Sara Gonzalez | Search PubMed

PubMed2004

EEG source imaging.

OBJECTIVE: Electroencephalography (EEG) is an important tool for studying the temporal dynamics of the human brain's large-scale neuronal circuits. However, most EEG applications fail to capitalize on all of the data's available information, particularly that concerning the location of active sources in the brain. Localizing the sources of a given scalp measurement is only achieved by solving the so-called inverse problem. By introducing reasonable a priori constraints, the inverse problem can be solved and the most probable sources in the brain at every moment in time can be accurately localized. METHODS AND RESULTS: Here, we review the different EEG source localization procedures applied during the last two decades. Additionally, we detail the importance of those procedures preceding and following source estimation that are intimately linked to a successful, reliable result. We discuss (1) the number and positioning of electrodes, (2) the varieties of inverse solution models and algorithms, (3) the integration of EEG source estimations with MRI data, (4) the integration of time and frequency in source imaging, and (5) the statistical analysis of inverse solution results. CONCLUSIONS AND SIGNIFICANCE: We show that modern EEG source imaging simultaneously details the temporal and spatial dimensions of brain activity, making it an important and affordable tool to study the properties of cerebral, neural networks in cognitive and clinical neurosciences.

Brain↗

PubMed2002

Chronic exposure to morphine, cocaine or ethanol in rats produced different effects in brain cannabinoid CB(1) receptor binding and mRNA levels.

Recent evidence suggest that the endocannabinoid system might be a component of the brain reward system and, then, play a role, not only in cannabinoid tolerance/dependence, but also in dependence/withdrawal to other drugs of abuse. However, there are not many studies that compare the changes in endocannabinoid ligands and/or receptors in brain regions (particularly in those areas related to reinforcement processes) during dependence to opiates, cocaine or alcohol. The present study addressed this objective, by examining the changes in CB(1) receptor binding (measured by [3H]-CP55,940 autoradiography) and its mRNA levels (measured by in situ hybridization) in different brain regions of animals chronically exposed to morphine, cocaine or ethanol. The results showed that these three drugs produced different changes in CB(1) receptor binding and mRNA levels, a finding that precludes the existence of a common alteration of the endocannabinoid system during dependence states to these habit-forming drugs. Thus, chronic ethanol exposure was usually uneffective in altering both CB(1) receptor binding and mRNA levels in all regions examined. In contrast, chronic cocaine exposure produced significant changes only at the level of CB(1) receptor mRNA, with decreases of the transcript levels in the ventromedial hypothalamic nucleus and the superficial and deep layers of the cerebral cortex, but no changes in the hippocampal, motor and limbic structures. Finally, chronic morphine exposure increased the density of CB(1) receptors in the medial caudate-putamen, but decreased their mRNA levels in this region and also in the lateral caudate-putamen and the cerebellum. In limbic structures, chronic morphine exposure increased both binding and mRNA levels for CB(1) receptors in the septum nuclei. Binding was also increased in the nucleus accumbens, but reduced in the basolateral amygdala. In hippocampal structures, chronic morphine exposure reduced CB(1) receptor binding in the dentate gyrus, although mRNA levels were unaffected in this region, but increased in the CA2 subfield of the Ammon's horn. The results indicate that mechanisms of dependence for alcohol, cocaine and morphine are different in terms of their impact on the endocannabinoid system. Alcohol did not produce any effects on CB(1) receptor binding and mRNA levels, whereas cocaine only affected transcript levels in selected regions and morphine produced divergent and region-dependent effects.

Animals↗