Acoustic noise concerns in functional magnetic resonance imaging

Magnetic resonance (MR) acoustic scanner noise may negatively affect the performance of functional magnetic resonance imaging (fMRI), a problem that worsens at the higher field strengths proposed to enhance fMRI. We present an overview of the current knowledge on the effects of confounding acoustic MR noise in fMRI experiments. The principles and effectiveness of various methods to reduce acoustic noise in fMRI are discussed, practical considerations are addressed and recommendations are made.     

Localization of semantic processing using functional magnetic resonance imaging

The relationship between the functional components of language and the anatomic foci of their neural systems represents a central issue in cognitive neuroscience. Conflicting results from a number of laboratories using positron emission tomography (PET) imaging techniques have led to a significant controversy over the specific neuroanatomic sites engaged by semantic processing. We report here results of an experiment designed to address this controversy, that is, whether semantic processing activates temporal and/or frontal brain regions. In this experiment we used cognitive tasks that emphasized either semantic or phonological information processing but that were similar on both memory search and responce generation components, together with functional magnetic resonance imaging, to examine the neuroanatomic loci of lexical-semantic as opposed to phonological processing. We studied nine right-handed men performing two silent generation tasks: rhyme, and semantic category. The former focuses on word form (phonological information) while the latter focuses on word meaning (semantic information). By “phonological” we mean the process of apprehending the sound structures of language. By “semantic” we mean information about the word's contextually specified meanings. Semantic processing makes demands on, and activates widespread areas within, brain including the inferior frontal regions bilaterally and the left posterior temporal region. Phonological processing engages a more restricted neuroanatomic assembly involving primarily anterior left temporal lobe sites. © 1995 Wiley-Liss, Inc.     

Applying independent component analysis to detect silent speech in magnetic resonance imaging signals

Independent component analysis (ICA) can be usefully applied to functional imaging studies to evaluate the spatial extent and temporal profile of task‐related brain activity. It requires no a priori assumptions about the anatomical areas that are activated or the temporal profile of the activity. We applied spatial ICA to detect a voluntary but hidden response of silent speech. To validate the method against a standard model‐based approach, we used the silent speech of a tongue twister as a ‘Yes’ response to single questions that were delivered at given times. In the first task, we attempted to estimate one number that was chosen by a participant from 10 possibilities. In the second task, we increased the possibilities to 1000. In both tasks, spatial ICA was as effective as the model‐based method for determining the number in the subject’s mind (80–90% correct per digit), but spatial ICA outperformed the model‐based method in terms of time, especially in the 1000‐possibility task. In the model‐based method, calculation time increased by 30‐fold, to 15 h, because of the necessity of testing 1000 possibilities. In contrast, the calculation time for spatial ICA remained as short as 30 min. In addition, spatial ICA detected an unexpected response that occurred by mistake. This advantage was validated in a third task, with 13 500 possibilities, in which participants had the freedom to choose when to make one of four responses. We conclude that spatial ICA is effective for detecting the onset of silent speech, especially when it occurs unexpectedly.     

Detecting deception using functional magnetic resonance imaging.

BACKGROUND: The ability to accurately detect deception is presently very limited. Detecting deception might be more accurately achieved by measuring the brain correlates of lying in an individual. In addition, a method to investigate the neurocircuitry of deception might provide a unique opportunity to test the neurocircuitry of persons in whom deception is a prominent component (i.e., conduct disorder, antisocial personality disorder, etc.). METHODS: In this study, we used functional magnetic resonance imaging (fMRI) to show that specific regions were reproducibly activated when subjects deceived. Subjects participated in a mock crime stealing either a ring or a watch. While undergoing an fMRI, the subjects denied taking either object, thus telling the truth with some responses, and lying with others. A Model-Building Group (MBG, n = 30) was used to develop the analysis methods, and the methods were subsequently applied to an independent Model-Testing Group (MTG, n = 31). RESULTS: We were able to correctly differentiate truthful from deceptive responses, correctly identifying the object stolen, for 93% of the subjects in the MBG and 90% of the subjects in the MTG. CONCLUSIONS: This is the first study to use fMRI to detect deception at the individual level. Further work is required to determine how well this technology will work in different settings and populations.     

