Miguel Mañanas - Academia.edu (original) (raw)

Papers by Miguel Mañanas

Journal of Neural Engineering, Mar 2, 2016

Objective. Medical intractable epilepsy is a common condition that affects 40% of epileptic patie... more Objective. Medical intractable epilepsy is a common condition that affects 40% of epileptic patients that generally have to undergo resective surgery. Magnetoencephalography (MEG) has been increasingly used to identify the epileptogenic foci through equivalent current dipole (ECD) modeling, one of the most accepted methods to obtain an accurate localization of interictal epileptiform discharges (IEDs). Modeling requires that MEG signals are adequately preprocessed to reduce interferences, a task that has been greatly improved by the use of blind source separation (BSS) methods. MEG recordings are highly sensitive to metallic interferences originated inside the head by implanted intracranial electrodes, dental prosthesis, etc and also coming from external sources such as pacemakers or vagal stimulators. To reduce these artifacts, a BSS-based fully automatic procedure was recently developed and validated, showing an effective reduction of metallic artifacts in simulated and real signals (Migliorelli et al 2015 J. Neural Eng. 12 046001). The main objective of this study was to evaluate its effects in the detection of IEDs and ECD modeling of patients with focal epilepsy and metallic interference. Approach. A comparison between the resulting positions of ECDs was performed: without removing metallic interference; rejecting only channels with large metallic artifacts; and after BSS-based reduction. Measures of dispersion and distance of ECDs were defined to analyze the results. Main results. The relationship between the artifact-to-signal ratio and ECD fitting showed that higher values of metallic interference produced highly scattered dipoles. Results revealed a significant reduction on dispersion using the BSS-based reduction procedure, yielding feasible locations of ECDs in contrast to the other two approaches. Significance. The automatic BSS-based method can be applied to MEG datasets affected by metallic artifacts as a processing step to improve the localization of epileptic foci.

IFAC Proceedings Volumes, 2002

The purpose of this work is to evaluate characteristics of a respiratory model, RS1, in the prese... more The purpose of this work is to evaluate characteristics of a respiratory model, RS1, in the presence of the following stimuli: exercise, hypercapnia and hypoxia. RS1 has a controller where the driving signal optimizes alveolar ventilation and respiratory frequency to minimize the respiratory work output. A comparative study of the steadystate and transient responses with other three models is performed by simulation. Alternative equations to calculate the optimum frequency are evaluated during exercise and a linear average of two of them is proposed and tested for a healthy subject and with restrictive/obstructive pathology. Additionally, the circulatory time delay in gas transport that produces periodic breathing is calculated.

ABSTRACT Analysis of the respiratory muscles activity is a promising technique for diagnosis of r... more ABSTRACT Analysis of the respiratory muscles activity is a promising technique for diagnosis of respiratory diseases, such as chronic obstructive pulmonary disease (COPD). The sternomastoid muscle was selected to study the activity of respiratory muscles, due to its accessibility. This work proposes the analysis of vibromyographic and electromyographic signals from the sternomastoid muscle, in order to evaluate the muscle function in a ventilatory test. Spectral analysis was performed. The Welch periodogram and autoregressive models were used. Results from a group of 5 patients with COPD are shown at different levels of inspiratory loads. Activity of sternomastoid muscle was measured by means of root-mean-square (rms) values and mean and median frequencies, and they were related to level of severity of COPD patients

