Electroencephalographic evidence on the strategies of adaptation to the factors of monotony.

In a series of studies, in which 19 apparently healthy male volunteers participated, on the basis of a comparative analysis of the bioelectric brain activity and work performance, it is shown that two strategies of adaptation to the factors of monotony are possible. One of them is based on the maintenance of a high quality of activity even at the price of a considerable reduction in the functional state of the brain; the second is based on the maintenance of the functional status of the brain even at the expense of the short-term loss of control over realizable performance. The factor conditioning the long term inability to support continual high quality of performance under the conditions of monotony is a high lability in nervous processes. The resistance to the effects of the factors of monotony is connected, on the other hand, with the low lability of nervous processes with a certain predominance of excitatory processes over inhibiting processes. The electrographic correlates of the development of the state of monotony represent an increase in the EEG of an alert person of the slow spectra (theta and alpha), and also beta-2 waves, as well as a reduction in the intrahemispheric coherence of alpha-waves. These results can be used for the development of control systems for the state of the operators who work in conditions of monotony (pilots, the operators of electric trains, the operators of power plants, including atomic power plants, and others), as well as in the occupational selection of individuals for jobs involving work under such conditions.

Antipsychotic effect of electroconvulsive therapy is related to normalization of subgenual cingulate theta activity in psychotic depression.

OBJECTIVE: Electroconvulsive therapy (ECT) is one of the most effective options available for treating depressive and psychotic symptoms in a variety of disorders. While the exact mechanism of ECT is unclear, it is known to increase metabolism and blood flow specifically in the anterior cingulate cortex (ACC). The ACC is a cortical generator of theta rhythms, which are abnormal in patients with depression and psychotic disorders. Since patients with psychotic depression are known to respond particularly robustly to ECT, we investigated whether the therapeutic effect of ECT in this population was related to normalization of abnormal theta activity in the ACC. METHOD: We obtained 19-lead electroencephalography (EEG) data from 17 participants with psychotic depression before and 2-3 weeks after a full course of ECT. EEG data was analyzed with quantitative measures and low-resolution electromagnetic tomography (LORETA) compared to an age-adjusted normative database. RESULTS: Quantitative EEG analyses revealed that theta band (4-7 Hz) activity was the only frequency band that changed with ECT. LORETA analyses revealed that the primary site of theta activity change was within the subgenual ACC (Brodmann area 25). There was a positive association between increased subgenual ACC theta activity and decreased psychotic symptoms. The degree of low theta activity in the subgenual ACC prior to ECT predicted the antipsychotic response of ECT. CONCLUSIONS: The antipsychotic effect of ECT is related to normalization of subgenual ACC theta hypoactivity.

Brain electrical source differences between depressed subjects and healthy controls.

Many brain regions show metabolic and perfusion abnormalities in major depressive disorder (MDD), including anterior cingulate and prefrontal cortices. Some of these same areas also show abnormal function with low resolution electromagnetic tomography (LORETA). However, LORETA results are not always consistent across studies, nor with findings from other imaging modalities. These discrepancies may be due, among other factors, to the sensitivity of EEG source localization to different electrode montages. Thirty-six channel EEG was collected from healthy controls and age- and gender-matched unmedicated subjects with MDD (n = 74). EEGs were analyzed with LORETA to assess resting state current density at each of 2,394 cortical voxels. For comparison to previous studies, LORETA was performed using all electrodes or with specific prefrontal electrodes removed. Voxel-by-voxel differences between the depressed and healthy groups were calculated using non-parametric statistics. MDD subjects showed significantly elevated current density in delta, theta, alpha, beta1, and beta2 frequency bands relative to controls in anterior cingulate and prefrontal cortices. Removal of certain prefrontal electrodes from input to LORETA decreased or eliminated significant differences between groups. LORETA detects differences in brain activity between MDD subjects and healthy controls that are consistent with previous findings using other imaging modalities. Inconsistent findings among LORETA studies, and between LORETA studies and those using other functional imaging techniques, may result from differences in electrode montages.

Blinded, multi-center validation of EEG and rating scales in identifying ADHD within a clinical sample.

