Neural substrates of the cognitive processes underlying spelling: Evidence from MR diffusion and perfusion imaging

Background: Despite a rich literature on the cognitive processes underlying spelling, there is little known about the neural substrates of these processes. Aims: The study aimed to identify regions of brain dysfunction associated with impairment of each cognitive process underlying spelling. It was hypothesised that impairments of distinct components of the spelling task would be associated with different areas of low blood flow or infarction in acute stroke patients. Methods & Procedures: Associations between impairment of each component of the spelling process and hypoperfusion and/or infarct of any of 11 Brodmann's areas (BAs) were identified in a consecutive series of 80 patients studied within 24 hours of onset of left hemisphere stroke. Impairment of each component of spelling was identified with tests of written naming, word comprehension, spelling words and pseudowords to dictation, direct and delayed copying, and case transcoding. Infarct and/or hypoperfusion in each BA was identified with MR diffusion-weighted imaging and perfusion-weighted imaging. Significant associations were identified with a correlation matrix, and the strongest associations were confirmed with chi square analysis. Outcomes & Results: Impairments of various cognitive processes were associated with separate regions of tissue dysfunction. Conclusions: It was concluded that spelling involves a network of relatively independent processes that rely on different brain regions.     

3-Tesla versus 1.5-Tesla magnetic resonance diffusion and perfusion imaging in hyperacute ischemic stroke

BACKGROUND: Clinical 3-tesla magnetic resonance imaging systems are becoming widespread. No studies have examined differences between 1.5-tesla and 3-tesla imaging for the assessment of hyperacute ischemic stroke (<6 h from symptom onset). Our objective was to compare 1.5-tesla and 3-tesla diffusion and perfusion imaging for hyperacute stroke using optimized protocols. METHODS: Three patients or their surrogate provided informed consent. Diffusion-weighted imaging (DWI) and perfusion-weighted imaging (PWI) was performed sequentially at 1.5 T and 3 T. DWI, apparent diffusion coefficient (ADC) maps and relative time-to-peak (TTP) maps were registered and assessed. DWI contrast-to-noise ratio (CNR) and ADC contrast were measured and compared. The infarct lesion volume (ILV) and thresholded ischemic volume (TIV) were estimated on the ADC and TTP maps, respectively, with the penumbral volume being defined as the difference between these volumes. RESULTS: Qualitatively, the 3-tesla TTP images exhibited greater feature detail. Quantitatively, the DWI CNR and ILV were similar at both field strengths, the ADC contrast was greater at 3 T and the TIV and penumbral volumes were much smaller at 3 T. CONCLUSIONS: Overall, the 3-tesla diffusion and perfusion images were at least as good and in some ways superior to the 1.5-tesla images for assessing hyperacute stroke. The TTP maps showed greater feature detail at 3 T. The ischemic and penumbra volumes were much greater at 1.5 T, indicating a potential difference in the diagnostic utility of the PWI-DWI mismatch between field strengths.     

Diffusion and perfusion magnetic resonance imaging in childhood stroke

Two magnetic resonance imaging techniques, diffusion and perfusion imaging, are being used increasingly for evaluation of pathophysiology of stroke. This article introduces these techniques and reports some initial studies using these approaches, together with conventional T2-weighted magnetic resonance imaging, for investigation of childhood stroke. It is shown that the combination of T2-weighted and diffusion images can provide information about the timing of stroke events in childhood, and perfusion imaging can detect abnormalities not visible by other magnetic resonance imaging techniques. These magnetic resonance methods therefore should play an important role in investigation of children with stroke and could be of particular value in studies of at-risk populations of children such as those with sickle cell disease.     

Altered neural substrates of cognitive control in childhood ADHD: evidence from functional magnetic resonance imaging

OBJECTIVE: The study compared the neural bases of two cognitive control operations, interference suppression and response inhibition, between children with and children without attention deficit hyperactivity disorder (ADHD). METHOD: Ten children (7-11 years of age) with combined-type ADHD and 10 comparison subjects matched for age and gender underwent rapid event-related functional magnetic resonance imaging (fMRI) during performance of a modified flanker task. Functional maps were generated through group averaging and performance-based correlational analyses. RESULTS: Interference suppression in ADHD subjects was characterized by reduced engagement of a frontal-striatal-temporal-parietal network that subserved healthy performance. In contrast, response inhibition performance relied upon different regions in the two groups, frontal-striatal in comparison subjects but right superior temporal in ADHD children. CONCLUSIONS: Alteration in the neural basis of two cognitive control operations in childhood ADHD was characterized by distinct, rather than unitary, patterns of functional abnormality. Greater between-group overlap in the neural network activated for interference suppression than in response inhibition suggests that components of cognitive control are differentially sensitive to ADHD. The ADHD children's inability to activate the caudate nucleus constitutes a core abnormality in ADHD. Observed functional abnormalities did not result from prolonged stimulant exposure, since most children were medication naive.     

