Eeg alpha rhythm and glucose metabolic rate in the thalamus in schizophrenia

Simultaneous EEG-fMRI Investigation of Rhythm-Dependent Thalamo-Cortical Circuits Alteration in Schizophrenia

Schizophrenia is accompanied by aberrant interactions of intrinsic brain networks. However, the modulatory effect of electroencephalography (EEG) rhythms on the functional connectivity (FC) in schizophrenia remains unclear. This study aims to provide new insight into network communication in schizophrenia by integrating FC and EEG rhythm information. After collecting simultaneous resting-state EEG-functional magnetic resonance imaging data, the effect of rhythm modulations on FC was explored using what we term "dynamic rhythm information." We also investigated the synergistic relationships among three networks under rhythm modulation conditions, where this relationship presents the coupling between two brain networks with other networks as the center by the rhythm modulation. This study found FC between the thalamus and cortical network regions was rhythm-specific. Further, the effects of the thalamus on the default mode network (DMN) and salience network (SN) were less similar under alpha rhythm modulation in schizophrenia patients than in controls ([Formula: see text]). However, the similarity between the effects of the central executive network (CEN) on the DMN and SN under gamma modulation was greater ([Formula: see text]), and the degree of coupling was negatively correlated with the duration of disease ([Formula: see text], [Formula: see text]). Moreover, schizophrenia patients exhibited less coupling with the thalamus as the center and greater coupling with the CEN as the center. These results indicate that modulations in dynamic rhythms might contribute to the disordered functional interactions seen in schizophrenia.

Alpha Event-Related Desynchronization During Reward Processing in Schizophrenia

BACKGROUND

Alterations in the brain's reward system may underlie motivation and pleasure deficits in schizophrenia (SZ). Neuro-oscillatory desynchronization in the alpha band is thought to direct resource allocation away from the internal state, to prioritize processing salient environmental events, including reward feedback. We hypothesized reduced reward-related alpha event-related desynchronization (ERD) in SZ, consistent with less externally focused processing during reward feedback.

METHODS

Electroencephalography was recorded while participants with SZ (n = 54) and healthy control participants (n = 54) played a simple slot machine task. Total alpha band power (8-14 Hz), a measure of neural oscillation magnitude, was extracted via principal component analysis and compared between groups and reward outcomes. The clinical relevance of hypothesized alpha power alterations was examined by testing associations with negative symptoms within the SZ group and with trait rumination, dimensionally, across groups.

RESULTS

A group × reward outcome interaction (p = .018) was explained by healthy control participants showing significant posterior-occipital alpha power suppression to wins versus losses (p < .001), in contrast to participants with SZ (p > .1). Among participants with SZ, this alpha ERD was unrelated to negative symptoms (p > .1). Across all participants, less alpha ERD to reward outcomes covaried with greater trait rumination for both win (p = .005) and loss (p = .002) outcomes, with no group differences in slope.

CONCLUSIONS

These findings demonstrate alpha ERD alterations in SZ during reward outcome processing. Additionally, higher trait rumination was associated with less alpha ERD during reward feedback, suggesting that individual differences in rumination covary with external attention to reward processing, regardless of reward outcome valence or group membership.

Two mechanisms facilitate regional independence between brain regions based on an examination of alpha-band activity in healthy control adult males

BACKGROUND

At rest, 8 to 12 Hz alpha rhythms are the dominant rhythm in the brain, with a common peak alpha frequency (PAF = the frequency at which alpha generators show maximum power) observed across brain regions. Although a common PAF across brain regions should result in high between-region connectivity, especially connectivity measures assessing the phase-similarity between alpha generators, high inter-regional alpha connectivity has not been observed. The present study was conducted as an initial step toward identifying mechanisms that allow brain regions to maintain functional independence in the presence of a common PAF.

METHODS

MEG data were obtained from 16 healthy control male adults (mean age = 24 years; range 21 to 30 years). A task requiring participants to alternate between a 10 s eyes-closed condition and a 5 s eyes-open condition was used to drive parietal-occipital alpha generators, with the 10 s eyes-closed condition eliciting large-amplitude alpha activity and thus providing alpha measures with good signal-to-noise ratio for source localization. Alpha source-space measures were obtained using Vector-based Spatial-Temporal Analysis using L1-minimum-norm. In each participant, the four strongest parietal-occipital alpha generators were identified. Connectivity between sources was assessed via a measure of phase-based connectivity called inter-site phase clustering (ISPC).

RESULTS

Intra-class correlations (ICC) showed very high similarity in the average PAF (=computed using all eyes-closed data) between the four alpha sources (ICC single measure = 0.88, p < 0.001). Despite a common average PAF, across participants, significant ISPC was often observed no more than that expected by chance. Examination of the alpha time course data indicated that low ISPC was often due to instantaneous changes in alpha phase (phase slips). ISPC analyses removing data with phase slips indicated that low ISPC was also due to slight continuous changes in the alpha frequency, with frequency drift more likely in non-significant than significant ISPC trials.

CONCLUSIONS

The present exploratory effort suggested two processes underlying the lack of observed inter-regional alpha phase coherence that may help maintain regional functional independence even in the presence of a common PAF. In particular, although the alpha generators were observed to oscillate at the same rate on average, across time each alpha generator oscillated a little slower or faster, and about every one and a half seconds an alpha generator abruptly lost the beat. Because of this, functional independence among alpha generators (and thus brain regions) was the rule rather than the exception. Studies replicating these processes that allow brain regions to maintain functional independence, using different source localization methods and in different conditions (e.g., a true resting state), are warranted.

IMPACT STATEMENT

Using source localization to measure parietal-occipital alpha generator activity, two properties that limit between-region alpha functional connectivity are proposed. In particular, a model of alpha generator activity is offered where via transient phase slips occurring approximately every 1.5 s, as well as slight non-stationarity in the alpha frequency, brain regions retain a common alpha frequency while also maintaining regional identity and presumably functionality. Findings also suggest novel markers for use in studies examining changes in alpha activity across maturation as well as in studies examining alpha activity in patient populations where alpha abnormalities have been reported.

Evoked responses to rhythmic visual stimulation vary across sources of intrinsic alpha activity in humans

Rhythmic flickering visual stimulation produces steady-state visually evoked potentials (SSVEPs) in electroencephalogram (EEG) recordings. Based on electrode-level analyses, two dichotomous models of the underpinning mechanisms leading to SSVEP generation have been proposed: entrainment or superposition, i.e., phase-alignment or independence of endogenous brain oscillations from flicker-induced oscillations, respectively. Electrode-level analyses, however, represent an averaged view of underlying 'source-level' activity, at which variability in SSVEPs may lie, possibly suggesting the co-existence of multiple mechanisms. To probe this idea, we investigated the variability of SSVEPs derived from the sources underpinning scalp EEG responses during presentation of a flickering radial checkerboard. Flicker was presented between 6 and 12 Hz in 1 Hz steps, and at individual alpha frequency (IAF i.e., the dominant frequency of endogenous alpha oscillatory activity). We tested whether sources of endogenous alpha activity could be dissociated according to evoked responses to different flicker frequencies relative to IAF. Occipitoparietal sources were identified by temporal independent component analysis, maximal resting-state alpha power at IAF and source localisation. The pattern of SSVEPs to rhythmic flicker relative to IAF was estimated by correlation coefficients, describing the correlation between the peak-to-peak amplitude of the SSVEP and the absolute distance of the flicker frequency from IAF across flicker conditions. We observed extreme variability in correlation coefficients across sources, ranging from -0.84 to 0.93, with sources showing largely different coefficients co-existing within subjects. This result demonstrates variation in evoked responses to flicker across sources of endogenous alpha oscillatory activity. Data support the idea of multiple SSVEP mechanisms.

