Combined functional magnetic resonance imaging and skin conductance to detect localized neural response to psychological stress: a pilot study.

OBJECTIVE: This preliminary study aims at investigating the neural correlates of the stress response, intended as an emotional and cognitive response, through the description of the activation of the autonomic nervous system in a problem-solving task and central functional data; in particular, we recorded skin conductance level (SCL) and response (SCR) and observed the correlation with fMRI data. MATERIALS AND METHODS: The results obtained from 6 healthy subjects, 3 males and 3 females, aged between 18 and 45 (average = 27, SD = 7.08) who voluntarily offered to participate in the study were examined. They were previously subjected to a brief clinical psychological assessment (MMPI-2) and then to a psychophysiological evaluation. The real experiment consisted in subjecting the participants to an adapted version of the Raven's Coloured Progressive Matrices 47 (CPM 47) test to evaluate some consequences on brain activity of attention, orientation, reflex and response to stress during fMRI data acquisition and SCL-SCR recording. RESULTS: SCR changes were found to be related to the activity of different brain regions such as bilateral precentral gyrus, right inferior frontal gyrus, right medial frontal gyrus, bilateral superior frontal gyri and left anterior cingulate suggesting a specific relationship between attentive processing and autonomic arousal. CONCLUSION: The association of SC measurement with neuroimaging allows to highlight the interaction between emotional and cognitive processes: although preliminary, these results partially confirm what previously found in literature on the neural correlates of psychological stress and underline the interaction between cognitive function and autonomic arousal system during a stressful problem-solving task.

Wavelet p-Leader Non-Gaussian Multiscale Expansions for EEG series: an Exploratory Study on Cold-Pressor Test.

Brain dynamics recorded through electroencephalography (EEG) have been proven to be the output of a nonstationary and nonlinear system. Thus, multifractality of EEG series has been exploited as a useful tool for a neurophysiological characterization in health and disease. However, the role of EEG multifractality under peripheral stress is unknown. In this study, we propose to make use of a novel tool, the recently defined non-Gaussian multiscale analysis, to investigate brain dynamics in the range of 4-8Hz following a cold-pressor test versus a resting state. The method builds on the wavelet p-leader multifractal spectrum to quantify different types of departure from Gaussian and linear properties, and is compared here to standard linear descriptive indices. Results suggest that the proposed non-Gaussian multiscale indices were able to detect expected changes over the somatosensory and premotor cortices, over regions different from those detected by linear analyses. They further indicate that preferred responses for the contralateral somatosensory cortex occur at scales 2.5s and 5s. These findings contribute to the characterization of the so-called central autonomic network, linking dynamical changes at a peripheral and a central nervous system levels.

A new Modelling Framework to Study Time-Varying Directional Brain-Heart Interactions: Preliminary Evaluations and Perspectives.

We propose a novel modelling framework to study non-stationary, directional brain-heart interplay in a time varying fashion. Considering electroencephalographic (EEG) signals and Heart Rate Variability (HRV) series as inputs, a new multivariate formulation is derived from proper coupling functions linking cortical electrical activity and heartbeat dynamics generation models. These neural-autonomic coupling rules are formalised according to the current knowledge on the central autonomic network and fully parametrised in adaptive coefficients quantifying the information outflow from-brain-to- heart as well as from-heart-to-brain. Such coefficients can be effectively estimated by solving the model inverse problem, and profitably exploited for a novel assessment of brain-heart interactions. Here we show preliminary experimental results gathered from 27 healthy volunteers undergoing significant sympatho-vagal perturbations through cold-pressor test and discuss prospective uses of this novel methodological frame- work. Specifically, we highlight how the directional brain-heart coupling significantly increases during prolonged baroreflex elicitation with specific time delays and throughout specific brain areas, especially including fronto-parietal regions and lateralisation mechanisms in the temporal cortices.

Systematic Review of fMRI Compatible Devices: Design and Testing Criteria.

Functional Magnetic Resonance Imaging (fMRI) is at present one of the most used methodologies for functional brain exploration, both in clinical and research settings. fMRI can noninvasively measure neural activity by using specific experimental paradigms. Often, these paradigms require the stimulation of the subject to perform sensorimotor tasks: in the past, the stimuli have been administered manually for investigating fundamental aspects of tactile perception and somatosensory processing. Nowadays, the use of mechatronic devices to stimulate the subject during fMRI studies is growing, also to assure reproducibility, control, and monitoring of task performances. For these reasons, researchers are interested in designing interfaces to be used inside the MRI environment during fMRI studies. For the design of every new device safety and compatibility constraints, imposed by the presence of high static magnetic field, switching magnetic gradients and radiofrequency electromagnetic pulses, must be satisfied. Moreover, it should be considered that functional imaging sequences are even more sensitive to perturbations of the magnetic field than MRI standard diagnostic sequences. Despite several existing devices for use in fMRI studies, an extensive review is still lacking. Our survey aims to introduce into the challenges imposed on the development of fMRI-compatible devices. The current state of the art of compatible devices in fMRI will be presented, pointing out the functionalities and peculiarities of various kinds of device. A particular emphasis will be placed on the tests for the evaluation of fMRI compatibility. This review will be useful both for designers of devices to be used in fMRI studies and for neuroscientists that are having to design fMRI experimental paradigm, and therefore require an overview of existing instruments, but also a knowledge of the benefits and criticism arising from their use.

