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PubMed1998

Differential participation of hippocampal formation in cocaine-induced cortical electroencephalographic desynchronization and penile erection in the rat.

We evaluated the role of the hippocampal formation in cocaine-induced cortical electroencephalographic (EEG) desynchronization and penile erection. Adult, male Sprague-Dawley rats anesthetized and maintained by chloral hydrate were used. Intravenous (1.5 or 3.0 mg/kg) administration of cocaine dose-dependently increased intracavernous pressure (ICP), our experimental index for penile erection. This was accompanied by desynchronization of EEG activity recorded from the somatosensory cortex (cEEG), as represented by a decrease in root mean square (RMS) and an increase in mean power frequency (MPF) values. There was a simultaneous increase in the RMS values, without significant changes in the MPF values of EEG signals recorded from the hippocampal formation (hEEG). In animals that received prior application of 10% xylocaine either intrathecally (i.t.) at the L6-S1 spinal levels or directly into the bilateral hippocampal formation, the RMS values of both cEEG and hEEG signals induced by cocaine (1.5 or 3.0 mg/kg, i.v.) were appreciably reduced, along with a further increase in ICP. Unilateral microinjection of cocaine (15 or 30 microg) into the hippocampal formation elicited discernible excitation of both cEEG and hEEG signals. Intriguingly, the ICP underwent a significant and dose-dependent reduction, which was discernibly antagonized by i.t. application of xylocaine. We conclude that cocaine may effect cortical EEG desynchronization but cause a reduction in ICP via an action on the hippocampal formation.

Animals↗
PubMed1999

Bradykinesia and impairment of EEG desynchronization in Parkinson's disease.

It has been suggested that the basal ganglia control the release of cortical elements from low-frequency rhythmic idling activity during voluntary movement. This hypothesis was tested by recording the local idling rhythms of the motor cortex, the alpha and beta rhythms, in 12 untreated and treated patients with Parkinson's disease as they moved a wrist. Recordings were made after overnight withdrawal of medication and again 1 hr after levodopa. The treatment-related attenuation of the alpha and beta rhythms picked up over the cortical motor areas contralateral to the active arm correlated with the improvement in size and speed of movement effected by levodopa. The distribution and degree of attenuation depended on the complexity of the task. These results demonstrate for the first time a specific effect of levodopa on the organization of motor cortical activity in the frequency domain, an effect that correlates with improvements in bradykinesia.

Aged↗
PubMed1999

Motor programming is more affected in progressive supranuclear palsy than in Parkinson's disease: a spatiotemporal study of event-related desynchronization.

To determine the benefit of motor programming analysis for distinguishing patients with parkinsonism, we compared the spatiotemporal pattern of event-related desynchronization (ERD) preceding a self-paced voluntary wrist flexion between two groups of 10 patients with progressive supranuclear palsy (PSP) and Parkinson's disease (PD) and 10 control subjects. ERD of the mu rhythm was computed from 11 source derivations covering the medial frontocentral, central, and parietocentral areas during two successive left and right experimental conditions (80 self-paced wrist flexions). ERD began in the control group 1750 ms before movement onset over the contralateral central area and then appeared bilaterally on movement execution. In both patient groups, spatiotemporal distribution differed from that in the control group. In the PSP group, ERD had a shorter latency over the contralateral primary sensorimotor area compared with the PD group (PSP: 375 ms before movement onset for both conditions; PD: right flexion 1125 ms before movement onset, left flexion 1000 ms). ERD was observed over the parietocentral area in both groups but also with a clear reduction of latency before movement onset in the PSP group. In both groups, a bilateral central pattern appeared 250 ms before movement execution. In conclusion, our study indicates that ERD analysis is a useful method for observing the changes in cortical activation and for measuring motor programming impairment in parkinsonism, which was more affected in PSP than in PD.

Aged↗
PubMed1982

Neurons in human epileptic cortex: correlation between unit and EEG activity.