Peak Alpha Frequency and Thalamic Structure in Children with Typical Development and Autism Spectrum Disorder

Associations between age, resting-state (RS) peak-alpha-frequency (PAF = frequency showing largest amplitude alpha activity), and thalamic volume (thalamus thought to modulate alpha activity) were examined to understand differences in RS alpha activity between children with autism spectrum disorder (ASD) and typically-developing children (TDC) noted in prior studies. RS MEG and structural-MRI data were obtained from 51 ASD and 70 TDC 6- to 18-year-old males. PAF and thalamic volume maturation were observed in TDC but not ASD. Although PAF was associated with right thalamic volume in TDC (R² = 0.12, p = 0.01) but not ASD (R² = 0.01, p = 0.35), this group difference was not large enough to reach significance. Findings thus showed unusual maturation of brain function and structure in ASD as well as an across-group thalamic contribution to alpha rhythms.

Electroencephalographic evidence of gray matter lesions among multiple sclerosis patients: A case-control study

This study aimed to investigate evidence of gray matter brain lesions in multiple sclerosis (MS) patients by evaluating the resting state alpha rhythm of brain electrical activity.The study included 50 patients diagnosed with MS recruited from the MS clinic with 50 age and gender-matched control participants. The study investigated parameters of posterior dominant rhythm (PDR) in the electroencephalography (EEG) recordings including wave frequency and amplitude. Functional disability among the patients was evaluated according to the expanded disability status scale. Univariate statistical analysis was completed using one-way analysis of variance and t test with a P value of less than .05 to indicate statistical significance.Patients with MS had significantly lower PDR frequency and amplitude values compared to the controls (P value < .01) and 34% of the MS patients had a PDR frequency of less than 8.5 Hz. The PDR frequency was negatively associated with the level of functional disability among the patients (P value <.001) and 4% of the patients had abnormal epileptiform discharges.Background slowing of resting alpha rhythms and epileptiform discharges are suggestive of gray matter degeneration and may help in the prediction and follow-up of cortical damage and functional disabilities among MS patients. Therefore, electroencephalography monitoring of the PDR spectrum may serve as an alternative or complementary tool with other imaging techniques to detect and monitor cerebral cortical lesions.

Disrupted Intersubject Variability Architecture in Functional Connectomes in Schizophrenia

Schizophrenia (SCZ) is a highly heterogeneous disorder with remarkable intersubject variability in clinical presentations. Previous neuroimaging studies in SCZ have primarily focused on identifying group-averaged differences in the brain connectome between patients and healthy controls (HCs), largely neglecting the intersubject differences among patients. We acquired whole-brain resting-state functional MRI data from 121 SCZ patients and 183 HCs and examined the intersubject variability of the functional connectome (IVFC) in SCZ patients and HCs. Between-group differences were determined using permutation analysis. Then, we evaluated the relationship between IVFC and clinical variables in SCZ. Finally, we used datasets of patients with bipolar disorder (BD) and major depressive disorder (MDD) to assess the specificity of IVFC alteration in SCZ. The whole-brain IVFC pattern in the SCZ group was generally similar to that in HCs. Compared with the HC group, the SCZ group exhibited higher IVFC in the bilateral sensorimotor, visual, auditory, and subcortical regions. Moreover, altered IVFC was negatively correlated with age of onset, illness duration, and Brief Psychiatric Rating Scale scores and positively correlated with clinical heterogeneity. Although the SCZ shared altered IVFC in the visual cortex with BD and MDD, the alterations of IVFC in the sensorimotor, auditory, and subcortical cortices were specific to SCZ. The alterations of whole-brain IVFC in SCZ have potential implications for the understanding of the high clinical heterogeneity of SCZ and the future individualized clinical diagnosis and treatment of this disease.

Neural Oscillations: Understanding a Neural Code of Pain

Neural oscillations play an important role in the integration and segregation of brain regions that are important for brain functions, including pain. Disturbances in oscillatory activity are associated with several disease states, including chronic pain. Studies of neural oscillations related to pain have identified several functional bands, especially alpha, beta, and gamma bands, implicated in nociceptive processing. In this review, we introduce several properties of neural oscillations that are important to understand the role of brain oscillations in nociceptive processing. We also discuss the role of neural oscillations in the maintenance of efficient communication in the brain. Finally, we discuss the role of neural oscillations in healthy and chronic pain nociceptive processing. These data and concepts illustrate the key role of regional and interregional neural oscillations in nociceptive processing underlying acute and chronic pains.

Awakening after a sleeping pill: Restoring functional brain networks after severe brain injury

Some patients with severe brain injury show short-term neurological improvements, such as recovery of consciousness, motor function, or speech after administering zolpidem, a GABA receptor agonist. The working mechanism of this paradoxical phenomenon remains unknown. In this study, we used electroencephalography and magnetoencephalography to investigate a spectacular zolpidem-induced awakening, including the recovery of functional communication and the ability to walk in a patient with severe hypoxic-ischemic brain injury. We show that cognitive deficits, speech loss, and motor impairments after severe brain injury are associated with stronger beta band connectivity throughout the brain and suggest that neurological recovery after zolpidem occurs with the restoration of beta band connectivity. This exploratory work proposes an essential role for beta rhythms in goal-directed behavior and cognition. It advocates further fundamental and clinical research on the role of increased beta band connectivity in the development of neurological deficits after severe brain injury.

Heritability of alpha and sensorimotor network changes in temporal lobe epilepsy

OBJECTIVE

Electroencephalography (EEG) features in the alpha band have been shown to differ between people with epilepsy and healthy controls. Here, in a group of patients with mesial temporal lobe epilepsy (mTLE), we seek to confirm these EEG features, and using simultaneous functional magnetic resonance imaging, we investigate whether brain networks related to the alpha rhythm differ between patients and healthy controls. Additionally, we investigate whether alpha abnormalities are found as an inherited endophenotype in asymptomatic relatives.

METHODS

We acquired scalp EEG and simultaneous EEG and functional magnetic resonance imaging in 24 unrelated patients with unilateral mTLE, 23 asymptomatic first-degree relatives of patients with mTLE, and 32 healthy controls. We compared peak alpha power and frequency from electroencephalographic data in patients and relatives to healthy controls. We identified brain networks associated with alpha oscillations and compared these networks in patients and relatives to healthy controls.

RESULTS

Patients had significantly reduced peak alpha frequency (PAF) across all parietal and occipital electrodes. Asymptomatic relatives also had significantly reduced PAF over 14 of 17 parietal and occipital electrodes. Both patients and asymptomatic relatives showed a combination of increased activation and a failure of deactivation in relation to alpha oscillations compared to healthy controls in the sensorimotor network.

INTERPRETATION

Genetic factors may contribute to the shift in PAF and alterations in brain networks related to alpha oscillations. These may not entirely be a consequence of anti-epileptic drugs, seizures or hippocampal sclerosis and deserve further investigation as mechanistic contributors to mTLE.