The neural response to emotional prosody,as revealed by functional magnetic resonance imaging

Prosody is an important feature of language, comprising intonation, loudness, and tempo. Emotional prosodic processing forms an integral part of our social interactions. The main aim of this study was to use bold contrast fMRI to clarify the normal functional neuroanatomy of emotional prosody, in passive and active contexts. Subjects performed six separate scanning studies, within which two different conditions were contrasted: (1) "pure" emotional prosody versus rest; (2) congruent emotional prosody versus 'neutral' sentences; (3) congruent emotional prosody versus rest; (4) incongruent emotional prosody versus rest; (5) congruent versus incongruent emotional prosody; and (6) an active experiment in which subjects were instructed to either attend to the emotion conveyed by semantic content or that conveyed by tone of voice. Data resulting from these contrasts were analysed using SPM99. Passive listening to emotional prosody consistently activated the lateral temporal lobe (superior and/or middle temporal gyri). This temporal lobe response was relatively right-lateralised with or without semantic information. Both the separate and direct comparisons of congruent and incongruent emotional prosody revealed that subjects used fewer brain regions to process incongruent emotional prosody than congruent. The neural response to attention to semantics, was left lateralised, and recruited an extensive network not activated by attention to emotional prosody. Attention to emotional prosody modulated the response to speech, and induced right-lateralised activity, including the middle temporal gyrus. In confirming the results of lesion and neuropsychological studies, the current study emphasises the importance of the right hemisphere in the processing of emotional prosody, specifically the lateral temporal lobes.     

Physiological noise reduction using volumetric functional magnetic resonance inverse imaging

Physiological noise arising from a variety of sources can significantly degrade the detection of task‐related activity in BOLD‐contrast fMRI experiments. If whole head spatial coverage is desired, effective suppression of oscillatory physiological noise from cardiac and respiratory fluctuations is quite difficult without external monitoring, since traditional EPI acquisition methods cannot sample the signal rapidly enough to satisfy the Nyquist sampling theorem, leading to temporal aliasing of noise. Using a combination of high speed magnetic resonance inverse imaging (InI) and digital filtering, we demonstrate that it is possible to suppress cardiac and respiratory noise without auxiliary monitoring, while achieving whole head spatial coverage and reasonable spatial resolution. Our systematic study of the effects of different moving average (MA) digital filters demonstrates that a MA filter with a 2 s window can effectively reduce the variance in the hemodynamic baseline signal, thereby achieving 57%–58% improvements in peak z‐statistic values compared to unfiltered InI or spatially smoothed EPI data (FWHM = 8.6 mm). In conclusion, the high temporal sampling rates achievable with InI permit significant reductions in physiological noise using standard temporal filtering techniques that result in significant improvements in hemodynamic response estimation. Hum Brain Mapp, 2012. © 2011 Wiley Periodicals, Inc.     

Objective perimetry using functional magnetic resonance imaging in patients with visual field loss

In ophthalmic clinics, subjective perimetry is a standard examination method. However, for certain patients, objective perimetry is useful since it avoids the need for subjective judgments. The purpose of the present study is to demonstrate the feasibility of objective perimetry using functional magnetic resonance imaging (fMRI). fMRI was performed in 8 patients with visual field defects caused by cerebral lesions. The composite stimulus was either the combination of an expanding ring and a clockwise rotating wedge, or a contracting ring and a counter-clockwise rotating wedge. The largest radius was a 10° visual angle with magnifying glasses. The cycle period for the ring and wedge components differed, enabling us to distinguish the two targets within a single time series. Data were analyzed using custom software that interprets the two stimuli and estimates visual field maps. Regions of interest (ROIs) were set covering the entirety of the occipital lobes, and the most effective visual field location for each voxel was calculated from these two response components. The visual field maps obtained with fMRI were compared with the 10-2 Humphrey visual field (HVF) program. While some divergences were observed, in most subjects the visual field defects on fMRI agreed with those on HVF. Cross-correlation coefficients between grayscale values of visual field maps obtained with fMRI and decibel values obtained with HVF were significant (P < 0.05) in all subjects. fMRI in conjunction with our method is feasible for objectively and efficiently measuring the visual field of patients with visual field loss.     

