2020 42nd Annual International Conference of the IEEE Engineering in Medicine & Biology Society (EMBC)
This study had two main objectives: (i) to study the effects of volume conduction on different co... more This study had two main objectives: (i) to study the effects of volume conduction on different connectivity metrics (Amplitude Envelope Correlation AEC, Phase Lag Index PLI, and Magnitude Squared Coherence MSCOH), comparing the coupling patterns at electrode- and sensor-level; and (ii) to characterize spontaneous EEG activity during different stages of Alzheimer's disease (AD) continuum by means of three complementary network parameters: node degree (k), characteristic path length (L), and clustering coefficient (C). Our results revealed that PLI and AEC are weakly influenced by volume conduction compared to MSCOH, but they are not immune to it. Furthermore, network parameters obtained from PLI showed that AD continuum is characterized by an increase in L and C in low frequency bands, suggesting lower integration and higher segregation as the disease progresses. These network changes reflect the abnormalities during AD continuum and are mainly due to neuronal alterations, because PLI is slightly affected by volume conduction effects.
2019 41st Annual International Conference of the IEEE Engineering in Medicine and Biology Society (EMBC), 2019
The aim of this study was to evaluate the effect of volume conduction on different connectivity m... more The aim of this study was to evaluate the effect of volume conduction on different connectivity metrics: Amplitude Envelope Correlation (AEC), Phase Lag Index (PLI), and Magnitude Squared Coherence (MSCOH). These measures were applied to: (i) a synthetic model of 64 coupled oscillators; and (ii) a resting-state EEG database of 72 patients with dementia due to Alzheimer’s disease (AD) and 37 cognitively healthy controls. Our results revealed that AEC and PLI are weakly influenced by the simulated volume conduction compared to MSCOH, although the three metrics are not immune to this effect. Furthermore, results with real EEG recordings showed that AD patients are characterized by an AEC increase in δ frequency band and widespread connectivity decreases in α and β1 bands. These coupling changes reflect the abnormalities in spontaneous EEG activity of AD patients and might provide further insights into the underlying brain dynamics associated with this disorder.
Objective. Schizophrenia is a psychiatric disorder that has been shown to disturb the dynamic top... more Objective. Schizophrenia is a psychiatric disorder that has been shown to disturb the dynamic top-down processing of sensory information. Various imaging techniques have revealed abnormalities in brain activity associated with this disorder, both locally and between cerebral regions. However, there is increasing interest in investigating dynamic network response to novel and relevant events at the network level during an attention-demanding task with high-temporal-resolution techniques. The aim of the work was: (i) to test the capacity of a novel algorithm to detect recurrent brain meta-states from auditory oddball task recordings; and (ii) to evaluate how the dynamic activation and behavior of the aforementioned meta-states were altered in schizophrenia, since it has been shown to impair top-down processing of sensory information. Approach. A novel unsupervised method for the detection of brain meta-states based on recurrence plots and community detection algorithms, previously tes...
Cerebral hypoperfusion impairs brain activity and leads to cognitive impairment. Left and right c... more Cerebral hypoperfusion impairs brain activity and leads to cognitive impairment. Left and right common carotid arteries (CCA) are the major source of cerebral blood supply. It remains unclear whether blood flow in both CCA contributes equally to brain activity. Here, CCA blood flow was evaluated using ultrasonography in 23 patients with cerebrovascular diseases. Resting-state brain activity and cognitive status were also assessed using magnetoencephalography and a cognitive subscale of the Functional Independence Measure, respectively, to explore the relationships between blood flow, functional brain activity, and cognitive status. Our findings indicated that there was an association between blood flow and resting-state brain activity, and between resting-state brain activity and cognitive status. However, blood flow was not significantly associated with cognitive status directly. Furthermore, blood velocity in the right CCA correlated with resting-state brain activity, but not with...
PICALM and CLU genes have been linked to alterations in brain biochemical processes that may have... more PICALM and CLU genes have been linked to alterations in brain biochemical processes that may have an impact on Alzheimer’s disease (AD) development and neurophysiological dynamics. The aim of this study is to analyze the relationship between the electroencephalographic (EEG) activity and the PICALM and CLU alleles described as conferring risk or protective effects on AD patients and healthy controls. For this purpose, EEG activity was acquired from: 18 AD patients and 12 controls carrying risk alleles of both PICALM and CLU genes, and 35 AD patients and 12 controls carrying both protective alleles. Relative power (RP) in the conventional EEG frequency bands (delta, theta, alpha, beta, and gamma) was computed to quantify the brain activity at source level. In addition, spatial entropy (SE) was calculated in each band to characterize the regional distribution of the RP values throughout the brain. Statistically significant differences in global RP and SE at beta band (p-values < 0....