Unsuccessful reduction of high-frequency alpha activity during cognitive activation in schizophrenia

AIMS

Electroencephalogram (EEG) alpha activity during resting state reflects the 'readiness' of an individual to respond to the environment; this includes the performance of cognitive processes. Alpha activity is reported to be attenuated in schizophrenia (SCZ). Understanding the interaction between alpha activity during rest and when cognitively engaged may provide insights into the neural circuitry, which is dysfunctional in SCZ. This study investigated the changes of alpha activity between resting state and cognitive engagement in SCZ patients.

METHODS

Thirty-four SCZ patients and 29 healthy controls (HC) were recruited. EEG was performed in the resting state and during an auditory P300 task. All experimental procedures followed the relevant institutional guidelines and regulations.

RESULTS

In SCZ, high-frequency alpha activity was reduced in the resting state. High-frequency alpha source density was decreased in both the resting-state and a P300 task condition in patients, compared to HC. HC, but not SCZ patients, showed a reduction in high-frequency alpha source density during the P300 task compared to the resting state. The negative correlation between high-frequency alpha source density in the resting state and positive symptoms was significant.

CONCLUSIONS

High-frequency alpha activity in SCZ patients and its unsuccessful reduction during cognitive processing may be biological markers of SCZ.

Occipital Alpha Connectivity During Resting-State Electroencephalography in Patients With Ultra-High Risk for Psychosis and Schizophrenia

Schizophrenia patients always show cognitive impairment, which is proved to be related to hypo-connectivity or hyper-connectivity. Further, individuals with an ultra-high risk for psychosis also show abnormal functional connectivity-related cognitive impairment, especially in the alpha rhythm. Thus, the identification of functional networks is essential to our understanding of the disorder. We investigated the resting-state functional connectivity of the alpha rhythm measured by electroencephalography (EEG) to reveal the relation between functional network and clinical symptoms. The participants included 28 patients with first-episode schizophrenia (FES), 28 individuals with ultra-high risk for psychosis (UHR), and 28 healthy controls (HC). After the professional clinical symptoms evaluation, all the participants were instructed to keep eyes closed for 3-min resting-state EEG recording. The 3-min EEG data were segmented into artefact-free epochs (the length was 3 s), and the functional connectivity of the alpha phase was estimated using the phase lag index (PLI), which measures the phase differences of EEG signals. The FES and UHR groups displayed increased resting-state PLI connectivity compared with the HC group [F(2,74) = 10.804, p < 0.001]. Significant increases in the global efficiency, the local efficiency, and the path length were found in the FES and UHR groups compared with those of the HC group. FES and UHR showed an increased degree of connectivity compared with HC. The degree of the left occipital lobe area was higher in the UHR group than in the FES group. The hypothesis of disconnection is confirmed. Furthermore, differences between the UHR and FES group were found, which is valuable for producing clinical significance before the onset of schizophrenia.

Topographic deficits in alpha-range resting EEG activity and steady state visual evoked responses in schizophrenia

Deficits in both resting alpha-range (8-12Hz) electroencephalogram (EEG) activity and steady state evoked potential (SSVEP) responses have been reported in schizophrenia. However, the topographic specificity of these effects, the relationship between resting EEG and SSVEP, as well as the impact of antipsychotic medication on these effects, have not been clearly delineated. The present study sought to address these questions with 256 channel high-density EEG recordings in a group of 13 schizophrenia patients, 13 healthy controls, and 10 non-schizophrenia patients with psychiatric diagnoses currently taking antipsychotic medication. At rest, the schizophrenia group demonstrated decreased alpha EEG power in frontal and occipital areas relative to healthy controls. With SSVEP stimulation centered in the alpha band (10Hz), but not with stimulation above (15Hz) or below (7Hz) this range, the occipital deficit in alpha power was partially reverted. However, the frontal deficit persisted and contributed to a significantly reduced topographic relationship between occipital and frontal alpha activity for resting EEG and 10Hz SSVEP alpha power in schizophrenia patients. No significant differences were observed between healthy and medicated controls or between medicated controls and schizophrenia. These findings suggest a potential intrinsic deficit in frontal eyes-closed EEG alpha oscillations in schizophrenia, whereby potent visual stimulation centered in that frequency range results in an increase in the occipital alpha power of these patients, which however does not extend to frontal regions. Future research to evaluate the cortical and subcortical mechanisms of these effects is warranted.

Relating Alpha Power and Phase to Population Firing and Hemodynamic Activity Using a Thalamo-cortical Neural Mass Model

Oscillations are ubiquitous phenomena in the animal and human brain. Among them, the alpha rhythm in human EEG is one of the most prominent examples. However, its precise mechanisms of generation are still poorly understood. It was mainly this lack of knowledge that motivated a number of simultaneous electroencephalography (EEG) - functional magnetic resonance imaging (fMRI) studies. This approach revealed how oscillatory neuronal signatures such as the alpha rhythm are paralleled by changes of the blood oxygenation level dependent (BOLD) signal. Several such studies revealed a negative correlation between the alpha rhythm and the hemodynamic BOLD signal in visual cortex and a positive correlation in the thalamus. In this study we explore the potential generative mechanisms that lead to those observations. We use a bursting capable Stefanescu-Jirsa 3D (SJ3D) neural-mass model that reproduces a wide repertoire of prominent features of local neuronal-population dynamics. We construct a thalamo-cortical network of coupled SJ3D nodes considering excitatory and inhibitory directed connections. The model suggests that an inverse correlation between cortical multi-unit activity, i.e. the firing of neuronal populations, and narrow band local field potential oscillations in the alpha band underlies the empirically observed negative correlation between alpha-rhythm power and fMRI signal in visual cortex. Furthermore the model suggests that the interplay between tonic and bursting mode in thalamus and cortex is critical for this relation. This demonstrates how biophysically meaningful modelling can generate precise and testable hypotheses about the underpinnings of large-scale neuroimaging signals.

Resting-state alpha in autism spectrum disorder and alpha associations with thalamic volume

Alpha circuits (8-12 Hz), necessary for basic and complex brain processes, are abnormal in autism spectrum disorder (ASD). The present study obtained estimates of resting-state (RS) alpha activity in children with ASD and examined associations between alpha activity, age, and clinical symptoms. Given that the thalamus modulates cortical RS alpha rhythms, associations between thalamic structure and alpha activity were examined. RS magnetoencephalography was obtained from 47 typically-developing children (TDC) and 41 children with ASD. RS alpha activity was measured using distributed source localization. Left and right thalamic volume measurements were also obtained. In both groups, the strongest alpha activity was observed in Calcarine Sulcus regions. In Calcarine regions, only TDC showed the expected association between age and alpha peak frequency. ASD had more alpha activity than TDC in regions bordering the Central Sulcus as well as parietal association cortices. In ASD, whereas greater left Central Sulcus relative alpha activity was associated with higher Social Responsiveness Scale (SRS) scores, greater Calcarine region relative alpha activity was associated with lower SRS scores. Although thalamic volume group differences were not observed, relationships between thalamic volume and Calcarine alpha power were unique to TDC. The present study also identified a failure to shift peak alpha frequency as a function of age in primary alpha-generating areas in children with ASD. Findings suggested that increased RS alpha activity in primary motor and somatosensory as well as parietal multimodal areas-with increased alpha thought to reflect greater inhibition-might impair the ability to identify or interpret social cues. Finally, to our knowledge, this is the first study to report associations between thalamic volume and alpha power, an association observed only in TDC. The lack of thalamic and alpha associations in ASD suggests thalamic contributions to RS alpha abnormalities in ASD.

