

Predicting visual working memory with multimodal magnetic resonance imaging

The indispensability of visual working memory (VWM) in human daily life suggests its importance in higher cognitive functions and neurological diseases. However, despite the extensive research efforts, most findings on the neural basis of VWM are limited to a unimodal context (either structure or function) and have low generalization. To address the above issues, this study proposed the usage of multimodal neuroimaging in combination with machine learning to reveal the neural mechanism of VWM across a large cohort (N = 547). Specifically, multimodal magnetic resonance imaging features extracted from voxel‐wise amplitude of low‐frequency fluctuations, gray matter volume, and fractional anisotropy were used to build an individual VWM capacity prediction model through a machine learning pipeline, including the steps of feature selection, relevance vector regression, cross‐validation, and model fusion. The resulting model exhibited promising predictive performance on VWM (r = .402, p < .001), and identified features within the subcortical‐cerebellum network, default mode network, motor network, corpus callosum, anterior corona radiata, and external capsule as significant predictors. The main results were then compared with those obtained on emotional regulation and fluid intelligence using the same pipeline, confirming the specificity of our findings. Moreover, the main results maintained well under different cross‐validation regimes and preprocess strategies. These findings, while providing richer evidence for the importance of multimodality in understanding cognitive functions, offer a solid and general foundation for comprehensively understanding the VWM process from the top down.     

Noninvasive magnetic resonance imaging techniques in mild traumatic brain injury research and diagnosis

Mild traumatic brain injury (mTBI), frequently referred to as concussion, is one of the most common neurological disorders. The underlying neural mechanisms of functional disturbances in the brains of concussed individuals remain elusive. Novel forms of brain imaging have been developed to assess patients postconcussion, including functional magnetic resonance imaging (fMRI), susceptibility‐weighted imaging (SWI), diffusion MRI (dMRI), and perfusion MRI [arterial spin labeling (ASL)], but results have been mixed with a more common utilization in the research environment and a slower integration into the clinical setting. In this review, the benefits and drawbacks of the methods are described: fMRI is an effective method in the diagnosis of concussion but it is expensive and time‐consuming making it difficult for regular use in everyday practice; SWI allows detection of microhemorrhages in acute and chronic phases of concussion; dMRI is primarily used for the detection of white matter abnormalities, especially axonal injury, specific for mTBI; and ASL is an alternative to the BOLD method with its ability to track cerebral blood flow alterations. Thus, the absence of a universal diagnostic neuroimaging method suggests a need for the adoption of a multimodal approach to the neuroimaging of mTBI. Taken together, these methods, with their underlying functional and structural features, can contribute from different angles to a deeper understanding of mTBI mechanisms such that a comprehensive diagnosis of mTBI becomes feasible for the clinician.     

Using magnetic resonance imaging to predict new learning outcome at 5 years after childhood traumatic brain injury

Memory and learning entail the recruitment of a number of neural areas, including the medial temporal lobes, temporal association areas, and prefrontal cortices. This study examined the effects of injury severity on long-term memory function in 55 children who sustained traumatic brain injury 5 years earlier and compared this with 17 healthy controls. It also investigated cortical damage and diffuse axonal injury and their association to memory and learning outcomes 5 years after traumatic brain injury. Children were administered memory tests of increasing complexity. Results indicated that injury severity affected aspects of complex memory, with no significant influence on working memory; that focal cortical damage was not predictive of working or complex memory, whereas diffuse axonal injury predicted outcome on complex memory tasks. Findings suggest that the implementation of diffuse axonal injury as an index of injury may assist in predicting memory outcome after childhood traumatic brain injury.     

Functional magnetic resonance imaging of source versus item memory

Both the frontal lobes and the medial temporal lobe (particularly the hippocampus) have been implicated in encoding and retrieval of episodic memory information. We report an experiment that manipulates whether source information, item information, or both are required at retrieval. Two sources were used in a factorial design in which the main effect of source and item retrieval, along with their interaction, could be measured by fMRI activations. When source information was required at retrieval the left frontal lobe showed significant activation but not when item retrieval was required. Hippocampal activation showed no difference between source and item retrieval. This pattern of results supports a model proposing a larger role for the frontal lobes in encoding and retrieval of source information.     

