Biomedical subjects

J F Gomez

Publications and source records attributed to J F Gomez.

5 recordsLinked to original sources

PubMed2001

Estimation of the EEG power spectrum using MRI T(2) relaxation time in traumatic brain injury.

OBJECTIVES: To study the relationship between magnetic resonance imaging (MRI) T(2) relaxation time and the power spectrum of the electroencephalogram (EEG) in long-term follow up of traumatic brain injury. METHODS: Nineteen channel quantitative electroencephalograms or qEEG, tests of cognitive function and quantitative MRI T(2) relaxation times (qMRI) were measured in 18 mild to severe closed head injured outpatients 2 months to 4.6 years after injury and 11 normal controls. MRI T(2) and the Laplacian of T(2) were then correlated with the power spectrum of the scalp electrical potentials and current source densities of the qEEG. RESULTS: qEEG and qMRI T(2) were related by a frequency tuning with maxima in the alpha (8-12Hz) and the lower EEG frequencies (0.5-5Hz), which varied as a function of spatial location. The Laplacian of T(2) acted like a spatial-temporal "lens" by increasing the spatial-temporal resolution of correlation between 3-dimensional T(2) and the ear referenced alert but resting spontaneous qEEG. CONCLUSIONS: The severity of traumatic brain injury can be modeled by a linear transfer function that relates the molecular qMRI to qEEG resonant frequencies.

Adult↗

PubMed2001

An EEG severity index of traumatic brain injury.

EEG spectral analyses were conducted from 19 scalp locations for patients with mild (n=40), moderate (n=25), and severe (n=43) traumatic brain injury (TBI), 15 days to 4 years after injury. Severity of TBI was judged by emergency hospital admission records (Glasgow Coma Score and duration of coma and amnesia). Highest-loading EEG variables on each factor that differed significantly between severe and mild TBI by univariate t-test were entered into a multivariate discriminant analysis, yielding 16 variables. Discriminant analysis between mild and severe TBI groups showed classification accuracy of 96.39%, sensitivity 95.45%, and specificity 97.44%. The EEG discriminant score also measured intermediate severity in moderate TBI patients. Results were cross-validated in 503 VA patients. Significant correlations between EEG discriminant scores, emergency admission measures, and post-trauma neuropsychological test scores validated the discriminant function as an index of severity of injury and a classifier of the extremes of severity.

Adolescent↗

PubMed2001

Frequency domain equivalence between potentials and currents using LORETA.

Analyzing the preferences of brain regions to oscillate at specific frequencies gives important functional information. Application of discrete inverse solutions for the EEG/MEG inverse problem in the frequency domain usually involves the use of many current sources (sometimes 10(4) or more) restricted to gray matter points, as the solution space for the possible generators. This number can progressively increase with the level of detail of the MRI when it is used in co-registration with EEG/MEG. However, the computation of the Fourier transform to all these sources is computationally intensive. We illustrate with a simple example how this procedure can be simplified by applying the Fourier transform to the signals in the sensors using a popular inverse method (LORETA). We also suggest how the search space of current sources at specific frequencies of oscillation can be limited to some regions constrained by other technologies such as fMRI, PET and SPECT.

Brain↗

PubMed2001

cAmp modulates exocytotic kinetics and increases quantal size in chromaffin cells.

The role of cAMP/cAMP-dependent protein kinase (PKA) on the late phase of exocytosis has been studied by amperometry on Ba(2+)-stimulated single bovine chromaffin cells. Forskolin (FSK) increases the intracellular cAMP levels in a concentration-dependent manner. Forskolin (100 nM) does not increase the number of exocytotic events, although it significantly increases the net granule content of catecholamines (CA), which is accompanied by a slowing of the process of degranulation. These effects are reversible, occur within 15 to 60 s, and are not due to newly synthesized CA. Isoprenaline, pituitary adenylate cyclase-activating polypeptide-38 or dB-cAMP reproduce FSK effects as does cholera toxin. The inhibition of phosphodiesterases with 3-isobutyl-1-methylxanthine mimics and potentiates the effect of FSK and isoprenaline. Rolipram and okadaic acid also produce a drastic increase in net granule content of CA, whereas H-89 attenuates the FSK response. These data indicate that cyclic AMP/PKA might favor the granule aggregation before its fusion with cell membrane and slow the late step of the exocytotic process.

Animals↗

PubMed1999

A topological hypothesis for the functional connections of the cortex. A principle of the cortical graphs' based on the neuroimaging.

Combined EEG and PET techniques show three activation levels of the cortex: deep sleep, relaxed state and alert. We propose, correspondingly, that a cortical module can be in one of three equivalent states: inactivated, pre-activated, and activated. Neuroimaging techniques can show activated cortical regions in detail. However, the functional connections (FCs) among them are not shown in the image. They can be found by EEG-coherence functions. This can be seen as a 'three-level- cortical graph'. A cortical graph is a mathematical representation where the cortical units (modules or regions) are represented by points (nodes) and the FCs are represented by lines between these points. At the upper level, activated modules can establish FCs implying high electrical coherence (they are the winners of a competitive process between preactivated modules at the middle level). We propose that, during alert state, the activated nodes and the dynamic switching among them always form connected graphs. It means that, for any possible configuration, there always exists a path (direct or indirect) between any couple of nodes. We base our view on (1) analysis of simple tasks by PET; (2) the existence of coordinated behavior in normal subjects; (3) cortical topologies previously proposed; and (4) computer simulations of cortico-cortical connections. We also suggest that disengaged (nonconnected) cortical graphs, produce 'functional disconnection syndromes' which cause some symptoms in schizophrenia, and Alzheimer disease.

Cerebral Cortex↗