Joint Coupling of Awake EEG Frequency Activity and MRI Gray Matter Volumes in the Psychosis Dimension: A BSNIP Study

BACKGROUND

Many studies have examined either electroencephalogram (EEG) frequency activity or gray matter volumes (GMV) in various psychoses [including schizophrenia (SZ), schizoaffective (SZA), and psychotic bipolar disorder (PBP)]. Prior work demonstrated similar EEG and gray matter abnormalities in both SZ and PBP. Integrating EEG and GMV and jointly analyzing the combined data fully elucidates the linkage between the two and may provide better biomarker- or endophenotype-specificity for a particular illness. Joint exploratory investigations of EEG and GMV are scarce in the literature and the relationship between the two in psychosis is even less explored. We investigated a joint multivariate model to test whether the linear relationship or linkage between awake EEG (AEEG) frequency activity and GMV is abnormal across the psychosis dimension and if such effects are also present in first-degree relatives.

METHODS

We assessed 607 subjects comprising 264 probands [105 SZ, 72 SZA, and 87 PBP], 233 of their first degree relatives [82 SZ relatives (SZR), 71 SZA relatives (SZAR), and 80 PBP relatives (PBPR)], and 110 healthy comparison subjects (HC). All subjects underwent structural MRI (sMRI) and EEG scans. Frequency activity and voxel-based morphometric GMV were derived from EEG and sMRI data, respectively. Seven AEEG frequency and gray matter components were extracted using Joint independent component analysis (jICA). The loading coefficients (LC) were examined for group differences using analysis of covariance. Further, the LCs were correlated with psychopathology scores to identify relationship with clinical symptoms.

RESULTS

Joint ICA revealed a single component differentiating SZ from HC (p < 0.006), comprising increased posterior alpha activity associated with decreased volume in inferior parietal lobe, supramarginal, parahippocampal gyrus, middle frontal, inferior temporal gyri, and increased volume of uncus and culmen. No components were aberrant in either PBP or SZA or any relative group. No significant association was identified with clinical symptom measures.

CONCLUSION

Our data suggest that a joint EEG and GMV model yielded a biomarker specific to SZ, not abnormal in PBP or SZA. Alpha activity was related to both increased and decreased volume in different cortical structures. Additionally, the joint model failed to identify endophenotypes across psychotic disorders.

Coupling between resting cerebral perfusion and EEG

While several studies have investigated interactions between the electroencephalography (EEG) and functional magnetic resonance imaging BOLD signal fluctuations, less is known about the associations between EEG oscillations and baseline brain haemodynamics, and few studies have examined the link between EEG power outside the alpha band and baseline perfusion. Here we compare whole-brain arterial spin labelling perfusion MRI and EEG in a group of healthy adults (n = 16, ten females, median age: 27 years, range 21-48) during an eyes closed rest condition. Correlations emerged between perfusion and global average EEG power in low (delta: 2-4 Hz and theta: 4-7 Hz), middle (alpha: 8-13 Hz), and high (beta: 13-30 Hz and gamma: 30-45 Hz) frequency bands in both cortical and sub-cortical regions. The correlations were predominately positive in middle and high-frequency bands, and negative in delta. In addition, central alpha frequency positively correlated with perfusion in a network of brain regions associated with the modulation of attention and preparedness for external input, and central theta frequency correlated negatively with a widespread network of cortical regions. These results indicate that the coupling between average EEG power/frequency and local cerebral blood flow varies in a frequency specific manner. Our results are consistent with longstanding concepts that decreasing EEG frequencies which in general map onto decreasing levels of activation.

Transdermal nicotine administration and the electroencephalographic activity of substance abusers in treatment

OBJECTIVES

It is widely recognized that individuals with alcohol or illicit substance abuse disorders often smoke cigarettes. However, few studies have examined the direct effects of nicotine among substance abuse subgroups. The current study examined patterns of electroencephalographic (EEG) activity in alcohol-dependent (AD), stimulant-dependent (StimD), alcohol- and stimulant-dependent (ASD) participants, as well as community controls (CC). All participants were regular smokers.

METHODS

After overnight nicotine abstinence, subjects were administered either a high (14 or 21 mg) or low (7mg) dose transdermal nicotine patch. EEG data were collected during a 2 minute eyes open and 5 minute eyes closed baseline recording session, which occurred as part of a larger study of brain electrophysiology.

RESULTS

The most interesting finding was a differential pattern of nicotine dose effects by group. EEGs of Controls and ASD participants did not distinguish between high and low nicotine doses; whereas, nicotine administration in the AD and StimD groups resulted in opposite findings across a range of spectral bands.

CONCLUSIONS

Although further research is warranted, these results may have implications for the study of smoking cessation and attentional functioning among substance abusers in treatment. These data suggest that nicotine-related changes in neurophysiology may be associated with specific brain areas and/or specific drug histories and reinforce the need for caution in generalizing among such groups.

Finding thalamic BOLD correlates to posterior alpha EEG

Oscillatory electrical brain activity in the alpha (8-13 Hz) band is a prominent feature of human electroencephalography (EEG) during alert wakefulness, and is commonly thought to arise primarily from the occipital and parietal parts of the cortex. While the thalamus is considered to play a supportive role in the generation and modulation of cortical alpha rhythms, its precise function remains controversial and incompletely understood. To address this, we evaluated the correlation between the blood oxygenation level dependent (BOLD) functional magnetic resonance imaging (fMRI) signals in the thalamus and the spontaneous modulation of posterior alpha rhythms based on EEG-fMRI data acquired concurrently during an eyes-closed task-free condition. We observed both negative and positive correlations in the thalamus. The negative correlations were mostly seen within the visual thalamus, with a preference for the pulvinar over lateral geniculate nuclei. The positive correlations were found at the anterior and medial dorsal nuclei. Through functional connectivity analysis of the fMRI data, the pulvinar was found to be functionally associated with the same widespread cortical visual areas where the fMRI signals were negatively correlated with the posterior alpha modulation. In contrast, the dorsal nuclei were part of a distinct functional network that included brain stem, cingulate cortex and cerebellum. These observations are consistent with previous animal electrophysiology studies and the notion that the visual thalamus, and the pulvinar in particular, is intimately involved in the generation and spontaneous modulation of posterior alpha rhythms, facilitated by its reciprocal and widespread interaction with the cortical visual areas. We further postulate that the anterior and medial dorsal nuclei, being part of the ascending neuromodulatory system, may indirectly modulate cortical alpha rhythms by affecting vigilance and arousal levels.

Clozapine augments delta, theta, and right frontal EEG alpha power in schizophrenic patients

Objective. To explore the Quantitative EEG (QEEG) effects of established clozapine therapy regimes compared to those of previous ineffective antipsychotic regimes among 64 chronic (DSM-IV) schizophrenic patients. Methods. Data from 20 EEG channels referenced to linked ears were collected before and during maintenance clozapine therapy (mean duration 1.4 years). Absolute power was calculated in six frequency bands: delta (0.4–3.6 Hz), theta (4.2–7.8 Hz), alpha (8.2–11.8 Hz), beta1 (12.2–15.8 Hz), beta2 (16.2–19.8 Hz), and beta3 (20.2–23.8 Hz). Results. Clozapine augments power globally in the delta and theta bands, but this effect is more pronounced over frontal areas. Beta3 power was reduced. Alpha showed a frontal increase, more pronounced in the right, coupled with a posterior decrease with no net change in overall power. Conclusion. The demonstration of a significant clozapine-induced alpha topographic shift frontally and to the right is a novel discovery that may serve to encourage further investigations of subcortical structures in attempts to better understand the diverse aetiologies and optimal treatments of the schizophrenias.