Previous validation studies of attention deficit/hyperactivity disorder (ADHD) assessment by rating scales or EEG have provided Class-IV evidence per standards of the American Academy of Neurology. To investigate clinical applications, we collected Class-I evidence, namely from a blinded, prospective, multi-center study of a representative clinical sample categorized with a clinical standard. Participating males (101) and females (58) aged 6 to 18 had presented to one of four psychiatric and pediatric clinics because of the suspected presence of attention and behavior problems. DSM-IV diagnosis was performed by clinicians assisted with a semi-structured clinical interview. EEG (theta/beta ratio) and ratings scales (Conners Rating Scales-Revised and ADHD Rating Scales-IV) were collected separately in a blinded protocol. ADHD prevalence in the clinical sample was 61%, whereas the remainder had other childhood/adolescent disorders or no diagnosis. Comorbidities were observed in 66% of ADHD patients and included mood, anxiety, disruptive, and learning disorders at rates similar to previous findings. EEG identified ADHD with 87% sensitivity and 94% specificity. Rating scales provided sensitivity of 38-79% and specificity of 13-61%. While parent or teacher identification of ADHD by rating scales was reduced in accuracy when applied to a diverse clinical sample, theta/beta ratio changes remained consistent with the clinician's ADHD diagnosis. Because theta/beta ratio changes do not identify comorbidities or alternative diagnoses, the results do not support the use of EEG as a stand-alone diagnostic and should be limited to the interpretation that EEG may complement a clinical evaluation for ADHD.

Instantaneous frequency and amplitude modulation of EEG in the hippocampus reveals state dependent temporal structure.

EEG and LFP activity reflect the dynamic and organized interactions of neural ensembles; therefore, it may be possible to use the features of brain rhythms to determine the computational state of a neuronal network. When neuronal networks are activated, physical principles predict that the frequency content of the field potential should reflect the network state, per se, and ergo the state transition. A novel way for characterizing brain states is by quantifying the temporal structure of AM and FM activity (change in amplitude and frequency over time) for brain rhythms of interest. The concept of AM and FM, in the quantitative sense, is virtually unexplored in systems neuroscience. This is not surprising considering estimation of FM activity requires fine temporal and precise estimation of instantaneous frequency. For AM activity, the absolute value of the Hilbert transform is sufficient. Here, we outline a practical pole tracking algorithm which uses a Kalman filter for univariate AR processes to estimate instantaneous frequency. We demonstrate the filter performance using simulated chirp and real EEG/LFP data recorded from the rat hippocampus; and show that AM/FM activity in EEG/LFP is temporally structured and dependent on behavioral and cognitive state. This algorithm has the potential to be a practical tool for characterizing fundamental structure in electrophysiology data and classifying computational states in the brain.

Assessing transient cross-frequency coupling in EEG data.

Synchronization of oscillatory EEG signals across different frequency bands is receiving waxing interest in cognitive neuroscience and neurophysiology, and cross-frequency coupling is being increasingly linked to cognitive and perceptual processes. Several methods exist to examine cross-frequency coupling, although each has its limitations, typically by being flexible only over time or over frequency. Here, a method for assessing transient cross-frequency coupling is presented, which allows one to test for the presence of multiple, dynamic, and flexible cross-frequency coupling structure over both time and frequency. The method is applied to intracranial EEG data, and strong coupling between gamma ( approximately 40-80 Hz) and upper theta ( approximately 7-9 Hz) was observed. This method might have useful applications in uncovering the electrophysiological correlates of cognitive processes.

Coherence in children with Attention-Deficit/Hyperactivity Disorder and excess beta activity in their EEG.

