Integration of High Resolution EEG and Functional Magnetic Resonance in the Study of Human Movement-Related Potentials

Cortical sources of human movement-related potentials (i.e. unilateral finger extension) were modeled using functional magnetic resonance imaging (fMR) data as a constraint of a linear inverse source estimation from highly sampled (128 channels) EEG data. Remarkably, this estimation was performed within realistic subject’s MR-constructed head models by boundary element techniques. An appropriate figure of merit served to set the optimal amount of fMR constraints. With respect to standard linear inverse source estimates, fMR-constrained ones presented increased spatial detail and provided a more reliable timing of activation in bilateral sensorimotor cortical regions of interest.

Cortical Source Estimate of Combined High Resolution EEG and fMRI Data Related to Voluntary Movements

Objectives: In this paper, we employed advanced methods for the modeling of human cortical activity related to voluntary right one-digit movements from combined high-resolution electroencephalography (EEG) and functional magnetic resonance imaging (fMRI).

Methods: Multimodal integration between EEG and fMRI data was performed by using realistic head models, a large number of scalp electrodes (128) and the estimation of current density strengths by linear inverse estimation.

Results: Increasing of spatial details of the estimated cortical density distributions has been detected by using the proposed integration method with respect to the estimation using EEG data alone.

Conclusion: The proposed method of multimodal EEG-fMRI data is useful to increase spatial resolution of movement-related potentials and can also be applied to other kinds of event-related potentials.

Integrated Software Suite for Magnetocardio-graphic Data Analysis

Objectives: This paper describes an integrated software suite (ISS) for the processing of magnetocardiographic (MCG) recordings obtained with super-conducting multi-channel systems having different characteristics. We aimed to develop a highly flexible suite including toolboxes for current MCG applications, organized consistently with an open architecture that allows function integrations and upgrades with minimal modifications; the suite was designed for the compliance not only of physicists and engineers but also of physicians, who have a different professional profile and are accustomed to retrieve information in different ways.

Methods: The MCG-ISS was designed to work with all common graphical user interface operative systems. MATLAB was chosen as the interactive programming environment (IPE), and the software was developed to achieve usability, interactivity, reliability, modularity, expansibility, interoperability, adaptability and graphics style tailoring. Three users, already experienced in MCG data analysis, have intensively tested MCG-ISS for six months. A great amount of MCG data on normal subjects and patients was used to assess software performances in terms of user compliance and confidence and total analysis time.

Results: The proposed suite is an all-in-one analysis tool that succeeded in speeding MCG data analysis up to about 55% with respect to standard reference routines; it consequently enhanced analysis performance and user compliance.

Conclusions: Those results, together with the MCG-ISS advantage of being independent on the acquisition system, suggest that software suites like the proposed one could uphold a wider diffusion of MCG as a diagnostic tool in the clinical setting.

Penile Cutaneous Temperature in Systemic Sclerosis: A Thermal Imaging Study

Systemic Sclerosis is a connective tissue disorder featuring vascular alterations and an immunological activation leading to a progressive and widespread fibrosis of several organs such as the skin, lung, gastrointestinal tract, heart and kidney. Moreover men with systemic sclerosis (SSc) present an increased risk of developing erectile dysfunction (ED). Recently, we evaluated the extent of penile vascular damage in sclerodermic patients using Duplex ultrasonography. The aim of this paper is to investigate whether penile thermal differences exist between sclerodermic patients and healthy controls. For this reason 10 men with SSc receiving current treatment for their disease, and 10 healthy controls were enroled; penile thermal properties were assessed through non-contact thermal imaging (functional Infra Red Imaging fIRI); erectile function was evaluated using the sexual health inventory for men (SHIM) questionnaire. The SHIM results confirmed the presence of ED in sclerodermic patients. Baseline penile temperature in patients (32.1 ± 1.4°C) was lower than in controls (34.1 ± 0.9°C). Recovery from cooling test was seen to be faster in healthy controls than in patients, both in terms of recovery amplitude (patients 3.75 ± 2.09°C, controls 9.80 ± 2.77°C) and amplitude to time constant ratio (patients 1.21 ± 0.64°C/min, controls 1.96 ± 0.48°C/min). These results show that penile thermal abnormalities occur in almost all sclerodermic patients. Non-contact thermal imaging not only identifies thermal alterations but also clearly distinguishes between SSc patients and healthy controls and therefore could represent a valuable instrument in identifying early ED in SSc patients.

A Dynamic Core Network and Global Efficiency in the Resting Human Brain

Spontaneous brain activity is spatially and temporally organized in the absence of any stimulation or task in networks of cortical and subcortical regions that appear largely segregated when imaged at slow temporal resolution with functional magnetic resonance imaging (fMRI). When imaged at high temporal resolution with magneto-encephalography (MEG), these resting-state networks (RSNs) show correlated fluctuations of band-limited power in the beta frequency band (14-25 Hz) that alternate between epochs of strong and weak internal coupling. This study presents 2 novel findings on the fundamental issue of how different brain regions or networks interact in the resting state. First, we demonstrate the existence of multiple dynamic hubs that allow for across-network coupling. Second, dynamic network coupling and related variations in hub centrality correspond to increased global efficiency. These findings suggest that the dynamic organization of across-network interactions represents a property of the brain aimed at optimizing the efficiency of communication between distinct functional domains (memory, sensory-attention, motor). They also support the hypothesis of a dynamic core network model in which a set of network hubs alternating over time ensure efficient global communication in the whole brain.

Iloprost treatment summer-suspension: effects on skin thermal properties and cytokine profile in systemic sclerosis patients

AIM

Aim of the study was to assess whether Iloprost treatment summer suspension modifies systemic cytokines levels, cutaneous thermal properties and functional response to a cold-induced stress in patients affected by systemic sclerosis (SSc).