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。     

AveLI: a robust lateralization index in functional magnetic resonance imaging using unbiased threshold-free computation

The laterality index (LI) is often applied in functional magnetic resonance imaging (fMRI) studies to determine functional hemispheric lateralization. A difficulty in using conventional LI methods lies in ensuring a legitimate computing procedure with a clear rationale. Another problem with LI is dealing with outliers and noise. We propose a method called AveLI that follows a simple and unbiased computational principle using all voxel t-values within regions of interest (ROIs). This method first computes subordinate LIs (sub-LIs) using each of the task-related positive voxel t-values in the ROIs as the threshold as follows: sub-LI = (Lt − Rt)/(Lt + Rt), where Lt and Rt are the sums of the t-values at and above the threshold in the left and right ROIs, respectively. The AveLI is the average of those sub-LIs and indicates how consistently lateralized the performance of the subject is across the full range of voxel t-value thresholds. Its intrinsic weighting of higher t-value voxels in a data-driven manner helps to reduce noise effects. The resistance against outliers is demonstrated using a simulation. We applied the AveLI as well as other “non-thresholding” and “thresholding” LI methods to two language tasks using participants with right- and left-hand preferences. The AveLI showed a moderate index value among 10 examined indices. The rank orders of the participants did not vary between indices. AveLI provides an index that is not only comprehensible but also highly resistant to outliers and to noise, and it has a high reproducibility between tasks and the ability to categorize functional lateralization.     

Cerebellum and speech perception: a functional magnetic resonance imaging study

A variety of data indicate that the cerebellum participates in perceptual tasks requiring the precise representation of temporal information. Access to the word form of a lexical item requires, among other functions, the processing of durational parameters of verbal utterances. Therefore, cerebellar dysfunctions must be expected to impair word recognition. In order to specify the topography of the assumed cerebellar speech perception mechanism, a functional magnetic resonance imaging study was performed using the German lexical items "Boden" ([bodn], Engl. "floor") and "Boten" ([botn], "messengers") as test materials. The contrast in sound structure of these two lexical items can be signaled either by the length of the wordmedial pause (closure time, CLT; an exclusively temporal measure) or by the aspiration noise of wordmedial "d" or "t" (voice onset time, VOT; an intrasegmental cue). A previous study found bilateral cerebellar disorders to compromise word recognition based on CLT whereas the encoding of VOT remained unimpaired. In the present study, two series of "Boden - Boten" utterances were resynthesized, systematically varying either in CLT or VOT. Subjects had to identify both words "Boden" and "Boten" by analysis of either the durational parameter CLT or the VOT aspiration segment. In a subtraction design, CLT categorization as compared to VOT identification (CLT - VOT) yielded a significant hemodynamic response of the right cerebellar hemisphere (neocerebellum Crus I) and the frontal lobe (anterior to Broca's area). The reversed contrast ( VOT - CLT) resulted in a single activation cluster located at the level of the supratemporal plane of the dominant hemisphere. These findings provide first evidence for a distinct contribution of the right cerebellar hemisphere to speech perception in terms of encoding of durational parameters of verbal utterances. Verbal working memory tasks, lexical response selection, and auditory imagery of word strings have been reported to elicit activation clusters of a similar location. Conceivably, representation of the temporal structure of speech sound sequences represents the common denominator of cerebellar participation in cognitive tasks acting on a phonetic code.     

Measuring brain beats: Cardiac-aligned fast functional magnetic resonance imaging signals

Blood and cerebrospinal fluid (CSF) pulse and flow throughout the brain, driven by the cardiac cycle. These fluid dynamics, which are essential to healthy brain function, are characterized by several noninvasive magnetic resonance imaging (MRI) methods. Recent developments in fast MRI, specifically simultaneous multislice acquisition methods, provide a new opportunity to rapidly and broadly assess cardiac-driven flow, including CSF spaces, surface vessels and parenchymal vessels. We use these techniques to assess blood and CSF flow dynamics in brief (3.5 min) scans on a conventional 3 T MRI scanner in five subjects. Cardiac pulses are measured with a photoplethysmography (PPG) on the index finger, along with functional MRI (fMRI) signals in the brain. We, retrospectively, align the fMRI signals to the heartbeat. Highly reliable cardiac-gated fMRI temporal signals are observed in CSF and blood on the timescale of one heartbeat (test–retest reliability within subjects R² > 50%). In blood vessels, a local minimum is observed following systole. In CSF spaces, the ventricles and subarachnoid spaces have a local maximum following systole instead. Slower resting-state scans with slice timing, retrospectively, aligned to the cardiac pulse, reveal similar cardiac-gated responses. The cardiac-gated measurements estimate the amplitude and phase of fMRI pulsations in the CSF relative to those in the arteries, an estimate of the local intracranial impedance. Cardiac aligned fMRI signals can provide new insights about fluid dynamics or diagnostics for diseases where these dynamics are important.     

