Carles Grau - Academia.edu (original) (raw)
Papers by Carles Grau
Acta Neurobiologiae Experimentalis, 2003
In this work we describe the performance evaluation of a system for stress detection. The analyse... more In this work we describe the performance evaluation of a system for stress detection. The analysed data is acquired by following an experimental protocol designed to induce cognitive stress to the subjects. The experimental set-up included the recording of electroencephalography (EEG) and facial (corrugator and zygomatic) electromyography (EMG). In a preliminary analysis we are able to correlate EEG features (alpha asymmetry and alpha/beta ratio using only 3 channels) with the stress level of the subjects statistically (by using averages over subjects) but also on a subject-to-subject basis by using computational intelligence techniques reaching classification rates up to 79% when classifying 3 minutes takes. On a second step, we apply fusion techniques to the overall multi-modal feature set fusing the formerly mentioned EEG features with EMG energy. We show that the results improve significantly providing a more robust stress index every second. Given the achieved performance the system described in this work can be successfully applied for stress therapy when combined with virtual reality.
The aim in this note is to define an algorithm to carry out minimal curvature spherical harmonics... more The aim in this note is to define an algorithm to carry out minimal curvature spherical harmonics interpolation, which is then used to calculate the Laplacian for multi-electrode EEG data analysis. The approach taken is to respect the data. That is, we implement a minimal curvature condition for the interpolating surface subject to the constraints determined from the multi-electrode data. We implement this approach using spherical harmonics interpolation. In this elegant example we show that minimization requirement and constraints complement each other to fix all degrees of freedom automatically, as occurs in gauge theories. That is, the constraints are respected, while only the orthogonal subspace minimization constraints are enforced. As an example, we discuss the application to interpolate control data and calculate the temporal sequence of laplacians from an EEG Mismatch Negativity (MMN) experiment (using an implementation of the algorithm in IDL).
Journal of Clinical and Experimental Neuropsychology, 1993
Folkard (1979, 1990) suggested that diurnal changes in performance may reflect a morning-evening ... more Folkard (1979, 1990) suggested that diurnal changes in performance may reflect a morning-evening decrease in the degree of left-hemisphere dominance. Forty-eight right-handed women performed verbal and spatial hemifield tachistoscopic tasks at four separate times of day. Supporting the above hypotheses, changes in accuracy over the day showed a left-hemisphere advantage at 12:00 and a right-hemisphere advantage at 19:45, whereas changes in speed were symmetrical both in verbal and spatial tasks. These changes occurred only when hemispheres received stimuli in the processing of which they were not specialized, that is, when verbal stimuli appeared at the left visual field and spatial stimuli at the right visual field. Evidence suggesting a separate oscillatory control of the circadian rhythms of left and right-hemisphere activity is discussed.
Clinical Neurophysiology, 2003
Conference proceedings : ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Conference, 2006
We describe the development and first tests of ENOBIO, a dry electrode sensor concept for biopote... more We describe the development and first tests of ENOBIO, a dry electrode sensor concept for biopotential applications. In the proposed electrodes the tip of the electrode is covered with a forest of multi-walled carbon nanotubes (CNTs) that can be coated with Ag/AgCl to provide ionic-electronic transduction. The CNT brush-like structure is to penetrate the outer layers of the skin improving electrical contact as well as increase the contact surface area. In this paper we report the results of the first tests of this concept--immersion on saline solution and pig skin signal detection. These indicate performance on a par with state of the art research-oriented wet electrodes.
Experimental Neurology, 1975
To study possible inhibitory functions of the globus pallidus, nine rhesus monkeys were equipped ... more To study possible inhibitory functions of the globus pallidus, nine rhesus monkeys were equipped with intracerebral electrodes, radio stimulators, and telerecorders of mobility. Results were: (a) Under restraint, pallidal stimulation induced contralateral head turning, and/or flexion of the contralateral arm without evoking detectable changes in electrical activity of the brain, emotionality, or reactivity to food or threats. (b)A single 5-set radio stimulation of the pallidum in the monkey, free and alone in a cage, produced discrete motor responses which did not disturb spontaneous behavior or taking of pellets, but inhibitory effects appeared when repeated feedback or programmed stimulations were used. (c) Stimulation of the pallidum in the dominant partner of a caged pair, triggered automatically by its mobility, changed the social status of both animals, inhibiting signs of dominance in the stimulated monkey and correspondingly increasing the social rank of the nonstimulated animal. (d) Effects of stimulation of the pallidum in the same animal depended on its hierarchical status. When dominant, it became submissive, while only minor stimulation effects were observed when it was the submissive partner. (e) It is suggested that the pallidum has an integrative role in the relation between the animal's motivational state and its environment.