METHODS

Twenty-eight patients fulfilling the American College of Rheumatology (ACR) criteria for SSc were included in the study. Patients recorded number, duration and pain-severity of Raynaud phenomenon (RP). Pain-severity was determined by a visual analog scale. Cytokines expression and production in peripheral blood mononuclear cells and serum were evaluated by RT-PCR and ELISA assay. Basal finger temperature (Tb), distal-dorsal difference temperature (DTdd) and thermal recovery time (tr) from cold stress were measured by means of functional infrared imaging (fIR). Measurements were performed in late spring, during routine Iloprost therapy (1-3 days infusion of 0.5-2 ng/kg every month), and in late summer after a therapy-withdrawal period.

RESULTS

Deterioration of SSc patients' skin thermal properties was observed in the period of therapy withdrawal (Tb reduction and tr enhancement; no DTdd differences) despite the improvement in symptoms of RP. A reduction in IL-12/23p40 gene expression was recorded after therapy withdrawal and a direct correlation between IL-12/23p40 and IL-23p19 gene expression was observed, stronger after therapy suspension.

CONCLUSION

Our data suggest that Iloprost treatment summer suspension may induce the loss of the therapy beneficial effect on microcirculation despite the objective reduction of RP, thus favouring a continuous use of Iloprost in absence of severe side effects. Iloprost showed to modulate only IL-23 expression corroborating the idea that this cytokine is crucial for SSc development and progression.

Comparison of cutaneous termic response to a standardised warm up in trained and untrained individuals

AIM

Warm up prior to exercise induces an increased production of metabolic heat, which triggers the thermoregulatory system to initiate heat loss mechanisms. Variations in cutaneous tissue temperature have been already reported in trained subjects, by means of high resolution thermal imaging. Purpose of this paper was to quantitatively evaluate, by means of infrared thermography, the differences in the cutaneous temperature among trained and untrained subjects.

METHODS

Forty male volunteers performed a standard warm up exercise on a stationary cycle, divided in three steps: 1) 0-5 minutes at 100 Watt; 2) 5-10 minutes at 130 Watt; and 3) 10-15 minutes at 160 Watt. Thermal images from thorax and upper limbs were collected during the exercise. Heart rate was also measured.

RESULTS

In comparison to baseline, trained subjects exhibited a significant temperature reduction in the third step (trunk, P<0.01; upper limbs, P<0.009), while no difference was observed in untrained subjects. In the comparison between groups, a statistically significant difference was observed in both regions of interest, in the second (trunk, P<0.01; upper limbs, P<0.02), and in the third step (trunk, P<0.0002; upper limbs, P<0.0008). During the whole exercise, heart rate increased progressively in all participants, but more markedly in untrained subjects.

CONCLUSION

Cutaneous thermoregulatory response differs among trained and untrained participants. Infrared thermal imaging is useful in detecting these differences, providing additional data to the physiological evaluation of subjects performing sport activities.

Reorganization of functional connectivity of the language network in patients with brain gliomas

BACKGROUND AND PURPOSE

fcMRI measures spontaneous and synchronous fluctuations of BOLD signal between spatially remote brain regions. The present study investigated potential LN fcMRI modifications induced by left hemisphere brain gliomas.

MATERIALS AND METHODS

We retrospectively evaluated fcMRI in 39 right-handed patients with a left hemisphere brain glioma and 13 healthy controls. Patients and controls performed a verb-generation task to identify individual BOLD activity in the left IFG (Broca area); the active region was used as seed to create whole-brain background connectivity maps and to identify the LN (including bilateral regions of the IFG, STS, and TPJ) following regression of task-evoked activity. We assessed differences between patients and controls in the pattern of functional connectivity of the LN, as well as potential effects of tumor position, histopathology, and volume.

RESULTS

Global fcMRI of the LN was significantly reduced in patients with tumor compared with controls. Specifically, fcMRI was significantly reduced within seed regions of the affected hemisphere (left intrahemispheric fcMRI) and between the TPJ of the 2 hemispheres. In patients, the left TPJ node showed the greatest decrease of functional connectivity within the LN.

CONCLUSIONS

The presence of a brain tumor in the left hemisphere significantly reduced the degree of fcMRI between language-related brain regions. The pattern of fcMRI was influenced by tumor position but was not restricted to the area immediately surrounding the tumor because the connectivity between remote and contralateral areas was also affected.

Comparison of hypothesis- and a novel hybrid data/hypothesis-driven method of functional MR imaging analysis in patients with brain gliomas

BACKGROUND AND PURPOSE

An alternative technique, which is less influenced by tumor- and patient-related factors, is required to overcome the limits of GLM analysis of fMRI data in patients. The aim of this study was to statistically assess differences in the identification of language regions and hemispheric lateralization of language function between controls and patients as estimated by both the GLM and a novel combined ICA-GLM procedure.

MATERIALS AND METHODS

We retrospectively evaluated 42 patients with pathologically confirmed brain gliomas of the left frontal and/or temporoparietal lobes and a control group of 14 age-matched healthy volunteers who underwent BOLD fMRI to lateralize language functions in the cerebral hemispheres. Data were processed by using a classic GLM and ICA-GLM.

RESULTS

ICA-GLM demonstrated a higher sensitivity in detecting language activation, specifically in the left TPJ of patients. There were no significant differences between the GLM and ICA-GLM in controls; however, statistically significant differences were observed by using ICA-GLM for the LI in patients. For the computation of the LI, ICA-GLM was less influenced by the chosen statistical threshold compared with the GLM.

CONCLUSIONS

We suggest the use of the ICA-GLM as a valid alternative to the classic GLM method for presurgical mapping in patients with brain tumors and to replicate the present results in a broader sample of patients.

