1,720,975 research outputs found
Single-Trial Characterization of BOLD fMRI Responses by Self-Organizing Neural Networks
No full textFunctional magnetic resonance imaging (fMRI) plays a dominant role in human brain mapping studies. As of today, no standards exist for processing fMRI data and analysis techniques are often associated to the different stimulation paradigms used to acquire functional data. Being able to estimate the hemodynamic response following a single execution of a task permits to characterize its relationship to different aspects of the stimulus, and of the subject’s performance. This works is aimed to test a strategy for the characterization of single trial-related BOLD fMRI responses based on the self-organizing maps method of Kohonen (SOMs). Analysis have been carried out on synthetic fMRI images modeling activation and on data from a single-event fMRI experiment on one human subject performing a basic motor task. Results were able to define the potentiality range for this data-driven methodology in monitoring the evolution of the BOLD response deriving from a single stimulation
Parietal/premotor lesions effects on visuomotor cognition in neuro-oncology patients: A multimodal study
Full text linkBackground: Assessing prior to surgery the functionality of brain areas exposed near the tumor requires a multimodal approach that combines the use of neuropsychological testing and fMRI tasks. Paradigms based on motor imagery, which corresponds to the ability to mentally evoke a movement, in the absence of actual action execution, can be used to test sensorimotor areas and the functionality of mental motor representations. Methods: The most commonly used paradigm is the Limb Laterality Recognition Task (LLRT), requiring judgments about whether a limb belongs to the left or right side of the body. The group studied included 38 patients with high-grade (N = 21), low-grade (N = 11) gliomas and meningiomas (N = 6) in areas anterior (N = 21) and posterior (N = 17) to the central sulcus. Patients before surgery underwent neuropsychological assessment and fMRI. They performed the LLRT as an fMRI task. Accuracy, and neuroimaging data were collected and combined in a multimodal study. Structural MRI data analyses were performed by subtracting the overlap of volumes of interest (VOIs) plotted on lesions from the impaired patient group vs the overlap of VOIs from the spared group. The fMRI analyses were performed comparing the impaired patients and spared group. Results: In general, patients were within normal limits on many neuropsychological screening tests. Compared with the control group, 17/38 patients had significantly different performance. The subtraction between the VOIs overlay of the impaired patients' group vs. the VOIs overlay of the spared group revealed that the areas maximally involved by lesions in the impaired patients' group were the right postcentral gyrus, right inferior parietal lobe, right supramarginal gyrus, right precentral gyrus, paracentral lobule, left postcentral gyrus, right superior parietal lobe, left inferior parietal lobe, and left superior and middle frontal gyrus. Analysis of the fMRI data showed which of these areas contributes to a correct LLRT performance. The task (vs. rest) in the group comparison (spared vs. impaired patients) activated a cluster in the left inferior parietal lobe. Conclusion: Underlying the altered performance at LLRT in patients with lesions to the parietal and premotor areas of the right and left hemispheres is a difference in activation of the left inferior parietal lobe. This region is involved in visuomotor processes and those related to motor attention, movement selection, and motor planning
An ARX model-based approach to trial by trial identification of fMRI-BOLD responses
No full textBeing able to estimate the fMRI-BOLD response following a single task or stimulus is certainly of value, since it allows to characterize its relationship to different aspects either of the stimulus, or of the subject's performance. In order to detect and characterize BOLD responses in single trials, we developed and validated a procedure based on an AutoRegressive model with eXogenous Input (ARX). The use of an individual exogenous input for each voxel makes the modeling sensitive enough to reveal differences across regions, avoiding any a priori assumption about the reference signal. The detection of variability across trials is ensured by a suitable choice, for each voxel, of the order of the moving average, which in our implementation determines the relative delay between the recorded and the reference signal. This is a quality useful in finding different time profiles of activation from high temporal resolution fMRI data. The results obtained from simulated fMRI data resulting from synthetic activations in actual noise indicate that such approach allows to evaluate important features of the response, such as the time to onset, and time to peak. Moreover, the results obtained from real high temporal resolution fMRI data acquired at l.5 T during a motor task are consistent with previous knowledge about the responses of different cortical areas in motor programming and execution. The proposed procedure should also prove useful as a pre-processing step in different approaches to the analysis of fMRI data