Anuario de Psicologia
En este informe se presenta una revisión de trabajos acerca de la utilización de distintos compon... more En este informe se presenta una revisión de trabajos acerca de la utilización de distintos componentes de 10s potenciales evocados como marcadores de riesgo para desarrollar alcoholisrno. Los jóvenes procedentes de familias con antecedentes de alcoholismo presentan anomalías en la amplitud de P3 semejantes a las observadas en alcohólicos crónicos abstinentes. La infuencia de factores genéticos sobre las características de este componente y sobre la aparición de la adicción, hacen de P3 un posible marcador genético de riesgo. También se discute la posible utilidad de otros componentes y de la respuesta de aumento/reducciÓn. Palabras clave: Alcoholisme, alto riesgo, potenciales evocados, marcador biológico.
Se exponen la base lógica y 10s antecedentes históricos de la presentación taquistoscópica en hem... more Se exponen la base lógica y 10s antecedentes históricos de la presentación taquistoscópica en hemicampos visuales y se comentan algunos aspectos fundamentales referente a 10s sujetos, aparotos, estímulos, respuestas y procedirnientos de 10s disefios experimentales con esta técrzica.
Revista de neurologia
The objective of this study is to review the main investigations into the secondary effects of th... more The objective of this study is to review the main investigations into the secondary effects of the antihistamine chlorpheniramine on the central nervous system (CNS). The antagonists of the H1 receptors of histamine, usually used in the treatment of symptoms of allergy or the common cold, have many adverse effects on the CNS. They cause day time drowsiness, cause poorer performance of tasks involving visuo motor coordination and make it more difficult to detect target auditory stimuli in tasks involving sustained concentration. When using evoked potentials (EP) it has been observed that they alter the system for maintaining auditory attention. They cause increased P300 latency, an EP related to the voluntary ability to discriminate between relevant stimuli, a reduction in the amplitude of mismatch negativity (MMN), an EP which is seen as a pre attention mechanism for automatic detection of environmental acoustic changes and alters selective attention capacity, reflected by a reduction in the amplitude of processing negativity (PN). These studies show that chlorpheniramine has major adverse effects on the CNS, and the patient may not be subjectively aware of this (e.g. selective attention). This means that in certain situations it is a dangerous substance. The characteristics of these adverse effects should lead to a review of the prescription of chlorpheniramine, and stimulate the search for other substances with similar therapeutic actions but fewer side effects on the CNS.
Revista de neurologia
The antihistamine chlorpheniramine presents multiple adverse side effects on the central nervous ... more The antihistamine chlorpheniramine presents multiple adverse side effects on the central nervous system. In earlier work it has been observed that a dose equal to the one used in this study alters the evoked potentials PN (processing negativity) and MMN (mismatch negativity), which are, respectively, indicators of selective attention and of an automatic mechanism for detecting changes in auditory stimulation. AIMS. The aim of the present study was to evaluate the effects of a single 4 mg dose of dexchlorpheniramine on the evoked potential P300, to enable us to better define its effects on the central nervous system. Subjects and methods. Using the double blind procedure, half a sample consisting in 20 subjects was administered 4 mg of dexchlorpheniramine and the other 10 received placebo. 150 minutes after ingestion the potential P300 was recorded using an active oddball paradigm. Likewise, efficiency in detecting target stimuli was also evaluated. results show that a single 4 mg dose of dexchlorpheniramine does not alter P300 nor efficiency in detecting target stimuli. Results show that the dose used has no effect on voluntary processes involving the categorization of target stimuli nor on their detection. However, the alteration of other attentional mechanisms observed in previous work using the same doses suggests that it would be advisable to employ different evoked potential paradigms in the evaluation of the side effects other active principles or psychoactive substances have on auditory attention.
Journal of Interdisiplinary Cycle Research, 1992
Psicothema, 2008
The nonlinear dynamical systems theory provides some tools for the analysis of electroencephalogr... more The nonlinear dynamical systems theory provides some tools for the analysis of electroencephalogram (EEG) at different sleep stages. Its use could allow the automatic monitoring of the states of the sleep and it would also contribute an explanatory level of the differences between stages. The goal of the present paper is to address this type of analysis, focusing on the most different stages. Estimations of dimensionality were compared when six subjects were awake and in a deep sleep stage. Greater dimensionality involves more complexity because the system receives more external influences. If this dimensionality is maximum, we can consider that the time series is a noisy one. A smaller dimensionality involves lower complexity because the system receives fewer inputs. We hypothesized that we would find greater dimensionality when subjects were awake than in a deep sleep stage. Results show a noisy time series during the awake stage, whereas in the sleep stage, dimensionality is smal...