Do resting brain dynamics predict oddball evoked-potential?

Background

The oddball paradigm is widely applied to the investigation of cognitive function in neuroscience and in neuropsychiatry. Whether cortical oscillation in the resting state can predict the elicited oddball event-related potential (ERP) is still not clear. This study explored the relationship between resting electroencephalography (EEG) and oddball ERPs. The regional powers of 18 electrodes across delta, theta, alpha and beta frequencies were correlated with the amplitude and latency of N1, P2, N2 and P3 components of oddball ERPs. A multivariate analysis based on partial least squares (PLS) was applied to further examine the spatial pattern revealed by multiple correlations.

Results

Higher synchronization in the resting state, especially at the alpha spectrum, is associated with higher neural responsiveness and faster neural propagation, as indicated by the higher amplitude change of N1/N2 and shorter latency of P2. None of the resting quantitative EEG indices predict P3 latency and amplitude. The PLS analysis confirms that the resting cortical dynamics which explains N1/N2 amplitude and P2 latency does not show regional specificity, indicating a global property of the brain.

Conclusions

This study differs from previous approaches by relating dynamics in the resting state to neural responsiveness in the activation state. Our analyses suggest that the neural characteristics carried by resting brain dynamics modulate the earlier/automatic stage of target detection.

Human cortical theta reactivity to high-frequency repetitive transcranial magnetic stimulation

Electroencephalography (EEG) can directly monitor the temporal progression of cortical changes induced by repetitive Transcranial Magnetic Stimulation (rTMS) and facilitate the understanding of cortical and subcortical influences in the genesis of oscillations. In this combined rTMS/EEG study, we aimed to investigate changes in oscillatory activity after high-frequency (∼11 Hz) rTMS relative to the number of applied pulses. Twenty intermittent trains of 20 or 60 rTMS pulses were delivered over the human primary motor cortex at rest and tuned to individual mu frequency. The regional and interregional oscillatory neural activity after stimulation were evaluated using event-related power (ERPow) and event-related coherence (ERCoh) transformations. The most prominent changes for ERPow were observed in the theta band (4-7 Hz), as an increase in ERPow up to 20 s following 60 rTMS pulses, whereas ERPow increases were smaller in mu (10-12 Hz) and beta (13-30 Hz). ERCoh revealed that rTMS 60 modulated the connectivity in the theta band for up to 20 s. The topography of mu and theta changes were not identical; mu was more focal and theta was more global. Our data suggested the presence of independent cortical theta and mu generators with different reactivity to rTMS but could not rule out possible thalamocortical contributions in generating theta and mu over the motor network.

Functional connectivity between the thalamus and visual cortex under eyes closed and eyes open conditions: a resting-state fMRI study

The thalamus and visual cortex are two key components associated with the alpha power of electroencephalography. However, their functional relationship remains to be elucidated. Here, we employ resting-state functional MRI to investigate the temporal correlations of spontaneous fluctuations between the thalamus [the whole thalamus and its three largest nuclei (bilateral mediodorsal, ventrolateral and pulvinar nuclei)] and visual cortex under both eyes open and eyes closed conditions. The whole thalamus show negative correlations with the visual cortex and positive correlations with its contralateral counterpart in eyes closed condition, but which are significantly decreased in eyes open condition, consistent with previous findings of electroencephalography desynchronization during eyes open resting state. Furthermore, we find that bilateral thalamic mediodorsal nuclei and bilateral ventrolateral nuclei have remarkably similar connectivity maps, and resemble to those of the whole thalamus, suggesting their crucial contributions to the thalamus-visual correlations. The bilateral pulvinar nuclei are found to show distinct functional connectivity patterns, compatible with previous findings of the asymmetry of anatomical and functional organization in the nuclei. Our data provides evidence for the associations of intrinsic spontaneous neuronal activity between the thalamus and visual cortex under different resting conditions, which might have implications on the understanding of the generation and modulation of the alpha rhythm.

Source analysis of alpha rhythm reactivity using LORETA imaging with 64-channel EEG and individual MRI

Conventional EEG and quantitative EEG visual stimuli (close-open eyes) reactivity analysis have shown their usefulness in clinical practice; however studies at the level of EEG generators are limited. The focus of the study was visual reactivity of cortical resources in healthy subjects and in a stroke patient. The 64 channel EEG and T1 magnetic resonance imaging (MRI) studies were obtained from 32 healthy subjects and a middle cerebral artery stroke patient. Low Resolution Electromagnetic Tomography (LORETA) was used to estimate EEG sources for both close eyes (CE) vs. open eyes (OE) conditions using individual MRI. The t-test was performed between source spectra of the two conditions. Thresholds for statistically significant t values were estimated by the local false discovery rate (lfdr) method. The Z transform was used to quantify the differences in cortical reactivity between the patient and healthy subjects. Closed-open eyes alpha reactivity sources were found mainly in posterior regions (occipito-parietal zones), extended in some cases to anterior and thalamic regions. Significant cortical reactivity sources were found in frequencies different from alpha (lower t-values). Significant changes at EEG reactivity sources were evident in the damaged brain hemisphere. Reactivity changes were also found in the "healthy" hemisphere when compared with the normal population. In conclusion, our study of brain sources of EEG alpha reactivity provides information that is not evident in the usual topographic analysis.

Phenotypic and genetic correlations between evoked EEG/ERP measures during the response anticipation period of a delayed response task

We investigated the relationship between three electrophysiological indices of response anticipation in a spatial delayed response task with a low and high memory load manipulation: a slow cortical potential (SCP), theta desynchronization, and upper alpha synchronization. Individual differences in these three measures were examined in 531 adult twins and siblings. Heritability of the SCP at occipital-parietal leads varied from 30% to 43%. Heritability of upper alpha synchronization (35% to 65%) and theta desynchronization (31% to 50%) was significant at all leads. Theta desynchronization and upper alpha synchronization were significantly correlated (r approximately 43%), but SCP was not correlated with either. The effect of working memory load on all three measures was not heritable. Response anticipation reliably evokes an SCP, upper alpha synchronization and theta desynchronization, but variation in these measures reflects different (genetic) sources.

EEG correlates of virtual reality hypnosis

The study investigated hypnosis-related electroencephalographic (EEG) coherence and power spectra changes in high and low hypnotizables (Stanford Hypnotic Clinical Scale) induced by a virtual reality hypnosis (VRH) induction system. In this study, the EEG from 17 participants (Mean age = 21.35, SD = 1.58) were compared based on their hypnotizability score. The EEG recording associated with a 2-minute, eyes-closed baseline state was compared to the EEG during a hypnosis-related state. This novel induction system was able to produce EEG findings consistent with previous hypnosis literature. Interactions of significance were found with EEG beta coherence. The high susceptibility group (n = 7) showed decreased coherence, while the low susceptibility group (n = 10) demonstrated an increase in coherence between medial frontal and lateral left prefrontal sites. Methodological and efficacy issues are discussed.

