Changes in the coherence of cortical biopotentials during performance of a verbal creative task in men and women

Changes in EEG coherence patterns evoked by performance of a verbal creative task were studied in 14 men and 13 women (university students). EEG coherence was calculated in six frequency ranges from 4 to 30 Hz. The experiment consisted of two series: in the first, the task was performed with the instruction to "create a sentence;" in the second, the instruction was to "create an original sentence." Independently of the instruction given, the reactivity of total coherence of biopotentials (experimental data minus the corresponding baseline measure) in all subjects was negative in the theta-1 and alpha-2 frequency ranges, while reactivity in the beta-2 range was positive. Gender-related differences linked with the type of experimental instruction were seen in changes in intrahemisphere coherence of biopotentials, and these were indifferent in relation to EEG frequencies. Performance of the verbal creative task with the instruction to "create an original sentence" was accompanied in women by substitution of right-hemisphere dominance (greater levels of coherence in the right hemisphere compared with the left) by left-hemisphere dominance as compared to performance with the instruction to "create a sentence," while the reverse changes were seen in men.

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.

[Gender differences in EEG coherence changes during figural creative thinking: the efficacy coupling]

The study was aimed to explore the features of interaction between cortical areas during figural creative task performance in high- and low-creative men and women. We divided the participants into two groups with high and low creativity by the median of originality score. EEG was recorded at rest and during task performance (Torrance Tests of Creative Thinking "Incomplete figures"). The EEG coherence was computed in six frequency bands from theta1 to beta2. We analyzed the total values of coherence for each of 16 sites, calculated separately for intrahemispheric and interhemispheric connections. In the theta2, alphal, and alpha2 bands, coherence values decreased in task performance as compared to baseline in subjects with lower originality scores, whereas in subjects with higher scores, they increased in the theta2 and alpha1 bands. The decrease in the alpha2 band in the higher-creativity group was significantly lower in comparison with the decrease in the lower-score group. In the alpha2 band, the interaction of gender, creativity, laterality, and electrode position factors was also found during analysis of task-induced coherence changes. Further examination of the interaction showed the similarity of EEG coherence patterns in men and women with opposite creative abilities and higher values of task-induced coherence changes in the anterior regions of the left hemisphere and posterior regions of the right hemisphere in high-creative in comparison with low-creative men. The findings are discussed in terms of different cognitive strategies used by men and women that may have the same results in creative problem solving.

EEG alpha peak frequency analysis during memorizing of figures in patients with mild cognitive impairment

OBJECTIVE

To investigate spectral analysis of electroencephalograms (EEG) for the alpha frequency band during rest and cognitive stimulation in healthy adults and individuals with mild cognitive impairment.

METHOD

We analyzed 56 EEGs from 28 patients, 7 men and 21 women, 12 of whom (40%) were controls, 16 patients with mild cognitive impairment (60%). Ages ranged from 61 to 83 years. All individuals were patients in the Psycho-geriatric Out-patients Clinic of LIM-27, of the Psychiatric Institute of the Clinicas Hospital of the Faculty of Medicine of the University of São Paulo, IPq-HCFMUSP, between 2004 and 2007. Each patient underwent two exams with an interval of at least six months between them. During the exam, performed after a period of wakefulness and rest, the patients memorized series of pictures.

RESULTS

Analysis of spectral potential both at rest and during the memorizing task showed no statistical differences between baseline and final recordings.

CONCLUSION

Spectral analysis of EEGs showed coherent results with the clinical stability of the patients evaluated but was unable to distinguish between the control group and patients with MCI. Future studies should include a larger sample and a longer follow up.

[Cortex biopotential coherence changes in men and women during performance of verbal creative task]

Patterns of EEG coherence changes induced by performance of a verbal creative task were studied in 14 male and 13 female university students. EEG coherence was computed for six frequency bands in the range from 4 to 30 Hz. Experiment consisted of two series: in the first series, the task was performed under the instruction "to create sentences", in the second series under the instruction "to create original sentences". Independently of the instruction, coherence reactivity values (data of the experiment minus corresponding baseline data) were negative in the tetal and alpha2 ranges and positive in the beta2 range in all subjects. Sex differences related to the type of instruction were found in changes in the total reactivity values of intrahemispheric coherence (sum of intrahemispheric coherence reactivity values for the all frequency bands studied). The task performance under the instruction "to create original sentences" vs. the task performance under the instruction "to create sentences" was accompanied by changes of the right-hemispheric dominance (i.e. higher values of coherence in the right hemisphere than in the left hemisphere) to the left-hemispheric dominance in women and the opposite effect in men.