Functional connectivity MR imaging of the language network in patients with drug-resistant epilepsy

BACKGROUND AND PURPOSE

Subtle linguistic dysfunction and reorganization of the language network were described in patients with epilepsy, suggesting the occurrence of plasticity changes. We used resting state FC-MRI to investigate the effects induced by chronic epilepsy on the connectivity of the language-related brain regions and correlated it with language performance.

MATERIALS AND METHODS

FC-MRI was evaluated in 22 right-handed patients with drug-resistant epilepsy (11 with LE and 11 with RE) and in 12 healthy volunteers. Neuropsychological assessment of verbal IQ was performed. Patients and controls underwent BOLD fMRI with a verb-generation task, and language function was lateralized by an LI. Intrinsic activity fluctuations for FC analysis were extracted from data collected during the task. Six seeding cortical regions for speech in both hemispheres were selected to obtain a measure of the connectivity pattern among the language networks.

RESULTS

Patients with LE presented atypical language lateralization and an overall reduced connectivity of the language network with respect to controls. In patients with both LE and RE, the mean FC was significantly reduced within the left (dominant) hemisphere and between the 2 hemispheres. In patients with LE, there was a positive correlation between verbal IQ scores and the left intrahemispheric FC.

CONCLUSIONS

In patients with intractable epilepsy, FC-MRI revealed an overall reduction and reorganization of the connectivity pattern within the language network. FC was reduced in the left hemisphere regardless of the epileptogenic focus side and was positively correlated with linguistic performance only in patients with LE.

Pharmacological functional MRI assessment of the effect of ibuprofen-arginine in painful conditions

Pharmacological functional magnetic resonance imaging (phMRI) is a valuable tool for the investigation of pharmacological effects of a drug on pain processing. We hypothesized that the ibuprofen-arginine combination, in line with its characteristic analgesic properties, may influence the phMRI response at the central level, as compared to placebo. Ten healthy subjects underwent a double-blind, placebo-controlled, randomized, cross-over phFMRI study with somatosensory painful stimulation of the right median nerve. We measured the blood oxygen level dependent (BOLD) signal variations induced in conditions of pain after oral administration of either ibuprofen-arginine or placebo formulations. Independent component analysis (ICA) was used for the analysis of the fMRI data, without assuming a specific hemodynamic response function (HRF), which may be altered by drug administration. Median nerve electrical painful stimulation mainly activated the primary contralateral and the secondary somatosensory cortices, the insula, the supplementary motor area, and the middle frontal gyrus. Placebo and ibuprofen-arginine administration induced activation bilaterally in the premotor cortex, and an overall reduction in the other pain-related areas, which was more prominent in the left hemisphere. A task-related increase of BOLD signal between drug and placebo was observed bilaterally in the primary somatosensory area and the middle frontal gyrus without any changes in subjective pain scores. Overall, our findings show that ibuprofen-arginine, in line with the characteristic analgesic properties of ibuprofen, influences the BOLD response in specific pain-related brain areas with respect to placebo, with a vasoactive effect possibly due to arginine.

Functional infrared imaging of paroxysmal ischemic events in patients with Raynaud's phenomenon

The use of thermal infrared (IR) imaging together with the study of the thermal recovery from a controlled cold challenge has been proposed in the diagnosis and follow-up of therapeutic response of Raynaud's Phenomenon (RP) and Systemic Sclerosis (SSc). The controlled cold challenge test usually performed during IR investigations may induce a RP in patients with the latter condition. In our Institution we routinely perform capillaroscopy and thermal IR to follow-up SSc patients. In this paper, we describe the thermal recovery patterns shown by two SSc patients (a 40 year-old male with diffuse variant of SSc and a 71 year-old female with a limited variant of SSc) who presented ischemic and paroxysmal RP attack while recovering from the routine controlled cold challenge test. During RP attack, the cutaneous temperature of some fingers continued to decrease for some minutes even after the cessation of the cold stress. To the best of our knowledge, to date, no literature report has documented the thermal behaviour of SSc patients' fingers which occasionally present ischemic and paroxysmal response. Triggering of ischemic RP attack appears to not rely only on morphological and structural finger impairment, but also upon other aspects, like the emotional attitude of the subject and the possible discomfort experienced with the proceeding of the functional cold stress test.

Persistent genital arousal disorder associated with functional hyperconnectivity of an epileptic focus

Persistent Genital Arousal Disorder (PGAD) refers to the experience of persistent sensations of genital arousal that are felt to be unprovoked, intrusive and unrelieved by one or several orgasms. It is often mistaken for hypersexuality since PGAD often results in a high frequency of sexual behaviour. At present little is known with certainty about the etiology of this condition. We described a woman with typical PGAD symptoms and orgasmic seizures that we found to be related to a specific epileptic focus. We performed a EEG/MEG and fMRI spontaneous activity study during genital arousal symptoms and after the chronic administration of 300 mg/day of topiramate. From MEG data an epileptic focus was localized in the left posterior insular gyrus (LPIG). FMRI data evidenced that sexual excitation symptoms with PGAD could be correlated with an increased functional connectivity (FC) between different brain areas: LPIG (epileptic focus), left middle frontal gyrus, left inferior and superior temporal gyrus and left inferior parietal lobe. The reduction of the FC observed after antiepileptic therapy was more marked in the left than in the right hemisphere in agreement with the lateralization identified by MEG results. Treatment completely abolished PGAD symptoms and functional hyperconnectivity. The functional hyperconnectivity found in the neuronal network including the epileptic focus could suggest a possible central mechanism for PGAD.

