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Biomedical subjects

D Mattia

Publications and source records attributed to D Mattia.

At least 19 recordsLinked to original sources
PubMed2006

Effect of graphitization on the wettability and electrical conductivity of CVD-carbon nanotubes and films.

The use of carbon nanomaterials in various applications requires precise control of their surface and bulk properties. In this paper, we present a strategy for modifying the surface chemistry, wettability, and electrical conductivity of carbon tubes and films through annealing in a vacuum. Experiments were conducted with 60-300 nm nanotubes (nanopipes), produced by noncatalytic chemical vapor deposition (CVD) in a porous alumina template, and with thin films deposited by the same technique on a glassy carbon substrate having the same structure and chemistry of the CNTs. The surface of the as-produced CVD-carbon, treated with sodium hydroxide to remove the alumina template, is hydrophilic, and the bulk electrical conductivity is lower by a factor of 20 than that of fully graphitic multiwalled nanotubes (MWNT) or bulk graphite. The bulk electrical conductivity increases to the conductivity of graphite after annealing at 2000 degrees C in a high vacuum. The analysis of CNTs by transmission electron microscopy (TEM) and Raman spectroscopy shows the ordering of carbon accompanied by an exponential increase of the in-plane crystallite size, L(a), with increasing annealing temperature. Environmental scanning electron microscopy (ESEM) was used to study the interaction of CNT with water, and contact angle measurements performed using the sessile drop method on CVD-carbon films demonstrate that the contact angle increases nearly linearly with increasing annealing temperature.

Journal Article↗
PubMed2006

Wetting of CVD carbon films by polar and nonpolar liquids and implications for carbon nanopipes.

The handling, dispersion, manipulation, and functionalization of carbon nanotubes and nanopipes often require the use of solvents. Therefore, a good understanding of the wetting properties of the carbon nanotubes is needed. Such knowledge is also essential for the design of nanotube-based nanofluidic devices, which hold the promise of revolutionizing chemical analysis, separation, drug delivery, filtration, and sensing. In this work, we investigated the wetting behavior of individual nanopipes produced by the chemical vapor deposition (CVD) of carbon in porous alumina templates and of thin carbon films produced by the same technique. The carbon pipes and films have the same chemistry and structure as determined by Raman and infrared spectroscopies and, when similarly treated, demonstrate the same qualitative wetting behavior, as determined by optical microscopy. Thus, measurements conducted on the carbon film surface are relevant to the nanopipes. In the case of the nanopipes, filling with various liquids was monitored. Contact angle experiments with both polar (water, glycerol, ethylene glycol, ethanol, tetra-hydro furan, and 2-propanol alcohol) and nonpolar liquids (cyclohexane, hexadecane, poly(dimethylsiloxane), and a fluoro-silicone) were conducted on films using the sessile drop method. The contact angles on the CVD carbon films ranged from 0 to 79 degrees. The exposure of the carbon films to a NaOH solution, typically used to dissolve the alumina template, led to a significant decrease of the contact angle, especially in the case of polar liquids.

Journal Article↗
PubMed2005

Estimation of the cortical functional connectivity with the multimodal integration of high-resolution EEG and fMRI data by directed transfer function.

Nowadays, several types of brain imaging device are available to provide images of the functional activity of the cerebral cortex based on hemodynamic, metabolic, or electromagnetic measurements. However, static images of brain regions activated during particular tasks do not convey the information of how these regions communicate with each other. In this study, advanced methods for the estimation of cortical connectivity from combined high-resolution electroencephalography (EEG) and functional magnetic resonance imaging (fMRI) data are presented. These methods include a subject's multicompartment head model (scalp, skull, dura mater, cortex) constructed from individual magnetic resonance images, multidipole source model, and regularized linear inverse source estimates of cortical current density. Determination of the priors in the resolution of the linear inverse problem was performed with the use of information from the hemodynamic responses of the cortical areas as revealed by block-designed (strength of activated voxels) fMRI. We estimate functional cortical connectivity by computing the directed transfer function (DTF) on the estimated cortical current density waveforms in regions of interest (ROIs) on the modeled cortical mantle. The proposed method was able to unveil the direction of the information flow between the cortical regions of interest, as it is directional in nature. Furthermore, this method allows to detect changes in the time course of information flow between cortical regions in different frequency bands. The reliability of these techniques was further demonstrated by elaboration of high-resolution EEG and fMRI signals collected during visually triggered finger movements in four healthy subjects. Connectivity patterns estimated for this task reveal an involvement of right parietal and bilateral premotor and prefrontal cortical areas. This cortical region involvement resembles that revealed in previous studies where visually triggered finger movements were analyzed with the use of separate EEG or fMRI measurements.