Dynamic and task-dependent encoding of speech and voice by phase reorganization of cortical oscillations

Speech and vocal sounds are at the core of human communication. Cortical processing of these sounds critically depends on behavioral demands. However, the neurocomputational mechanisms enabling this adaptive processing remain elusive. Here we examine the task-dependent reorganization of electroencephalographic responses to natural speech sounds (vowels /a/, /i/, /u/) spoken by three speakers (two female, one male) while listeners perform a one-back task on either vowel or speaker identity. We show that dynamic changes of sound-evoked responses and phase patterns of cortical oscillations in the alpha band (8-12 Hz) closely reflect the abstraction and analysis of the sounds along the task-relevant dimension. Vowel categorization leads to a significant temporal realignment of responses to the same vowel, e.g., /a/, independent of who pronounced this vowel, whereas speaker categorization leads to a significant temporal realignment of responses to the same speaker, e.g., speaker 1, independent of which vowel she/he pronounced. This transient and goal-dependent realignment of neuronal responses to physically different external events provides a robust cortical coding mechanism for forming and processing abstract representations of auditory (speech) input.

[Motivation effect on frequency-spatial characteristics of figural and verbal creativity: coherence changes in biopotentials]

Effect of extrinsic motivation stimulating the most original problem solving during verbal and figural creativity testing was studied using the EEG coherence in the range of 4-30 Hz. The right-handed university students (27 males and 26 females) participated in the experiments. The instruction "to create the most original solution" (INS2) as compared to the instruction "to create any solution" (INS1) produced an increase in baseline coherence and task-related desynchronization in the alphal2 bands. This effect was more pronounced in the anterior cortex. Changes in the beta2 rhythm were found mostly in the posterior cortex and were presented by a decreased task-induced beta2 synchronization after INS2 vs. INS1. Instruction-related coherence changes in the alphal band did not depend on factors of gender and task type, whereas the effects of these factors on the alpha2 and beta2 bands were significant. Gender differences in instruction-related coherence changes were found in the alpha2 band during verbal creativity testing, whereas figural creativity was associated with gender-dependent instruction-related changes in the beta2 band. These differences were more pronounced in the INS1 condition. The results demonstrate that extrinsic motivation of creative thinking promotes the frequency-specific reorganization of hemispheric interactions. High-frequency widespread cortical oscillations are of greater significance in men, whereas low-frequency rhythms and, mainly, functioning of the frontal cortex greatly contribute to creative activity in women.

[Characteristics of ladasten effect in neurasthenia patients with various EEG parameters]

Clinical and electroencephalographic (EEG) analysis ofladasten action in anxiety-asthenic patients with respect to their EEG-defined individual typological characteristics was carried out. Primary psychopathologic disorders and ladasten effects were assessed by objective classification methods (factor and cluster analyses), and individual EEG types characterized by marked or reduced alpha rhythm were determined. No significant correlations between baseline EEG results and the initial mental condition indices were found. Significant differences ofladasten action in patients with different EEG types were found. It was established that, in patients with marked alpha rhythm corresponding to asthenic personal traits, ladasten exhibits predominantly a psychostimulant action assessed by clinical rating scales, which is accompanied by high frequencies of alpha rhythm increase and beta 1 and beta 2 rhythms decrease. In patients with reduced alpha rhythm and the EEG type corresponding to asthenic personal traits, ladasten action was characterized by an increase of alpha-rhythm low frequencies and the opposite reaction of beta 1 and beta 2 rhythms, whose are typical for the EEG pattern of anxiolytic effect. These results may indicate that the effect of ladasten depends on the initial brain activity level, which varies in patients with different individual typological traits.

A study of the brain's resting state based on alpha band power, heart rate and fMRI

Considering that there are several theoretical reasons why fMRI data is correlated to variations in heart rate, these correlations are explored using experimental resting state data. In particular, the possibility is discussed that the "default network", being a brain area that deactivates during non-specific general tasks, is a hemodynamic effect caused by heart rate variations. Of fifteen healthy controls ECG, EEG and fMRI were co-registered. Slice time dependent heart rate regressors were derived from the ECG data and correlated to fMRI using a linear correlation analysis where the impulse response is estimated from the data. It was found that in most subjects substantial correlations between heart rate variations and fMRI exist, both within the brain and at the ventricles. The brain areas with high correlation to heart rate are different from the "default network" and the response functions deviate from the canonical hemodynamic response function. Furthermore, a general negative correlation was found between heart beat intervals (reverse of heart rate) and alpha power. We interpret this finding by assuming that subject's state varies between drowsiness and wakefulness. Finally, given this large correlation, we re-examined the contribution of heart rate variations to earlier reported fMRI/alpha band correlations, by adding heart rate regressors as confounders. It was found that inclusion of these confounders most often had a negligible effect. From its strong correlation to alpha power, we conclude that the heart rate variations contain important physiological information about subject's resting state. However, it does not provide a full explanation of the behaviour of the "default network". Its application as confounder in fMRI experiments is a relatively small computational effort, but may have a substantial impact in paradigms where heart rate is controlled by the stimulus.

The effect of GSM-like ELF radiation on the alpha band of the human resting EEG

Mobile phone handsets such as those operating in the GSM network emit extremely low frequency electromagnetic fields ranging from DC to at least 40 kHz. As a subpart of an extended protocol, the influence of these fields on the human resting EEG has been investigated in a fully counter balanced, double blind, cross-over design study that recruited 72 healthy volunteers. A decrease in the alpha frequency band was observed during the 20 minutes of ELF exposure in the exposed hemisphere only. This result suggests that ELF fields as emitted from GSM handsets during the DTX mode may have an effect on the resting alpha band of the human EEG.