REM sleep EEG spectral analysis in patients with first-episode schizophrenia

The pathophysiology of schizophrenia includes abnormalities in subcortical-cortical transfer of information that can be studied using REM sleep EEG spectral analysis, a measure that reflects spontaneous and endogenous thalamocortical activity. We recorded 10 patients with first-episode schizophrenia and 30 healthy controls for two consecutive nights in a sleep laboratory, using a 10-electrode EEG montage. Sixty seconds of REM sleep EEG without artifact were analyzed using FFT spectral analysis. Absolute and relative spectral amplitudes of five frequency bands (delta, theta, alpha, beta1 and beta2) were extracted and compared between the two groups. Frequency bands with significant differences were correlated with BPRS positive and negative symptoms scores. Patients with schizophrenia showed lower relative alpha and higher relative beta2 spectral amplitudes compared to healthy controls over the averaged total scalp. Analysis using cortical regions showed lower relative alpha over frontal, central and temporal regions and higher relative beta2 over the occipital region. Absolute spectral amplitude was not different between groups for any given EEG band. However, absolute alpha activity correlated negatively with BPRS positive symptoms scores and correlated positively with negative symptoms scores. Since similar results have been reported following EEG spectral analysis during the waking state, we conclude that abnormalities of subcortical-cortical transfer of information in schizophrenia could be generated by mechanisms common to REM sleep and waking.

Quantitative analysis of the EEG posterior-dominant rhythm in healthy adolescents

OBJECTIVE

Pivotal studies of the normal EEG posterior-dominant rhythm (PDR) typically relied on visual inspection of a few seconds of EEG data from a relatively small number of subjects in each age category. We sought to analyze and characterize the PDR in a large cohort of healthy 15-year-olds, and to determine if PDR characteristics mature over the following year.

METHODS

Seventy-nine healthy 15-year-olds free of neurologic and psychiatric disease underwent a resting-awake EEG, which was repeated 1 year later. In each study, PDR frequency was determined with fast Fourier transform analysis of a continuous 2-min EEG segment. t-Tests were used to compare relevant variables.

RESULTS

From age 15 to 16 the mean PDR frequency increased from 9.9 to 10.0Hz, a small but statistically significant difference. The PDR frequency range at both ages was 8.9-11.0Hz, similar to values reported in prior studies on healthy young adults. There was no significant difference in PDR frequency between genders or hemispheres.

CONCLUSIONS

Maturation of the PDR is nearly complete at age 16. The frequency range of the PDR in healthy adolescents and adults is substantially narrower than the alpha band.

SIGNIFICANCE

Based on this and prior studies, a PDR frequency of less than 8.5 or greater than 11.5Hz should be considered abnormal in adolescents and adults.

Impaired Percent Alpha Variability on Continuous Electroencephalography Is Associated with Thalamic Injury and Predicts Poor Long-Term Outcome after Human Traumatic Brain Injury

Continuous electroencephalography (cEEG) is potentially useful in determining prognosis in patients with traumatic brain injuries (TBI). The objective of this prospective, observational cohort study was to determine if the percent alpha variability (PAV) on cEEG was predictive of outcome following TBI. Injury characteristics were indexed to assess whether lesions in specific cerebral loci were correlated with PAV and patient recovery. Fifty-three TBI patients were studied using cEEG recording and serial neuroimaging. Clinical recovery was assessed at regular intervals in hospital and following discharge. The principal outcome measures included the mean 3-day PAV score, the 7-day PAV pattern, delineation of the anatomical sites of brain injury, and the 6-month clinical outcome, as measured by the Glasgow Outcome Scale (GOS). Significant univariate (p = 0.030) and multivariate (p = 0.008) relations were identified between PAV and GOS scores. PAV offered good discrimination between favorable and unfavorable 6-month outcomes (AUC 0.76) and, with a cutpoint of 0.20, had a sensitivity of 87% and negative predictive value of 82%. Multivariate modeling revealed that injuries of the thalamus (p = 0.009) and basal ganglia (p = 0.016), and the presence of diffuse edema (p = 0.009), were the key anatomical predictors of PAV. Brainstem injuries (p = 0.020) and indicators of diffuse cerebral trauma, such as deep white matter shearing (p = 0.036) and multiple subcortical lesions (p = 0.033), were the principal determinants of 6-month recovery. Inclusion of PAV enhanced the accuracy of prediction models that encompassed a selective combination of clinical and anatomical variables (adjusted R(2) = 0.458, p < 0.001). The two main results of this study are (1) PAV is a sensitive predictor of 6-month clinical outcomes following TBI, and (2) injury to the thalamus is related to impaired PAV. PAV appears best utilized as a functional adjunct to traditional clinical and anatomical predictors.

Diffusion tensor imaging of frontal lobe white matter tracts in schizophrenia

We acquired diffusion tensor and structural MRI images on 103 patients with schizophrenia and 41 age-matched normal controls. The vector data was used to trace tracts from a region of interest in the anterior limb of the internal capsule to the prefrontal cortex. Patients with schizophrenia had tract paths that were significantly shorter in length from the center of internal capsule to prefrontal white matter. These tracts, the anterior thalamic radiations, are important in frontal-striatal-thalamic pathways. These results are consistent with findings of smaller size of the anterior limb of the internal capsule in patients with schizophrenia, diffusion tensor anisotropy decreases in frontal white matter in schizophrenia and hypothesized disruption of the frontal-striatal-thalamic pathway system.

Correlation of PET and qEEG in normal subjects

Positron emission tomography (PET) and quantitative electroencephalography (qEEG) were obtained in 15 normal male subjects with eyes closed at rest. Correlations between qEEG variables and regional metabolism were examined as an approach to investigating the metabolic and neuroanatomical basis of the generation of the EEG. Analogous to the neurometric approach to qEEG, a normative 2-fluoro-deoxyglucose voxel data base was developed for the PET image. The PET image was transformed to an idealized cylindrical set of coordinates to allow registration with the Talairach stereotactic atlas. PET regions of interest for the thalamus, the left and right temporal lobes, the medial frontal cortex and the dorsolateral prefrontal cortex were defined using Talairach coordinates and correlated to the QEEG. Salient findings included a negative correlation of thalamic metabolism to alpha power and a positive correlation of medial frontal cortical metabolism to delta EEG power. The significance of these findings is discussed with reference to the existing literature on the physiology of the generation of the EEG.

Thalamic mechanisms of EEG alpha rhythms and their pathological implications

During relaxed wakefulness, the human brain exhibits pronounced rhythmic electrical activity in the alpha frequency band (8-13 Hz). This activity consists of 3 main components: the classic occipital alpha rhythm, the Rolandic mu rhythm, and the so-called third rhythm. In recent years, the long-held belief that alpha rhythms are strongly influenced by the thalamus has been confirmed in several animal models and, in humans, is well supported by numerous noninvasive imaging studies. Of specific importance is the emergence of 2 key cellular thalamic mechanisms, which come together to generate locally synchronized alpha activity. First, a novel form of rhythmic burst firing, termed high-threshold (HT) bursting, which occurs in a specialized subset of thalamocortical (TC) neurons, and second, the interconnection of this subset via gap junctions (GJs). Because repetitive HT bursting in TC neurons occurs in the range of 2 to 13 Hz, with the precise frequency increasing with increasing depolarization, the same cellular components that underlie thalamic alpha rhythms can also lead to theta (2-7 Hz) rhythms when the TC neuron population is less depolarized. As such, this scenario can explain both the deceleration of alpha rhythms that takes place during early sleep and the chronic slowing that characterizes a host of neurological and psychiatric disorders.