OBJECTIVE: This study investigated differences in coherence measures between two groups of children with Attention-Deficit/Hyperactivity Disorder (ADHD) - with the typical EEG profile (increased theta and decreased beta activity), and with excess beta activity - and a normal control group. METHODS: Thirty-four children with ADHD were included in each of the typical and excess beta groups, and were age and sex matched with 34 control subjects. EEG was recorded from 21 sites during an eyes-closed resting condition. Wave-shape coherence was calculated for eight intrahemispheric and eight interhemispheric electrode pairs, for the delta, theta, alpha and beta bands. RESULTS: In comparison to the controls, the typical ADHD group primarily had increased intrahemispheric theta and beta coherence at short-medium inter-electrode distances, and increased interhemispheric coherence for theta in the frontal and central/parietal/occipital regions. Their laterality effect for interhemispheric short-medium inter-electrode distances was reduced in the theta band. Differences between the excess beta group and the control group were primarily found in laterality of the intrahemispheric theta coherence at short-medium electrode distances, and increased interhemispheric theta coherence in the frontal regions. Reduced delta coherence in the temporal regions was also found. CONCLUSIONS: These results suggest that ADHD children with excess beta power have an underlying brain dysfunction in the frontal lobes which is found in common with children with the typical EEG profile. However a number of qualitative differences exist which could be associated with other aspects of the ADHD diagnosis or another comorbid condition. SIGNIFICANCE: This is the first study to investigate EEG coherence in ADHD children who have increased beta power.

Characteristic distribution of interictal brain electrical activity in idiopathic generalized epilepsy.

PURPOSE: To demonstrate the anatomic localization of the cortical sources of the interictal EEG activity in human idiopathic generalized epilepsy (IGE). METHODS: Multiple cortical and hippocampal sources of the interictal spontaneous EEG activity were investigated by low-resolution electromagnetic tomography in 15 untreated IGE patients and in 15 healthy controls. EEG activity (current density) in four frequency bands (delta: 1.5-3.5 Hz, theta: 3.5-7.5 Hz, alpha: 7.5-12.5 Hz, beta: 12.5-25.0 Hz) was computed for 2,397 voxels. Voxel-by-voxel group comparison was done between the patient and the control group. Voxels with p < 0.01 differences (between the two groups) were correlated with cortical anatomy. RESULTS: Areas of significantly increased or decreased activity were characterized by their anatomical extension and the frequency bands involved. Five areas of bilaterally increased activity were found: rostral part of the prefrontal cortex (delta, theta); posterior part of the insula (delta); hippocampus and mediobasal temporal cortex (all frequency bands); medial parietooccipital cortex (theta, alpha, beta); dorsal and polar parts of the occipital cortex (alpha). Bilaterally decreased delta, theta, alpha activity was found in the majority of the frontal and anterior parietal cortex on the lateral surface, and in parts of the medial surface of the hemispheres. The area of decreased beta activity was less extensive. The right lateral and laterobasal temporal cortex showed decreased delta, theta, alpha, and beta activity, while its left counterpart only showed decreased delta and alpha activity in a limited part of this area. CONCLUSIONS: (1) Pathological interictal EEG activity is not evenly distributed across the cortex in IGE. The prefrontal area of increased activity corresponds to the area that is essential in the buildup of the ictal spike-wave paroxysms (absence seizures). The existence of the posterior "center of gravity" of increased EEG activity in IGE was confirmed. The frontal area of decreased activity might be related to the cognitive deficit described in IGE patients. (2) Increased activity in a lot of ontogenetically older areas (including the hippocampi) and decreased activity in the majority of the isocortex is a peculiar pattern that argues for a developmental hypothesis for IGE.

Hippocampal CA1 spiking during encoding and retrieval: relation to theta phase.