Journal of Neural Engineering, May 17, 2016

Objective: The development of modern assistive and rehabilitation devices requires reliable and e... more Objective: The development of modern assistive and rehabilitation devices requires reliable and easy-to-use methods to extract neural information for control of devices. Group-specific pattern recognition identifiers are influenced by intersubject variability. Based on high-density EMG (HD-EMG) maps, our research group has already shown that inter-subject muscle activation patterns exist in a population of healthy subjects. The aim of this paper is to analyze muscle activation patterns associated with four tasks (flexion/extension of the elbow, and supination/pronation of the forearm) at three different effort levels in a group of patients with incomplete Spinal Cord Injury (iSCI). Approach: Muscle activation patterns were evaluated by the automatic identification of these four isometric tasks along with the identification of levels of voluntary contractions. Two types of classifiers were considered in the identification: linear discriminant analysis and support vector machine. Main Results: Results show that performance of classification increases when combining features extracted from intensity and spatial information of HD-EMG maps (Accuracy = 97.5%). Moreover, when compared to a population with injuries at different levels, a lower variability between activation maps was obtained within a group of patients with similar injury suggesting stronger task-specific and effortlevel-specific co-activation patterns, which enable better prediction results. Significance: Despite the challenge of identifying both the four tasks and the three effort levels in patients with iSCI, promising results were obtained which support the use of HD-EMG features for providing useful information regarding motion and force intention.

PLOS ONE, Aug 31, 2015

Multiple sclerosis (MS) is a chronic central nervous system disorder characterized by white matte... more Multiple sclerosis (MS) is a chronic central nervous system disorder characterized by white matter inflammation, demyelination and neurodegeneration. Although cognitive dysfunction is a common manifestation, it may go unnoticed in recently-diagnosed patients. Prior studies suggest MS patients develop compensatory mechanisms potentially involving enhanced performance monitoring. Here we assessed the performance monitoring system in early-stage MS patients using the error-related negativity (ERN), an event-related brain potential (ERP) observed following behavioral errors. Twenty-seven early-stage MS patients and 31 controls were neuropsychologically assessed. Electroencephalography recordings were obtained while participants performed: a) a stop task and b) an auditory oddball task. Behavior and ERP measures were assessed. No differences in performance were found between groups in most neuropsychological tests or in behavior or ERP components in the auditory oddball task. However, the amplitude of the ERN associated with stop errors in the stop task was significantly higher in patients. ERN amplitude correlated positively with scores on the Expanded Disability Status Scale and the Multiple Sclerosis Severity Score, and negatively with the time since last relapse. Patients showed higher neuronal recruitment in tasks involving performance monitoring. Results suggest the development of compensatory brain mechanisms in early-stage MS and reflect the sensitivity of the ERN to detect these changes.

The Journal of Neuroscience, Apr 23, 2014

Apathy is one of the most common and debilitating nonmotor manifestations of Parkinson's disease ... more Apathy is one of the most common and debilitating nonmotor manifestations of Parkinson's disease (PD) and is characterized by diminished motivation, decreased goal-directed behavior, and flattened affect. Despite its high prevalence, its underlying mechanisms are still poorly understood, having been associated with executive dysfunction, and impaired emotional processing and decision making. Apathy, as a syndrome, has recently been associated with reduced activation in the ventral striatum, suggesting that early-to middlestage Parkinson's disease patients with this manifestation may have a compromised mesocorticolimbic dopaminergic pathway and impaired incentive processing. To test this hypothesis, we measured the amplitude of the feedback-related negativity, an event-related brain potential associated with performance outcome valence, following monetary gains and losses in human PD patients (12 women) and healthy controls (6 women) performing a gambling task. Early-to middle-stage PD patients presenting clinically meaningful symptoms of apathy were compared with nonapathetic PD patients and healthy controls. Patients with cognitive impairment, depression, and other psychiatric disturbances were excluded. Results showed that the amplitude of the feedback-related negativity, measured as the difference wave in the event-related brain potential between gains and losses, was significantly reduced in PD patients with apathy compared with nonapathetic patients and healthy controls. These findings indicate impaired incentive processing and suggest a compromised mesocorticolimbic pathway in cognitively intact PD patients with apathy.

