Epileptiform Activity in Alcohol Dependent Patients and Possibilities of Its Indirect Measurement

Background: Alcohol dependence during withdrawal and also in abstinent period in many cases is related to reduced inhibitory functions and kindling that may appear in the form of psychosensory symptoms similar to temporal lobe epilepsy frequently in conditions of normal EEG and without seizures. Because temporal lobe epileptic activity tend to spread between hemispheres, it is possible to suppose that measures reflecting interhemispheric information transfer such as electrodermal activity (EDA) might be related to the psychosensory symptoms. Methods and Findings: We have performed measurement of bilateral EDA, psychosensory symptoms (LSCL-33) and alcohol craving (ACQ) in 34 alcohol dependent patients and 32 healthy controls. The results in alcohol dependent patients show that during rest conditions the psychosensory symptoms (LSCL-33) are related to EDA transinformation (PTI) between left and right EDA records (Spearman r = 0.44, p,0.01). Conclusions: The result may present potentially useful clinical finding suggesting a possibility to indirectly assess epileptiform changes in alcohol dependent patients

Selective attention I: Theories, brain structures and neurochemical mechanisms implied [LA ATENCION SELECTIVA I: TEORIAS, ESTRUCTURAS CEREBRALES, Y MECANISMOS NEUROQUIMICOS IMPLICADOS]

In order that the central nervous system (CNS) processes the baggage of sensory information to which it is constantly exposed a selection of the information must be made. The brain processes that make this possible is called selective attention. In this review, we describe the distinct stages involved in the evolution of our concept of selective attention. Initially, for some time, this concept was ignored. This oblivion was due, in part, to the dominant influence of behavioral psychology. The description in 1949 of the arousal reaction produced by electrical stimulation of the reticular formation of the brain stem changed this appraisal. And more recently, with the advent of techniques allowing higher temporal and spatial resolution, the study of brain function in general, and of cognitive processes in particular, has attained a new momentum. Based on theories of information processing, several models have been proposed to explain how the selection of sensory stimulus takes place. The 'filter' theories propound that irrelevant signals must be excluded from the analysis in order to attend to the meaningful messages. Information processing theories attribute a different location in the CNS, where the main selection of information takes place. Some theories emphasize the very fine sensory relays as being the most important in the process of selecting relevant information. Other theories suggest that during the processing of information, different types of associations are established according to a specific hierarchy. In this manner, selection occurs at different levels. Searching for the locus, if any, at which a selection of information takes place, various schools of thought have evolved. There are advocates of the localizationism, globalism or anti-localizationism, while others suggest the existence of a funcional hierarchy or a link between distributed systems. The latter derives from Hebb's concept of neuronal assemblies, which eventually was incorporated in Mountcastle's definition of modules of information processing. Using imaging techniques in patients with localized lesions, or in animal models, it has been possible to determine brain regions participating in attentional processes. Regions with important interconnectivity with the brain stem, diencephalon and cerebral cortex, appear to form specific neuronal pathways and ensembles involved in attention. Recently, Posner has suggested that cognitive functions are constituted by ensenibles of elementary operations occurring at defined brain levels. In order to determine neurochemical mechanisms involved in selective attention, specific neurotransmitter systems have also been investigated. Particular prominence has been given to the catecholamines, as it has been observed that neurons containing these molecules display variations in the levels of activation associated with various levels of arousal, or with the application of sensory stimuli. Thus, the locus coeruleus, a noradrenergic nucleus with widespread projections to the cerebral cortex, has been associated with changes in cortical 'signal-to-noise' ratio allowing the selection of relevant stimuli among many signals from the background. Moreover, a relationship has been established between catecholaminergic systems and pathology. In addition, it is possible to induce attentional deficits lesioning these systems. In the second part of this review we will describe electrophysiological correlates of selective attention. We will address studies using recordings of evoked potentials, unitary activity and otoacoustic response, and will refer to the most frequent attentional alterations in man: hemi-inattention, learning disabilities, and epileptic absences

Selective attention I: Theories, brain structures and neurochemical mechanisms implied [LA ATENCION SELECTIVA I: TEORIAS, ESTRUCTURAS CEREBRALES, Y MECANISMOS NEUROQUIMICOS IMPLICADOS]

In order that the central nervous system (CNS) processes the baggage of sensory information to which it is constantly exposed a selection of the information must be made. The brain processes that make this possible is called selective attention. In this review, we describe the distinct stages involved in the evolution of our concept of selective attention. Initially, for some time, this concept was ignored. This oblivion was due, in part, to the dominant influence of behavioral psychology. The description in 1949 of the arousal reaction produced by electrical stimulation of the reticular formation of the brain stem changed this appraisal. And more recently, with the advent of techniques allowing higher temporal and spatial resolution, the study of brain function in general, and of cognitive processes in particular, has attained a new momentum. Based on theories of information processing, several models have been proposed to explain how the selection of sensory stimulus takes place. The 'filter' theories propound that irrelevant signals must be excluded from the analysis in order to attend to the meaningful messages. Information processing theories attribute a different location in the CNS, where the main selection of information takes place. Some theories emphasize the very fine sensory relays as being the most important in the process of selecting relevant information. Other theories suggest that during the processing of information, different types of associations are established according to a specific hierarchy. In this manner, selection occurs at different levels. Searching for the locus, if any, at which a selection of information takes place, various schools of thought have evolved. There are advocates of the localizationism, globalism or anti-localizationism, while others suggest the existence of a funcional hierarchy or a link between distributed systems. The latter derives from Hebb's concept of neuronal assemblies, which eventually was incorporated in Mountcastle's definition of modules of information processing. Using imaging techniques in patients with localized lesions, or in animal models, it has been possible to determine brain regions participating in attentional processes. Regions with important interconnectivity with the brain stem, diencephalon and cerebral cortex, appear to form specific neuronal pathways and ensembles involved in attention. Recently, Posner has suggested that cognitive functions are constituted by ensenibles of elementary operations occurring at defined brain levels. In order to determine neurochemical mechanisms involved in selective attention, specific neurotransmitter systems have also been investigated. Particular prominence has been given to the catecholamines, as it has been observed that neurons containing these molecules display variations in the levels of activation associated with various levels of arousal, or with the application of sensory stimuli. Thus, the locus coeruleus, a noradrenergic nucleus with widespread projections to the cerebral cortex, has been associated with changes in cortical 'signal-to-noise' ratio allowing the selection of relevant stimuli among many signals from the background. Moreover, a relationship has been established between catecholaminergic systems and pathology. In addition, it is possible to induce attentional deficits lesioning these systems. In the second part of this review we will describe electrophysiological correlates of selective attention. We will address studies using recordings of evoked potentials, unitary activity and otoacoustic response, and will refer to the most frequent attentional alterations in man: hemi-inattention, learning disabilities, and epileptic absences