Revista de neurologia
The antihistamine chlorpheniramine presents multiple adverse side effects on the central nervous ... more The antihistamine chlorpheniramine presents multiple adverse side effects on the central nervous system. In earlier work it has been observed that a dose equal to the one used in this study alters the evoked potentials PN (processing negativity) and MMN (mismatch negativity), which are, respectively, indicators of selective attention and of an automatic mechanism for detecting changes in auditory stimulation. AIMS. The aim of the present study was to evaluate the effects of a single 4 mg dose of dexchlorpheniramine on the evoked potential P300, to enable us to better define its effects on the central nervous system. Subjects and methods. Using the double blind procedure, half a sample consisting in 20 subjects was administered 4 mg of dexchlorpheniramine and the other 10 received placebo. 150 minutes after ingestion the potential P300 was recorded using an active oddball paradigm. Likewise, efficiency in detecting target stimuli was also evaluated. results show that a single 4 mg do...
Revista de neurologia
The objective of this study is to review the main investigations into the secondary effects of th... more The objective of this study is to review the main investigations into the secondary effects of the antihistamine chlorpheniramine on the central nervous system (CNS). The antagonists of the H1 receptors of histamine, usually used in the treatment of symptoms of allergy or the common cold, have many adverse effects on the CNS. They cause day time drowsiness, cause poorer performance of tasks involving visuo motor coordination and make it more difficult to detect target auditory stimuli in tasks involving sustained concentration. When using evoked potentials (EP) it has been observed that they alter the system for maintaining auditory attention. They cause increased P300 latency, an EP related to the voluntary ability to discriminate between relevant stimuli, a reduction in the amplitude of mismatch negativity (MMN), an EP which is seen as a pre attention mechanism for automatic detection of environmental acoustic changes and alters selective attention capacity, reflected by a reducti...
Acta Neurobiologiae Experimentalis, 2003
In this work we describe the performance evaluation of a system for stress detection. The analyse... more In this work we describe the performance evaluation of a system for stress detection. The analysed data is acquired by following an experimental protocol designed to induce cognitive stress to the subjects. The experimental set-up included the recording of electroencephalography (EEG) and facial (corrugator and zygomatic) electromyography (EMG). In a preliminary analysis we are able to correlate EEG features (alpha asymmetry and alpha/beta ratio using only 3 channels) with the stress level of the subjects statistically (by using averages over subjects) but also on a subject-to-subject basis by using computational intelligence techniques reaching classification rates up to 79% when classifying 3 minutes takes. On a second step, we apply fusion techniques to the overall multi-modal feature set fusing the formerly mentioned EEG features with EMG energy. We show that the results improve significantly providing a more robust stress index every second. Given the achieved performance the system described in this work can be successfully applied for stress therapy when combined with virtual reality.
The aim in this note is to define an algorithm to carry out minimal curvature spherical harmonics... more The aim in this note is to define an algorithm to carry out minimal curvature spherical harmonics interpolation, which is then used to calculate the Laplacian for multi-electrode EEG data analysis. The approach taken is to respect the data. That is, we implement a minimal curvature condition for the interpolating surface subject to the constraints determined from the multi-electrode data. We implement this approach using spherical harmonics interpolation. In this elegant example we show that minimization requirement and constraints complement each other to fix all degrees of freedom automatically, as occurs in gauge theories. That is, the constraints are respected, while only the orthogonal subspace minimization constraints are enforced. As an example, we discuss the application to interpolate control data and calculate the temporal sequence of laplacians from an EEG Mismatch Negativity (MMN) experiment (using an implementation of the algorithm in IDL).