腹腔内毒素刺激后的大鼠脑功能磁共振成像研究

大鼠腹腔内给予内毒素脂多糖(LPS)后,应用无创性、可连续观察的功能磁共振成像(fMRI)技术观察前脑部分脑区局部血氧水平的变化.结果显示,视前区、下丘脑室旁核、扣带回和海马/脉络组织区的fMRI信号强度在腹腔注射LPS后不同时间点呈现不规则的上升状态,提示这些区域参与了对外周注射LPS的反应.本研究说明fMRI可用于在神经免疫调节领域的研究中对实验动物脑内活动的无创性、可连续性观察.     

An efficient functional magnetic resonance imaging data reduction strategy using neighborhood preserving embedding algorithm

High dimensionality data have become common in neuroimaging fields, especially group‐level functional magnetic resonance imaging (fMRI) datasets. fMRI connectivity analysis is a widely used, powerful technique for studying functional brain networks to probe underlying mechanisms of brain function and neuropsychological disorders. However, data‐driven technique like independent components analysis (ICA), can yield unstable and inconsistent results, confounding the true effects of interest and hindering the understanding of brain functionality and connectivity. A key contributing factor to this instability is the information loss that occurs during fMRI data reduction. Data reduction of high dimensionality fMRI data in the temporal domain to identify the important information within group datasets is necessary for such analyses and is crucial to ensure the accuracy and stability of the outputs. In this study, we describe an fMRI data reduction strategy based on an adapted neighborhood preserving embedding (NPE) algorithm. Both simulated and real data results indicate that, compared with the widely used data reduction method, principal component analysis, the NPE‐based data reduction method (a) shows superior performance on efficient data reduction, while enhancing group‐level information, (b) develops a unique stratagem for selecting components based on an adjacency graph of eigenvectors, (c) generates more reliable and reproducible brain networks under different model orders when the outputs of NPE are used for ICA, (d) is more sensitive to revealing task‐evoked activation for task fMRI, and (e) is extremely attractive and powerful for the increasingly popular fast fMRI and very large datasets.     

Functional magnetic resonance imaging of verbal fluency and confrontation naming using compressed image acquisition to permit overt responses

Verbal fluency and confrontation naming, two tests of word retrieval, are of great utility in the field of cognitive neuroscience. However, in the context of functional magnetic resonance imaging (fMRI), movement artefact has necessitated the use of covert paradigms, which has limited clinical application. We developed two overt fMRI paradigms that allowed for performance measurement and hence were appropriate for use with patient groups. The paradigms incorporated a blocked-design and compressed-acquisition methodology where cues were presented and responses made in a "silent" period allowing for performance measurement. The slow response pace was specifically designed for older and potentially cognitively impaired participants. Verbal fluency was associated with activation in the middle frontal gyrus (Brodmann areas 46 and 9), anterior cingulate gyrus and inferior frontal gyrus (area 44 and 45). Confrontation naming activated areas of the temporo-occipital cortices (areas 18, 19, and 37) and the inferior frontal gyrus. The two paradigms successfully activated regions involved in executive and word retrieval processes and overcame the potential artefacts resulting from overt speech during image acquisition, providing useful neuropsychological tools to investigate cognitive deficits in clinical populations.     