Objective. Nested into slow oscillations (SOs) and modulated by their up-states, spindles are ele... more Objective. Nested into slow oscillations (SOs) and modulated by their up-states, spindles are electrophysiological hallmarks of N2 sleep stage that present a complex hierarchical architecture. However, most studies have only described spindles in basic statistical terms, which were limited to the spindle itself without analyzing the characteristics of the pre-spindle moments in which the SOs are originated. The aim of this study was twofold: (a) to apply spectral and temporal measures to the pre-spindle and spindle periods, as well as analyze the correlation between them, and (b) to evaluate the potential of these spectral and temporal measures in future automatic detection algorithms. Approach. An automatic spindle detection algorithm was applied to the overnight electroencephalographic recordings of 26 subjects. Ten complementary features (five spectral and five temporal parameters) were computed in the pre-spindle and spindle periods after their segmentation. These features were ...
Resting-state neural oscillations are used as biomarkers for functional diseases such as dementia... more Resting-state neural oscillations are used as biomarkers for functional diseases such as dementia, epilepsy, and stroke. However, accurate interpretation of clinical outcomes requires the identification and minimisation of potential confounding factors. While several studies have indicated that the menstrual cycle also alters brain activity, most of these studies were based on visual inspection rather than objective quantitative measures. In the present study, we aimed to clarify the effect of the menstrual cycle on spontaneous neural oscillations based on quantitative magnetoencephalography (MEG) parameters. Resting-state MEG activity was recorded from 25 healthy women with normal menstrual cycles. For each woman, resting-state brain activity was acquired twice using MEG: once during their menstrual period (MP) and once outside of this period (OP). Our results indicated that the median frequency and peak alpha frequency of the power spectrum were low, whereas Shannon spectral entro...
The analysis of the electromagnetic brain activity can provide important information to help in t... more The analysis of the electromagnetic brain activity can provide important information to help in the diagnosis of several mental diseases. Both electroencephalogram (EEG) and magnetoencephalogram (MEG) record the neural activity with high temporal resolution (Hämäläinen, Hari, Ilmoniemi, Knuutila, & Lounasmaa, 1993). Nevertheless, MEG offers some advantages over EEG. For example, in contrast to EEG, MEG does not depend on any reference point. Moreover, the magnetic fields are less distorted than the electric ones by the skull and the scalp (Hämäläinen et al., 1993). Despite these advantages, the use of MEG data involves some problems. One of the most important difficulties is that MEG recordings may be severely contaminated by additive external noise due to the intrinsic weakness of the brain magnetic fields. Hence, MEG must be recorded in magnetically shielded rooms with low-noise SQUID (Superconducting QUantum Interference Devices) gradiometers (Hämäläinen et al., 1993).
Data supporting the paper "Continuous wavelet transform in the study of the time-scale prope... more Data supporting the paper "Continuous wavelet transform in the study of the time-scale properties of intracranial pressure in hydrocephalus"
A. Martín Montero, G.C. Gutiérrez Tobal, J. Poza Crespo, D. Álvarez González, F. Vaquerizo Villar... more A. Martín Montero, G.C. Gutiérrez Tobal, J. Poza Crespo, D. Álvarez González, F. Vaquerizo Villar, V. Barroso García, S.J. Ruiz Gómez, L. Kheirandish Gozal, F. del Campo, D. Gozal, R. Hornero Sánchez 1 Grupo de Ingeniería Biomédica, Universidad de Valladolid, Valladolid, España, adrian.martin@gib.uva.es 2 Servicio de Neumología, Hospital Universitario Río Hortega, Valladolid, España, fsas@telefonica.net 3 Dept. of Pediatrics, Pritzker School of Medicine, Biological Sciences Division, The University of Chicago, Chicago, EEUU, dgozal@peds.bsd.uchicago.edu
Objective. Although magnetoencephalography and electroencephalography (M/EEG) signals at sensor l... more Objective. Although magnetoencephalography and electroencephalography (M/EEG) signals at sensor level are robust and reliable, they suffer from different degrees of distortion due to changes in brain tissue conductivities, known as field spread and volume conduction effects. To estimate original neural generators from M/EEG activity acquired at sensor level, diverse source localisation algorithms have been proposed; however, they are not exempt from limitations and usually involve time-consuming procedures. Connectivity and network-based M/EEG analyses have been found to be affected by field spread and volume conduction effects; nevertheless, the influence of the aforementioned effects on widely used local activation parameters has not been assessed yet. The goal of this study is to evaluate the consistency of various local activation parameters when they are computed at sensor- and source-level. Approach. Six spectral (relative power, median frequency, and individual alpha frequenc...