A total of 90 neurons were recorded extracellularly from 17 awake patients undergoing craniotomy for excision of epileptogenic cortex. Relationships between single-unit activity and gross epileptiform spikes recorded locally by the microelectrode or from the immediate overlying cortical surface by electrocorticography (ECoG) were examined. Similar relationships were also sought between interictal bursts from nearby cells when action potentials from several neurons had been recorded simultaneously by the tungsten electrodes. Although 40 single units fired action potentials in some relation to ECoG spikes, the relationships were variable between units and, often, for the same unit. For many units, action potentials were more consistently related to one phase of the local field potential recorded through tungsten microelectrodes than to the ECoG recorded from the overlying cortical surface. Synchronous firing between single units recorded simultaneously by the same microelectrode was rarely seen except at the onset of an ictal event. In addition, a high degree of synchrony between unit firing and local ECoG spikes was recorded in a few patients, but these patients had frequent focal spontaneous seizures. The data imply that in human epilepsy, unlike some animal models of the disorder, relationships between surface epileptiform events and single-unit burst firing are not easily found in interictal recordings. The data also suggest that synchrony between unit and surface events requires a high degree of synchrony among neurons within the epileptogenic focus.

Electroencephalography↗
PubMed1995

Variability and partial synchrony of the cell cycle in the germinal zone of the early embryonic cerebral cortex.

Cell cycle parameters were estimated using the cumulative 3H-thymidine S-phase labeling and percentage of labeled mitoses methods in the embryonic day 14 and 15 germinal zone of the rat cerebral cortex. The shortest cell cycle time was seen in the dorsal neocortex and the longest in the lateral neocortex and fimbria (the latter also had a low growth fraction). No differences were observed in cell cycle times between the cells in the ventricular and subventricular zone in the same neocortical region. The results suggest gradients of lengthening cell cycle times extending ventrolaterally and ventromedially from the dorsomedial neocortex. Although a majority of proliferating cells in individual cortical regions seem to belong to one population in terms of cell kinetics, several pieces of evidence suggest some heterogeneity: the asymmetric shapes of the percentages of labeled mitoses curves, the small population of noncycling neuroepithelial cells in the neocortex and mesocortex, and small population of cells that become pyknotic. Groups of DNA-synthesizing nuclei that were ectopically located in the inner half of the ventricular zone also indicate the existence of different subpopulations of neuroepithelial cells. In addition, after a pulse injection of 3H-thymidine the germinal zone is characterized by alternating clusters of heavily and lightly labeled cell nuclei that may reflect the simultaneous passage of a cluster of cells through the same portion of S-phase. We suggest that partial cell cycle synchrony within groups of ventricular cells may explain the presence of these iterative cell kinetic patterns in the developing cortex.

Animals↗
PubMed1975

The effect of chronic protein malnutrition on trans-callosal evoked responses in the rat.

Studies were carried out on the trans-callosal evoked response in rats born of dams fed either a low (8%) or normal (25%) protein diet beginning 5 weeks prior to mating and throughout gestation and lactation. After weaning, pups were fed the same diets as their mothers. Bipolar (surface vs depth) stainless steel stimulating and recording electrodes were positioned at corresponding loci in the right and left sensorimotor cortices. Trans-callosal evoked responses were measured under urethane anesthesia using twice-threshold bipolar pulses of .1 msec duration at ages 13, 21, and 60-66 days. Evoked response latency was significantly greater in malnourished animals at 13 days of age, whereas at adulthood no latency differences were seen. Poststimulation excitability (15-100 msec range) was not significantly affected by the dietary treatment. These results are interpreted as corroborating previous reports on rats undernourished during development using sensory evoked potentials. By avoiding the use of extrinsic sensory stimulation, the present study demonstrates a dietary effect upon ontogeny of cortical evoked potentials independent of any possible effect on sensory receptor mechanisms.

Age Factors↗
PubMed2002

Nonlinear phase desynchronization in human electroencephalographic data.