Modulation of gamma and alpha activity during a working memory task engaging the dorsal or ventral stream

Despite extensive experimental work in both animals and humans, the actual role of oscillatory brain activity for working memory maintenance remains elusive. Gamma band activity (30-100 Hz) has been hypothesized to reflect either the maintenance of neuronal representations or changing demands in attention. Regarding posterior alpha activity (8-13 Hz), it is under debate whether it reflects functional inhibition or neuronal processing required for the task. The aim of the present study was to further elucidate the role of oscillatory brain activity in humans using a working memory task engaging either the dorsal or ventral visual stream. We recorded brain activity using magnetoencephalography from subjects performing a delayed-match-to-sample task. Subjects were instructed to remember either the identity or the spatial orientation of shortly presented faces. The analysis revealed stronger alpha power around the parieto-occipital sulcus during retention of face identities (ventral stream) compared with the retention of face orientations (dorsal stream). In contrast, successful retention of face orientations was associated with an increase in gamma power in the occipital lobe relative to the face identity condition. We propose that gamma activity reflects the actual neuronal maintenance of visual representations, whereas the alpha increase is a result of functional inhibition.

Reduction in event-related alpha attenuation during performance of an auditory oddball task in schizophrenia

EEG frequency-domain analyses have demonstrated that cognitive performance produces a reduction in alpha activity, i.e., alpha attenuation, such as event-related desynchronization (ERD), reflecting brain activation. To examine whether schizophrenic patients have abnormalities in frequency-domain, event-related alpha attenuation, as well as in time-domain EEG phenomena, such as event-related potential, we compared alpha power change and P300 elicited simultaneously in response to the presentation of target tones in an auditory oddball paradigm between patients with schizophrenia and normal control subjects. In both patients and controls, alpha power was smaller during the time window of 512 ms following targets than following non-targets, particularly at the parietal and the posterior temporal locations (Pz, T5, and T6). The size of alpha attenuation measured as percent reduction in alpha power produced by targets relative to non-targets was smaller in patients than in controls at the posterior temporal locations. The size of alpha attenuation showed no correlation with P300 amplitude or latency in either patients or controls. Furthermore, in patients, the size of alpha attenuation showed no correlation with symptom severity, while P300 amplitude was correlated negatively with the positive subscale score of the Positive and Negative Syndrome Scale. These findings suggest that the symptom-independent reduction in event-related alpha attenuation in schizophrenia may be useful as an electrophysiological index of the impairment of neural processes distinct from that indexed by symptom-dependent P300 abnormalities.

Computing the center of mass for traveling alpha waves in the human brain

The phenomenon of traveling waves of the brain is an intriguing area of research, and its mechanisms and neurobiological bases have been unknown since the 1950s. The present study offers a new method to compute traveling alpha waves using the center of mass algorithm. Electroencephalographic alpha waves are oscillations with a characteristic frequency range and reactivity to closed eyes. Several lines of evidence derived from qualitative observations suggest that the alpha waves represent a spreading wave process with specific trajectories in the human brain. We found that during a certain alpha wave peak recorded with 30 electrodes the trajectory starts and ends in distinct regions of the brain, mostly frontal-occipital, frontal-frontal, or occipital-frontal, but the position of the trajectory at the time in which the maximal positivity of the alpha wave occurs has a definite position near the central regions. Thus we observed that the trajectory always crossed around the central zones, traveling from one region to another region of the brain. A similar trajectory pattern was observed for different alpha wave peaks in one alpha burst, and in different subjects, with a mean velocity of 2.1+/-0.29 m/s. We found that all our results were clear and reproducible in all of the subjects. To our knowledge, the present method documents the first explicit description of a spreading wave process with a singular pattern in the human brain in terms of the center of mass algorithm.

On light as an alerting stimulus at night

Light exposure at night increases alertness; however, it is not clear if light affects nocturnal alertness in the same way that it affects measures of circadian regulation. The purpose of this study was to determine if a previously established functional relationship between light and nocturnal melatonin suppression was the same as that relating light exposure and nocturnal alertness. Four levels of narrow-band blue light at the cornea were presented during nighttime sessions. The ratio of electroencephalographic alpha power density with eyes closed to eyes open (alpha attenuation coefficient, AAC) and the Norris mood scale were used. The AAC and ratings of alertness increased monotonically with irradiance and were highly correlated. Both measures of alertness were highly correlated with model predictions of nocturnal melatonin suppression for the same circadian light stimulus, consistent with the inference that the suprachiasmatic nuclei play an important role in nocturnal alertness as well as circadian regulation.

Extraction and localization of alpha activity of the brain in EEG and fMRI using constrained ICA

In order to extract only the alpha activity related EEG signals of the brain, we have applied constrained Independent Component Analysis (cICA), a new extension of ICA in which some a priori knowledge of alpha activity is utilized to extract desired components. Its performance has been compared to that of conventional band-pass filtering via the scalp power maps of alpha activity. The preliminary results show that cICA-extracted alpha signals produce the alpha power maps which spatially match the activated regions of the brain mapped using fMRI more closely than those from the band-pass filtered alpha EEG signals. The use of cICA might provide a more effective means of extracting EEG alpha activity of the brain.

