Benjamin Xu

Language dominance in partial epilepsy patients identified with an fMRI reading task

Background fMRI language tasks readily identify frontal language areas; temporal activation has been less consistent. No studies have compared clinical visual judgment to quantitative region of interest (ROI) analysis. Objective To identify temporal language areas in patients with partial epilepsy using a reading paradigm with clinical and ROI interpretation. Methods Thirty patients with temporal lobe epilepsy, aged 8 to 56 years, had 1.5-T fMRI. Patients silently named an object described by a sentence compared to a visual control. Data were analyzed with ROI analysis from t-maps. Regional asymmetry indices (AI) were calculated ([L−R]/[L+R]) and language dominance defined as >0.20. t-Maps were visually rated by three readers at three t thresholds. Twenty-one patients had intracarotid amobarbital test (IAT). Results The fMRI reading task provided evidence of language lateralization in 27 of 30 patients with ROI analysis. Twenty-five were left dominant, two right, one bilateral, and two were nondiagnostic; IAT and fMRI agreed in most patients, three had partial agreement, none overtly disagreed. Interrater agreement ranged between 0.77 to 0.82 (Cramer V;p < 0.0001); agreement between visual and ROI reading with IAT was 0.71 to 0.77 (Cramer V;p < 0.0001). Viewing data at lower thresholds added interpretation to 12 patients on visual analysis and 8 with ROI analysis. Conclusions An fMRI reading paradigm can identify language dominance in frontal and temporal areas. Clinical visual interpretation is comparable to quantitative ROI analysis.

fMRI language task panel improves determination of language dominance.

Background: fMRI language tasks reliably identify language areas in presurgical epilepsy patients, but activation using single paradigms may disagree with the intracarotid amobarbital test (IAT). Objective: To determine whether a panel of fMRI tasks targeting different aspects of language processing increases accuracy in determining hemisphere language dominance. Methods: Twenty-six patients age 12 to 56 years, predominantly with temporal lobe epilepsy, were studied using whole-brain 1.5 T fMRI (echo planar imaging, blood oxygenation level–dependent) with three task categories using a block design: verbal fluency, reading comprehension, and auditory comprehension. fMRI t maps were visually rated at three thresholds. All patients had assessment of language lateralization by IAT. Results: fMRI showed left dominance in 21 patients, right dominance in 2, and bilateral activation in 2; raters disagreed over a left vs right bilateral rating in 1 patient. There was full agreement between IAT and fMRI in 21 of 25 patients (IAT failed in 1). In three instances of partial disparity with IAT, the fMRI panel showed consistent findings across raters. Agreement between raters was excellent (partial disagreement in only one patient); the panel of tasks was superior to any single task for interrater agreement (Cramer V 0.93 [range 0.91 to 1.0] vs 0.72 [range 0.60 to 0.86]). Conclusions: A panel of fMRI language paradigms may be more accurate for evaluating partial epilepsy patients than a single task. A panel of tasks reduces the likelihood of nondiagnostic findings, improves interrater reliability, and helps confirm language laterality.

Auditory comprehension of language in young children Neural networks identified with fMRI

Objective: The organization of neuronal systems that process language in young children is poorly understood. The authors used fMRI to identify brain regions underlying auditory comprehension in healthy young children. Methods: Fifteen right-handed children (mean age 6.8 years) underwent fMRI at 1.5-T using blood oxygen level dependent echoplanar imaging. They listened to stories with a reverse speech control condition. Group data were analyzed with statistical parametric mapping. Individual subject data were analyzed with a region of interest approach based on t-maps. An asymmetry index (AI = [(L−R)/(L+R)]) was calculated for each region. Results: Group analysis showed significant activation in the left middle temporal gyrus (Brodmann area [BA] 21) and left superior temporal gyrus (BA 22) along the superior temporal sulcus extending back to the angular gyrus (BA 39). Individual maps showed lateralized activation in temporal regions (AI > 0.49 ± 0.39). There was minimal activation in the frontal lobe. There were no significant correlations between age and regional AI. Conclusion: Networks for auditory language processing are regionally localized and lateralized by age 5. These data may provide a means to interpret language fMRI studies performed in preparation for brain surgery, and may be employed to investigate the effect of chronic disease states, such as epilepsy, on language organization during critical periods for plasticity.

fMRI identifies regional specialization of neural networks for reading in young children