Adult↗
PubMed2004

Assessing cortical functional connectivity by linear inverse estimation and directed transfer function: simulations and application to real data.

OBJECTIVE: To test a technique called Directed Transfer Function (DTF) for the estimation of human cortical connectivity, by means of simulation study and human study, using high resolution EEG recordings related to finger movements. METHODS: The method of the Directed Transfer Function (DTF) is a frequency-domain approach, based on a multivariate autoregressive modeling of time series and on the concept of Granger causality. Since the spreading of the potential from the cortex to the sensors makes it difficult to infer the relation between the spatial patterns on the sensor space and those on the cortical sites, we propose the use of the DTF method on cortical signals estimated from high resolution EEG recordings, which exhibit a higher spatial resolution than conventional cerebral electromagnetic measures. The simulation study was followed by an analysis of variance (ANOVA) of the results obtained for different levels of Signal to Noise Ratio (SNR) and temporal length, as they have been systematically imposed on simulated signals. The whole methodology was then applied to high resolution EEG data recorded during a visually paced finger movement. RESULTS: The statistical analysis performed returns that during simulations, DTF is able to estimate correctly the imposed connectivity patterns under reasonable operative conditions, i.e. when data exhibit a SNR of at least 3 and a length of at least 75 s of non-consecutive recordings at 64 Hz of sampling rate, equivalent, more generally, to 4800 data samples. CONCLUSIONS: Functional connectivity patterns of cortical activity can be effectively estimated under general conditions met in any practical EEG recordings, by combining high resolution EEG techniques, linear inverse estimation and the DTF method. SIGNIFICANCE: The estimation of cortical connectivity can be performed not only with hemodynamic measurements, by using functional MRI recordings, but also with modern EEG recordings treated with advanced computational techniques.

Analysis of Variance↗
PubMed2004

GABAA receptor-dependent synchronization leads to ictogenesis in the human dysplastic cortex.

Patients with Taylor's type focal cortical dysplasia (FCD) present with seizures that are often medically intractable. Here, we attempted to identify the cellular and pharmacological mechanisms responsible for this epileptogenic state by using field potential and K+-selective recordings in neocortical slices obtained from epileptic patients with FCD and, for purposes of comparison, with mesial temporal lobe epilepsy (MTLE), an epileptic disorder that, at least in the neocortex, is not characterized by any obvious structural aberration of neuronal networks. Spontaneous epileptiform activity was induced in vitro by applying 4-aminopyridine (4AP)-containing medium. Under these conditions, we could identify in FCD slices a close temporal relationship between ictal activity onset and the occurrence of slow interictal-like events that were mainly contributed by GABAA receptor activation. We also found that in FCD slices, pharmacological procedures capable of decreasing or increasing GABAA receptor function abolished or potentiated ictal discharges, respectively. In addition, the initiation of ictal events in FCD tissue coincided with the occurrence of GABAA receptor-dependent interictal events leading to [K+]o elevations that were larger than those seen during the interictal period. Finally, by testing the effects induced by baclofen on epileptiform events generated by FCD and MTLE slices, we discovered that the function of GABAB receptors (presumably located at presynaptic inhibitory terminals) was markedly decreased in FCD tissue. Thus, epileptiform synchronization leading to in vitro ictal activity in the human FCD tissue is initiated by a synchronizing mechanism that paradoxically relies on GABAA receptor activation causing sizeable increases in [K+]o. This mechanism may be facilitated by the decreased ability of GABAB receptors to control GABA release from interneuron terminals.

4-Aminopyridine↗
PubMed2002

Classification of EEG mental patterns by using two scalp electrodes and Mahalanobis distance-based classifiers.

OBJECTIVES: In this paper, we explored the use of quadratic classifiers based on Mahalanobis distance to detect mental EEG patterns from a reduced set of scalp recording electrodes. METHODS: Electrodes are placed in scalp centro-parietal zones (C3, P3, C4 and P4 positions of the international 10-20 system). A Mahalanobis distance classifier based on the use of full covariance matrix was used. RESULTS: The quadratic classifier was able to detect EEG activity related to imagination of movement with an affordable accuracy (97% correct classification, on average) by using only C3 and C4 electrodes. CONCLUSIONS: Such a result is interesting for the use of Mahalanobis-based classifiers in the brain computer interface area.

Biomedical Engineering↗
PubMed2000

Transcranial magnetic stimulation reveals an interhemispheric asymmetry of cortical inhibition in focal epilepsy.