Analysis of Residual Dependencies of Independent Components Extracted from fMRI Data.

Independent component analysis (ICA) of functional magnetic resonance imaging (fMRI) data can be employed as an exploratory method. The lack in the ICA model of strong a priori assumptions about the signal or about the noise leads to difficult interpretations of the results. Moreover, the statistical independence of the components is only approximated. Residual dependencies among the components can reveal informative structure in the data. A major problem is related to model order selection, that is, the number of components to be extracted. Specifically, overestimation may lead to component splitting. In this work, a method based on hierarchical clustering of ICA applied to fMRI datasets is investigated. The clustering algorithm uses a metric based on the mutual information between the ICs. To estimate the similarity measure, a histogram-based technique and one based on kernel density estimation are tested on simulated datasets. Simulations results indicate that the method could be used to cluster components related to the same task and resulting from a splitting process occurring at different model orders. Different performances of the similarity measures were found and discussed. Preliminary results on real data are reported and show that the method can group task related and transiently task related components.

On the deconvolution analysis of electrodermal activity in bipolar patients.

People affected by bipolar disorders experience alternating states of depression with episodes of mania or hypomania. This mental can lead to a poor handling of daily routines, can worsen personal relationships, and often can be life-threatening. This preliminary study aims at investigating how the autonomic nervous system, in terms of electrodermal activity, responds to specific controlled emotional stimuli in bipolar patients. More specifically, we present here a method to deploy the analysis of ElectroDermal Activity (EDA) to discriminate clinical mood states. EDA was analyzed by using a deconvolution method to separate tonic from phasic components. The three subjects recruited and the experimental protocol used here is part of the European project PSYCHE. Preliminary results show that the bipolar mood states can be related to electrodermal tonic activity.

Spatiotemporal dynamics of single-letter reading: a combined ERP-FMRI study.

This work investigates the neural correlates of single-letter reading by combining event-related potentials (ERPs) and functional magnetic resonance imaging (fMRI), thus exploiting their complementary spatiotemporal resolutions. Three externally-paced reading tasks were administered with an event-related design: passive observation of letters and symbols and active reading aloud of letters. ERP and fMRI data were separately recorded from 8 healthy adults during the same experimental conditions. Due to the presence of artifacts in the EEG signals, two subjects were discarded from further analysis. Independent Component Analysis was applied to ERPs, after dimensionality reduction by Principal Component Analysis: some independent components were clearly related to specific reading functions and the associated current density distributions in the brain were estimated with Low Resolution Electromagnetic Tomography Analysis method (LORETA). The impulse hemodynamic response function was modeled as a linear combination of linear B-spline functions and fMRI statistical analysis was performed by multiple linear regression. fMRI and LORETA maps were superimposed in order to identify the overlapping activations and the activated regions specifically revealed by each modality. The results showed the existence of neuronal networks functionally specific for letter processing and for explicit verbal-motor articulation, including the temporo-parietal and frontal regions. Overlap between fMRI and LORETA results was observed in the inferior temporal-middle occipital gyrus, suggesting that this area has a crucial and multifunctional role for linguistic and reading processes, likely because its spatial location and strong interconnection with the main visual and auditory sensory systems may have favored its specialization in grapheme-phoneme matching.

Tactile spatial working memory activates the dorsal extrastriate cortical pathway in congenitally blind individuals.