El objetivo de este estudio fue caracterizar las propiedades dinámicas de la conectividad funcion... more El objetivo de este estudio fue caracterizar las propiedades dinámicas de la conectividad funcional de la actividad electroencefalográfica (EEG) espontánea en la enfermedad de Alzheimer (EA). Se calculó el módulo al cuadrado de la coherencia (MSCOH) de 62 enfermos con demencia debida a EA y 36 controles cognitivamente sanos. Se estimó la MSCOH en tramas de 30 segundos con ventanas no solapadas de diferentes longitudes (1, 2, 3, 5 y 10 segundos) y se estudió:(i) la variabilidad de la conectividad funcional entre cada par de electrodos en la banda alfa (8 13 Hz) en función del tamaño de la ventana; (ii) si las fluctuaciones observadas reflejaban cambios reales de conectividad funcional mediante un análisis de subrogación; y (iii) la estabilidad de la medida en función del tamaño de la ventana. Los resultados muestran una reducción significativa de la conectividad dinámica de los enfermos de EA respecto a los controles en las ventanas de 2 y 3 segundos. Asimismo, se concluye que parte ...
Dementia due to Alzheimer’s disease (AD) is a neurological syndrome which has an increasing impac... more Dementia due to Alzheimer’s disease (AD) is a neurological syndrome which has an increasing impact on society, provoking behavioral, cognitive, and functional impairments. AD lacks an effective pharmacological intervention; thereby, non-pharmacological treatments (NPTs) play an important role, as they have been proven to ameliorate AD symptoms. Nevertheless, results associated with NPTs are patient-dependent, and new tools are needed to predict their outcome and to improve their effectiveness. In the present study, 19 patients with AD underwent an NPT for 83.1 ± 38.9 days (mean ± standard deviation). The NPT was a personalized intervention with physical, cognitive, and memory stimulation. The magnetoencephalographic activity was recorded at the beginning and at the end of the NPT to evaluate the neurophysiological state of each patient. Additionally, the cognitive (assessed by means of the Mini-Mental State Examination, MMSE) and behavioral (assessed in terms of the Dementia Behavio...
2020 42nd Annual International Conference of the IEEE Engineering in Medicine & Biology Society (EMBC)
This study had two main objectives: (i) to study the effects of volume conduction on different co... more This study had two main objectives: (i) to study the effects of volume conduction on different connectivity metrics (Amplitude Envelope Correlation AEC, Phase Lag Index PLI, and Magnitude Squared Coherence MSCOH), comparing the coupling patterns at electrode- and sensor-level; and (ii) to characterize spontaneous EEG activity during different stages of Alzheimer's disease (AD) continuum by means of three complementary network parameters: node degree (k), characteristic path length (L), and clustering coefficient (C). Our results revealed that PLI and AEC are weakly influenced by volume conduction compared to MSCOH, but they are not immune to it. Furthermore, network parameters obtained from PLI showed that AD continuum is characterized by an increase in L and C in low frequency bands, suggesting lower integration and higher segregation as the disease progresses. These network changes reflect the abnormalities during AD continuum and are mainly due to neuronal alterations, because PLI is slightly affected by volume conduction effects.
2019 41st Annual International Conference of the IEEE Engineering in Medicine and Biology Society (EMBC), 2019
The aim of this study was to evaluate the effect of volume conduction on different connectivity m... more The aim of this study was to evaluate the effect of volume conduction on different connectivity metrics: Amplitude Envelope Correlation (AEC), Phase Lag Index (PLI), and Magnitude Squared Coherence (MSCOH). These measures were applied to: (i) a synthetic model of 64 coupled oscillators; and (ii) a resting-state EEG database of 72 patients with dementia due to Alzheimer’s disease (AD) and 37 cognitively healthy controls. Our results revealed that AEC and PLI are weakly influenced by the simulated volume conduction compared to MSCOH, although the three metrics are not immune to this effect. Furthermore, results with real EEG recordings showed that AD patients are characterized by an AEC increase in δ frequency band and widespread connectivity decreases in α and β1 bands. These coupling changes reflect the abnormalities in spontaneous EEG activity of AD patients and might provide further insights into the underlying brain dynamics associated with this disorder.