Journal of Clinical and Experimental Neuropsychology, 1993
Folkard (1979, 1990) suggested that diurnal changes in performance may reflect a morning-evening ... more Folkard (1979, 1990) suggested that diurnal changes in performance may reflect a morning-evening decrease in the degree of left-hemisphere dominance. Forty-eight right-handed women performed verbal and spatial hemifield tachistoscopic tasks at four separate times of day. Supporting the above hypotheses, changes in accuracy over the day showed a left-hemisphere advantage at 12:00 and a right-hemisphere advantage at 19:45, whereas changes in speed were symmetrical both in verbal and spatial tasks. These changes occurred only when hemispheres received stimuli in the processing of which they were not specialized, that is, when verbal stimuli appeared at the left visual field and spatial stimuli at the right visual field. Evidence suggesting a separate oscillatory control of the circadian rhythms of left and right-hemisphere activity is discussed.
Clinical Neurophysiology, 2003
Conference proceedings : ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Conference, 2006
We describe the development and first tests of ENOBIO, a dry electrode sensor concept for biopote... more We describe the development and first tests of ENOBIO, a dry electrode sensor concept for biopotential applications. In the proposed electrodes the tip of the electrode is covered with a forest of multi-walled carbon nanotubes (CNTs) that can be coated with Ag/AgCl to provide ionic-electronic transduction. The CNT brush-like structure is to penetrate the outer layers of the skin improving electrical contact as well as increase the contact surface area. In this paper we report the results of the first tests of this concept--immersion on saline solution and pig skin signal detection. These indicate performance on a par with state of the art research-oriented wet electrodes.
Experimental Neurology, 1975
To study possible inhibitory functions of the globus pallidus, nine rhesus monkeys were equipped ... more To study possible inhibitory functions of the globus pallidus, nine rhesus monkeys were equipped with intracerebral electrodes, radio stimulators, and telerecorders of mobility. Results were: (a) Under restraint, pallidal stimulation induced contralateral head turning, and/or flexion of the contralateral arm without evoking detectable changes in electrical activity of the brain, emotionality, or reactivity to food or threats. (b)A single 5-set radio stimulation of the pallidum in the monkey, free and alone in a cage, produced discrete motor responses which did not disturb spontaneous behavior or taking of pellets, but inhibitory effects appeared when repeated feedback or programmed stimulations were used. (c) Stimulation of the pallidum in the dominant partner of a caged pair, triggered automatically by its mobility, changed the social status of both animals, inhibiting signs of dominance in the stimulated monkey and correspondingly increasing the social rank of the nonstimulated animal. (d) Effects of stimulation of the pallidum in the same animal depended on its hierarchical status. When dominant, it became submissive, while only minor stimulation effects were observed when it was the submissive partner. (e) It is suggested that the pallidum has an integrative role in the relation between the animal's motivational state and its environment.
Anuario de Psicologia
En este informe se presenta una revisión de trabajos acerca de la utilización de distintos compon... more En este informe se presenta una revisión de trabajos acerca de la utilización de distintos componentes de 10s potenciales evocados como marcadores de riesgo para desarrollar alcoholisrno. Los jóvenes procedentes de familias con antecedentes de alcoholismo presentan anomalías en la amplitud de P3 semejantes a las observadas en alcohólicos crónicos abstinentes. La infuencia de factores genéticos sobre las características de este componente y sobre la aparición de la adicción, hacen de P3 un posible marcador genético de riesgo. También se discute la posible utilidad de otros componentes y de la respuesta de aumento/reducciÓn. Palabras clave: Alcoholisme, alto riesgo, potenciales evocados, marcador biológico.
Se exponen la base lógica y 10s antecedentes históricos de la presentación taquistoscópica en hem... more Se exponen la base lógica y 10s antecedentes históricos de la presentación taquistoscópica en hemicampos visuales y se comentan algunos aspectos fundamentales referente a 10s sujetos, aparotos, estímulos, respuestas y procedirnientos de 10s disefios experimentales con esta técrzica.
Revista de neurologia
The objective of this study is to review the main investigations into the secondary effects of th... more The objective of this study is to review the main investigations into the secondary effects of the antihistamine chlorpheniramine on the central nervous system (CNS). The antagonists of the H1 receptors of histamine, usually used in the treatment of symptoms of allergy or the common cold, have many adverse effects on the CNS. They cause day time drowsiness, cause poorer performance of tasks involving visuo motor coordination and make it more difficult to detect target auditory stimuli in tasks involving sustained concentration. When using evoked potentials (EP) it has been observed that they alter the system for maintaining auditory attention. They cause increased P300 latency, an EP related to the voluntary ability to discriminate between relevant stimuli, a reduction in the amplitude of mismatch negativity (MMN), an EP which is seen as a pre attention mechanism for automatic detection of environmental acoustic changes and alters selective attention capacity, reflected by a reduction in the amplitude of processing negativity (PN). These studies show that chlorpheniramine has major adverse effects on the CNS, and the patient may not be subjectively aware of this (e.g. selective attention). This means that in certain situations it is a dangerous substance. The characteristics of these adverse effects should lead to a review of the prescription of chlorpheniramine, and stimulate the search for other substances with similar therapeutic actions but fewer side effects on the CNS.