Physiological Measurement, May 27, 2015

The biological response to stress originates in the brain but involves different biochemical and ... more The biological response to stress originates in the brain but involves different biochemical and physiological effects. Many common clinical methods to assess stress are based on the presence of specific hormones and on features extracted from different signals, including electrocardiogram, blood pressure, skin temperature, or galvanic skin response. The aim of this paper was to assess stress using EEG-based variables obtained from univariate analysis and functional connectivity evaluation. Two different stressors, Stroop test and sleep deprivation, were applied to 30 volunteers to find common EEG patterns related to stress effects. Results showed a decrease of high alpha power (11 to 12 Hz), an increase in the high beta band (23 to 36 Hz, considered a busy brain indicator), and a decrease in the approximate entropy. Moreover, connectivity showed that the high beta coherence and the interhemispheric nonlinear couplings, measured by the cross mutual information function, increased significantly for both stressors, suggesting that useful stress indexes may be obtained from EEG-based features.

ABSTRACT Spectral analysis of myographic signals from respiratory muscles is a promising non-inva... more ABSTRACT Spectral analysis of myographic signals from respiratory muscles is a promising non-invasive technique to study respiratory diseases. However, it requires that the signal be at least weakly stationary. Electromyographic (EMG) and vibromyographic (VMG) signals are related to electrical and mechanical activity, respectively. Local stationarity of the signals from an accessory respiratory muscle is evaluated by means of the reverse arrangement test. A methodology for change detection and to analyze the evolution of the stationarity during the respiratory cycle in myographic signals is also presented. These studies are performed in healthy subjects and patients with chronic obstructive pulmonary disease. Local stationarity decreases with the increase of the level of ventilation and when a maintained exercise goes forward. High levels of ventilation and respiratory muscle fatigue produce statistical changes in myographic signals

Magnetoencephalography is a technique that can noninvasively measure the brain signal. There are ... more Magnetoencephalography is a technique that can noninvasively measure the brain signal. There are many advantages of using this technique rather than similar procedures such as the EEG for the evaluation of medical diseases. However, one of its main problems is its high sensitivity to sources causing metallic distortion of the signal, and the removal of this type of artifacts remains unsolved. In this study a technique for reducing metallic interference was presented. This algorithm was based on AMUSE, a second order blind source separation method, and a procedure for choosing the artifactual independent components was also presented. The results showed that the elimination of these artifacts would be possible by means of the application of this AMUSE-based interference reduction procedure.

ABSTRACT Analysis of the sternomastoid muscle activity in respiration can be a new non-invasive t... more ABSTRACT Analysis of the sternomastoid muscle activity in respiration can be a new non-invasive tool to assess the significance of chronic obstructive pulmonary disease (COPD). The aim of this work is the evaluation of vibromyographic (VMG) signals from the sternomastoid muscle, in order to study the muscle function in a ventilatory test. Simultaneous electromyographic (EMG) signals were recorded and a comparative analysis with VMG was done. Results from a group of 6 patients with COPD are shown, following two respiratory tests. The root-mean-square (RMS) showed the same behaviour of VMG and EMG signals in both tests. H/L ratios of power spectral density pointed out muscle fatigue in the last steps of the respiratory test. Cross-correlation of EMG and VMG found different patterns of relationship between the electrical and mechanical activity of muscle and allow the study of EMG-VMG time delay, during execution of respiratory load tests