Multimodal integration of fMRI and EEG data for high spatial and temporal resolution analysis of brain networks

Two major non-invasive brain mapping techniques, electroencephalography (EEG) and functional magnetic resonance imaging (fMRI), have complementary advantages with regard to their spatial and temporal resolution. We propose an approach based on the integration of EEG and fMRI, enabling the EEG temporal dynamics of information processing to be characterized within spatially well-defined fMRI large-scale networks. First, the fMRI data are decomposed into networks by means of spatial independent component analysis (sICA), and those associated with intrinsic activity and/or responding to task performance are selected using information from the related time-courses. Next, the EEG data over all sensors are averaged with respect to event timing, thus calculating event-related potentials (ERPs). The ERPs are subjected to temporal ICA (tICA), and the resulting components are localized with the weighted minimum norm (WMNLS) algorithm using the task-related fMRI networks as priors. Finally, the temporal contribution of each ERP component in the areas belonging to the fMRI large-scale networks is estimated. The proposed approach has been evaluated on visual target detection data. Our results confirm that two different components, commonly observed in EEG when presenting novel and salient stimuli, respectively, are related to the neuronal activation in large-scale networks, operating at different latencies and associated with different functional processes.

Combined thermal and laser Doppler imaging in the assessment of cutaneous tissue perfusion

Infrared thermal imaging permits to non-invasively obtain, throughout bioheat models using a series of thermal images, the cutaneous blood perfusion. Laser Doppler imaging measures blood flow in the very small blood vessels of the microvascular network. In this paper, we compare findings from the two methods on a set of healthy volunteers. Cutaneous blood perfusion values obtained from thermal imaging correlate to those obtained by means of Laser Doppler imaging with the advantage of a better time resolution. Combined imaging of the two modalities may provide a useful tool for monitoring diseases affecting cutaneous tissue and/or microcirculation.

Thermal signatures of emotional arousal: a functional infrared imaging study

Functional Infrared Imaging was used to study the facial thermal signatures of three fundamental emotional conditions: stress, fear and pleasure arousal. Facial cutaneous temperature and its topographic distribution exhibited specific features clearly correlated to emotional arousal and concomitant measures of standard physiological signals of the sympathetic activity. The results of this study indicate functional infrared imaging as an alternative, touch less, non invasive method for assessing individual's emotional arousal in psychophysiology.

Functional infrared imaging in medicine: a quantitative diagnostic approach

The role and the potentialities of high-resolution infrared thermography, combined to bio-heat modelling, have been largely described in the last years in a wide variety of biomedical applications. Quantitative assessment over time of the cutaneous temperature and/or of other biomedical parameters related to the temperature (e.g., cutaneous blood flow, thermal inertia, sympathetic skin response) allows for a better and more complete understanding and description of functional processes involved and/or altered in presence of ailment and interfering with the regular cutaneous thermoregulation. Such an approach to thermal medical imaging requires both new methodologies and tools, like diagnostic paradigms, appropriate software for data analysis and, even, a completely new way to look at data processing. In this paper, some of the studies recently made in our laboratory are presented and described, with the general intent of introducing the reader to these innovative methods to obtain quantitative diagnostic tools based on thermal imaging.

Superimposition of thermal imaging to visual imaging using homography

InfraRed Thermal Imaging (IR) permits to non-invasively map the skin temperature distribution of the human body. Combining together thermal and visual imaging enriches the informative content of IR images and provides to the physician an anatomically-based and more friendly visualization--on the thermal images--of the presence of possible pathological processes. In this paper we use a homography technique to overlap a thermal image to a visible one. The technique provides an effective pixel-to-pixel correspondences between the two images or their portions.

New morphologic variants of the hand motor cortex as seen with MR imaging in a large study population

BACKGROUND AND PURPOSE

The hand motor cortex (HMC) has been classically described as having an omega or epsilon shape in axial-plane images obtained with CT and MR imaging. The aim of this study was to use MR imaging and Talairach normalization in a large sample population that was homogeneous for age and handedness to evaluate in a sex model a new classification with 5 morphologic variants of the HMC in the axial plane (omega, medially asymmetric epsilon, epsilon, laterally asymmetric epsilon, and null).

MATERIALS AND METHODS

Structural brain MR images were obtained from 257 right-handed healthy subjects (143 men and 114 women; mean age, 23.1 +/- 1.1 years) via a Talairach space transformed 3D magnetization-prepared rapid acquisition of gradient echo sequence. The frequencies of the different HMC variants were reported for hemisphere and sex.

RESULTS

The new variants of the HMC (medially asymmetric epsilon, laterally asymmetric epsilon, and null) were observed in 2.9%, 7.0%, and 1.8% of the hemispheres, respectively. Statistically significant sex differences were observed: The epsilon variant was twice as frequent in men, and an interhemispheric concordance for morphologic variants was observed only for women.

CONCLUSION

The large study population permitted the description of a new morphologic classification that included 3 new variants of the HMC. This new morphologic classification should facilitate the identification of the precentral gyrus in subsequent studies and in everyday practice.

A frontoparietal network for spatial attention reorienting in the auditory domain: a human fMRI/MEG study of functional and temporal dynamics

Several studies have identified a supramodal network critical to the reorienting of attention toward stimuli at novel locations and which involves the right temporoparietal junction and the inferior frontal areas. The present functional magnetic resonance imaging (fMRI)\magnetoencephalography (MEG) study investigates: 1) the cerebral circuit underlying attentional reorienting to spatially varying sound locations; 2) the circuit related to the regular change of sound location in the same hemifield, the change of sound location across hemifields, or sounds presented randomly at different locations on the azimuth plane; 3) functional temporal dynamics of the observed cortical areas exploiting the complementary characteristics of the fMRI and MEG paradigms. fMRI results suggest 3 distinct roles: the supratemporal plane appears modulated by variations of sound location; the inferior parietal lobule is modulated by the cross-meridian effect; and the inferior frontal cortex is engaged by the inhibition of a motor response. MEG data help to elucidate the temporal dynamics of this network by providing high-resolution time series with which to measure latency of neural activation manipulated by the reorienting of attention.