A review of magnetic resonance imaging and diffusion tensor imaging findings in mild traumatic brain injury

Mild traumatic brain injury (mTBI), also referred to as concussion, remains a controversial diagnosis because the brain often appears quite normal on conventional computed tomography (CT) and magnetic resonance imaging (MRI) scans. Such conventional tools, however, do not adequately depict brain injury in mTBI because they are not sensitive to detecting diffuse axonal injuries (DAI), also described as traumatic axonal injuries (TAI), the major brain injuries in mTBI. Furthermore, for the 15 to 30 % of those diagnosed with mTBI on the basis of cognitive and clinical symptoms, i.e., the "miserable minority," the cognitive and physical symptoms do not resolve following the first 3 months post-injury. Instead, they persist, and in some cases lead to long-term disability. The explanation given for these chronic symptoms, i.e., postconcussive syndrome, particularly in cases where there is no discernible radiological evidence for brain injury, has led some to posit a psychogenic origin. Such attributions are made all the easier since both posttraumatic stress disorder (PTSD) and depression are frequently co-morbid with mTBI. The challenge is thus to use neuroimaging tools that are sensitive to DAI/TAI, such as diffusion tensor imaging (DTI), in order to detect brain injuries in mTBI. Of note here, recent advances in neuroimaging techniques, such as DTI, make it possible to characterize better extant brain abnormalities in mTBI. These advances may lead to the development of biomarkers of injury, as well as to staging of reorganization and reversal of white matter changes following injury, and to the ability to track and to characterize changes in brain injury over time. Such tools will likely be used in future research to evaluate treatment efficacy, given their enhanced sensitivity to alterations in the brain. In this article we review the incidence of mTBI and the importance of characterizing this patient population using objective radiological measures. Evidence is presented for detecting brain abnormalities in mTBI based on studies that use advanced neuroimaging techniques. Taken together, these findings suggest that more sensitive neuroimaging tools improve the detection of brain abnormalities (i.e., diagnosis) in mTBI. These tools will likely also provide important information relevant to outcome (prognosis), as well as play an important role in longitudinal studies that are needed to understand the dynamic nature of brain injury in mTBI. Additionally, summary tables of MRI and DTI findings are included. We believe that the enhanced sensitivity of newer and more advanced neuroimaging techniques for identifying areas of brain damage in mTBI will be important for documenting the biological basis of postconcussive symptoms, which are likely associated with subtle brain alterations, alterations that have heretofore gone undetected due to the lack of sensitivity of earlier neuroimaging techniques. Nonetheless, it is noteworthy to point out that detecting brain abnormalities in mTBI does not mean that other disorders of a more psychogenic origin are not co-morbid with mTBI and equally important to treat. They arguably are. The controversy of psychogenic versus physiogenic, however, is not productive because the psychogenic view does not carefully consider the limitations of conventional neuroimaging techniques in detecting subtle brain injuries in mTBI, and the physiogenic view does not carefully consider the fact that PTSD and depression, and other co-morbid conditions, may be present in those suffering from mTBI. Finally, we end with a discussion of future directions in research that will lead to the improved care of patients diagnosed with mTBI.     