Anticipatory electroencephalography alpha rhythm predicts subjective perception of pain intensity

This high-resolution electroencephalography (EEG) study tested the hypothesis that the suppression of rolandic alpha power before predictable painful stimulation affects the subject's subsequent evaluation of pain intensity, as a reflection of the influence of expectancy processes on painful stimulus processing. High-resolution EEG data were recorded (126 channels) from 10 healthy adult volunteers during the expectancy of a painful CO(2)-laser stimulation at the right wrist. Surface laplacian estimation enhanced the EEG spatial information content over 6 scalp regions of interest (left frontal, right frontal, left central, right central, left parietal, and right parietal areas). Spectral power was computed for 3 alpha sub-bands with reference to the individual alpha frequency peak (about 5-7 Hz for alpha 1, 7-9 Hz for alpha 2, and 9-11 Hz for alpha 3). The suppression of the alpha power before the painful stimulation [as reflected by the event-related desynchronization (ERD)] indexed the anticipatory cortical processes. Results showed maximum (negative) correlations between the alpha 2 and alpha 3 ERD amplitude at the left central area and the subjective evaluation of pain intensity (P < .001). The stronger the anticipatory alpha 2 and alpha 3 ERD, the higher the subjective evaluation of pain intensity. For alpha 3, that correlation was confirmed even when the effect of habituation across the recording session was taken into account. These results suggest that the anticipatory suppression of the alpha rhythms over the contralateral primary sensorimotor cortex predicts subsequent subjects' evaluation of pain intensity, in line with its crucial role for the discrimination of that intensity.

PERSPECTIVE

This electroencephalographic study showed that anticipatory activation/deactivation of sensorimotor cortex roughly predicts subjective evaluation of pain. This motivates further investigation on possible implications for the understanding of central chronic pain. Chronic pain patients might exaggerate the anticipatory activation of sensorimotor cortex to negligible pain stimuli.

How finger tapping practice enhances efficiency of motor control

Maximum-speed movements have been suggested to put maximum neural control demands on the primary motor cortex; hence, we are asking how primary motor cortex function changes to enable enhanced maximum movement rates induced by long-lasting practice. Cortical function was assessed by recording task-related spectral electroencephalogram alpha-power. Low-resolution brain electromagnetic tomography was used to localize intracortical neuronal sources. The main result is a decrease in neural activity in the left hemisphere (ipsilateral to trained hand) from pretraining to posttraining, whereas right hemispheric activity remained constant across training. This likely reflects the initially limited capacity of the right hemisphere to control demanding left-hand movements, but also highlights its ability to become more efficient with training, indicated by reduced involvement of the left primary motor cortex after training.

10 Hz flicker improves recognition memory in older people

BACKGROUND

10 Hz electroencephalographic (EEG) alpha rhythms correlate with memory performance. Alpha and memory decline in older people. We wished to test if alpha-like EEG activity contributes to memory formation. Flicker can elicit alpha-like EEG activity. We tested if alpha-frequency flicker enhances memory in older people. Pariticpants aged 67-92 identified short words that followed 1 s of flicker at 9.0 Hz, 9.5 Hz, 10.0 Hz, 10.2 Hz, 10.5 Hz, 11.0 Hz, 11.5 Hz or 500 Hz. A few minutes later, we tested participants' recognition of the words (without flicker).

RESULTS

Flicker frequencies close to 10 Hz (9.5-11.0 Hz) facilitated the identification of the test words in older participants. The same flicker frequencies increased recognition of the words more than other frequencies (9.0 Hz, 11.5 Hz and 500 Hz), irrespective of age.

CONCLUSION

The frequency-specificity of flicker's effects in our participants paralleled the power spectrum of EEG alpha in the general population. This indicates that alpha-like EEG activity may subserve memory processes. Flicker may be able to help memory problems in older people.

Classic electroencephalographic parameters: Median frequency, spectral edge frequency etc

Even today many anaesthesiologists rely on parameters of the autonomic nervous system, such as blood pressure and heart rate to decide if a patient is adequately anaesthetized. It is thought that the electroencephalogram (EEG) may provide more information on the state of anaesthesia. Because full EEG analysis is not possible in the operating room, processed EEG parameters have been developed comprising complex information into a single value. Time and frequency domain parameters are calculated. The power spectrum results from a Fourier analysis and can be described by parameters such as median frequency, spectral edge frequency and others. It was noted, however, that anaesthetics at low doses increase frequency of the EEG, whereas at high doses the EEG is depressed. This biphasic response makes it difficult to clearly distinguish the exact anaesthetic state of a patient. Median frequency and spectral edge frequency have been studied in numerous studies. However, no sole indicator has been derived from the EEG that could serve as a descriptor of anaesthetic depth.