Transcranial magnetic stimulation (TCS) was applied to both hemispheres of 16 patients affected by criptogenic focal epilepsy to evaluate the interhemispheric symmetry of the motor cortex excitability. The amplitude of the motor evoked potentials (MEPs) and the duration of the post-MEP silent period (SP) were measured at threshold (THR) and at increasing TCS stimulation intensities. The THR was significantly higher in patients than in 16 age-matched control subjects (p < 0.01). No interhemispheric differences were found in MEP amplitude. In controls, the correlation between SP duration and increasing TCS stimulus intensity was linear with a symmetrical progression of the SP duration over the two hemispheres. In patients this linear SP progression was lacking on the 'epileptic' hemisphere: the SP duration did not increase following TCS > 40% above THR, indicating abnormal interhemispheric asymmetry. This finding suggests a selective dysfunction of inhibition in the epileptic hemisphere as signaled by an abnormal SP duration in response to progressively higher TCS intensities.

Adolescent↗
PubMed2000

Gabapentin-induced modulation of interictal epileptiform activity related to different vigilance levels.

OBJECTIVES: Gabapentin (GBP) is a novel antiepileptic drug (AED), currently used as add-on therapy in patients with partial seizures. Similar to other AEDs, little is known about its effects on nocturnal sleep, despite the strict relationship between sleep and epileptic discharges. The aim of our study was to evaluate the effects of chronic therapy with GBP on both nocturnal sleep and on interictal epileptiform abnormalities (IEA) in relation to the different sleep stages. METHODS: Eighteen patients affected by partial seizures resistant to common AEDs were submitted to nocturnal polygraphic recordings under baseline conditions and after 4 months of add-on GBP treatment. RESULTS: We observed a significant increase in unilateral/focal IEA during light NREM sleep and a significant reduction in bilateral/diffuse IEA during wakefulness after sleep onset (WASO) with respect to the baseline condition. A significant increase in REM sleep and slow wave sleep (SWS) associated with a reduction in the number of awakenings and Stage 1 was also observed after GBP chronic therapy. CONCLUSIONS: GBP therapy improves the sleep pattern of epileptic patients and it seems to modulate the expression of IEA with different effects in relation to the various vigilance levels.

Acetates↗
PubMed2000

Gabapentin as add-on therapy in focal epilepsy: a computerized EEG study.

OBJECTIVES: Gabapentin (GBP) possesses a well documented clinical efficacy in those types of focal epilepsy otherwise resistant to conventional antiepileptic drugs (AEDs); on the basis of this, it appears important to investigate the drug effects on the EEG epileptiform and background activity. METHODS: Twenty-five patients with cryptogenic or symptomatic partial epilepsy resistant to conventional AED treatment were included in the study. All patients underwent long-term video-EEG recordings before and after GBP addition (900-1200 mg/day). RESULTS: Quantitative analysis of the interictal EEG paroxysms revealed that GBP had no effect on the rate of occurrence of interictal and ictal EEG abnormalities. GBP was active in delimiting the spatial extent of the interictal spiking activity in those patients who displayed a significant reduction (> or =50%) in seizure occurrence (32% of the patients). EEG background activity recorded under rest condition from 18 out of 25 epileptic patients, before GBP therapy, was characterised by a higher content of the slow spectral components (delta and theta) with respect to control subjects. After GBP addition, the increase of theta relative power was also evident during task performance. CONCLUSIONS: These findings suggest that GBP does not interfere with the generation of interictal EEG spiking while it appears to reduce the susceptibility to seizures concomitantly with a limiting effect on the spiking activity spatial extent. The utilization of GBP in controlling focal seizures is reinforced by the absence of negative influence on cognitive functioning.

Acetates↗
PubMed1999

Epileptiform discharges in the human dysplastic neocortex: in vitro physiology and pharmacology.