Microscopic magnetic resonance elastography of traumatic brain injury model

Traumatic brain injury (TBI) is a major cause of death and disability for which there is no cure. One of the issues inhibiting clinical trial success is the lack of targeting specific patient populations due to inconsistencies between clinical diagnostic tools and underlying pathophysiology. The development of reliable, noninvasive markers of TBI severity and injury mechanisms may better identify these populations, thereby improving clinical trial design. Magnetic resonance elastography (MRE), by assessing tissue mechanical properties, can potentially provide such marker. MRE synchronizes mechanical excitations with a phase contrast imaging pulse sequence to noninvasively register shear wave propagation, from which local values of tissue viscoelastic properties can be deduced. The working hypothesis of this study is that TBI involves a compression of brain tissue large enough to bring the material out of its elastic range, sufficiently altering mechanical properties to generate contrast on MRE measurements. To test this hypothesis, we combined microscopic MRE with brain tissue collected from adult male rats subjected to a controlled cortical impact injury. Measurements were made in different regions of interest (somatosensory cortex, hippocampus, and thalamus), and at different time points following the injury (immediate, 24 h, 7 days, 28 days). Values of stiffness in the somatosensory cortex were found to be 23-32% lower in the injured hemisphere than in the healthy one, when no significant difference was observed in the case of sham brains. A preliminary in vivo experiment is also presented, as well as alternatives to improve the faithfulness of stiffness recovery.     

Functional magnetic resonance imaging of working memory reveals frontal hypoactivation in middle-aged adults with cognitive complaints

Older adults with cardiovascular disease (CVD) often complain about cognitive difficulties including reduced processing speed and attention. On cross-sectional examination, such reports relate more closely to mood than to cognitive performance; yet, in longitudinal studies, these complaints have foreshadowed cognitive decline over time. To test the hypothesis that self-reported cognitive difficulties reflect early changes in brain function, we examined cognitive complaints and depression in relation to blood oxygen level dependent (BOLD) response to a cognitive task in middle-aged adults at risk for CVD. Forty-nine adults (ages 40 to 60 years) completed a measure of perceived cognitive dysfunction (Cognitive Difficulties Scale), medical history questionnaire, neuropsychological assessment and functional magnetic resonance imaging (fMRI) during a working memory task. Increased report of cognitive difficulties was significantly associated with weaker task-related activation in the right superior frontal/ middle frontal gyrus (F(4,44) = 3.26; p = .020, CDS ? = -0.39; p = .009) and the right inferior frontal gyrus (F(4,44) = 3.14; p = .024, CDS ? = -0.45; p = .003), independent of age, education, and self-reported depressive symptoms. Lower activation intensity in the right superior frontal gyrus was related to trends toward poorer task performance. Thus, self-reported cognitive difficulties among cognitively normal middle-aged adults may provide important clinical information about early brain vulnerability that should be carefully monitored.     

Working memory after severe traumatic brain injury.

The aim of the present study was to assess the functioning of the different subsystems of working memory after severe traumatic brain injury (TBI). A total of 30 patients with severe chronic TBI and 28 controls received a comprehensive assessment of working memory addressing the phonological loop (forward and backward digit span; word length and phonological similarity effects), the visuospatial sketchpad (forward and backward visual spans), and the central executive (tasks requiring simultaneous storage and processing of information, dual-task processing, working memory updating). Results showed that there were only marginal group differences regarding the functioning of the two slave systems, whereas patients with severe TBI performed significantly poorer than controls on most central executive tasks, particularly on those requiring a high level of controlled processing. These results suggest that severe TBI is associated with an impairment of executive aspects of working memory. The anatomic substrate of this impairment remains to be elucidated. It might be related to a defective activation of a distributed network, including the dorsolateral prefrontal cortex.     

Working memory after traumatic brain injury in children

To investigate the effects of traumatic brain injury on working memory in children, we administered semantic (letter identity) and phonological (letter rhyme) N-back tasks to children who were on average 5 years post-mild (n = 54) or -severe (n = 26) traumatic brain injury and 44 typically developing children who were comparable in age. The correct detection of targets and false alarms were measured for each task. Memory load (which varied from 0 to 3 letters back) and age significantly affected the detection of targets and false alarms in both tasks. The severity of traumatic brain injury affected the correct detection of letters on the identity task and false alarms on the rhyme task. Traumatic brain injury severity also interacted with memory load in its effect on false alarms on the rhyme task. Traumatic brain injury results in impaired working memory and diminished inhibition in children. The N-back working memory task is feasible for administration to brain-injured children and potentially could be useful for studying brain activation associated with working memory and effects of drug therapy in this group of patients.