In sighted individuals, both the visual and tactile version of the same spatial working memory task elicited neural responses in the dorsal "where" cortical pathway (Ricciardi et al., 2006). Whether the neural response during the tactile working memory task is due to visually-based spatial imagery or rather reflects a more abstract, supramodal organization of the dorsal cortical pathway remains to be determined. To understand the role of visual experience on the functional organization of the dorsal cortical stream, using functional magnetic resonance imaging (fMRI) here we examined brain response in four individuals with congenital or early blindness and no visual recollection, while they performed the same tactile spatial working memory task, a one-back recognition of 2D and 3D matrices. The blind subjects showed a significant activation in bilateral posterior parietal cortex, dorsolateral and inferior prefrontal areas, precuneus, lateral occipital cortex, and cerebellum. Thus, dorsal occipito-parietal areas are involved in mental imagery dealing with spatial components in subjects without prior visual experience and in response to a non-visual task. These data indicate that recruitment of the dorsal cortical pathway in response to the tactile spatial working memory task is not mediated by visually-based imagery and that visual experience is not a prerequisite for the development of a more abstract functional organization of the dorsal stream. These findings, along with previous data indicating a similar supramodal functional organization within the ventral cortical pathway and the motion processing brain regions, may contribute to explain how individuals who are born deprived of sight are able to interact effectively with the surrounding world.

Independent component analysis applied to the removal of motion artifacts from electrocardiographic signals.

Electrocardiographic (ECG) signals are affected by several kinds of artifacts that may hide vital signs of interest. In this study we apply independent component analysis (ICA) to isolate motion artifacts. Standard or instantaneous ICA, which is currently the most addressed ICA model within the context of artifact removal, is compared to two other ICA techniques. The first technique is a frequency domain approach to convolutive mixture separation. The second is based on temporally constrained ICA, which enables the estimation of only one component close to a particular reference signal. Performance indexes evaluate ECG complex enhancement and relevant heart rate errors. Our results show that both convolutive and constrained ICA implementations perform better than standard ICA, thus opening up a new field of application for these two methods. Moreover, statistical analysis reveals that constrained ICA and convolutive ICA do not significantly differ concerning heart rate estimation, even though the latter overcomes the former in ECG morphology recovery.

Multichannel techniques for motion artifacts removal from electrocardiographic signals.

Electrocardiographic (ECG) signals are affected by several kinds of artifacts, that may hide vital signs of interest. Motion artifacts, due to the motion of the electrodes in relation to patient skin, are particularly frequent in bioelectrical signals acquired by wearable systems. In this paper we propose different approaches in order to get rid of motion confounds. The first approach we follow starts from measuring electrode motion provided by an accelerometer placed on the electrode and use this measurement in an adaptive filtering system to remove the noise present in the ECG. The second approach is based on independent component analysis methods applied to multichannel ECG recordings; we propose to use both instantaneous model and a frequency domain implementation of the convolutive model that accounts for different paths of the source signals to the electrodes.

A compatible electrocutaneous display for functional magnetic resonance imaging application.

In this paper we propose an MR (magnetic resonance) compatible electrocutaneous stimulator able to inject an electric current, variable in amplitude and frequency, into the fingertips in order to elicit tactile skin receptors (mechanoreceptors). The desired goal is to evoke specific tactile sensations selectively stimulating skin receptors by means of an electric current in place of mechanical stimuli. The field of application ranges from functional magnetic resonance imaging (fMRI) tactile studies to augmented reality technology. The device here proposed is designed using safety criteria in order to comply with the threshold of voltage and current permitted by regulations. Moreover, MR safety and compatibility criteria were considered in order to perform experiments inside the MR scanner during an fMRI acquisition for functional brain activation analysis. Psychophysical laboratory tests are performed in order to define the different evoked tactile sensation. After verifying the device MR safety and compatibility on a phantom, a test on a human subject during fMRI acquisition is performed to visualize the brain areas activated by the simulated tactile sensation.

An electrodeless system for measurement of liquid sample dielectric properties in radio frequency band.

An electrodeless measurement system based on a resonant circuit is proposed for the measurement of dielectric properties of liquid samples at RF (radio frequency). Generally, properties as dielectric constant, loss factor and conductivity are measured by parallel plate capacitor cells: this method has several limitations in the case of particular liquid samples and in the range of radiofrequencies. Our method is based on the measurements of resonance frequency and quality factor of a LC resonant circuit in different measuring conditions, without and with the liquid sample placed inside a test tube around which the home made coil is wrapped. The measurement is performed using a network analyzer and a dual loop probe, inductively coupled with the resonant circuit. One of the advantages of this method is the contactless between the liquid sample and the measurement electrodes. In this paper the measurement system is described and test measurements of conventional liquids dielectric properties are reported.

Non-linear prediction for oesophageal voice analysis.

Herein, non-linear prediction methods are applied to oesophageal voice analysis. The research aims to investigate normal and pathological subjects, in order to improve knowledge of the oesophageal voice behaviour. Analysis is performed in the reconstructed phase space, using both non-linear prediction with local linear approximation and the S-Map method. Preliminary results seem to confirm that in normal subjects a non-linear stable deterministic behaviour takes place, while in pathological subjects the non-linear contribution reduces while the time series becomes unstable.