Functional Responses in the Human Spinal Cord during Willed Motor Actions: Evidence for Side- and Rate-Dependent Activity
No full textAlthough the spinal cord is the output station of the central motor system, little is known about the relationships between its functionalactivity and willed movement parameters in humans. We investigated here blood oxygenation level-dependent functional magneticresonance imaging (fMRI) signal changes in the cervical spinal cord during a simple finger-to-thumb opposition task in 13 right-handedvolunteers, using a dedicated array of 16 receive-only surface coils on a 3 Tesla MRI system. In a first experiment, we found significantfMRI signal increases on both sides of the lower cervical spinal cord while subjects performed the motor task at a comfortable pace (0.5Hz) using either hand. Both the spatial extent of movement-related clusters and peak signal increases were significantly higher on the sideof the cord ipsilateral to the moving hand than on the contralateral side. Movement-related activity was consistently larger than signalfluctuations during rest. In a second experiment, we recorded spinal cord responses while the same motor sequence was performed usingthe dominant hand at two different rates (0.5 or 1 Hz). The intensity but not the spatial extent of the response was larger during higherrates, and it was higher on the ipsilateral side of the cord. Notwithstanding the limited spatial resolving power of the adopted technique,the present results clearly indicate that the finger movement-related fMRI signals recorded from the spinal cord have a neural origin andthat as a result of recent technological advances, fMRI can be used to obtain novel and quantitative physiological information on theactivity of spinal circuit
Analisi di dati fMRI-BOLD a singolo evento: un approccio con reti neurali non supervisionate
No full textNegli studi di risonanza magnetica funzionale (fMRI) cerebrale hanno assunto particolare rilevanza i protocolli di stimolazione basati su singoli eventi. Nel lavoro viene descritta una strategia di analisi di dati fMRI-BOLD, con lo scopo di rilevare il profilo temporale della risposta ad ogni singola stimolazione, nelle diverse aree cerebrali coinvolte. Il metodo si avvale di una fase di pre-elaborazione dei dati finalizzata ad incrementare il basso contrasto segnale-rumore tipico di dati derivanti da un singolo evento e di una fase di classificazione, caratterizzazione e localizzazione delle risposte realizzata implementando una rete neurale basata sull’algoritmo di Kohonen delle mappe auto-organizzanti (SOMs). I risultati, ottenuti sia su immagini fMRI simulate, che su dati reali relativi ad un soggetto umano, mostrano la validita’ di questo approccio guidato dai dati nell’identificazione delle risposte ad una singola stimolazione e ne forniscono i limiti di applicabilita’
Percept-related activity in the human somatosensory system: functional magnetic resonance imaging studies
No full textIn this paper, we review blood oxygenation level-dependent (BOLD) functional magnetic resonance imaging (fMRI) studies addressing the neural correlates of touch, thermosensation, pain and the mechanisms of their cognitive modulation in healthy human subjects. There is evidence that fMRI signal changes can be elicited in the parietal cortex by stimulation of single mechanoceptive afferent fibers at suprathreshold intensities for conscious perception. Positive linear relationships between the amplitude or the spatial extents of BOLD fMRI signal changes, stimulus intensity and the perceived touch or pain intensity have been described in different brain areas. Some recent fMRI studies addressed the role of cortical areas in somatosensory perception by comparing the time course of cortical activity evoked by different kinds of stimuli with the temporal features of touch, heat or pain perception. Moreover, parametric single-trial functional MRI designs have been adopted in order to disentangle subprocesses within the nociceptive system. Available evidence suggest that studies that combine fMRI with psychophysical methods may provide a valuable approach for understanding complex perceptual mechanisms and top-down modulation of the somatosensory system by cognitive factors specifically related to selective attention and to anticipation. The brain networks underlying somatosensory perception are complex and highly distributed. A deeper understanding of perceptual-related brain mechanisms therefore requires new approaches suited to investigate the spatial and temporal dynamics of activation in different brain regions and their functional interaction