The hippocampal theta rhythm is a prominent oscillation in the field potential observed throughout the hippocampus as a rat investigates stimuli in the environment. A recent computational model [Hasselmo, M. E., Bodelon, C., & Wyble, B. P. (2002a). A proposed function for hippocampal theta rhythm: separate phases of encoding and retrieval enhance reversal of prior learning. Neural Computation, 14, 793-817. Neuromodulation, theta rhythm and rat spatial navigation. Neural Networks, 15, 689-707] suggested that the theta rhythm allows the hippocampal formation to alternate rapidly between conditions that promote memory encoding (strong synaptic input from entorhinal cortex to areas CA3 and CA1) and conditions that promote memory retrieval (strong synaptic input from CA3 to CA1). That model predicted that the preferred theta phase of CA1 spiking should differ for information being encoded versus information being retrieved. In the present study, the spiking activity of CA1 pyramidal cells was recorded while rats performed either an odor-cued delayed nonmatch-to-sample recognition memory test or an object recognition memory task based on the animal's spontaneous preference for novelty. In the test period of both tasks, the preferred theta phase exhibited by CA1 pyramidal cells differed between moments when the rat inspected repeated (match) and non-repeated (nonmatch) items. Also in the present study, additional modeling work extended the previous model to address the mean phase of CA1 spiking associated with stimuli inducing varying levels of retrieval relative to encoding, ranging from novel nonmatch stimuli with no retrieval to highly familiar repeated stimuli with extensive retrieval. The modeling results obtained here demonstrated that the experimentally observed phase differences are consistent with different levels of CA3 synaptic input to CA1 during recognition of repeated items.

Changes in brain function (quantitative EEG cordance) during placebo lead-in and treatment outcomes in clinical trials for major depression.

OBJECTIVE: Decreases in prefrontal electroencephalogram (EEG) cordance that are detectable as early as 48 hours after the start of medication have been related to clinical outcome in treatment trials for major depressive disorder. The relationship between brain changes during the placebo lead-in phase and medication treatment outcome is unknown. The authors hypothesized that decreases in prefrontal cordance during the placebo lead-in phase would be associated with better clinical outcome in subjects treated with antidepressants. METHOD: Data were pooled examining 51 adults with major depressive disorder from two independent double-blind placebo-controlled trials. A 1-week single-blind placebo lead-in phase preceded 8 weeks of randomized treatment with medication (fluoxetine 20 mg or venlafaxine 150 mg) or placebo. The authors obtained quantitative EEG cordance measures at baseline and at the end of the placebo lead-in period. Relationships between regional cordance changes at the end of the placebo lead-in period and clinical outcome (the final 17-item Hamilton Rating Scale for Depression scores) were examined using multiple linear regression analysis. RESULTS: As hypothesized, decreases in prefrontal cordance during the placebo lead-in period were associated with lower final Hamilton depression scale scores in subjects randomly assigned to medication. Prefrontal changes explained 19% of the variance in final Hamilton depression scale scores. CONCLUSIONS: Neurophysiological changes during a placebo lead-in period may serve as nonpharmacodynamic biomarkers of eventual treatment outcomes in clinical trials for major depressive disorder.

Occurrence of a prolonged nonepileptic motor status after a febrile seizure.

PURPOSE: Febrile seizures are very common events in the pediatric population, and this disorder could be inherited. A previous article on nonepileptic status after a febrile seizure was published by Japanese authors. They described convulsive manifestations after a febrile seizure with an EEG counterpart characterized by delta activity and rhythmic theta discharges. We report two cases of nonepileptic prolonged motor status occurring after a simple febrile seizure, erroneously diagnosed as an epileptic status. METHODS: An EEG was obtained during the episode in both of the children; for one of them, we performed a video-EEG recording. RESULTS: In both children, this state was characterized by tonic, vibratory posture, and fluctuation of consciousness. The face was not involved, eyes were closed, and the children were not cyanotic. Ictal EEG showed alternating and mixed theta-delta activity. This activity appeared to be rhythmic in some periods. Clinical and EEG features did not change after administration of benzodiazepine. CONCLUSIONS: We believe this uncommon condition to be a nonepileptic phenomenon, occurring after a simple febrile seizure, with favorable prognosis.

Dissociation, resting EEG, and subjective sleep experiences in undergraduates.

In this study, we explored whether individual differences in dissociation are related to certain resting electroencephalographic (EEG) parameters. Baseline EEG with eyes open and closed was recorded in an undergraduate sample (N = 67). Cortical power in the alpha range was inversely related to dissociative symptoms as measured by the Dissociative Experiences Scale, while both delta and theta power where positively related to dissociation. However, sleep experiences, as indexed with the Iowa Sleep Experiences Survey, were unrelated to resting EEG characteristics. We propose that suppression in the alpha band and raised levels of theta activity, which are typical for high dissociators, might help to explain why dissociative symptoms are accompanied by attentional and memory deficits.