Ensembles of coupled nonlinear systems represent natural candidates for the modeling of brain dynamics. The objective of this study is to examine the complex signal produced by coupled chaotic attractors, to discuss their potential relevance to distributed processes in the brain, and to illustrate a method of detecting their contribution to human EEG morphology. Two measures of quantifying the behavior of coupled nonlinear systems are presented: a measure of phase synchrony and a novel measure of intermittent phase desynchronization. These are used to quantify the behavior of numerical examples of coupled chaotic attractors. Experimental evidence of their contribution to the morphology of the human alpha rhythm is then illustrated in a study of EEG recordings from 40 healthy human subjects. Amplitude-adjusted phase-randomized surrogate data is used to test the null hypothesis that the observed patterns of phase coherence can be described by purely linear methods. Statistical analysis reveals that this null hypothesis can be robustly rejected in a small number (approximately 4%) of EEG epochs. These findings are discussed with reference to the adaptive function and complex dynamics of the brain.

Adult↗
PubMed2005

Human alpha rhythms during visual delayed choice reaction time tasks: a magnetoencephalography study.

Magnetoencephalography (MEG) includes fast and comfortable recording procedures very suitable for the neurophysiological study of cognitive functions in aged people. In this exploratory MEG study in normal young adults, we tested whether very simple short-term memory (STM) demands induce visible changes in amplitude and latency of surface alpha rhythms. Two delayed response tasks were used. In the STM condition, a simple cue stimulus (one bit) was memorized along a brief delay period (3.5-5.5 s). In the control (no short-term memory; NSTM) condition, the cue stimulus remained available along the delay period. To make extremely simple the tasks, the explicit demand was visuospatial but the retention could be also based on phonological and somatomotor coding. Compared to the control condition, the amplitude of the alpha 1 (6-8 Hz) ERD decreased in the left hemisphere, whereas the amplitude of the alpha 2 (8-10 Hz) and alpha 3 (10-12 Hz) event-related desynchronization (ERD) increased in right and left parietal areas, respectively. Furthermore, the latency of the alpha ERD peak was slightly but significantly (P < 0.05) later in STM compared to control condition. In conclusion, whole-head MEG technology and very simple STM demands revealed significant changes of human neuromagnetic alpha rhythms in normal young adults.

Adult↗
PubMed2005

A new approach to neuroimaging with magnetoencephalography.

We discuss the application of beamforming techniques to the field of magnetoencephalography (MEG). We argue that beamformers have given us an insight into the dynamics of oscillatory changes across the cortex not explored previously with traditional analysis techniques that rely on averaged evoked responses. We review several experiments that have used beamformers, with special emphasis on those in which the results have been compared to those observed in functional magnetic resonance imaging (fMRI) and on those studying induced phenomena. We suggest that the success of the beamformer technique, despite the assumption that there are no linear interactions between the mesoscopic local field potentials across distinct cortical areas, may tell us something of the balance between functional integration and segregation in the human brain. What is more, MEG beamformer analysis facilitates the study of these complex interactions within cortical networks that are involved in both sensory-motor and cognitive processes.

Algorithms↗
PubMed2005

Ripple activity in the dentate gyrus of dishinibited hippocampus-entorhinal cortex slices.