灌注及弥散磁共振成像在急性缺血性脑卒中的应用

目的　评估磁共振 (MRI)弥散加权成像 (DWI)及灌注加权成像 (PWI)在急性缺血性卒中指导溶栓治疗的应用价值。方法　对 44例急性 (≤ 6h)缺血性卒中患者行DWI、PWI扫描 ,DWI及PWI的不匹配区为缺血半暗带 ,根据半暗带是否存在确定患者是否适合溶栓治疗。结果　脑梗死患者 33例 ,其中 2 3例 (52 3 % )有明显半暗带存在 (PWI >DWI) ;1 0例 (2 2 7% )无明显半暗带 (PWI=DWI)。临床表现为短暂性缺血发作 (TIA)者 1 1例 (2 5 0 % )。结论　PWI及DWI对照研究有助于发现超早期脑梗死半暗带 ,指导溶栓治疗 ;临床表现结合DWI有助于除外TIA     

Neural substrates of emotion as revealed by functional magnetic resonance imaging.

OBJECTIVES: To examine the brain circuitry involved in emotional experience and determine whether the cerebral hemispheres are specialized for positive and negative emotional experience. BACKGROUND: Recent research has provided a preliminary sketch of the neurologic underpinnings of emotional processing involving specialized contributions of limbic and cortical brain regions. Electrophysiologic, functional imaging, and Wada test data have suggested positive, approach-related emotions are associated with left cerebral hemisphere regions, whereas negative, withdrawal-related emotions appear to be more aligned with right hemisphere mechanisms. METHOD: These emotional-neural associations were investigated using functional magnetic resonance imaging in 10 healthy controls with 20 positively and 20 negatively valenced pictures from the International Affective Picture System in a counterbalanced order. Pictures were viewed within a 1.5 Telsa scanner through computerized video goggles. RESULTS: Emotional pictures resulted in significantly increased blood flow bilaterally in the mesial frontal lobe/anterior cingulate gyrus, dorsolateral frontal lobe, amygdala/anterior temporal regions, and cerebellum. Negative emotional pictures resulted in greater activation of the right hemisphere, and positive pictures caused greater activation of the left hemisphere. CONCLUSIONS: Results are consistent with theories emphasizing the importance of circuitry linking subcortical structures with mesial temporal, anterior cingulate, and frontal lobe regions in emotion and with the valence model of emotion that posits lateralized cerebral specialization for positive and negative emotional experience.     

Magnetic resonance perfusion imaging evaluation in perfusion abnormalities of the cerebellum after supratentorial unilateral hyperacute cerebral infarction

Magnetic resonance imaging (MRI) data of 10 patients with hyperacute cerebral infarction (≤6 hours) were retrospectively analyzed.Six patients exhibited perfusion defects on negative enhancement integral maps,four patients exhibited perfusion differences in pseudo-color on mean time to enhance maps,and three patients exhibited perfusion differences in pseudo-color on time to minimum maps.Dynamic susceptibility contrast-enhanced perfusion weighted imaging revealed a significant increase in region negative enhancement integral in the affected hemisphere of patients with cerebral infarction.The results suggest that dynamic susceptibility contrast-enhanced perfusion weighted imaging can clearly detect perfusion abnormalities in the cerebellum after unilateral hyperacute cerebral infarction.     

Ultrafast magnetic resonance imaging protocols in stroke

Stroke is the third leading cause of death and morbidity in the Western world. Ever since the publication of the major randomized trials showing the benefit of thrombolysis in early acute stroke, there has been growing impetus for the diagnosis of acute stroke to become a medical emergency. Currently, computed tomography (CT) remains the diagnostic method of choice in the assessment of acute strokes. It is practical, rapid, and widely available and, as used in these trials, can robustly exclude acute hemorrhage before potential thrombolysis. Although magnetic resonance imaging (MRI) has a number of advantages over unenhanced CT, the practicalities of performing MRI in the acute setting have hampered its widespread use. There are several reasons why speed of imaging is paramount in acute strokes. Firstly, such patients are often unwell and agitated and, as such, require close monitoring. Moreover, because of the short window within which intravenous thrombolysis can be given, time-consuming imaging studies decrease the therapeutic options available and likelihood of successful intervention. This review summarizes the latest developments in ultrafast imaging protocols that have the potential to improve practical feasibility, and thus propel MRI back to the forefront of acute stroke imaging.     