The International Journal of Neuropsychopharmacology, Apr 27, 2015

Background: Psychedelics induce intense modifications in the sensorium, the sense of "self," and ... more Background: Psychedelics induce intense modifications in the sensorium, the sense of "self," and the experience of reality. Despite advances in our understanding of the molecular and cellular level mechanisms of these drugs, knowledge of their actions on global brain dynamics is still incomplete. Recent imaging studies have found changes in functional coupling between frontal and parietal brain structures, suggesting a modification in information flow between brain regions during acute effects. Methods: Here we assessed the psychedelic-induced changes in directionality of information flow during the acute effects of a psychedelic in humans. We measured modifications in connectivity of brain oscillations using transfer entropy, a nonlinear measure of directed functional connectivity based on information theory. Ten healthy male volunteers with prior experience with psychedelics participated in 2 experimental sessions. They received a placebo or a dose of ayahuasca, a psychedelic preparation containing the serotonergic 5-HT 2A agonist N,N-dimethyltryptamine. Results: The analysis showed significant changes in the coupling of brain oscillations between anterior and posterior recording sites. Transfer entropy analysis showed that frontal sources decreased their influence over central, parietal, and occipital sites. Conversely, sources in posterior locations increased their influence over signals measured at anterior locations. Exploratory correlations found that anterior-to-posterior transfer entropy decreases were correlated with the intensity of subjective effects, while the imbalance between anterior-to-posterior and posterior-to-anterior transfer entropy correlated with the degree of incapacitation experienced. Conclusions: These results suggest that psychedelics induce a temporary disruption of neural hierarchies by reducing topdown control and increasing bottom-up information transfer in the human brain.

The aim of this work is to evaluate responses and characteristics of three respiratory models (RS... more The aim of this work is to evaluate responses and characteristics of three respiratory models (RS1, RS2 and RS13) in the presence of the following stimuli: exercise, hypercapnia and hypoxia. A comparative study among the three closed-loop systems is performed in simulation: RS1 has a controller to minimize the mechanical and chemical work rate of breathing. RS2 and RS3 fit better to physiological systems with peripheral and central components. The steady state response is evaluated at different levels of stimulus by means of the variables: ventilation, PaCO/sub 2/ and PaO/sub 2/. In general, the stimulus and variable that produces more differences among models are exercise and ventilation, respectively. The best model to indicate the homeostasis during the exercise is RS1 but it is not possible to analyze hypoxia because there is no feedback of PaO/sub 2/. In the transient response, a settling time of several seconds is found in RS1 and a more realistic value around some minutes is obtained in the other models. Besides, whereas there are no overshoots in the responses of RS1, they appear in PaO/sub 2/ with RS2 and RS3 models because an exponential feedback of PaO/sub 2/ is considered. The influence of these time constants and gains on the transient response is analyzed to obtain the maximum values to keep the system stable. Finally, the sensitivity of the system response with the dead space is studied during exercise.

Journal of Neural Engineering, May 27, 2015

Objective. One of the principal drawbacks of magnetoencephalography (MEG) is its high sensitivity... more Objective. One of the principal drawbacks of magnetoencephalography (MEG) is its high sensitivity to metallic artifacts, which come from implanted intracranial electrodes and dental ferromagnetic prosthesis and produce a high distortion that masks cerebral activity. The aim of this study was to develop an automatic algorithm based on blind source separation (BSS) techniques to remove metallic artifacts from MEG signals. Approach. Three methods were evaluated: AMUSE, a second-order technique; and INFOMAX and FastICA, both based on high-order statistics. Simulated signals consisting of real artifact-free data mixed with real metallic artifacts were generated to objectively evaluate the effectiveness of BSS and the subsequent interference reduction. A completely automatic detection of metallic-related components was proposed, exploiting the known characteristics of the metallic interference: regularity and low frequency content. Main results. The automatic procedure was applied to the simulated datasets and the three methods exhibited different performances. Results indicated that AMUSE preserved and consequently recovered more brain activity than INFOMAX and FastICA. Normalized mean squared error for AMUSE decomposition remained below 2%, allowing an effective removal of artifactual components. Significance. To date, the performance of automatic artifact reduction has not been evaluated in MEG recordings. The proposed methodology is based on an automatic algorithm that provides an effective interference removal. This approach can be applied to any MEG dataset affected by metallic artifacts as a processing step, allowing further analysis of unusable or poor quality data.