Revista de neurologia
The antihistamine chlorpheniramine presents multiple adverse side effects on the central nervous ... more The antihistamine chlorpheniramine presents multiple adverse side effects on the central nervous system. In earlier work it has been observed that a dose equal to the one used in this study alters the evoked potentials PN (processing negativity) and MMN (mismatch negativity), which are, respectively, indicators of selective attention and of an automatic mechanism for detecting changes in auditory stimulation. AIMS. The aim of the present study was to evaluate the effects of a single 4 mg dose of dexchlorpheniramine on the evoked potential P300, to enable us to better define its effects on the central nervous system. Subjects and methods. Using the double blind procedure, half a sample consisting in 20 subjects was administered 4 mg of dexchlorpheniramine and the other 10 received placebo. 150 minutes after ingestion the potential P300 was recorded using an active oddball paradigm. Likewise, efficiency in detecting target stimuli was also evaluated. results show that a single 4 mg dose of dexchlorpheniramine does not alter P300 nor efficiency in detecting target stimuli. Results show that the dose used has no effect on voluntary processes involving the categorization of target stimuli nor on their detection. However, the alteration of other attentional mechanisms observed in previous work using the same doses suggests that it would be advisable to employ different evoked potential paradigms in the evaluation of the side effects other active principles or psychoactive substances have on auditory attention.
Journal of Interdisiplinary Cycle Research, 1992
Psicothema, 2008
The nonlinear dynamical systems theory provides some tools for the analysis of electroencephalogr... more The nonlinear dynamical systems theory provides some tools for the analysis of electroencephalogram (EEG) at different sleep stages. Its use could allow the automatic monitoring of the states of the sleep and it would also contribute an explanatory level of the differences between stages. The goal of the present paper is to address this type of analysis, focusing on the most different stages. Estimations of dimensionality were compared when six subjects were awake and in a deep sleep stage. Greater dimensionality involves more complexity because the system receives more external influences. If this dimensionality is maximum, we can consider that the time series is a noisy one. A smaller dimensionality involves lower complexity because the system receives fewer inputs. We hypothesized that we would find greater dimensionality when subjects were awake than in a deep sleep stage. Results show a noisy time series during the awake stage, whereas in the sleep stage, dimensionality is smal...
Revista de neurologia
The antihistamine chlorpheniramine presents multiple adverse side effects on the central nervous ... more The antihistamine chlorpheniramine presents multiple adverse side effects on the central nervous system. In earlier work it has been observed that a dose equal to the one used in this study alters the evoked potentials PN (processing negativity) and MMN (mismatch negativity), which are, respectively, indicators of selective attention and of an automatic mechanism for detecting changes in auditory stimulation. AIMS. The aim of the present study was to evaluate the effects of a single 4 mg dose of dexchlorpheniramine on the evoked potential P300, to enable us to better define its effects on the central nervous system. Subjects and methods. Using the double blind procedure, half a sample consisting in 20 subjects was administered 4 mg of dexchlorpheniramine and the other 10 received placebo. 150 minutes after ingestion the potential P300 was recorded using an active oddball paradigm. Likewise, efficiency in detecting target stimuli was also evaluated. results show that a single 4 mg do...
Revista de neurologia
The objective of this study is to review the main investigations into the secondary effects of th... more The objective of this study is to review the main investigations into the secondary effects of the antihistamine chlorpheniramine on the central nervous system (CNS). The antagonists of the H1 receptors of histamine, usually used in the treatment of symptoms of allergy or the common cold, have many adverse effects on the CNS. They cause day time drowsiness, cause poorer performance of tasks involving visuo motor coordination and make it more difficult to detect target auditory stimuli in tasks involving sustained concentration. When using evoked potentials (EP) it has been observed that they alter the system for maintaining auditory attention. They cause increased P300 latency, an EP related to the voluntary ability to discriminate between relevant stimuli, a reduction in the amplitude of mismatch negativity (MMN), an EP which is seen as a pre attention mechanism for automatic detection of environmental acoustic changes and alters selective attention capacity, reflected by a reducti...