Neural substrates for voluntary suppression of negative affect: a functional magnetic resonance imaging study.

BACKGROUND: Successful control of affect partly depends on the capacity to modulate negative emotional responses through the use of cognitive strategies. Although the capacity to regulate emotions is critical to mental well-being, its neural substrates remain unclear. METHODS: We used functional magnetic resonance imaging to ascertain brain regions involved in the voluntary regulation of emotion and whether dynamic changes in negative emotional experience can modulate their activation. Fourteen healthy subjects were scanned while they either maintained the negative affect evoked by highly arousing and aversive pictures (e.g., experience naturally) or suppressed their affect using cognitive reappraisal. In addition to a condition-based analysis, online subjective ratings of intensity of negative affect were used as covariates of brain activity. RESULTS: Inhibition of negative affect was associated with activation of dorsal anterior cingulate, dorsal medial prefrontal, and lateral prefrontal cortices, and attenuation of brain activity within limbic regions (e.g., nucleus accumbens/extended amygdala). Furthermore, activity within dorsal anterior cingulate was inversely related to intensity of negative affect, whereas activation of the amygdala was positively covaried with increasing negative affect. CONCLUSIONS: These findings highlight a functional dissociation of corticolimbic brain responses, involving enhanced activation of prefrontal cortex and attenuation of limbic areas, during volitional suppression of negative emotion.     

Identifying the perfusion deficit in acute stroke with resting‐state functional magnetic resonance imaging

Temporal delay in blood oxygenation level–dependent (BOLD) signals may be sensitive to perfusion deficits in acute stroke. Resting‐state functional magnetic resonance imaging (rsfMRI) was added to a standard stroke MRI protocol. We calculated the time delay between the BOLD signal at each voxel and the whole‐brain signal using time‐lagged correlation and compared the results to mean transit time derived using bolus tracking. In all 11 patients, areas exhibiting significant delay in BOLD signal corresponded to areas of hypoperfusion identified by contrast‐based perfusion MRI. Time delay analysis of rsfMRI provides information comparable to that of conventional perfusion MRI without the need for contrast agents. ANN NEUROL 2013.     

Neural indicators of inference processes in text comprehension: an event-related functional magnetic resonance imaging study

During language comprehension, readers or listeners routinely infer information that has not been stated literally in a given text or utterance in order to construct a coherent mental representation (situation model). We used a verification task in a behavioral study and in an event-related functional magnetic resonance imaging (fMRI) experiment to investigate the inference construction process. After having read sentences that mention the outcome of an event explicitly, implicitly, or not at all, participants verified the plausibility of short statements with respect to the context of the just read sentence. The results of the behavioral study established the verification task as a valid method for studying inferences. In the fMRI study, the dorsomedial prefrontal cortex was the most prominent area that was involved in the processing of inference statements. Regions in the left and right temporal lobes were associated with comparison processes that are based on the propositional representations of context sentence and test statements. The results are discussed with respect to levels of representations and the memory systems that underlie the verification process in the different sentence conditions.     

Diffusion and perfusion magnetic resonance imaging for the evaluation of acute stroke: potential use in guiding thrombolytic therapy

Recent data indicate that diffusion/perfusion weighted imaging could eventually play a significant role in acute stroke management, particularly in determining the suitability of acute stroke patients for thrombolytic therapy. The evidence supporting these uses is reviewed, and the future role of diffusion and perfusion weighted imaging in acute stroke management is discussed.     

Echoplanar magnetic resonance imaging in acute stroke.

Echoplanar magnetic resonance imaging (EPI) enables rapid, non-invasive imaging and analysis of cerebral pathophysiology in acute stroke. It represents an important clinical advance over computed tomography (CT) and conventional magnetic resonance (MR) scanning. It can rapidly delineate infarcted cerebral tissue and distinguish acute from chronic stroke. In addition, EPI has the potential to quickly determine the presence and degree of potentially viable brain tissue in the ischaemic penumbra. Thrombolysis is thought to reperfuse the penumbra and hence reduce infarct size. The thrombolytic agent tissue plasminogen activator (t-PA) improves outcome in ischaemic stroke when administered within the first 3 hours of onset. However, there is a significant risk of haemorrhage, and the time window for benefit may well exceed 3 hours in some patients. Hence, by facilitating diagnosis of 'at-risk' tissue in the ischaemic penumbra, a major clinical role of EPI may well become the rational selection of patients for acute interventional stroke therapy.