Cortical and Subcortical Correlates of Electroencephalographic Alpha Rhythm Modulation

Neural correlates of electroencephalographic (EEG) alpha rhythm are poorly understood. Here, we related EEG alpha rhythm in awake humans to blood-oxygen-level-dependent (BOLD) signal change determined by functional magnetic resonance imaging (fMRI). Topographical EEG was recorded simultaneously with fMRI during an open versus closed eyes and an auditory stimulation versus silence condition. EEG was separated into spatial components of maximal temporal independence using independent component analysis. Alpha component amplitudes and stimulus conditions served as general linear model regressors of the fMRI signal time course. In both paradigms, EEG alpha component amplitudes were associated with BOLD signal decreases in occipital areas, but not in thalamus, when a standard BOLD response curve (maximum effect at ∼6 s) was assumed. The part of the alpha regressor independent of the protocol condition, however, revealed significant positive thalamic and mesencephalic correlations with a mean time delay of ∼2.5 s between EEG and BOLD signals. The inverse relationship between EEG alpha amplitude and BOLD signals in primary and secondary visual areas suggests that widespread thalamocortical synchronization is associated with decreased brain metabolism. While the temporal relationship of this association is consistent with metabolic changes occurring simultaneously with changes in the alpha rhythm, sites in the medial thalamus and in the anterior midbrain were found to correlate with short time lag. Assuming a canonical hemodynamic response function, this finding is indicative of activity preceding the actual EEG change by some seconds.

Estimation of neurophysiological parameters from the waking EEG using a biophysical model of brain dynamics

This paper presents the results from using electroencephalographic (EEG) data to estimate the values of key neurophysiological parameters using a detailed biophysical model of brain activity. The model incorporates spatial and temporal aspects of cortical function including axonal transmission delays, synapto-dendritic rates, range-dependent connectivities, excitatory and inhibitory neural populations, and intrathalamic, intracortical, corticocortical and corticothalamic pathways. Parameter estimates were obtained by fitting the model's theoretical spectrum to EEG spectra from each of 100 healthy human subjects. Statistical analysis was used to infer significant parameter variations occurring between eyes-closed and eyes-open states, and a correlation matrix was used to investigate links between the parameter variations and traditional measures of quantitative EEG (qEEG). Accurate fits to all experimental spectra were observed, and both inter-subject and between-state variability were accounted for by the variance in the fitted biophysical parameters, which were in turn consistent with known independent experimental and theoretical estimates. These values thus provide physiological information regarding the state. transitions (eyes-closed vs. eyes-open) and phenomena including cortical idling and alpha desynchronization. The parameters are also consistent with traditional qEEG, but are more informative, since they provide links to underlying physiological processes. To our knowledge, this is the first study where a detailed biophysical model of the brain is used to estimate neurophysiological parameters underlying the transitions in a broad range (0.25-50 Hz) of EEG spectra obtained from a large set of human data.

Where arousal meets attention: a simultaneous fMRI and EEG recording study

In this fMRI study, we looked for the regions supporting interaction between cortical arousal and attention during three conditions: detection, observation, and rest. Arousal measurements were obtained from the EEG low-frequency (LF) power (5-9.5 Hz) recorded continuously together with fMRI. Whatever the condition, arousal was positively correlated with the fMRI signal of the right dorsal-lateral prefrontal and superior parietal cortices, closely overlapping regions involved in the maintenance of attention. Although the inferior temporal areas also presented a correlation with arousal during detection, path analysis suggests that this influence may be indirect, through the top-down influence of the previously mentioned network. However, those visual-processing areas could account for the correlation between arousal and performances. Lastly, the medial frontal cortex, frontal opercula, and thalamus were inversely correlated with arousal but only during detection and observation so that they could account for the control of arousal.

Synchronized oscillations at alpha and theta frequencies in the lateral geniculate nucleus

In relaxed wakefulness, the EEG exhibits robust rhythms in the alpha band (8-13 Hz), which decelerate to theta (approximately 2-7 Hz) frequencies during early sleep. In animal models, these rhythms occur coherently with synchronized activity in the thalamus. However, the mechanisms of this thalamic activity are unknown. Here we show that, in slices of the lateral geniculate nucleus maintained in vitro, activation of the metabotropic glutamate receptor (mGluR) mGluR1a induces synchronized oscillations at alpha and theta frequencies that share similarities with thalamic alpha and theta rhythms recorded in vivo. These in vitro oscillations are driven by an unusual form of burst firing that is present in a subset of thalamocortical neurons and are synchronized by gap junctions. We propose that mGluR1a-induced oscillations are a potential mechanism whereby the thalamus promotes EEG alpha and theta rhythms in the intact brain.

The thalamus as the generator and modulator of EEG alpha rhythm: a combined PET/EEG study with lorazepam challenge in humans

BACKGROUND

Purpose of this study was to investigate the functional relationship between electroencephalographic (EEG) alpha power and cerebral glucose metabolism before and after pharmacological alpha suppression by lorazepam.

METHODS

Ten healthy male volunteers were examined undergoing two F18-fluorodeoxyglucose (18-FDG) positron emission tomography (PET) scans with simultaneous EEG recording: 1x placebo, 1x lorazepam. EEG power spectra were computed by means of Fourier analysis. The PET data were analyzed using SPM99, and the correlations between metabolism and alpha power were calculated for both conditions.

RESULTS

The comparison lorazepam versus placebo revealed reduced glucose metabolism of the bilateral thalamus and adjacent subthalamic areas, the occipital cortex and temporo-insular areas (P < 0.001). EEG alpha power was reduced in all derivations (P < 0.001). Under placebo, there was a positive correlation between alpha power and metabolism of the bilateral thalamus and the occipital and adjacent parietal cortex (P < 0.001). Under lorazepam, the thalamic and parietal correlations were maintained, whereas the occipital correlation was no longer detectable (P < 0.001). The correlation analysis of the difference lorazepam-placebo showed the alpha power exclusively correlated with the thalamic activity (P < 0.0001).

CONCLUSIONS

These results support the hypothesis of a close functional relationship between thalamic activity and alpha rhythm in humans mediated by corticothalamic loops which are independent of sensory afferences. The study paradigm could be a promising approach for the investigation of cortico-thalamo-cortical feedback loops in neuropsychiatric diseases.

Regional glucose metabolism within cortical Brodmann areas in healthy individuals and autistic patients

A new Brodmann area (BA) delineation approach was applied to FDG-PET scans of autistic patients and healthy volunteers (n = 17 in each group) to examine relative glucose metabolism (rGMR) during performance of a verbal memory task. In the frontal lobe, patients had lower rGMR in medial/cingulate regions (BA 32, 24, 25) but not in lateral regions (BA 8-10) compared with healthy controls. Patients had higher rGMR in occipital (BA 19) and parietal regions (BA 39) compared with controls, but there were no group differences in temporal lobe regions. Among controls, better recall and use of the semantic-clustering strategy was associated with greater lateral and medial frontal rGMR, while decreased rGMR in medial-frontal regions was associated with greater perseverative/intrusion errors. Patients failed to show these patterns. Autism patients have dysfunction in some but not all of the key brain regions subserving verbal memory performance, and other regions may be recruited for task performance.