The influence of methylphenidate on the power spectrum of ADHD children - an MEG study.

BACKGROUND: The present study was dedicated to investigate the influence of Methylphenidate (MPH) on cortical processing of children who were diagnosed with different subtypes of Attention Deficit Hyperactivity Disorder (ADHD). As all of the previous studies investigating power differences in different frequency bands have been using EEG, mostly with a relatively small number of electrodes our aim was to obtain new aspects using high density magnetoencephalography (MEG). METHODS: 35 children (6 female, 29 male) participated in this study. Mean age was 11.7 years (+/- 1.92 years). 17 children were diagnosed of having an Attention-Deficit/Hyperactivity Disorder of the combined type (ADHDcom, DSM IV code 314.01); the other 18 were diagnosed for ADHD of the predominantly inattentive type (ADHDin, DSM IV code 314.0). We measured the MEG during a 5 minute resting period with a 148-channel magnetometer system (MAGNES 2500 WH, 4D Neuroimaging, San Diego, USA). Power values were averaged for 5 bands: Delta (D, 1.5-3.5 Hz), Theta (T, 3.5-7.5 Hz), Alpha (A, 7.5-12.5 Hz), Beta (B, 12.5-25 Hz) and Global (GL, 1.5-25 Hz).). Additionally, attention was measured behaviourally using the D2 test of attention with and without medication. RESULTS: The global power of the frequency band from 1.5 to 25 Hz increased with MPH. Relative Theta was found to be higher in the left hemisphere after administration of MPH than before. A positive correlation was found between D2 test improvement and MPH-induced power changes in the Theta band over the left frontal region. A linear regression was computed and confirmed that the larger the improvement in D2 test performance, the larger the increase in Theta after MPH application. CONCLUSION: Main effects induced by medication were found in frontal regions. Theta band activity increased over the left hemisphere after MPH application. This finding contradicts EEG results of several groups who found lower levels of Theta power after MPH application. As relative Theta correlates with D2 test improvement we conclude that MEG provide complementary and therefore important new insights to ADHD.

Basal ganglia--hippocampal interactions support the role of the hippocampal formation in sensorimotor integration.

Experiments were carried out to evaluate whether neural activity in the basal ganglia is functionally related to the neural activity underlying mechanisms of theta band oscillation and synchrony in the hippocampal formation. Experiment 1 demonstrated that electrical stimulation administered to the substantia nigra, globus pallidus (GP) and caudate-putamen (CPu) in urethane anesthetized rats elicited theta field activity in the hippocampal formation. Subsequent microinfusion of the local anesthetic procaine hydrochloride into the medial septum reversibly abolished this effect. In Experiment 2, single cell discharge profiles established for 152 cells recorded in nuclei of the basal ganglia resulted in 101 (66%) being classified as theta-related and 51 (34%) classified as nonrelated. Theta-related cells were further subclassified as tonic theta-ON cells (n = 79) and tonic theta-OFF (n = 22). Tonic theta-ON and tonic theta-OFF cells displayed irregular or regular (tonic) discharge patterns. Rhythmic discharge patterns did not occur in any theta-related cells in the nuclei of the basal ganglia. However, analyses using Kaneoke and Vitek's [J. Neurosci. Methods 68, (1996) 211] algorithms revealed that 51/101 (50%) theta-related cells displayed periodicity in their discharge patterns whereas 27/51 (53%) of the nonrelated cells displayed periodicity in their discharge patterns. The periodicities in the majority of cells were in frequency ranges above that of theta band oscillation and synchrony. The results support the following conclusions: (1) the cellular activity of the basal ganglia, composed of nuclei traditionally associated with motor functions, is functionally connected with the neural circuitry involved in the generation of theta band oscillation and synchrony in the hippocampal formation; (2) the observed functional connectivity provides support for the role of the hippocampal formation in sensorimotor integration.

Theta power in the EEG of alcoholics.