Fast oscillations at approximately 200 Hz, termed ripples, occur in the hippocampus and cortex of several species, including humans, and are thought to play a role in physiological (e.g., sensory information processing or memory consolidation) and pathological (e.g., seizures) processes. Blocking gamma-aminobutyric acid type A (GABA(A)) receptor-mediated inhibition represents one of the most often used models of epileptiform discharge. Here we found that bath application of the GABA(A) receptor antagonist picrotoxin (50 microM) to mouse hippocampus-entorhinal cortex slices induced spontaneous epileptiform activity (duration 536.6 +/- 146.1 msec, mean +/- SD; interval of occurrence 14.8 +/- 3.3 sec, n = 12) with two distinct phases of discharge; the first was characterized, in the dentate gyrus only, by high-frequency, field oscillations (ripples) at 206.3 +/- 23.4 Hz (n = 12), whereas the second component corresponded to afterdischarges in the theta range frequency. Ripples, which were also recorded in "minislices" only of the dentate gyrus, were unaffected by application of the mu-opioid receptor agonist (D-Ala2-N-Me-Phe,Gly-ol)enkephalin (10 microM; n = 6) or the N-methyl-D-aspartate (NMDA) receptor antagonist 3-(2-carboxy-piperazine-4-yl)-propyl-l-phosphonate (10 microM; n = 5). In contrast, the non-NMDA glutamatergic receptor antagonist 6-cyano-7-nitro-quinoxaline-2,3-dione (10 microM; n = 5) completely blocked all picrotoxin-induced activities. In addition, application of the GABA(B) receptor agonist baclofen (0.01-0.5 microM; n = 6) dose dependently and reversibly abolished all picrotoxin-induced activities. We also found that application of the gap-junction decouplers carbenoxolone (0.2-0.5 mM; n = 6) or octanol (0.2-0.5 mM; n = 3) blocked the second phase while leaving ripples unchanged. These findings demonstrate that the disinhibited dentate gyrus can generate ripple activity at approximately 200 Hz that is contributed by ionotropic glutamatergic mechanisms and is not dependent on either GABA(A) receptor-mediated or gap-junction mechanisms.

Analgesics, Opioid↗
PubMed2003

Oscillatory nature of human basal ganglia activity: relationship to the pathophysiology of Parkinson's disease.

Alterations of basal ganglia physiology in parkinsonism may consist of two elements, an increase in the firing rate of neurones and a change in the pattern of synchronisation of discharges between neurones. Recent findings suggest the presence of two principal modes of synchronised activity within the human subthalamo-pallidal-thalamo-cortical circuit, at <30 Hz and >60 Hz. These oscillations are dynamically and systematically modulated by task, thereby suggesting a functional role in movement. More importantly, the two frequency modes are inversely affected by movement, consistent with opposing actions, and differentially expressed according to the prevailing level of dopaminergic activity. It is argued that the balance between these modes determines the effects of basal ganglia-thalamocortical projections on the motor areas of the cortex. The lower frequency oscillations facilitate slow idling rhythms in the motor areas of the cortex, whereas synchronisation at high frequency restores dynamic task-related cortical ensemble activity in the gamma band.

Basal Ganglia↗
PubMed1998

Event-related desynchronization to contingent negative variation and self-paced movement paradigms in Parkinson's disease.

The event-related desynchronization (ERD) to voluntary movement is an indicator of cortical activation with a high time resolution and a specific spatial representation. We have evaluated 10 patients affected by Parkinson's disease (PD), free from L-dopa treatment for at least 12 hours, and 10 control subjects. Each subject underwent ERD examination during self-paced movement (SPM) and during contingent negative variation (CNV) paradigms. ERD was measured as the percentage decrease of alpha band power and calculated for frequency bands of 1 Hz, ranging between 8 and 12 Hz. For group comparisons, the frequency showing the highest ERD was selected for each subject and for each side. In the control group, ERD in the CNV paradigm began over the contralateral centroparietal electrodes 1475 ms before movement onset of the right hand and 1375 ms for the left. In the SPM paradigm, ERD started over the contralateral central electrodes 2150 ms and 1775 ms before movement onset of the right and left hand, respectively. In the PD group, ERD started over the contralateral central areas 800 ms and 475 ms before movement onset of the right and left hand, respectively, for CNV paradigm and 1200 ms and 750 ms for the right and left hand, respectively, for SPM paradigm. Therefore, contralateral ERD began closer to movement onset in PD compared with the control group in both paradigms. ERD over the sensorimotor areas ipsilateral to the movement was not significantly different in PD compared with the control group. The finding of delayed contralateral ERD in PD is according to the view that functional cortical activation related to movement preparation is impaired in PD. The lack of group differences in the onset of ipsilateral ERD, which appears close to movement execution than contralateral ERD both in normal subjects and in PD, suggests that different mechanisms may be involved in generating ERD over the hemispheres ipsilateral and contralateral to the movement, and that only the latter are impaired in PD.