Electrophysiological signatures of resting state networks in the human brain

Functional neuroimaging and electrophysiological studies have documented a dynamic baseline of intrinsic (not stimulus- or task-evoked) brain activity during resting wakefulness. This baseline is characterized by slow (<0.1 Hz) fluctuations of functional imaging signals that are topographically organized in discrete brain networks, and by much faster (1-80 Hz) electrical oscillations. To investigate the relationship between hemodynamic and electrical oscillations, we have adopted a completely data-driven approach that combines information from simultaneous electroencephalography (EEG) and functional magnetic resonance imaging (fMRI). Using independent component analysis on the fMRI data, we identified six widely distributed resting state networks. The blood oxygenation level-dependent signal fluctuations associated with each network were correlated with the EEG power variations of delta, theta, alpha, beta, and gamma rhythms. Each functional network was characterized by a specific electrophysiological signature that involved the combination of different brain rhythms. Moreover, the joint EEG/fMRI analysis afforded a finer physiological fractionation of brain networks in the resting human brain. This result supports for the first time in humans the coalescence of several brain rhythms within large-scale brain networks as suggested by biophysical studies.

A cartesian time--frequency approach to reveal brain interaction dynamics

The study of large-scale interactions from magnetoencephalographic data based on the magnitude of the complex coherence computed at channel level is a widely used method to track the coupling between neural signals. Traditionally, a measure based on the magnitude of the complex coherence estimated by Fourier analysis, has been used under the assumption that the neural signals are stationary. Here, we split the complex coherence in its real and imaginary parts and focus on the latter with the advantage that the imaginary part is insensitive to spurious connectivity resulting from volume conducted "self interaction". Furthermore, interacting sources alone contribute to a non-vanishing imaginary part of the complex coherence whereas the contribute of non-interacting sources is also mapped from the magnitude of the complex coherence. Since it has been extensively shown that non-stationary stochastic processes contribute to the generation of neural signals, it is fundamental to be able to define interaction measures that are able to follow the temporal variations in the coupling between neural signals. To this purpose time-frequency domain techniques to estimate the magnitude of the complex coherence have been developed in the past decades. Similarly, we extend the analysis of the imaginary part of complex coherence to the time-frequency domain, by using the short-time Fourier transform to analyze the complex coherence as a function of time. In this way, it is possible to get an indication about the dynamic of the underlying source interaction pattern by looking at channel level interactions without the bias introduced by artifactual self-interaction by volume conduction or by the contribute of non-interacting sources. Furthermore, the corresponding imaginary part of the cross-spectrogram can be used to estimate interactions on a source level by localizing pools of sources interacting at a given frequency and by characterizing their dynamics. The method has been applied to magnetoencephalographic data from a cross-modal visual auditory stimulation and provided evidence for the involvement of temporal and occipital areas in the integrated information processing for simultaneous audio-visual stimulation. Furthermore, the source interaction pattern shows a variation in time that reflects a dynamical synchronization of the involved brain sources in the frequency bands of interest.

Cerebro-muscular and cerebro-cerebral coherence in patients with pre- and perinatally acquired unilateral brain lesions

The cerebral networks involved in motor control were analyzed in four young hemi-paretic patients (21-25 years) with pre- and perinatally acquired brain lesions (3 with left periventricular brain lesions, 1 with left schizencephaly) by means of MEG source coherence analysis. Previous TMS and fMRI studies on the same patients had investigated their residual ability to move the paretic hand by means of a reorganized primary motor cortex (M1) representation in the contralesional hemisphere. The purpose of this study is to identify the effects of such a cerebral reorganization and the related dynamic aspects which allow the patients to move the paretic arm. Patients underwent a pinch grip task (1-N isometric contraction) using their paretic and non-paretic hands in alternation. MEG signals were recorded using a whole-head 151-channel magnetoencephalograph. EMG was simultaneously recorded as a reference for coherence calculations. 3D coherence mapping was performed in the beta frequency range (14-30 Hz). This approach confirmed the relocation of motor functions from the lesioned (left) to the contralesional (right) hemisphere. In case of left, non-paretic pinch grip, coherent activity originated from contralateral (right) M1 exclusively. In the case of right (paretic) grip, coherent activity in ipsilateral M1 as well as significant coherence of ipsilateral cerebellum with both muscle activity and M1 itself was detected in 3 out of 4 subjects. As expected, the patient with no cerebellar involvement during paretic hand contraction showed the worst motor performance in the grip task. Coupling direction analysis demonstrated that throughout pinch grip the coupling direction goes from M1 to cerebellum. The present study verified the assumption that the intact hemisphere takes over motor control from the paretic (ipsilateral) hand in the presence of early unilateral brain lesion. Moreover, the role of cerebellum in motor deficit compensation and its close interaction with ipsilateral primary motor cortex was studied in detail.

Functional infrared imaging in the diagnosis of the myofascial pain

Functional infrared imaging has been used to study 17 patients, affected by myofascial pain, and 19 healthy subjects during maximal voluntary clenching (MCV). Aim of the study was to attempt to discriminate patients from healthy subjects through the analysis of the skin temperature distribution and its change during the clenching. The prestress and the post-stress temperatures were evaluated bilaterally for several regions of interest. We calculated differences in temperature between sides (DeltaTs) at each time (pre and post), and between times (DeltaTt) for each side (left and right). Subsequently, we compared DeltaTs and DeltaTt between the healthy and myofascial pain groups. DeltaTs was significantly higher in sufferers compared to healthy people (p<0.05) for both types of evaluation (by side and by time). DeltaTs was significantly different for masseter and sternocleidomastoid, whereas DeltaTt was higher in almost all sites (masseter, sternocleidomastoid, cervical and upper trapezius). Healthy subjects, undergoing MVC, showed the lowest DeltaT value variability, suggesting that temperature remained constant despite the induced physical exercise. Functional infrared imaging seems to distinguish healthy subjects from the patients suffering myofascial pain in almost all the investigated sites.

