Biomedical subjects

G L Romani

Publications and source records attributed to G L Romani.

At least 19 recordsLinked to original sources

PubMed2006

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.

Adult↗

PubMed2006

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.

Adult↗

PubMed2006

"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.

Acoustic Stimulation↗

PubMed2006

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.

Bias↗

PubMed2005

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.

Algorithms↗

PubMed2005

Decrease of functional coupling between left and right auditory cortices during dichotic listening: an electroencephalography study.

The present study focused on functional coupling between human bilateral auditory cortices and on possible influence of right over left auditory cortex during dichotic listening of complex non-verbal tones having near (competing) compared with distant non-competing fundamental frequencies. It was hypothesized that dichotic stimulation with competing tones would induce a decline of functional coupling between the two auditory cortices, as revealed by a decrease of electroencephalography coherence and an increase of directed transfer function from right (specialized for the present stimulus material) to left auditory cortex. Electroencephalograph was recorded from T3 and T4 scalp sites, overlying respectively left and right auditory cortices, and from Cz scalp site (vertex) for control purposes. Event-related coherence between T3 and T4 scalp sites was significantly lower for all electroencephalography bands of interest during dichotic listening of competing than non-competing tone pairs. This was a specific effect, since event-related coherence did not differ in a monotic control condition. Furthermore, event-related coherence between T3 and Cz and between T4 and Cz scalp sites showed no significant effects. Conversely, the directed transfer function results showed negligible influence at group level of right over left auditory cortex during dichotic listening. These results suggest a decrease of functional coupling between bilateral auditory cortices during competing dichotic stimuli as a possible neural substrate for the lateralization of auditory stimuli during dichotic listening.

Acoustic Stimulation↗

PubMed2005

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.

Aged↗

PubMed2005

Automatic detection of cardiac waves on fetal magnetocardiographic signals.

Fetal magnetocardiography (fMCG) provides fetal cardiac traces useful for the prenatal monitoring of fetal heart function. In this paper, we describe an analytical model (ACWD) for the automatic detection of cardiac waves boundaries that works on fetal signals reconstructed from fMCG by means of independent component analysis. ACWD was validated for 45 healthy and 4 arrhythmic fetuses ranging from 22 to 37 weeks; ACWD outcomes were compared with the estimates of three independent investigators. Descriptive statistics were used to assess correspondence between the outcomes of the automatic and manual approaches. The parametric two-tailed Pearson correlation test (alpha=0.01) was employed to quantify, by means of the coefficients of determination, the amount of common variation between the sequences of intervals quantified automatically and manually. ACWD performances on short and long rhythm strips were investigated. ACWD demonstrated to be a robust tool providing dependable estimates of cardiac intervals and their variability during the third gestational trimester also in case of fetal arrhythmias. SNR and stability of fetal traces were the factors limiting ACWD performances. ACWD computation time, which was approximately 1:600 with respect to the manual procedure, was comparable with the time required for fCTI estimation on averaged beats.

Algorithms↗

PubMed2005

Functional MRI study of diencephalic amnesia in Wernicke-Korsakoff syndrome.

Anterograde amnesia in Wernicke-Korsakoff syndrome is associated with diencephalic lesions, mainly in the anterior thalamic nuclei. Whether diencephalic and temporal lobe amnesias are distinct entities is still not clear. We investigated episodic memory for faces using functional MRI (fMRI) in eight controls and in a 34-year-old man with Wernicke-Korsakoff syndrome and diencephalic lesions but without medial temporal lobe (MTL) involvement at MRI. fMRI was performed with a 1.5 tesla unit. Three dual-choice tasks were employed: (i) face encoding (18 faces were randomly presented three times and subjects were asked to memorize the faces); (ii) face perception (subjects indicated which of two faces matched a third face); and (iii) face recognition (subjects indicated which of two faces belonged to the group they had been asked to memorize during encoding). All activation was greater in the right hemisphere. In controls both the encoding and recognition tasks activated two hippocampal regions (anterior and posterior). The anterior hippocampal region was more activated during recognition. Activation in the prefrontal cortex was greater during recognition. In the subject with Wernicke-Korsakoff syndrome, fMRI did not show hippocampal activation during either encoding or recognition. During recognition, although behavioural data showed defective retrieval, the prefrontal regions were activated as in controls, except for the ventrolateral prefrontal cortex. fMRI activation of the visual cortices and the behavioural score on the perception task indicated that the subject with Wernicke-Korsakoff syndrome perceived the faces, paid attention to the task and demonstrated accurate judgement. In the subject with Wernicke-Korsakoff syndrome, although the anatomical damage does not involve the MTL, the hippocampal memory encoding has been lost, possibly as a consequence of the hippocampal-anterior thalamic axis involvement. Anterograde amnesia could therefore be the expression of damage to an extended hippocampal system, and the distinction between temporal lobe and diencephalic amnesia has limited value. In the subject with Wernicke-Korsakoff syndrome, the preserved dorsolateral prefrontal cortex activation during incorrect recognition suggests that this region is more involved in either the orientation or attention at retrieval than in retrieval. The lack of activation of the prefrontal ventrolateral cortex confirms the role of this area in episodic memory formation.