Field potential and intracellular recordings were made in slices of human neocortical tissue obtained during surgery for the treatment of seizures associated with focal cortical dysplasia. Ictal-like epileptiform discharges, along with isolated field potentials, were induced by bath application of 4-aminopyridine (50-100 microM). Some of the isolated field potentials were associated with fast transients representing population spikes. Field potential profile analysis indicated that both types of synchronous activity had maximal negative values at 1,400 to 1,600 microm from the pia. The intracellular counterpart of the ictal-like discharge was a prolonged membrane depolarization capped by repetitive action potential burst firing. By contrast, the isolated field potentials were mirrored by long-lasting depolarizations with minimal action potential firing; only when population spikes occurred, the isolated field potentials were associated with epileptiform action potential bursting. Ictal-like discharges were abolished by either N-methyl-D-aspartate or non-N-methyl-D-aspartate receptor antagonists. In contrast, the isolated field potentials continued to occur synchronously during excitatory transmission blockade (although they lacked fast transients) but were abolished by the gamma-aminobutyric acid(A) receptor antagonist bicuculline methiodide (n = 2 slices). Our study demonstrates that focal cortical dysplasia tissue maintained in vitro has an intrinsic ability to generate ictal-like epileptiform events when challenged with 4-aminopyridine. These discharges depend on excitatory amino acid receptor-mediated mechanisms. Our results also show the presence in focal cortical dysplasia tissue of glutamatergic-independent synchronous potentials that are mainly contributed by gamma-aminobutyric acid(A) receptor-mediated conductances.

4-Aminopyridine↗
PubMed1998

Asymmetry of cortical excitability revealed by transcranial stimulation in a patient with focal motor epilepsy and cortical myoclonus.

Motor cortex excitability was analyzed with transcranial stimulation in a patient with motor focal epilepsy and cortical myoclonus originating from the right motor cortex. The motor threshold to single transcranial magnetic shocks, but not to electric stimuli, was higher in the epileptic motor cortex than the normal left motor cortex. Single magnetic shocks elicited a short cortical silent period (50 ms) in the epileptic motor cortex. Paired magnetic stimuli also showed reduced cortico-cortical inhibition. These findings reveal an asymmetry in cortical excitability presumably due to impaired inhibition in the epileptic motor cortex.

Adolescent↗
PubMed1998

Changes of the EEG paroxysmal pattern during felbamate therapy in Lennox-Gastaut syndrome: a case report.

We report a case of a 43-year old woman with Lennox-Gastaut syndrome who exhibited atypical absence seizures, atonic seizures and generalized toniclonic seizures which were not controlled by antiepileptic drug (AED) treatment. Because of this, felbamate (FBM) (1800 mg per day) was progressively added to the pre-existent therapy. The patient underwent a 24-hour-video-EEG monitoring before and after 4 months of FBM therapy. Analysis of the video-EEG signal recorded during wakefulness revealed the presence of ictal activity represented by repetitive, bilateral, slow spike and wave bursts underlying atypical absence seizures; the ictal activity occurring during non-REM sleep was characterized by runs of bilateral, rapid, high-voltage spikes followed by slow spike and wave complexes corresponding to brief tonic seizures. FBM therapy induced disappearance of the EEG ictal slow, spike and wave complexes leaving rather unaffected the runs of spikes. Computerized analysis of both the EEG background activity and the sleep structure displayed a better organization of the global cerebral rhythms under FBM treatment. Our findings suggest a selective effect of FBM on the ictal atypical spike and wave pattern. The differential effect of FBM on ictal patterns may be a reflection of a different action on the excitatory and inhibitory systems.

Adult↗
PubMed1997

In vitro electrophysiology of rat subicular bursting neurons.

Intracellular recordings were used to study the electrophysiological properties of rat subicular neurons in a brain slice preparation in vitro. Cells were classified as bursting neurons (n = 102) based on the firing pattern induced by depolarizing current pulses. The bursting response recorded at resting membrane potential (-66.1 +/- 6.2 mV, mean +/- SD n = 94) was made up of a cluster of fast action potentials riding on a slow depolarization and was followed by an afterhyperpolarization. Tonic firing occurred at a membrane potential of approximately -55 mV. A burst also occurred upon termination of a hyperpolarizing current pulse. Tetrodotoxin (TTX, 1 microM) blocked the burst and decreased or abolished the underlying slow depolarization. These effects were not induced by the concomitant application of the Ca2+ channel blockers Co2+ (2 mM) and Cd2+ (1 mM). Subicular bursting neurons displayed voltage- and time-dependent inward rectifications of the membrane during depolarizing and hyperpolarizing current pulses. The inward rectification in the depolarizing direction was abolished by TTX, while that in the hyperpolarizing direction was blocked by extracellular Cs+ (3 mM), but not modified by Ba2+ (0.5-1 mM), TTX, or Co2+ and Cd2+. Tetraethylammonium (10 mM)-sensitive, outward rectification became apparent in the presence of TTX. These results suggest that neurons in the rat subiculum can display voltage-dependent bursts of action potentials as well as membrane rectification in the depolarizing and hyperpolarizing directions. These results also indicate that activation of a voltage-gated Na+ conductance may be instrumental in the initiation of bursting activity.