Brain network for passive word listening as evaluated with ICA and Granger causality

Brain network modeling is probably the biggest challenge in fMRI data analysis. Higher cognitive processes in fact, rely on complex dynamics of temporally and spatially segregated brain activities. A number of different techniques, mostly derived from paradigmatic hypothesis-driven methods, have been successfully applied for such purpose. This paper instead, presents a new data-driven analysis approach that applies both independent components analysis (ICA) and the Granger causality (GC). The method includes two steps: (1) ICA is used to extract the independent functional activities; (2) the GC is applied to the independent component (IC) most correlated with the stimuli, to indicate its functional relation with other ICs. This new method is applied to the analysis of fMRI study of listening to high-frequency trisyllabic words, non-words and reversed words. As expected, activity was found in the primary and secondary auditory cortices. Additionally, a parieto-frontal network of activations, supported by temporal and causality relationships, was found. This network is modulated by experimental conditions in agreement with the most recent models presented for word perception. The results have confirmed the validity of the proposed method, and seem promising for the detection of cognitive causal relationships in neuroimaging data.

Conditioning transcutaneous electrical nerve stimulation induces delayed gating effects on cortical response: A magnetoencephalographic study

The present study was undertaken to investigate after-effects of 7 Hz non-painful prolonged stimulation of the median nerve on somatosensory-evoked fields (SEFs). The working hypothesis that conditioning peripheral stimulations might produce delayed interfering ("gating") effects on the response of somatosensory cortex to test stimuli was evaluated. In the control condition, electrical thumb stimulation induced SEFs in ten subjects. In the experimental protocol, a conditioning median nerve stimulation at wrist preceded 6 electrical thumb stimulations. Equivalent current dipoles fitting SEFs modeled responses of contralateral primary area (SI) and bilateral secondary somatosensory areas (SII) following control and experimental conditions. Compared to the control condition, conditioning stimulation induced no amplitude modulation of SI response at the initial stimulus-related peak (20 ms). In contrast, later response from SI (35 ms) and response from SII were significantly weakened in amplitude. Gradual but fast recovery towards control amplitude levels was observed for the response from SI-P35, while a slightly slower cycle was featured from SII. These findings point to a delayed "gating" effect on the synchronization of somatosensory cortex after peripheral conditioning stimulations. This effect was found to be more lasting in SII area, as a possible reflection of its integrative role in sensory processing.

The use of standardized infinity reference in EEG coherency studies

The study of large scale interactions in the brain from EEG signals is a promising method for the identification of functional networks. However, the validity of a large scale parameter is limited by two factors: the use of a non-neutral reference and the artifactual self-interactions between the measured EEG signals introduced by volume conduction. In this paper, we propose an approach to study large scale EEG coherency in which these factors are eliminated. Artifactual self-interaction by volume conduction is eliminated by using the imaginary part of the complex coherency as a measure of interaction and the Reference Electrode Standardization Technique (REST) is used for the approximate standardization of the reference of scalp EEG recordings to a point at infinity that, being far from all possible neural sources, acts like a neutral virtual reference. The application of our approach to simulated and real EEG data shows that the detection of interaction, as opposed to artifacts due to reference and volume conduction, is a goal that can be achieved from the study of a large scale parameter.

Functional imaging with MEG and fMRI

The possibility of integrating functional data from magnetoencephalografic (MEG) measurements and functional Magnetic Resonance Imaging (fMRI) offers new insight on the brain organization. In fact, MEG and fMRI integration can provide accurate identification of active brain areas as well as a precise identification of the timing of brain response. In this paper two examples will be discussed: the first aiming at the characterization of the human primary (SI) and secondary (SII) somatosensory cortices, the second concerning how brain reacts to sound coming from different spatial directions.

Entropy-based automated classification of independent components separated from fMCG

Fetal magnetocardiography (fMCG) is a noninvasive technique suitable for the prenatal diagnosis of the fetal heart function. Reliable fetal cardiac signals can be reconstructed from multi-channel fMCG recordings by means of independent component analysis (ICA). However, the identification of the separated components is usually accomplished by visual inspection. This paper discusses a novel automated system based on entropy estimators, namely approximate entropy (ApEn) and sample entropy (SampEn), for the classification of independent components (ICs). The system was validated on 40 fMCG datasets of normal fetuses with the gestational age ranging from 22 to 37 weeks. Both ApEn and SampEn were able to measure the stability and predictability of the physiological signals separated with ICA, and the entropy values of the three categories were significantly different at p <0.01. The system performances were compared with those of a method based on the analysis of the time and frequency content of the components. The outcomes of this study showed a superior performance of the entropy-based system, in particular for early gestation, with an overall ICs detection rate of 98.75% and 97.92% for ApEn and SampEn respectively, as against a value of 94.50% obtained with the time-frequency-based system.

Complete artifact removal for EEG recorded during continuous fMRI using independent component analysis

The simultaneous recording of EEG and fMRI is a promising method for combining the electrophysiological and hemodynamic information on cerebral dynamics. However, EEG recordings performed in the MRI scanner are contaminated by imaging, ballistocardiographic (BCG) and ocular artifacts. A number of processing techniques for the cancellation of fMRI environment disturbances exist: the most popular is averaged artifact subtraction (AAS), which performs well for the imaging artifact, but has some limitations in removing the BCG artifact, due to the variability in cardiac wave duration and shape; furthermore, no processing method to attenuate ocular artifact is currently used in EEG/fMRI, and contaminated epochs are simply rejected before signal analysis. In this work, we present a comprehensive method based on independent component analysis (ICA) for simultaneously removing BCG and ocular artifacts from the EEG recordings, as well as residual MRI contamination left by AAS. The ICA method has been tested on event-related potentials (ERPs) obtained from a visual oddball paradigm: it is very effective in attenuating artifacts in order to reconstruct clear brain signals from EEG acquired in the MRI scanner. It performs significantly better than the AAS method in removing the BCG artifact. Furthermore, since ocular artifacts can be completely suppressed, a larger number of trials is available for analysis. A comparison of ERPs inside the magnetic environment with those obtained out of the MRI scanner confirms that no systematic bias in the ERP waveform is produced by the ICA method.