Background: fMRI allows mapping of neural networks underlying cognitive networks during development, but few studies have systematically examined children 7 and younger, in whom language networks may be more diffusely organized than in adults. Objective: To identify neural networks during early reading consolidation in young children. Methods: The authors studied 16 normal, right-handed, native English-speaking children with a mean age of 7.2 years (range 5.8 to 7.9) with fMRI reading paradigms adjusted for reading level. Data were acquired with the echoplanar imaging BOLD technique at 1.5 T. Group data were analyzed with statistical parametric mapping (SPM-99); individual data sets were analyzed with a region of interest approach from individual study t maps (t = 4). The number of activated pixels in brain regions was determined and an asymmetry index (AI) ([L-R]/[L+R]) calculated for each region. Results: In group analysis the authors found prominent activation in left inferior temporal occipital junction and left fusiform gyrus (Brodmann area [BA] 37), middle temporal gyrus (BA 21, 22), middle frontal gyrus (BA 44, 45), and the supplementary motor area. Activation was strongly lateralized in middle frontal gyrus and Wernicke areas (AI 0.54, 0.62). Fourteen subjects had left-sided language lateralization, one was bilateral, and one had poor activation. Conclusions: The neural networks that process reading are strongly lateralized and regionally specific by age 6 to 7 years. Neural networks in early readers are similar to those in adults.

Cortical localization of reading in normal children An fMRI language study

Background: fMRI provides a noninvasive means of identifying the location and organization of neural networks that underlie cognitive functions. Objective: To identify, using fMRI, brain regions involved in processing written text in children. Methods: The authors studied nine normal right-handed native English-speaking children, aged 10.2 years (range 7.9 to 13.3 years), with two paradigms: reading Aesop’s Fables and “Read Response Naming” (reading a description of an object that was then silently named). Data were acquired using blood oxygen level-dependent fMRI. Group data were analyzed with statistical parametric mapping; individual data sets were analyzed with a region-of-interest approach from individual study t maps. The number of activated pixels was determined in brain regions and an asymmetry index (AI = [L − R]/[L + R]) calculated for each region. Results: The authors found strong activation in the left middle temporal gyrus and left midfrontal gyrus and variable activation in left inferior frontal gyrus for both reading tasks in the group analysis (z > 5.5 to 9.1). All subjects had strong left-sided lateralization for both tasks in middle/superior temporal gyrus, inferior frontal gyrus, and middle frontal gyrus (AI = 0.76 to 1.0 for t = 4). Reading Fables activated twice as many pixels in temporal cortex as the Read Response Naming task; activation in dorsolateral prefrontal cortex was similar for both tasks. Small homologous right middle temporal region activation was seen with reading a fable. Conclusions: The neural networks that process reading appear to be lateralized and localized by middle to late childhood. Reading text paradigms may prove useful for identifying frontal and temporal language-processing areas and for determining language dominance in children experiencing epilepsy or undergoing tumor surgery.

Effects of different viewing perspectives on somatosensory activations during observation of touch

Previous studies showed that neurons in the monkey premotor cortex became active when performing a particular action and also when observing the same action performed by others. These findings suggest a mirror system for action observation. Recently, bimodal neurons, sensitive both to visual and tactile stimulation, were reported in the parietal cortex, suggesting a potential mirror neuron system for observing and experiencing tactile stimulation. Subsequently, a mirror neuron system for observed touch has been suggested. The current study was designed to determine whether the activation of a sensory mirror system during touch observation is affected by possible attributions of the observed touch to oneself (subjective view) or to somebody else (objective view). In the study, healthy volunteers observed video clips of a touched or nontouched hand either in an egocentric or in an allocentric perspective during functional magnetic resonance imaging. Results showed activation of somatosensory cortices when observing the hand being touched in egocentric as well as in the allocentric perspectives. Moreover, somatosensory responses differed depending on the perspective of the observed touch. We discuss the results in terms of a possible mirror neuron system for observed and experienced touch. Hum Brain Mapp 2009.

Seizure focus affects regional language networks assessed by fMRI.