Psychopharmacology, Nov 30, 2011

Rationale Quantitative analysis of electroencephalographic signals (EEG) and their interpretation... more Rationale Quantitative analysis of electroencephalographic signals (EEG) and their interpretation constitute a helpful tool in the assessment of the bioavailability of psychoactive drugs in the brain. Furthermore, psychotropic drug groups have typical signatures which relate biochemical mechanisms with specific EEG changes. Objectives To analyze the pharmacological effect of a dose of alprazolam on the connectivity of the brain during wakefulness by means of linear and nonlinear approaches. Methods EEG signals were recorded after alprazolam administration in a placebo-controlled crossover clinical trial. Nonlinear couplings assessed by means of corrected cross-conditional entropy were compared to linear couplings measured with the classical magnitude squared coherence. Results Linear variables evidenced a statistically significant drug-induced decrease, whereas nonlinear variables showed significant increases. All changes were highly correlated to drug plasma concentrations. The spatial distribution of the observed connectivity changes clearly differed from a previous study: changes before and after the maximum drug effect were mainly observed over the anterior half of the scalp. Additionally, a new variable with very low computational cost was defined to evaluate nonlinear coupling. This is particularly interesting when all pairs of EEG channels are assessed as in this study. Conclusions Results showed that alprazolam induced changes in terms of uncoupling between regions of the scalp, with opposite trends depending on the variables: decrease in linear ones and increase in nonlinear features. Maps provided consistent information about the way brain changed in terms of connectivity being definitely necessary to evaluate separately linear and nonlinear interactions.

The use of mathematical models of physiological systems in medicine has allowed the development o... more The use of mathematical models of physiological systems in medicine has allowed the development of diagnostic, treatment, and medical educational tools, but their application for predictive, preventive, and personalized purposes is restricted by their complexity. Although there are strategies that reduce the complexity of applying models by fitting techniques, they focus on a single instant of time, neglecting the effect of the system's temporal evolution. The aim of this work is to propose a dynamic fitting strategy of physiological models with large number of parameters and a constrained amount of experimental data, focused on obtaining better predictions based on the system's temporal trend and useful to predict future states. It was applied in a cardiorespiratory model as a case study. Experimental data from a longitudinal study of healthy adult subjects under aerobic exercise were used for fitting and validation. The model predictions obtained at steady-state using the proposed strategy and the nominal values of the parameters were compared. The best results corresponded mostly to the proposed strategy, mainly regarding the overall prediction error. The results evidenced the usefulness of the dynamic fitting strategy, highlighting its use for predictive, preventive, and personalized applications.

Transactions of Japanese Society for Medical and Biological Engineering, 2013

This paper presents a comparative study of dynamic responses of three respiratory models under ex... more This paper presents a comparative study of dynamic responses of three respiratory models under exercise, which one of them is proposed in this study in order to be included in an integrative model that simulates mechanical ventilation. Transients of the proposed model matches better with the known response from physiological point of view.

IOP Publishing eBooks, Jun 1, 2023

Understanding the respiratory control system and the ventilatory pattern under hypercapnic stimul... more Understanding the respiratory control system and the ventilatory pattern under hypercapnic stimulus is important to interpret the acute exacerbation of COPD and the condition of patients connected to mechanical ventilation. The purpose of this study is the analysis of respiratory and muscle parameters in order to obtain the most sensitive and characteristic of different levels of hypercapnic stimulus. Parameters defined

Frontiers in Neuroscience

The performance of myoelectric control highly depends on the features extracted from surface elec... more The performance of myoelectric control highly depends on the features extracted from surface electromyographic (sEMG) signals. We propose three new sEMG features based on the kernel density estimation. The trimmed mean of density (TMD), the entropy of density, and the trimmed mean absolute value of derivative density were computed for each sEMG channel. These features were tested for the classification of single tasks as well as of two tasks concurrently performed. For single tasks, correlation-based feature selection was used, and the features were then classified using linear discriminant analysis (LDA), non-linear support vector machines, and multi-layer perceptron. The eXtreme gradient boosting (XGBoost) classifier was used for the classification of two movements simultaneously performed. The second and third versions of the Ninapro dataset (conventional control) and Ameri’s movement dataset (simultaneous control) were used to test the proposed features. For the Ninapro dataset,...