Frontal alpha power asymmetry in aggressive children and adolescents with mood and disruptive behavior disorders

Building on prior research, which has suggested a relationship between aggression and left frontal activity, our study tested the hypothesis that proneness to impulsive aggression would be related to relative left frontal overactivation. EEG one-hertz resting alpha power frontal asymmetry was examined in 65 pediatric male psychiatric patients with a history of impulsive aggression and comorbid mood and disruptive behavior disorders. The strongest finding, which emerged from this analysis, was a finding of relative increases in left frontal activity compared with right frontal activity. The results also indicated that greater left frontal activity correlated positively with the severity of psychiatric disturbance. These findings suggest that relative increases in left frontal activity may be related to a locus of neurophysiological disruption associated with psychopathology characterized by behavioral and affective disinhibition. Results are discussed within a model of behavioral inhibition system-behavioral activation system theory.

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.

Amplitude and phase relationship between alpha and beta oscillations in the human electroencephalogram

The relationship between the electro-encephalographic (EEG) alpha and beta oscillations in the resting condition was investigated in the study. EEGs were recorded in 33 subjects, and alpha (7.5-12.5 Hz) and beta (15-25 Hz) oscillations were extracted with the use of a modified wavelet transform. Power, peak frequency and phase synchronisation were evaluated for both types of oscillation. The average beta-alpha peak frequency ratio was about 1.9-2.0 for all electrode derivations. The peak frequency of beta activity was within 70-90 % of the 95 % confidence interval of twice the alpha frequency. A significant (p < 0.05) linear regression was found between beta and alpha power in all derivations in 32 subjects, with the slope of the regression line being approximately 0.3. There was no significant difference in the slope of the line in different electrode locations, although the power correlation was strongest in the occipital locations where alpha and beta oscillations had the largest power. A significant 1:2 phase synchronisation was present between the alpha and beta oscillations, with a phase lag of about pi/2 in all electrode derivations. The strong frequency relationship between the resting beta and alpha oscillations suggests that they are generated by a common mechanism. Power and phase relationships were weaker, suggesting that these properties can be modulated by additional mechanisms as well as be influenced by noise. A careful distinction between alpha-dependent and alpha-independent beta activity should be considered when making statements about the possible significance of genuine beta activity in different neurophysiological mechanisms.

Frontal Brain Asymmetry and Reward Responsiveness: A Source-Localization Study

The influence of approach and avoidance tendencies on affect, reasoning, and behavior has attracted substantial interest from researchers across various areas of psychology. Currently, frontal electroencephalographic (EEG) asymmetry in favor of left prefrontal regions is assumed to reflect the propensity to respond with approach-related tendencies. To test this hypothesis, we recorded resting EEG in 18 subjects, who separately performed a verbal memory task under three incentive conditions (neutral, reward, and punishment). Using a source-localization technique, we found that higher task-independent alpha2 (10.5-12 Hz) activity within left dorsolateral prefrontal and medial orbitofrontal regions was associated with stronger bias to respond to reward-related cues. Left prefrontal resting activity accounted for 54.8% of the variance in reward bias. These findings not only confirm that frontal EEG asymmetry modulates the propensity to engage in appetitively motivated behavior, but also provide anatomical details about the underlying brain systems.

[Neurofeedback-based EEG alpha and EEG beta training. Effectiveness in patients with chronically decompensated tinnitus]

BACKGROUND

Persisting tinnitus is an often devastating disease condition with restricted and rarely successful therapeutic options.

PATIENTS AND METHODS

The present study investigates the therapeutic effect of short term neurofeedback-based EEG-Alpha- and EEG-Beta-training in 40 patients suffering from "chronic decompensated tinnitus". Patients were assigned to the Alpha or Beta group according to results of an initial EEG monitored stress-test. Four patients were excluded because they showed abnormal reactions in both EEG patterns.

RESULTS

During 12 sessions, 23 patients succeeded to increase EEG Alpha activity by 16% (p< or =0.042) while 13 patients achieved no decrease of EEG Beta activity. However, both groups showed a significant reduction of subjective tinnitus annoyance by the end of the therapy (p< or =0.001)

CONCLUSIONS

The results indicate that neurofeedback may represent a new promising technique in the therapy of chronic decompensated tinnitus. However, it remains to be established whether the reduction of tinnitus annoyance results from the altered brain activity patterns supported by the neurofeedback learning process.

Improvement of occipital alpha activity by repetitive hyperbaric oxygen therapy in patients with carbon monoxide poisoning: A possible indicator for treatment efficacy

OBJECTIVES

The main aim of this study was to evaluate the efficacy of repetitive hyperbaric oxygen (HBO) treatments with monitoring of quantitative electroencephalography (qEEG) for symptoms of acute carbon monoxide (CO) poisoning and prevention of delayed neuropsychiatric sequelae.

METHODS

Eight patients with acute CO poisoning received repetitive HBO treatments five times a week and qEEG was recorded once a week. Peak alpha frequency, peak alpha power, and absolute and relative alpha power in the occipital region were evaluated. The repetitive HBO treatments were discontinued when the peak alpha frequency increased to and maintained a maximum in each patient.