Objective. Schizophrenia is a psychiatric disorder that has been shown to disturb the dynamic top... more Objective. Schizophrenia is a psychiatric disorder that has been shown to disturb the dynamic top-down processing of sensory information. Various imaging techniques have revealed abnormalities in brain activity associated with this disorder, both locally and between cerebral regions. However, there is increasing interest in investigating dynamic network response to novel and relevant events at the network level during an attention-demanding task with high-temporal-resolution techniques. The aim of the work was: (i) to test the capacity of a novel algorithm to detect recurrent brain meta-states from auditory oddball task recordings; and (ii) to evaluate how the dynamic activation and behavior of the aforementioned meta-states were altered in schizophrenia, since it has been shown to impair top-down processing of sensory information. Approach. A novel unsupervised method for the detection of brain meta-states based on recurrence plots and community detection algorithms, previously tes...
Cerebral hypoperfusion impairs brain activity and leads to cognitive impairment. Left and right c... more Cerebral hypoperfusion impairs brain activity and leads to cognitive impairment. Left and right common carotid arteries (CCA) are the major source of cerebral blood supply. It remains unclear whether blood flow in both CCA contributes equally to brain activity. Here, CCA blood flow was evaluated using ultrasonography in 23 patients with cerebrovascular diseases. Resting-state brain activity and cognitive status were also assessed using magnetoencephalography and a cognitive subscale of the Functional Independence Measure, respectively, to explore the relationships between blood flow, functional brain activity, and cognitive status. Our findings indicated that there was an association between blood flow and resting-state brain activity, and between resting-state brain activity and cognitive status. However, blood flow was not significantly associated with cognitive status directly. Furthermore, blood velocity in the right CCA correlated with resting-state brain activity, but not with...
PICALM and CLU genes have been linked to alterations in brain biochemical processes that may have... more PICALM and CLU genes have been linked to alterations in brain biochemical processes that may have an impact on Alzheimer’s disease (AD) development and neurophysiological dynamics. The aim of this study is to analyze the relationship between the electroencephalographic (EEG) activity and the PICALM and CLU alleles described as conferring risk or protective effects on AD patients and healthy controls. For this purpose, EEG activity was acquired from: 18 AD patients and 12 controls carrying risk alleles of both PICALM and CLU genes, and 35 AD patients and 12 controls carrying both protective alleles. Relative power (RP) in the conventional EEG frequency bands (delta, theta, alpha, beta, and gamma) was computed to quantify the brain activity at source level. In addition, spatial entropy (SE) was calculated in each band to characterize the regional distribution of the RP values throughout the brain. Statistically significant differences in global RP and SE at beta band (p-values < 0....
Objective. Nested into slow oscillations (SOs) and modulated by their up-states, spindles are ele... more Objective. Nested into slow oscillations (SOs) and modulated by their up-states, spindles are electrophysiological hallmarks of N2 sleep stage that present a complex hierarchical architecture. However, most studies have only described spindles in basic statistical terms, which were limited to the spindle itself without analyzing the characteristics of the pre-spindle moments in which the SOs are originated. The aim of this study was twofold: (a) to apply spectral and temporal measures to the pre-spindle and spindle periods, as well as analyze the correlation between them, and (b) to evaluate the potential of these spectral and temporal measures in future automatic detection algorithms. Approach. An automatic spindle detection algorithm was applied to the overnight electroencephalographic recordings of 26 subjects. Ten complementary features (five spectral and five temporal parameters) were computed in the pre-spindle and spindle periods after their segmentation. These features were ...
Resting-state neural oscillations are used as biomarkers for functional diseases such as dementia... more Resting-state neural oscillations are used as biomarkers for functional diseases such as dementia, epilepsy, and stroke. However, accurate interpretation of clinical outcomes requires the identification and minimisation of potential confounding factors. While several studies have indicated that the menstrual cycle also alters brain activity, most of these studies were based on visual inspection rather than objective quantitative measures. In the present study, we aimed to clarify the effect of the menstrual cycle on spontaneous neural oscillations based on quantitative magnetoencephalography (MEG) parameters. Resting-state MEG activity was recorded from 25 healthy women with normal menstrual cycles. For each woman, resting-state brain activity was acquired twice using MEG: once during their menstrual period (MP) and once outside of this period (OP). Our results indicated that the median frequency and peak alpha frequency of the power spectrum were low, whereas Shannon spectral entro...