High-frequency somatosensory thalamocortical oscillations and psychopathology in schizophrenia

Human cortical somatosensory evoked potentials (SEPs), which are presumably generated in afferent thalamocortical and early cortical fibers, reveal a burst of superimposed early (N20) high-frequency oscillations (HFOs), around 600 Hz. There is increasing evidence of an imbalance of thalamocortical systems in schizophrenic patients. In order to assess correlations between somatosensory evoked oscillations and symptoms of schizophrenia, we investigated median nerve SEPs in 20 inpatients and their age-matched and gender-matched healthy controls using a multichannel EEG. Dipole source analysis and wavelet transformation were performed before and after application of a 450-Hz high-pass filter. In schizophrenics, the maximum HFOs occurred with a significantly prolonged latency. There was also a higher amplitude (energy) in the low-frequency range of the N20 component compared with the controls. Importantly, amplitudes (energy) of HFOs were inversely correlated with symptoms of formal thought disorder and delusions. Alterations of the thalamocortical somatosensory signal processing in schizophrenia with absence of an early HFO - assumed to be of inhibitory nature - could indicate a dysfunctional thalamic inhibition with increased amplitudes of N20, paralleled by enhanced positive schizophrenic symptoms.

Functional coupling of simultaneous electrical and metabolic activity in the human brain

The relationships between brain electrical and metabolic activity are being uncovered currently in animal models using invasive methods; however, in the human brain this relationship remains not well understood. In particular, the relationship between noninvasive measurements of electrical activity and metabolism remains largely undefined. To understand better these relations, cerebral activity was measured simultaneously with electroencephalography (EEG) and positron emission tomography using [(18)f]-fluoro-2-deoxy-D-glucose (PET-FDG) in 12 normal human subjects during rest. Intracerebral distributions of current density were estimated, yielding tomographic maps for seven standard EEG frequency bands. The PET and EEG data were registered to the same space and voxel dimensions, and correlational maps were created on a voxel-by-voxel basis across all subjects. For each band, significant positive and negative correlations were found that are generally consistent with extant understanding of EEG band power function. With increasing EEG frequency, there was an increase in the number of positively correlated voxels, whereas the lower alpha band (8.5-10.0 Hz) was associated with the highest number of negative correlations. This work presents a method for comparing EEG signals with other more traditionally tomographic functional imaging data on a 3-D basis. This method will be useful in the future when it is applied to functional imaging methods with faster time resolution, such as short half-life PET blood flow tracers and functional magnetic resonance imaging.

Reduced facilitation effect of collinear flankers on contrastdetection reveals impaired lateral connectivity in the visual cortex of schizophrenia patients

The aim of this study was to investigate lateral connectivity in early visual cortex of schizophrenia patients. Contrast thresholds were measured for centrally presented Gabor patches which were surrounded by two collinear or orthogonal flankers. The healthy subjects (n = 15) showed lower contrast thresholds for central Gabor patches when collinear flankers were presented. This effect was significantly reduced in unmedicated highly functioning schizophrenia patients (n = 20) who performed normally on the continuous performance test. The performance of the patients did not correlate with the positive and negative symptoms. The facilitation effect of collinear flankers is believed to reflect lateral interactions between feature-specific units in early visual cortex (V1). Our results therefore suggest abnormal lateral interactions in early visual cortex of schizophrenia patients.

Four facets of a single brain: behaviour, cerebral blood flow/metabolism, neuronal activity and neurotransmitter dynamics

Is functional neuroimaging a royal way to understand brain function or is it a new phrenology without an exact understanding what we measure? After two decades of imaging revolution, more and more authors ask this question. Brain functions are multidimensional, which can be approached from the point of (1) behavioural measures, (2) brain activation as reflected by blood flow and metabolic changes, (3) electrical activity of cells and cell-populations, and (4) neurotransmitter dynamics (release, receptor binding and reuptake). Using imaging techniques, we must take into consideration that even during the simplest task all of these processes operate in a closely interacting manner. Therefore, before drawing final conclusions about brain functions on the basis of a single aspect of these mechanisms, we must clarify the exact relationship among them. In this paper, we address this issue in order to draw attention to a number of uncertainties and controversies in the relationship of the four facets of brain functions.

Comparative analysis of acute and chronic administration of haloperidol and clozapine using [3H] 2-deoxyglucose metabolic mapping

In an effort to compare and contrast the mechanisms of action of typical and atypical antipsychotic drugs, [3H] 2-deoxyglucose metabolic mapping was employed following acute and chronic administration of haloperidol (1 mg/kg i.p. acute and 0.5 mg/kg i.p. chronic) and clozapine (20 mg/kg i.p., both acute and chronic). Optical density ratios (ODR) were measured in 62 brain structures. An overall decrease in ODR was observed in many of the regions analyzed. Acute haloperidol elicited significant decreases, particularly in the thalamus and hippocampus. Acute clozapine decreased glucose uptake in the caudate putamen, hippocampus, central gray, locus coreleus, and the thalamus. In both chronically treated haloperidol and clozapine animals, significant decreases in ODR were seen in the thalamus and hippocampal areas most dramatically, with other changes in the superior colliculus, retrospenial cortex, and the cerebellum. Clozapine caused significant effects in 32 nuclei acutely and only 19 nuclei chronically. Haloperidol caused significant effects in 23 nuclei acutely and 15 nuclei chronically. The pattern of change induced by haloperidol and clozapine were remarkably similar when considering their pharmacology is somewhat different. Both antipsychotics elicited fewer significant changes upon chronic administration.

Quantitative electroencephalogram (qEEG) in combat veterans with post-traumatic stress disorder (PTSD)

Only a small number of studies have used quantitative electroencephalography (qEEG) in research of the post-traumatic stress disorder (PTSD). The results are not consistent. The aim of the present investigation was to compare qEEG in combat veterans with and without PTSD. The hypothesis is that differences among qEEG characteristics will be found regarding the presence/absence of PTSD. Seventy-nine combat veterans with PTSD comprised the experimental group and 37 veterans without PTSD were included as controls. After the informed consent, they were investigated by the resting EEG recordings. The results demonstrate that PTSD veterans had decreased alpha power and increased beta power. These results suggest an altered neurobiology in PTSD. Various explanations have been offered for alpha activity decrease observed in PTSD veterans. Increased beta rhythm may play a role as a potential marker in differentiating subtypes of PTSD.

Effects of low-dose ketamine on neuropathic pain: An electroencephalogram-electrooculogram/behavioral study

The aim of the present study was to clarify the neurophysiological changes associated with analgesic and behavioral effects of low-dose ketamine HCl in patients suffering from chronic neuropathic pain. Ten in-patients with neuropathic pain participated in this single-blind, placebo-controlled study after giving written informed consent. Following intravenous injections of a saline solution (placebo), three bolus injections of 5 mg ketamine HCl were administered at 5 min intervals. Changes in pain perception were assessed using a numerical rating scale for pain. Behavioral changes, including psychotomimetic effects, were assessed using the Brief Psychiatric Rating Scale (BPRS). Electroencephalograms (EEG) and electrooculograms (EOG) were recorded continuously throughout the testing period. One minute EEG and closed-eye eye movements were quantified. The effects of ketamine were evaluated by comparing the neurophysiological and behavioral parameters obtained from the placebo and ketamine trials. Pain reduction was significantly correlated with ketamine-induced changes in hallucinatory behavior and excitement as measured by the BPRS. Ketamine injections caused a significant decrease in the EEGalpha amplitude without an accompanying reduction in EEG frequency. The EEGalpha amplitude reduction at the right central electrode was significantly related to subjective pain relief. Subanesthetic doses of ketamine significantly decreased rapid eye movements, but did not initiate slow eye movements. In conclusion, the present EEG-EOG/behavioral results indicate that ketamine-induced failure of neural integration between cortical-subcortical regions induces psychotic symptoms and alters pain perception on neuropathic pain.