RESULTS

The mean number of HBO treatments was 20.3. The peak alpha frequency and the relative alpha power significantly increased after repetitive HBO treatments. The absolute alpha power and the peak alpha power insignificantly improved. Total numbers of HBO treatments were not correlated with age, duration of CO exposure, initial level of COHb, or interval to the first HBO treatment. After the completion of repetitive HBO treatments, no patient developed delayed neuropsychiatric sequelae.

CONCLUSIONS

These results suggest that repetitive HBO treatments may prevent the delayed neuropsychiatric sequelae of CO poisoning when applied individually with monitoring of the peak alpha frequency as an indicator of efficacy.

Evaluating the entrainment of the alpha rhythm during stroboscopic flash stimulation by means of coherence analysis

Two major conflicting hypotheses propose that alpha rhythm activity should be either the output of a linear filter having a white noise as input or reflect the output of a nonlinear oscillator. External stimulation can be employed to test for nonlinearity in alpha genesis, since an entrainment of such rhythmic activity (shift in the alpha peak) could only be explained by nonlinear relationships. Flash photic stimulation has been used to investigate such entrainment. Nevertheless, only entrainments due to the second harmonic of the stimulation could be suitably measured. Aiming at overcoming this limitation, a coherence-based technique is proposed for evaluating the strength of responses due to rhythmic stimulation. It was applied to the occipital EEG derivations of 12 normal subjects during stroboscopic stimulation. Entrainment of alpha rhythm by the second harmonic of the stimulation occurred in 75% of the subjects, whilst no spectral shifts were observed for the remained that exhibited broadband alpha peak at rest. However, stimulating with fundamental frequency close to that peak led to entrainment in all subjects. These differences in the degree of synchronization due to stimulation at the first and second harmonics should reflect complex nonlinear mechanisms in alpha genesis.

Anterior limbic alpha-like activity: a low resolution electromagnetic tomography study with lorazepam challenge

OBJECTIVE

To verify findings of an independently regulated anterior limbic alpha band source.

METHODS

In a randomised cross-over study, the spontaneous EEG was recorded in nine healthy subjects after i.v. lorazepam or placebo. Intracerebral current densities within classical frequency bands were estimated with low resolution electromagnetic tomography [LORETA] and compared between groups with t-statistical parametric mapping [SPM[t]]. A region-of-interest [ROI] based method was used to compare frontal and occipital alpha band activity changes.

RESULTS

Irrespective of treatment group, local maxima of alpha band power were localised both in the occipital lobe, Brodman area [BA] 18, and in the anterior cingulate cortex [ACC], BA 32. Statistical parametric mapping showed reduced parieto-occipital, but unaltered frontal alpha band power after lorazepam. This result was confirmed by ROI-based comparison of BA 18 and BA 32.

CONCLUSIONS

There was an anterior limbic maximum of alpha band activity which, unlike occipital alpha, was not suppressed by lorazepam.

SIGNIFICANCE

The well-known anterior alpha band components may originate from a narrowly circumscribed source, located in the ACC. Frontal and occipital alpha band activities appear to be independently regulated.

Alpha event-related desynchronization preceding a go/no-go task: a high-resolution EEG study

The authors delineated the time evolution of alpha event-related desynchronization over human frontal, parietal, and primary sensorimotor areas during the expectancy of a go/no-go task. The main issue under investigation was whether anticipatory processes impinged upon cortical areas in sequential or parallel mode. Compared with the control condition, in the experimental condition there was an Alpha 1 desynchronization over the central midline, an Alpha 2 desynchronization increasing over primary sensorimotor areas, and an Alpha 3 desynchronization increasing in parallel over bilateral primary sensorimotor areas. These processes had different temporal features. Results disclose an anticipatory activity of central midline areas and primary sensorimotor areas in both parallel and sequential modes. This reflects an adaptive, energy-consuming strategy rather than an economic waiting for the go stimulus.

Appearance of high-frequency alpha band with disappearance of low-frequency alpha band in EEG is produced during voluntary abdominal breathing in an eyes-closed condition

This study examined the effects of voluntary abdominal breathing (VAB) on the electroencephalogram (EEG) in 22 healthy subjects. VAB was characterized by prolonged rhythmic contraction of abdominal muscles for 20 min in an eyes-closed condition. The breathing rate was instructed to be very slow, i.e., 3-4 breaths/min (inspiratory time for 6-8s and expiratory time for 9-12s). A low-frequency alpha band appeared immediately after eye closing, but it later disappeared and was replaced by a new development of a high-frequency alpha band 4-5 min after the onset of VAB. The subjects had a feeling of vigor-activity with a tendency of reduced anxiety during and/or after VAB, as assessed by POMS and STAI questionnaire scores. On the other hand, during resting in the eye-closed condition, the disappearance of the low-frequency alpha band was replaced by the occurrence of a theta/delta band. The subjects became drowsy in this condition. We therefore conclude that the increase in high-frequency alpha activity is linked to the state of vigor-activity with a tendency of reduced anxiety. Since the urinary serotonergic level significantly increased after the VAB, we suggest that the serotonergic neurons within the brain may produce the changes in the EEG patterns.