Objective: To investigate the degree of language dominance in patients with left and right hemisphere seizure foci compared to normal volunteers using a fMRI reading comprehension task. Methods: Fifty patients with complex partial epilepsy, aged 8 to 56 years and 33 normal volunteers, aged 7 to 34 had fMRI (1.5 T) and neuropsychological testing. Participants silently named an object described by a sentence compared to a visual control. Data were analyzed with region of interest (ROI) analysis based on t maps for inferior frontal gyrus (IFG), midfrontal gyrus (MFG), and Wernicke area (WA). Regional asymmetry indices (AIs) were calculated [(L − R)/(L + R)]; AI >0.20 was deemed left dominant and AI <0.20 as atypical language. Results: Left hemisphere focus patients had a higher likelihood of atypical language than right hemisphere focus patients (21% vs 0%, χ2 < 0.002). Left hemisphere focus patients, excluding those with atypical language, had lower regional AI in IFG, MFG, and WA than controls. Right hemisphere focus patients were all left language dominant and had a lower AI than controls in WA and MFG, but not for IFG. AI in MFG and WA were similar between left hemisphere focus/left language patients and right hemisphere focus patients. Patients activated more voxels than healthy volunteers. Lower AIs were attributable to greater activation in right homologous regions. Less activation in the right-side WA correlated with better verbal memory performance in right focus/left hemisphere-dominant patients, whereas less strongly lateralized activation in IFG correlated better with Verbal IQ in left focus/left hemisphere-dominant patients. Conclusions: Patients had lower asymmetry indices than healthy controls, reflecting increased recruitment of homologous right hemisphere areas for language processing. Greater right hemisphere activation may reflect greater cognitive effort in patient populations, the effect of epilepsy, or its treatment. Regional activation patterns reflect adaptive efforts at recruiting more widespread language processing networks that are differentially affected based on hemisphere of seizure focus.

MR compatible force sensing system for real-time monitoring of wrist moments during fMRI testing.

The ability to monitor and quantify force exertions made by individuals during fMRI scans of the brain would provide researchers and clinicians a standardized, well-controlled behavioral task that could improve the repeatability and accuracy of imaging studies. In this work, we present a MRI compatible wrist module that is capable of measuring isometric forces generated at the hand and joint moments along wrist flexion-extension and wrist ulna-radial deviation axes. Joint moments measured by the system can be visually displayed to the individual and used during target matching tasks. In a small set of pilot tests, it was found that the noise on the force and moment signals were not affected by the magnetic fields nor were the fMRI images influenced by the presence of the device. In future studies, we plan to use the wrist module to investigate cortical reorganization in stroke patients following prolonged neurorehabilitation.

PreSMA stimulation changes task-free functional connectivity in the fronto-basal-ganglia that correlates with response inhibition efficiency

Previous work using transcranial magnetic stimulation (TMS) demonstrated that the right presupplementary motor area (preSMA), a node in the fronto‐basal‐ganglia network, is critical for response inhibition. However, TMS influences interconnected regions, raising the possibility of a link between the preSMA activity and the functional connectivity within the network. To understand this relationship, we applied single‐pulse TMS to the right preSMA during functional magnetic resonance imaging when the subjects were at rest to examine changes in neural activity and functional connectivity within the network in relation to the efficiency of response inhibition evaluated with a stop‐signal task. The results showed that preSMA‐TMS increased activation in the right inferior‐frontal cortex (rIFC) and basal ganglia and modulated their task‐free functional connectivity. Both the TMS‐induced changes in the basal‐ganglia activation and the functional connectivity between rIFC and left striatum, and of the overall network correlated with the efficiency of response inhibition and with the white‐matter microstructure along the preSMA–rIFC pathway. These results suggest that the task‐free functional and structural connectivity between the rIFCop and basal ganglia are critical to the efficiency of response inhibition. Hum Brain Mapp 37:3236–3249, 2016.

Effect of foreknowledge on neural activity of primary "go" responses relates to response stopping and switching

Being able to stop (or inhibit) an action rapidly as in a stop-signal task (SST) is an essential human ability. Previous studies showed that when a pre-stimulus cue warned of the possible need to stop a response in an upcoming trial, participants’ response time (RT) increased if the subsequent trial required a “go” response (i.e., “go” RT cost) relative to a trial where this uncertainty was not present. This increase of the “go” RT correlated with more efficient response stopping. However, it remains a question whether foreknowledge of upcoming inhibition trials given prior to the task is sufficient to modulate neural activity associated with the primary “go” responses irrespective of whether stopping an overt response is required. We presented three task conditions with identical primary (i.e., “go”) response trials but without pre-stimulus cues. Participants were informed that Condition 1 had only “go” trials (All-go condition), Condition 2 required a “stop” response for some trials (Stop condition), and Condition 3 required a response incongruent with the primary response (i.e., Switch response) for some trials (Switch condition). Participants performed the tasks during functional magnetic resonance imaging (fMRI) scans. Results showed a significant increase in the “go” RT (cost) in the Stop and Switch conditions relative to the All-go condition. The “go” RT cost was correlated with decreased inhibition time. fMRI activation in the frontal-basal-ganglia regions during the “go” responses in the Stop and Switch conditions was also correlated with the efficiency of Stop and Switch responses. These results suggest that foreknowledge prior to the task is sufficient to influence neural activity associated with the primary response and modulate inhibition efficiency, irrespective of whether stopping an overt response is required.