脑震荡综合征与功能性核磁共振成像

脑震荡综合征是轻型外伤性颅脑损伤后常见的一组临床症候群。虽然大多数轻型颅脑损伤患者在一个月之内能治愈,但是部分患者在脑外伤后会持续存在脑震荡综合征达数月或数年,甚至终生。目前。关于脑震荡综合征的病理改变还不是很清楚,但是大家普遍认为脑震荡结局是功能的改变而不是解剖结构的改变。因此,应用功能性核磁共振技术就能发现结构性影像所不能发现的脑组织功能变化,对轻型外伤性颅脑损伤作出及时而准确的诊断。本文就功能性核磁共振成像技术在脑震荡综合征中的应用做一综述。     

Quantitative functional magnetic resonance imaging of brain activity using bolus-tracking arterial spin labeling

Blood oxygen level dependent (BOLD) functional magnetic resonance imaging (fMRI) is the most widely used method for mapping neural activity in the brain. The interpretation of altered BOLD signals is problematic when cerebral blood flow (CBF) or cerebral blood volume change because of aging and/or neurodegenerative diseases. In this study, a recently developed quantitative arterial spin labeling (ASL) approach, bolus-tracking ASL (btASL), was applied to an fMRI experiment in the rat brain. The mean transit time (MTT), capillary transit time (CTT), relative cerebral blood volume of labeled water (rCBV_lw), relative cerebral blood flow (rCBF), and perfusion coefficient in the forelimb region of the somatosensory cortex were quantified during neuronal activation and in the resting state. The average MTT and CTT were 1.939±0.175 and 1.606±0.106 secs, respectively, in the resting state. Both times decreased significantly to 1.616±0.207 and 1.305±0.201 secs, respectively, during activation. The rCBV_lw, rCBF, and perfusion coefficient increased on average by a factor of 1.123±0.006, 1.353±0.078, and 1.479±0.148, respectively, during activation. In contrast to BOLD techniques, btASL yields physiologically relevant indices of the functional hyperemia that accompanies neuronal activation.     

超高场磁共振功能成像辅助切除躯体感觉区胶质瘤(附5例报告)

目的应用超高场磁共振功能成像技术进行手术前后研究脑躯体感觉功能区肿瘤与功能区的定位,辅助切除躯体感觉功能区胶质瘤。方法5例邻近或累及躯体感觉功能区的胶质瘤患者,术前行双手持物对接刺激策略,在3.0T磁共振采用血氧水平依赖(BOLD)原理进行图像采集,经工作站(Leonardo syngo 2003A,Siemens)提供的BOLD功能图像分析软件包进行分析获得脑运动功能区的激活图像,参与神经外科手术方案的制定。所有患者均在唤醒麻醉下进行显微外科手术,在术前脑功能磁共振图像指导下利用皮质直接电刺激定位感觉区与运动区。在保护脑功能区功能不受损的前提下,最大程度地切除胶质瘤。术前、术后均行KPS评分,判断患者的状态。结果(1)5例躯体感觉功能区胶质瘤,通过此项技术获得了较好的BOLD功能磁共振成像感觉功能区激活图像,定位躯体感觉功能区。(2)患者在唤醒麻醉下,在术前脑功能磁共振图像指导下利用直接皮质电刺激快捷、准确进行中央后回定位,两者具有良好的一致性。结论应用3.0T MRI可以于术前更好地利用BOLD技术显示躯体感觉功能区与脑胶质瘤的解剖关系,以指导唤醒麻醉下直接皮质电刺激定位躯体感觉功能区的手术,实现最大程度保护患者重要的功能并最大程度地切除肿瘤。     

Establishing a counter-empathy processing model: evidence from functional magnetic resonance imaging

Counter-empathy significantly affects people’s social lives. Previous evidence indicates that the degree of counter-empathy can be either strong or weak. Strong counter-empathy easily occurs when empathizers are prejudiced against the targets of empathy (e.g. prejudice against outgroup members) and activates brain regions that are opposite to those activated by empathy. Weak counter-empathy may have different neural processing paths from strong ones, but its underlying neural mechanisms remain unclear. In this work, we used an unfair distribution paradigm, which can reduce participants’ prejudice against persons empathized with, and functional magnetic resonance imaging to explore the neural mechanisms underlying counter-empathy. Here, empathy and counter-empathy shared a common neural mechanism, induced by unfair distribution, in the right middle temporal gyrus. Counter-empathy activated distinct brain regions that differed from those of empathic responses in different situations. The functions of these brain regions, which included the middle frontal, middle temporal and left medial superior gyri, were similar and mostly related to emotional regulation and cognitive processing. Here, we propose a process model of counter-empathy, involving two processing paths according to whether or not prejudice exists. This study has theoretical significance and broadens our understanding of the cognitive neural mechanisms underlying empathy and counter-empathy.