Removal of time-varying gradient artifacts from EEG data acquired during continuous fMRI

OBJECTIVE

Recording low amplitude electroencephalography (EEG) signals in the face of large gradient artifacts generated by changing functional magnetic resonance imaging (fMRI) magnetic fields continues to be a challenge. We present a new method of removing gradient artifacts with time-varying waveforms, and evaluate it in continuous (non-interleaved) simultaneous EEG-fMRI experiments.

METHODS

The current method consists of an analog filter, an EEG-fMRI timing error correction algorithm, and a temporal principal component analysis based gradient noise removal algorithm. We conducted a phantom experiment and a visual oddball experiment to evaluate the method.

RESULTS

The results from the phantom experiment showed that the current method reduced the number of averaged samples required to obtain high correlation between injected and recovered signals, compared to a conventional average waveform subtraction method with adaptive noise cancelling. For the oddball experiment, the results obtained from the two methods were very similar, except that the current method resulted in a higher P300 amplitude when the number of averaged trials was small.

CONCLUSIONS

The current method enabled us to obtain high quality EEGs in continuous simultaneous EEG-fMRI experiments.

SIGNIFICANCE

Continuous simultaneous EEG-fMRI acquisition enables efficient use of data acquisition time and better monitoring of rare EEG events.

The EEG in metabolic encephalopathy and coma

Excellent early work on stupor and coma can be found (particularly with regard to anoxia) in the work of Fischgold and Mathis (1959) in France, and Pamela Prior in England (1973a). These workers correlated deepening levels of coma with particular EEG patterns, and the suppression of EEG reactivity. Alpha frequency patterns in coma (alpha coma), spindle-like sleep patterns in coma (spindle coma) and "triphasic waves" are among the wide variety of endocrine disorders discussed in case reports and series leading to identification of particular EEG patterns. EEG correlations with prognosis are most reliable with cardiorespiratory arrest (CRA) with its consequent anoxic-ischemic insult. If etiology is known, EEG can often be a reliable predictor of outcome. EEG usually has little specificity with regards to etiology, but some patterns do favor particular diagnoses: for example, triphasic waves (TWs) are frequently seen with hepatic and renal insufficiency in young adults; spindle coma patterns are believed to indicate dysfunction at the brainstem level (Chatrian, 1990). EEG is most useful in differentiating organic from psychiatric conditions, in excluding nonconvulsive status epilepticus (NCSE), and in providing a rough guide as to the degree of cortical and subcortical dysfunction.

Long-range temporal correlations in alpha and beta oscillations: effect of arousal level and test–retest reliability

OBJECTIVE

The aim of the present study was to evaluate test-retest reliability and condition sensitivity of long-range temporal correlations in the amplitude dynamics of electroencephalographic alpha and beta oscillations.

METHODS

Twelve normal subjects were measured two times with a test-retest interval of several days. Open- and closed-eyes conditions were used, representing different levels of arousal. The amplitude of the alpha and beta oscillations was extracted with bandpass filtering and the Hilbert transform. The long-range temporal correlations were quantified with detrended fluctuation analysis.

RESULTS

The amplitude dynamics of the alpha and beta oscillations demonstrated power-law long-range temporal correlations lasting for tens of seconds. These correlations were degraded in the open- compared to the closed-eyes condition. Test-retest statistics demonstrated that the long-range temporal correlations had significant reliability, which was greatest in the closed-eyes condition.

CONCLUSIONS

The presence of long-range temporal correlations indicates that the amplitude of neuronal oscillations at a given time is dependent on the amplitude at times as remote in the past as tens of seconds. The reliability of long-range temporal correlations suggests that the mechanisms generating the amplitude fluctuations are not perturbed over several days. The systematic changes in the scaling exponents at different levels of arousal indicate that these changes occur on many time scales (5-80 s) as a result of modifications in the intrinsic dynamics of the neuronal oscillations.

SIGNIFICANCE

This study demonstrates that the dynamics of spontaneous neuronal oscillations possess long-range temporal correlations with properties suitable for functional and clinical studies.

Frontal and central oscillatory changes related to different aspects of the motor process: a study in go/no-go paradigms

We studied alpha and beta EEG oscillatory changes in healthy volunteers during two different auditory go/no-go paradigms, in order to investigate their relationship with different components of the motor process. In the first paradigm (S2-centered), the initial tone (S1) was constant (warning), and the second tone (S2) indicated the subject whether to move or not. In the second paradigm (S1-centered), S1 indicated whether to move or not, while S2 just indicated the timing of the movement. A medial frontal beta energy increase was found in all conditions after the stimulus that forces the subject to decide whether to move or not (S1 or S2 depending on the paradigm). In both go conditions, a central alpha and beta energy decrease began after the go decision, reaching minimum values during the movement; it was followed by a beta post-movement increase, limited to the central contralateral area. In the no-go conditions, a marked fronto-central beta synchronization appeared after the decision not to move. In conclusion, our study was able to dissociate the beta oscillatory changes related to movement preparation and execution (central decrease/increase) from those associated with decision-making (medial frontal increase) and motor inhibition (fronto-central increase).