“What” versus “Where” in the audiovisual domain: An fMRI study

Similar "what/where" functional segregations have been proposed for both visual and auditory cortical processing. In this fMRI study, we investigated if the same segregation exists in the crossmodal domain, when visual and auditory stimuli have to be matched in order to perform either a recognition or a localization task. Recent neuroimaging research highlighted the contribution of different heteromodal cortical regions during various forms of crossmodal binding. Interestingly, crossmodal effects during audiovisual speech and object recognition have been found in the superior temporal sulcus, while crossmodal effects during the execution of spatial tasks have been found over the intraparietal sulcus, suggesting an underlying "what/where" segregation. In order to directly compare the specific involvement of these two heteromodal regions, we scanned ten male right-handed subjects during the execution of two crossmodal matching tasks. Participants were simultaneously presented with a picture and an environmental sound, coming from either the same or the opposite hemifield and representing either the same or a different object. The two tasks required a manual YES/NO response respectively about location or semantic matching of the presented stimuli. Both group and individual subject analysis were performed. Task-related differences in BOLD response were observed in the right intraparietal sulcus and in the left superior temporal sulcus, providing a direct confirmation of the "what-where" functional segregation in the crossmodal audiovisual domain.

Somatotopy of anterior cingulate cortex (ACC) and supplementary motor area (SMA) for electric stimulation of the median and tibial nerves: an fMRI study

In this study, we tested whether there is a somatotopic sensory organization in human anterior cingulate cortex (ACC) and supplementary motor area (SMA), as a reflection of central feed-back sensory processing for motor control. To this aim, fMRI recordings were performed in 15 normal young adults during nonpainful and painful electric stimulation of median nerve at the wrist and tibial nerve at the medial malleolus. Results showed that the representation of median nerve area was more anterior in the ACC and more inferior in the SMA than the one of tibial nerve area. This was true for both nonpainful and painful stimulation intensities. These results point to a somatotopic sensory organization of human ACC and SMA.

Localizing complex neural circuits with MEG data

During cognitive processing, the various cortical areas, with specialized functions, supply for different tasks. In most cases then, the information flows are processed in a parallel way by brain networks which work together integrating the single performances for a common goal. Such a step is generally performed at higher processing levels in the associative areas. The frequency range at which neuronal pools oscillate is generally wider than the one which is detectable by bold changes in fMRI studies. A high time resolution technique like magnetoencephalography or electroencephalography is therefore required as well as new data processing algorithms for detecting different coherent brain areas cooperating for one cognitive task. Our experiments show that no algorithm for the inverse problem solution is immune from bias. We propose therefore, as a possible solution, our software LOCANTO (LOcalization and Coherence ANalysis TOol). This new package features a set of tools for the detection of coherent areas. For such a task, as a default, it employs the algorithm with best performances for the neural landscape to be detected. If the neural landscape under attention involves more than two interacting areas the SLoreta algorithm is used. Our study shows in fact that SLoreta performance is not biased when the correlation among multiple sources is high. On the other hand, the Beamforming algorithm is more precise than SLoreta at localizing single or double sources but it gets a relevant localization bias when the sources are more than three and are highly correlated.

Human brain activation during passive listening to sounds from different locations: an fMRI and MEG study

Recent animal and human studies indicate the existence of a neural pathway for sound localization, which is similar to the "where" pathway of the visual system and distinct from the sound identification pathway. This study sought to highlight this pathway using a passive listening protocol. We employed fMRI to study cortical areas, activated during the processing of sounds coming from different locations, and MEG to disclose the temporal dynamics of these areas. In addition, the hypothesis of different activation levels in the right and in the left hemispheres, due to hemispheric specialization of the human brain, was investigated. The fMRI results indicate that the processing of sound, coming from different locations, activates a complex neuronal circuit, similar to the sound localization system described in monkeys known as the auditory "where" pathway. This system includes Heschl's gyrus, the superior temporal gyrus, the supramarginal gyrus, and the inferior and middle frontal lobe. The MEG analysis allowed assessment of the timing of this circuit: the activation of Heschl's gyrus was observed 139 ms after the auditory stimulus, the peak latency of the source located in the superior temporal gyrus was at 156 ms, and the inferior parietal lobule and the supramarginal gyrus peaked at 162 ms. Both hemispheres were found to be involved in the processing of sounds coming from different locations, but a stronger activation was observed in the right hemisphere.

Optimal filter design for shielded and unshielded ambient noise reduction in fetal magnetocardiography

The greatest impediment to extracting high-quality fetal signals from fetal magnetocardiography (fMCG) is environmental magnetic noise, which may have peak-to-peak intensity comparable to fetal QRS amplitude. Being an unstructured Gaussian signal with large disturbances at specific frequencies, ambient field noise can be reduced with hardware-based approaches and/or with software algorithms that digitally filter magnetocardiographic recordings. At present, no systematic evaluation of filters' performances on shielded and unshielded fMCG is available. We designed high-pass and low-pass Chebychev II-type filters with zero-phase and stable impulse response; the most commonly used band-pass filters were implemented combining high-pass and low-pass filters. The achieved ambient noise reduction in shielded and unshielded recordings was quantified, and the corresponding signal-to-noise ratio (SNR) and signal-to-distortion ratio (SDR) of the retrieved fetal signals was evaluated. The study regarded 66 fMCG datasets at different gestational ages (22-37 weeks). Since the spectral structures of shielded and unshielded magnetic noise were very similar, we concluded that the same filter setting might be applied to both conditions. Band-pass filters (1.0-100 Hz) and (2.0-100 Hz) provided the best combinations of fetal signal detection rates, SNR and SDR; however, the former should be preferred in the case of arrhythmic fetuses, which might present spectral components below 2 Hz.