Adult↗

PubMed2005

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.

Adult↗

PubMed2005

Simultaneous monitoring of separate fetal magnetocardiographic signals in twin pregnancy.

Fetal magnetocardiography (fMCG) allows the non-invasive recording of fetal cardiac electrical activity with increasing efficacy as gestation progresses. Many reports on the successful extraction of reliable fetal magnetocardiographic traces in singleton pregnancies exist in the literature, whereas there is only one report on the reconstruction of averaged fetal cardiac signals obtained in a twin pregnancy with the use of a double sensor array system. In this paper, we aimed at assessing the effectiveness of an ICA-based procedure to reconstruct the time course of fetal cardiac signals recorded with a single-shot multi-channel fMCG device in an uncomplicated twin pregnancy at 27 weeks. The evaluation of heart rate and beats synchronicity permitted the differentiation of fetal components; the quality of reconstructed fetal signals allowed visual inspection on single cycles and the simultaneous monitoring of separate fetal heart rate patterns. The proposed technique might be applied in twin pregnancies not only to characterize fetal arrhythmias, but also in all cases of discordant fetal growth, either in the case of intra-uterine growth retardation affecting one fetus, or in the case of twin-twin transfusion syndrome, a life-threatening condition where both fetuses are at risk of heart failure.

Adult↗

PubMed2005

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.

Acoustic Stimulation↗

PubMed2005

Integrated software suite for magnetocardiographic data analysis--a proposal based on an interactive programming environment.

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.

Diagnosis, Computer-Assisted↗

PubMed2004

Temporal dynamics of alpha and beta rhythms in human SI and SII after galvanic median nerve stimulation. A MEG study.

In this MEG study, we investigated cortical alpha/sigma and beta ERD/ERS induced by median nerve stimulation to extend previous evidence on different resonant and oscillatory behavior of SI and SII (NeuroImage 13 [2001] 662). Here, we tested whether simple somatosensory stimulation could induce a distinctive sequence of alpha/sigma and beta ERD/ERS over SII compared to SI. We found that for both alpha/sigma (around 10 Hz) and beta (around 20 Hz) rhythms, the latencies of ERD and ERS were larger in bilateral SII than in contralateral SI. In addition, the peak amplitude of alpha/sigma and beta ERS was smaller in bilateral SII than in contralateral SI. These results indicate a delayed and prolonged activation of SII responses, reflecting a protracted information elaboration possibly related to SII higher order role in the processing of somatosensory information. This temporal dynamics of alpha/sigma and beta rhythms may be related to a sequential activation scheme of SI and SII during the somatosensory information processes. Future studies should evaluate in SII the possible different functional significance of alpha/sigma with respect to beta rhythms during somatosensory processing.

Adult↗

PubMed2004

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.

Brain Mapping↗

PubMed2004

Coupling between "hand" primary sensorimotor cortex and lower limb muscles after ulnar nerve surgical transfer in paraplegia.

Previous neuroimaging evidence revealed an "invasion" of "hand" over "lower limb" primary sensorimotor cortex in paraplegic subjects, with the exception of a rare patient who received a surgical motor reinnervation of hip-thigh muscles by the ulnar nerve. Here, the authors show that a functional reorganization of cortico-muscular and cortico-cortical oscillatory coupling was related to the recovery of the rare patient, as a paradigmatic case of long-term plasticity in human sensorimotor cortex after motor reinnervation of paraplegic muscles. This conclusion was based on electroencephalographic and electromyographic data collected while the patient and normal control subjects performed isometric muscle contraction of the left hand or lower limb. Cortico-muscular and cortico-cortical coupling was estimated by electroencephalographic-electromyographic coherence and directed transfer function of a multivariate autoregressive model.

Adult↗

PubMed2004

Time course reconstruction of fetal cardiac signals from fMCG: independent component analysis versus adaptive maternal beat subtraction.

M-mode and pulsed Doppler echocardiography, cardiotocography and transabdominal fetal ECG are available in clinical practice to monitor fetal cardiac activity during advancing gestation, but none of these methods allows the direct measurement of morphological and temporal parameters for fetal rhythm assessment. Fetal magnetocardiograms (fMCGs) are noninvasive recordings of magnetic field variations associated with electrical activity of the fetal heart obtained with superconducting sensors positioned over the maternal abdomen inside a shielded room. Because of maternal cardiac activity, fMCGs are contaminated by maternal components that need to be eliminated to reconstruct fetal cardiac traces. The aim of the present work was to use two methods working in the time domain, an independent component analysis algorithm (FastICA) and an adaptive maternal beat subtraction technique (AMBS), for the retrieval of fetal cardiac signals from fMCGs. Detection rates of both methods were calculated, and FastICA and AMBS performances were compared in the context of clinical applications by estimating several temporal and morphological characteristics of the retrieved fetal traces, such as the shape and duration P-QRS-T waves, arrhythmic beat detection and classification, and noise reduction. Quantitative and qualitative comparison produced figures that always suggested that FastICA was superior to AMBS from the perspective of clinical use of the recovered fetal signals.

Adult↗

PubMed2004

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.

Algorithms↗