BACKGROUND: In this study, the magnitude and spatial distribution of theta power in the resting EEG were examined to explore the changes in the neurophysiological status of the alcoholic brain. Some state- and trait-related issues of theta power increases in the EEG of alcoholics were also examined. METHODS: Absolute theta (3-7 Hz) power in eyes-closed EEGs of 307 alcohol-dependent subjects and 307 age- and gender-matched unaffected controls were compared by using a repeated-measures ANOVA for the entire region and three subregions (frontal, central, and parietal) separately. Supplementary to the main analysis, the effect of three clinical variables on absolute theta power was examined separately for each gender by using correlation and regression analyses. Gender differences in the theta log power difference between alcoholics and controls were explored by using regional repeated-measures ANOVA. RESULTS: Increased absolute theta power was seen in alcohol-dependent subjects at all scalp locations. The theta log power increase in male alcoholics was prominent at the central and parietal regions and in female alcoholics at the parietal region when compared with the respective matched controls. Correlation of drinking variables with log theta power exhibited no group-specific differences. CONCLUSIONS: Increased tonic theta power in the EEG may reflect a deficiency in the information-processing capacity of the central nervous system in alcoholics. The theta power increase may also be an electrophysiological index of the imbalance in the excitation-inhibition homeostasis in the cortex. It is likely that the theta power increase is a trait-related phenomenon and is expressed to differing degrees in the two genders.

Correlação entre a freqüência das ondas teta dos eletroscilogramas corticais e hipocampais e a capacidade de aprender dos ratos Wistar / A correlation between theta waves frequency in the cortical and hipocampal electro-oscillograms and the speed of learning in Wistar rats

Ratos Wistar foram treinados a ativar a liberação de uma solução de sacarose em resposta a um estímulo luminoso e mediu-se o número de tentativas necessárias para se atingir 90 por cento de acertos. Por outro lado, registramos as ondas teta de áreas corticais e hipocampais em vigília atenta e em sono dessincronizado. Demonstrou-se que a freqüência das ondas teta nesses dois estados é tanto mais alta quanto menos tentativas o animal faz para aprender o comportamento, correlação essa linear. Esta é a primeira demonstração de relação entre a inteligência (que é medida como a velocidade com que se aprende algo) e potenciais eletrofisiológicos, o que abre interessante linha de pesquisa para se estudar a inteligência inclusive no homem.Wistar rats were trained to activate delivery of a saccharose solution as response to a light stimulus and the number of trials to reach a 90 per cent index of correct responses. Cortical and hipoccampal theta waves were recorded during attentive wakefulness and desynchronized sleep. We demonstrated that theta waves frequency in both states is inversely related to the number of trials to learn the task. This is the first demonstration of a correlation between intelligence (that is usually measured as the speed of learning) and electrophysiological potentials, what may be an interesting way of studying intelligence, including in humans...

Topographic quantitative EEG response to acute caffeine withdrawal: a comprehensive analysis of multiple quantitative variables.

Most previous studies of the neurophysiological effects of caffeine have focused on the effects of caffeine ingestion, and few studies have examined the effects of caffeine withdrawal. This open study evaluated the quantitative EEG (QEEG) changes occurring during a 4-day period of abstinence in subjects who habitually consume 300 mg or more of caffeine daily. Thirteen subjects underwent QEEG studies during their usual caffeine consumption (baseline) and on days 1, 2, and 4 of a 4-day period of caffeine abstinence. Ten of the subjects underwent a second QEEG on day 4 that consisted of a period of recording after reinstitution of caffeine. A comprehensive analysis of multiple quantitative variables was performed for each study during the abstinence period and compared to the variables obtained at baseline for each subject. Changes occurring during caffeine abstinence included: 1) increases in theta absolute power over all cortical areas, 2) increases in delta absolute power over the frontal cortex, 3) decreases in the mean frequency of both the alpha and beta rhythm, 4) increase in theta relative power and decrease in beta relative power, and 5) significant changes in interhemispheric coherence. Most of these changes tended to return to pre-abstinence baseline levels rapidly after resumption of caffeine consumption. The caffeine withdrawal state affects a number of neurophysiological variables. Further investigation of the neurophysiological aspects of caffeine withdrawal using placebo controlled double blind assessment methods is warranted.