Solving the neuroimaging puzzle: the multimodal integration of neuroelectromagnetic and functional magnetic resonance recordings

In this chapter, advanced methods for the modeling of human cortical activity from combined high-resolution electroencephalography (EEG) and functional magnetic resonance imaging (fMRI) data are reviewed. These methods include a subject's multicompartment head model (scalp, skull, dura mater, cortex) constructed from magnetic resonance images, multidipole source model, and regularized linear inverse source estimates. Determination of the priors in the resolution of the linear inverse problem was performed with the use of information from the hemodynamic responses of the cortical areas as revealed by block-designed (strength of activated voxels) and event-related (coupling of activated voxels) fMRI. As an example, these methods were applied to EEG (128 electrodes) and fMRI data, which were recorded in separate sessions while normal subjects executed voluntary right one-digit movements.

Cortical rhythms reactivity in AD, LBD and normal subjects: a quantitative MEG study

The present study evaluated the reactivity of cortical rhythms in 15 Alzheimer's disease (AD) patients, 7 Lewy body dementia (LBD) patients and 9 control subjects using a 165 SQUID whole-head MEG system. The absolute power values of the rhythms recorded over different areas over the brain (frontal, parietal, temporal, occipital) were analysed in the 3-47Hz frequency range. The cortical reactivity of the alpha (9-14Hz) and pre-alpha rhythms (7-9Hz) during open and closed eyes conditions differentiated the control group from the patient groups and moderate AD from severe AD and LBD groups, respectively. The cortical reactivity of the slow-band (3-7Hz) obtained by comparing a simple mental task and the rest discriminated the severe AD group from the other groups. In addition, spectral coherence analysis in the alpha band showed that the loss of coherence in AD and LBD patients mainly involved long connections. These results suggest that investigations on rhythms reactivity and spectral coherence might help on the study of the dementias with different etiology.

Fetal magnetocardiographic mapping using independent component analysis

Fetal magnetocardiography (fMCG) is the only noninvasive technique allowing effective assessment of fetal cardiac electrical activity during the prenatal period. The reconstruction of reliable magnetic field mapping associated with fetal heart activity would allow three-dimensional source localization. The efficiency of independent component analysis (ICA) in restoring reliable fetal traces from multichannel fMCG has already been demonstrated. In this paper, we describe a method of reconstructing a complete set of fetal signals hidden in multichannel fMCG preserving their correct spatial distribution, waveform, polarity and amplitude. Fetal independent components, retrieved with an ICA algorithm (FastICA), were interpolated (fICI method) using information gathered during FastICA iterations. The restored fetal signals were used to reconstruct accurate magnetic mapping for every millisecond during the average beat. The procedure was validated on fMCG recorded from the 22nd gestational week onward with a multichannel MCG system working in a shielded room. The interpolated traces were compared with those obtained with a standard technique, and the consistency of fetal mapping was checked evaluating source localizations relative to fetal echocardiographic information. Good magnetic field distributions during the P-QRS-T waves were attained with fICI for all gestational periods; their reliability was confirmed by three-dimensional source localizations.

Nociceptive and non-nociceptive sub-regions in the human secondary somatosensory cortex: An MEG study using fMRI constraints

Previous evidence from functional magnetic resonance imaging (fMRI) has shown that a painful galvanic stimulation mainly activates a posterior sub-region in the secondary somatosensory cortex (SII), whereas a non-painful sensory stimulation mainly activates an anterior sub-region of SII [Ferretti, A., Babiloni, C., Del Gratta, C., Caulo, M., Tartaro, A., Bonomo, L., Rossini, P.M., Romani, G.L., 2003. Functional topography of the secondary somatosensory cortex for non-painful and painful stimuli: an fMRI study. Neuroimage 20 (3), 1625-1638.]. The present study, combining fMRI with magnetoencephalographic (MEG) findings, assessed the working hypothesis that the activity of such a posterior SII sub-region is characterized by an amplitude and temporal evolution in line with the bilateral functional organization of nociceptive systems. Somatosensory evoked magnetic fields (SEFs) recordings after alvanic median nerve stimulation were obtained from the same sample of subjects previously examined with fMRI [Ferretti, A., Babiloni, C., Del Gratta, C., Caulo, M., Tartaro, A., Bonomo, L., Rossini, P.M., Romani, G.L., 2003. Functional topography of the secondary somatosensory cortex for non-painful and painful stimuli: an fMRI study. Neuroimage 20 (3), 1625-1638.]. Constraints for dipole source localizations obtained from MEG recordings were applied according to fMRI activations, namely, at the posterior and the anterior SII sub-regions. It was shown that, after painful stimulation, the two posterior SII sub-regions of the contralateral and ipsilateral hemispheres were characterized by dipole sources with similar amplitudes and latencies. In contrast, the activity of anterior SII sub-regions showed statistically significant differences in amplitude and latency during both non-painful and painful stimulation conditions. In the contralateral hemisphere, the source activity was greater in amplitude and shorter in latency with respect to the ipsilateral. Finally, painful stimuli evoked a response from the posterior sub-regions peaking significantly earlier than from the anterior sub-regions. These results suggested that both ipsi and contra posterior SII sub-regions process painful stimuli in parallel, while the anterior SII sub-regions might play an integrative role in the processing of somatosensory stimuli.