Adult↗
PubMed1994

Power spectral analysis of electroencephalographic desynchronization induced by cocaine in rats: correlation with microdialysis evaluation of dopaminergic neurotransmission at the medial prefrontal cortex.

We evaluated the effect and action mechanisms of cocaine on electroencephalographic (EEG) activity in adult male Sprague-Dawley rats anesthetized with chloral hydrate (400 mg/kg, i.p., with 80 mg/kg/h supplements). On-line and real-time power spectral analysis of the EEG activity continuously quantified its root mean square (RMS) and mean power frequency (MPF) values, and the power of its spectral frequency components (low frequency: 0-4 Hz; high frequency: 4-20 Hz). Administration of cocaine (1.5 or 3.0 mg/kg, i.v.) dose-dependently induced EEG desynchronization, as manifested by a reduction in RMS and an elevation in MPF values, coupled with a differential decrease in both high and low frequency components. Samples collected by in vivo microdialysis at the medial prefrontal cortex (mPFC) and analyzed by HPLC showed that the elevation of cocaine and dopamine (DA) level in the dialysate reached its peak during the time interval when maximal activation of EEG occurred. This EEG activation was antagonized by microinfusion into the mPFC via reverse microdialysis of R(+)-SCH 23390, a selective antagonist for D-1 receptors; sulpiride, a selective antagonist for D-2 receptors; or haloperidol, a nonspecific dopamine antagonist. These results suggest that dopaminergic neurotransmission at the mPFC may be intimately related to the specific spectral pattern of alteration in EEG activity elicited by cocaine in the rat and that both D-1 and D-2 receptors may be involved in the process.

Animals↗
PubMed1999

Temporal binding, binocular rivalry, and consciousness.

Cognitive functions like perception, memory, language, or consciousness are based on highly parallel and distributed information processing by the brain. One of the major unresolved questions is how information can be integrated and how coherent representational states can be established in the distributed neuronal systems subserving these functions. It has been suggested that this so-called "binding problem" may be solved in the temporal domain. The hypothesis is that synchronization of neuronal discharges can serve for the integration of distributed neurons into cell assemblies and that this process may underlie the selection of perceptually and behaviorally relevant information. As we intend to show here, this temporal binding hypothesis has implications for the search of the neural correlate of consciousness. We review experimental results, mainly obtained in the visual system, which support the notion of temporal binding. In particular, we discuss recent experiments on the neural mechanisms of binocular rivalry which suggest that appropriate synchronization among cortical neurons may be one of the necessary conditions for the buildup of perceptual states and awareness of sensory stimuli.

Arousal↗
PubMed1999

Human movement-related potentials vs desynchronization of EEG alpha rhythm: a high-resolution EEG study.

Movement-related potentials (MRPs) and event-related desynchronization (ERD) of alpha rhythm were investigated with an advanced high-resolution electroencephalographic technology (128 channels, surface Laplacian estimate, realistic head modeling). The working hypothesis was that MRPs and alpha ERD reflect different aspects of sensorimotor cortical processes. Both MRPs and alpha ERD modeled the responses of primary sensorimotor (M1-S1), supplementary motor (SMA), and posterior parietal (PP, area 5) areas during the preparation and execution of unilateral finger movements. Maximum responses were modeled in the contralateral M1-S1 during both preparation and execution of the movement. The SMA and PP responses were modeled mainly from the MRPs and alpha ERD, respectively. The modeled ipsilateral M1-S1 responses were larger and stronger in the alpha ERD than MRPs. These results may suggest that alpha ERD reflects changes in the background oscillatory activity in wide cortical sensorimotor areas, whereas MRPs represent mainly increased, task-specific responses of SMA and contralateral M1-S1.

Adult↗