Microinjection of procaine into the pedunculopontine tegmental nucleus suppresses hippocampal theta rhythm in urethane-anesthetized rats.

It was found that the cholinergic component of the pedunculopontine tegmental nucleus (PPN) is involved in the generation of theta rhythm in the hippocampus. However, it is still not known how important PPN is in the brainstem theta-generating system, where the nucleus reticularis pontis oralis is regarded as a primary generator. In the present experiment, performed on urethane-anesthetized rats, we studied the effect on the tail pinch-elicited hippocampal theta of unilateral inactivation of PPN by means of direct procaine microinjection. Procaine induced ipsilateral suppression of theta rhythm, manifested as desynchronization of hippocampal EEG, a shift of the fast Fourier transformation (FFT) power peak toward lower frequencies, and a reduction of FFT peak magnitude at theta band. Hippocampal field activity returned to normal (both its FFT peak frequency and magnitude) within 30 min after the injection. The results obtained indicate that PPN is critical for hippocampal theta generation but it may not be involved in encoding theta frequency.

The relationship between rhythmic activities during a mental task and sleep spindles: a correlative analysis.

In a previous study, we suggested that the characteristics of theta, alpha, and beta rhythms during a mental task were similar to those during sleep. Building upon the previous data, correlations between rhythmic activities during a mental task and during sleep were investigated in the present study. Patterns of correlation and no correlation between rhythmic activities during the mental task were similar to those during sleep for subjects with and without frontal midline theta (Fmtheta) activity. In the Fmtheta group, there were no correlations between rhythmic activities in the two situations, while in the non-Fmtheta subjects, theta and alpha rhythms showed a positive correlation with one another, and theta and beta rhythms correlated negatively during sleep. In both groups, there were many correlations between rhythmic activities during the mental task and those in Sleep Stage 2, while there were few correlations between rhythmic activities during the mental task and those in other sleep stages. These results suggest that the mechanism generating rhythmic activities during the appearance of rhythmic activities induced by a mental task may be closely related to those of rhythmic activities during sleep, and that the membrane potentials in reticular thalamic (RE) neurons during the appearance of rhythmic activities induced by a mental task may be nearly equivalent to that in Sleep Stage 2, and that the correlation pattern between the rhythmic activities in each group may be well explained by the appearance pattern of each rhythm in the previous report.

Spatial distribution of EEG theta activity as a function of lifetime lead exposure in 9-year-old children.

The relationship between low-level childhood lead exposure and developmental retardation has been proposed but the existing evidence is weak. We examined the EEG of 42 children participating in the Mexico City Prospective Lead Study to determine if relative theta power and distribution across the scalp was related to history of lifetime lead exposure as measured by sequential blood lead concentration of the mother during pregnancy and the child after delivery. EEG was recorded from scalp electrodes placed according to the 10-20 system during eyes-closed. Theta activity (4-7 Hz) was filtered with a fast Fourier transform (FFT) and relative power calculated. The expected distribution of theta was found, with the greatest relative power centrally located and lesser amounts at frontal, occipital, and lateral derivations. Multiple regression models of theta at each electrode showed that increasing postnatal blood lead from 6 to 96 months was related to increasing relative theta power adjusted for age, sex and fetal suffering at delivery, in occipital derivations. The most significant increases in theta power were associated with blood lead levels (geometric mean = 10.3 microg/dl) measured between 54 and 72 months. Spatially weighted regression demonstrated that there was a significant antero-posterior gradient in lead-induced increase in relative theta power associated with postnatal blood lead levels at 54-72 months and 78-96 months. The greatest lead effect on both occipital relative theta power and the antero-posterior gradient of theta power was found with lead at an age during which relative theta power reaches its developmental maximum and starts to decrease. Results suggest that 54-72 months represent a critical period during which lead can exert lasting effects on the developmental pattern of theta activity. Occipital derivation of the largest effects of lead on theta activity may also be related to other lead-related developmental deficits.