Action Potentials↗
PubMed1997

Repetitive firing and oscillatory activity of pyramidal-like bursting neurons in the rat subiculum.

Electrophysiological characterization of neurons within the rat subiculum was carried out with intracellular recordings in an in vitro slice preparation. Subicular neurons responded to threshold pulses of depolarizing current delivered at a resting membrane potential (RMP) of 45.7+/-5.8 mV (mean+/-SD, n=85) with an initial burst of three to five fast action potentials that rode on a depolarizing envelope and was terminated by an afterhyperpolarization (burst AHP) (duration 113+/-35 ms; peak amplitude 2.7+/-0.6 mV, n=10). Tonic firing replaced the bursting mode at membrane potential less negative than -55 mV. Suprathreshold depolarizing pulses evoked at RMP both an initial burst and successive tonic firing. Intracellular staining with biocytin showed morphological features typical of pyramidal cells (n=8). The relationship between frequency of repetitive firing and injected current (f-I) revealed that the burst firing frequency (250-300 Hz) was only slightly influenced by the amount of injected current. By contrast, the f-I curve of the tonic firing phase depended upon current intensity: it displayed an initial segment that increased at first linearly and then turned into a plateau for both the early and the late inter-spike intervals. The frequency of the tonic firing declined only slightly with time, thus suggesting a lack of adaptation. During tonic firing, each single action potential was followed by a fast AHP and a depolarizing afterpotential. Termination of repetitive firing was followed by an AHP (spike-train AHP; duration 223+/-101 ms, peak amplitude 5.6+/-2.4 mV, n=17). Fast spike-train and burst AHPs were reduced by bath application of the Ca2+-channel blockers Co2+ (2 mM) and Cd2+ (1 mM) (n=8), thus suggesting the participation of Ca2+-dependent K+ conductances in these AHPs. Subicular bursting neurons generated persistent, subthreshold voltage oscillations at 5.3+/-1 Hz (n=20) during steady depolarization positive to -60 mV; at values positive to -55 mV, the oscillatory activity could trigger clusters of single action potentials with a periodicity of 0.9-2 Hz. Oscillations were not prevented by application of excitatory amino acid receptor and GABA(A) receptor antagonists (n=5), Ca2+-channel blockers (n=5), or Cs+ (3 mM; n=4), but were abolished by the Na+-channel blocker tetrodotoxin (1 microM; n=6). Our findings demonstrate that pyramidal-like subicular neurons generate both bursting and non-adapting tonic firing, depending upon their membrane potential. These neurons also display oscillatory activity in the range of theta frequency that depends on the activation of a voltage-gated Na+ conductance. These electrophysiological properties may play a role in the process of signals arising from the hippocampal formation before being funnelled towards other limbic structures.

Action Potentials↗
PubMed1997

Delayed appearance of interictal EEG abnormalities in early onset childhood epilepsy with occipital paroxysms.

Childhood epilepsy with occipital paroxysms is an age-related idiopathic focal epilepsy. Occipital EEG paroxysms are considered necessary for diagnosis. We carried out a close clinical and EEG follow-up (range, 2-12 years; mean, 6 years 7 months; median, 7 years) in 24 patients (age range, 4-19 years; mean, 11 years 8 months; median, 11 years). In five children with early seizure onset and particularly benign prognosis without any treatment, EEG abnormalities appeared 3-10 months after the first seizure. Four of them exhibited the ictal pattern of versive seizures with vomiting. Our findings confirm that in the early idiopathic focal seizure disorders, interictal EEG abnormalities may be lacking at the beginning of the disorder.

Adolescent↗
PubMed1997

EEG changes induced by vigabatrin monotherapy in focal epilepsy.

The effect of vigabatrin (GVG) monotherapy on EEG interictal abnormalities and on background activity recorded at rest and during mental tasks was studied in 14 patients suffering from focal epilepsy. A long-term EEG monitoring was performed in each patient before and 3 months after the beginning of GVG therapy. Ictal and interictal EEG abnormalities (IEA) were quantified by specific computer programs. Background activity was evaluated by spectral analysis at rest with eyes closed (EC), during blocking reaction (BR) and during fixation of cartoons (FIX). During treatment, IEA was either decreased or unmodified independently from seizure occurrence, which clearly improved in the majority of patients. The only EEG modifications induced by GVG monotherapy were a more pronounced slowing of the background activity at rest with EC and a reduced responsiveness to BR. EEG data suggest a GVG monotherapy induced mild "sedative" action on attentive tasks rather than on cognitive function.

4-Aminobutyrate Transaminase↗