Is there a systematic bias of apparent diffusion coefficient (ADC) measurements of the breast if measured on different workstations? An inter- and intra-reader agreement study
No full textOBJECTIVES To evaluate the influence of post-processing systems, intra- and inter-reader agreement on the variability of apparent diffusion coefficient (ADC) measurements in breast lesions. METHODS Forty-one patients with 41 biopsy-proven breast lesions gave their informed consent and were included in this prospective IRB-approved study. Magnetic resonance imaging (MRI) examinations were performed at 1.5 T using an EPI-DWI sequence, with b-values of 0 and 1000 s/mm(2). Two radiologists (R1, R2) reviewed the images in separate sessions and measured the ADC for lesion, using MRI-workstation (S-WS), PACS-workstation (P-WS) and a commercial DICOM viewer (O-SW). Agreement was evaluated using the intraclass correlation coefficient (ICC), Bland-Altman plots and coefficient of variation (CV). RESULTS Thirty-one malignant, two high-risk and eight benign mass-like lesions were analysed. Intra-reader agreement was almost perfect (ICC-R1 = 0.974; ICC-R2 = 0.990) while inter-reader agreement was substantial (ICC from 0.615 to 0.682). Bland-Altman plots revealed a significant bias in ADC values measured between O-SW and S-WS (P = 0.025), no further systematic differences were identified. CV varied from 6.8 % to 7.9 %. CONCLUSION Post-processing systems may have a significant, although minor, impact on ADC measurements in breast lesions. While intra-reader agreement is high, the main source of ADC variability seems to be caused by inter-reader variation. KEY POINTS • ADC provides quantitative information on breast lesions independent from the system used. • ADC measurement using different workstations and software systems is generally reliable. • Systematic, but minor, differences may occur between different post-processing systems. • Inter-reader agreement of ADC measurements exceeded intra-reader agreement
Cortical activation and motor body representations in a patient with subacute sclerosing panencephalitis
No full textThe current neuroimaging study investigated the sensorimotor maps during hand, feet and lips movements at one year after diagnosis of of subacute sclerosing panencephalitis (SSPE) in a 17 years-old patient. A lesion prediction algorithm showed that the posterior thalamic radiations, the splenium of the corpus callosum, the posterior and superior corona radiate, and the cingolum, showed a high lesion probability. Comparing the fMRI activations of the left and right hemisphere, we found that the representation of the left hand movement was more inferior/anterior and less represented than the representation of the right one; and the representation of the right foot movement was more superior, less represented than the representation of the left one and poorly activated at the predefined statistical threshold. The fMRI results are in line with the clinical report, describing an asymmetrical distribution of the periodic stereotyped myoclonic jerks, which mainly occurred for the left arm/hand and for the right leg/foot. This is the first fMRI study investigating the representation of the body parts in patients with SSPE. Results show that in SSPE the hyper-stimulation of the motor system (dedicated to the arm/hand and leg/foot more involved by the occurrence of the jerks) is accompanied by an under-activation of the corresponding motor representations in coincidence with voluntary movements
What’s behind drawing for an artist with left temporal lobe epilepsy? A multimodal neurophysiological study
Full text linkThere are few studies in literature reporting drawing as a strong trigger of praxis-induced focal seizures. The aim of the present case report was describing a case of focal epilepsy with praxis induced EEG activation, due to a cavernoma, in the left middle anterior temporal lobe by using a multimodal approach. We combined video-EEG, showing that drawing increased a sustained monomorphic delta activity localized on left anterior temporal region (F7-T1a), diffusing to the vertex (Fz) and the fronto-polar electrodes (F3), with DTI data, showing that the left uncinate fasciculus, connecting the temporal pole to the orbitofrontal cortex, significantly differed from controls. fMRI confirmed that drawing increased activation in these areas. The congruence between findings supports the role of the left uncinated fasciculus linking the temporal lobe to the orbitofrontal cortex in the present focal epilepsy mainly facilitated by drawing
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