The analysis of the electromagnetic brain activity can provide important information to help in t... more The analysis of the electromagnetic brain activity can provide important information to help in the diagnosis of several mental diseases. Both electroencephalogram (EEG) and magnetoencephalogram (MEG) record the neural activity with high temporal resolution (Hämäläinen, Hari, Ilmoniemi, Knuutila, & Lounasmaa, 1993). Nevertheless, MEG offers some advantages over EEG. For example, in contrast to EEG, MEG does not depend on any reference point. Moreover, the magnetic fields are less distorted than the electric ones by the skull and the scalp (Hämäläinen et al., 1993). Despite these advantages, the use of MEG data involves some problems. One of the most important difficulties is that MEG recordings may be severely contaminated by additive external noise due to the intrinsic weakness of the brain magnetic fields. Hence, MEG must be recorded in magnetically shielded rooms with low-noise SQUID (Superconducting QUantum Interference Devices) gradiometers (Hämäläinen et al., 1993).
Data supporting the paper "Continuous wavelet transform in the study of the time-scale prope... more Data supporting the paper "Continuous wavelet transform in the study of the time-scale properties of intracranial pressure in hydrocephalus"
A. Martín Montero, G.C. Gutiérrez Tobal, J. Poza Crespo, D. Álvarez González, F. Vaquerizo Villar... more A. Martín Montero, G.C. Gutiérrez Tobal, J. Poza Crespo, D. Álvarez González, F. Vaquerizo Villar, V. Barroso García, S.J. Ruiz Gómez, L. Kheirandish Gozal, F. del Campo, D. Gozal, R. Hornero Sánchez 1 Grupo de Ingeniería Biomédica, Universidad de Valladolid, Valladolid, España, adrian.martin@gib.uva.es 2 Servicio de Neumología, Hospital Universitario Río Hortega, Valladolid, España, fsas@telefonica.net 3 Dept. of Pediatrics, Pritzker School of Medicine, Biological Sciences Division, The University of Chicago, Chicago, EEUU, dgozal@peds.bsd.uchicago.edu
Objective. Although magnetoencephalography and electroencephalography (M/EEG) signals at sensor l... more Objective. Although magnetoencephalography and electroencephalography (M/EEG) signals at sensor level are robust and reliable, they suffer from different degrees of distortion due to changes in brain tissue conductivities, known as field spread and volume conduction effects. To estimate original neural generators from M/EEG activity acquired at sensor level, diverse source localisation algorithms have been proposed; however, they are not exempt from limitations and usually involve time-consuming procedures. Connectivity and network-based M/EEG analyses have been found to be affected by field spread and volume conduction effects; nevertheless, the influence of the aforementioned effects on widely used local activation parameters has not been assessed yet. The goal of this study is to evaluate the consistency of various local activation parameters when they are computed at sensor- and source-level. Approach. Six spectral (relative power, median frequency, and individual alpha frequenc...
El objetivo de este estudio fue caracterizar las propiedades dinámicas de la conectividad funcion... more El objetivo de este estudio fue caracterizar las propiedades dinámicas de la conectividad funcional de la actividad electroencefalográfica (EEG) espontánea en la enfermedad de Alzheimer (EA). Se calculó el módulo al cuadrado de la coherencia (MSCOH) de 62 enfermos con demencia debida a EA y 36 controles cognitivamente sanos. Se estimó la MSCOH en tramas de 30 segundos con ventanas no solapadas de diferentes longitudes (1, 2, 3, 5 y 10 segundos) y se estudió:(i) la variabilidad de la conectividad funcional entre cada par de electrodos en la banda alfa (8 13 Hz) en función del tamaño de la ventana; (ii) si las fluctuaciones observadas reflejaban cambios reales de conectividad funcional mediante un análisis de subrogación; y (iii) la estabilidad de la medida en función del tamaño de la ventana. Los resultados muestran una reducción significativa de la conectividad dinámica de los enfermos de EA respecto a los controles en las ventanas de 2 y 3 segundos. Asimismo, se concluye que parte ...
Dementia due to Alzheimer’s disease (AD) is a neurological syndrome which has an increasing impac... more Dementia due to Alzheimer’s disease (AD) is a neurological syndrome which has an increasing impact on society, provoking behavioral, cognitive, and functional impairments. AD lacks an effective pharmacological intervention; thereby, non-pharmacological treatments (NPTs) play an important role, as they have been proven to ameliorate AD symptoms. Nevertheless, results associated with NPTs are patient-dependent, and new tools are needed to predict their outcome and to improve their effectiveness. In the present study, 19 patients with AD underwent an NPT for 83.1 ± 38.9 days (mean ± standard deviation). The NPT was a personalized intervention with physical, cognitive, and memory stimulation. The magnetoencephalographic activity was recorded at the beginning and at the end of the NPT to evaluate the neurophysiological state of each patient. Additionally, the cognitive (assessed by means of the Mini-Mental State Examination, MMSE) and behavioral (assessed in terms of the Dementia Behavio...
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