Spatially uniform and nonuniform analyses of electroencephalographic dynamics,with application to the topography of the alpha rhythm

Corticothalamic dynamics are investigated using a model in which spatial nonuniformities are incorporated via the coupling of spatial eigenmodes. Comparison of spectra generated using the nonuniform analysis with those generated using a uniform one demonstrates that, for most frequencies, local activity is only weakly dependent on activity elsewhere in the cortex; however, dispersion of low-wave-number activity ensures that distant dynamics influence local dynamics at low frequencies (below approximately 2 Hz ), and at the alpha frequency (approximately 10 Hz ), where propagating signals are inherently weakly damped, and wavelengths are large. When certain model parameters have similar spatial profiles, as is expected from physiology, the low-frequency discrepancies tend to cancel, and the uniform analysis with local parameter values is an adequate approximation to the full nonuniform one across the whole spectrum, at least for large-scale nonuniformities. After comparing the uniform and nonuniform analyses, we consider one possible application of the nonuniform analysis: studying the phenomenon of occipital alpha dominance, whereby the alpha frequency and power are greater at the back of the head (occipitally) than at the front. In order to infer realistic nonuniformities in the model parameters, the uniform version of the model is first fitted to data recorded from 98 normal subjects in a waking, eyes-closed state. This yields a set of parameters at each of five electrode sites along the midline. The inferred parameter nonuniformities are consistent with anatomical and physiological constraints. Introducing these spatial profiles into the full nonuniform model then quantitatively reproduces observed site-dependent variations in the alpha power and frequency. The results confirm that the frequency shift is mainly due to a decrease in the corticothalamic propagation delay, but indicate that the delay nonuniformity cannot account for the observed occipital increase in alpha power; the occipital alpha dominance is due to decreased cortical gains and increased thalamic gains in occipital regions compared to frontal ones.

Gamma→Alpha Linkage and Persistent Firing of Ia Fibers by Pudendal Nerve Stimulation in the Decerebrate Cat

The sensory pudendal nerve (SPN) was stimulated in decerebrate female cats. Spikes of single Ia muscle spindle afferents from the medial gastrocnemius (MG) muscle were recorded in dorsal root filaments. Electroneurography (ENG) was recorded in a cut nerve filament to the MG muscle; MG electromyography (EMG) was also recorded. Single shock to SPN induced discharges of small ENG spikes (SS) with similar amplitude to that of gamma spikes elicited by ventral root stimulation. Thus SS were identified as gamma spikes. The latency of the gamma discharge was ∼15 ms. As expected, the onset of the gamma discharge preceded a discharge of Ia spikes; the time difference between both discharges was ∼5 ms. After the initial bursts, the Ia and the gamma activities paused during 20–30 ms but later increased again to last ∼1 s. After the shock, the EMG activity was depressed during ∼50 ms; later, motor-unit spikes may show transient activation. Thus the onset of the gamma activation preceded the activation of motor units (gamma→alpha link). Trains of shocks (1 or 100 Hz) to SPN induced a sustained increase in the frequency of gamma spikes, Ia spikes, and motor units that outlasted the train by 20–120 s. The sustained firing of Ia fibers might trigger or help to trigger and maintain the response of alpha-motoneurons.

Sub-second "temporal attention" modulates alpha rhythms. A high-resolution EEG study

In the present high-resolution electroencephalographic (EEG) study, event-related desynchronization/synchronization (ERD/ERS) of alpha rhythms was computed during an S1-S2 paradigm, in which a visual cue (S1) predicted a SHORT (600 ms) or LONG (1400 ms) foreperiod, preceding a visual go stimulus (S2) triggering right or left finger movement. Could orienting attention to a selective point in time influence the alpha rhythms as a function of the SHORT vs. LONG foreperiod? Stronger selective attentional modulations were predicted for the SHORT than LONG condition. EEG data from 54 channels were "depurated" from phase-locked visual evoked potentials and spatially enhanced by surface Laplacian estimation (i.e., final data analysis was conducted on 16 subjects having a sufficient number of artifact-free EEG single trials). Low-band alpha rhythms (about 6-10 Hz) were supposed to be related to anticipatory attentional processes, whereas high-band alpha rhythms (10-12 Hz) would indicate task-specific visuo-motor processes. Compared to the LONG condition (foreperiod), the SHORT condition induced a quicker and stronger ERS at low-band alpha rhythm (about 6-8 Hz) over midline and bilateral prefrontal, sensorimotor, and posterior parietal areas. In contrast, the concomitant high-band alpha (about 10-12 Hz) ERD/ERS showed no significant difference between the two conditions. In conclusion, temporal attention for a sub-second delay (800 ms) did modulate low-band alpha rhythm over large regions of both cortical hemispheres.

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.

EEG alpha power changes reflect response inhibition deficits after traumatic brain injury (TBI) in humans

Brain damage due to traumatic brain injury (TBI) has been associated with deficits in executive functions and the dynamic control of behaviour. Event-related brain potentials and spectral power data were recorded from eight TBI participants and eight matched controls while they completed a Go/NoGo response inhibition task. The TBI group was found to be significantly impaired at the task compared to controls, and exhibited abnormal N2 and P3 waveform components in response to NoGo stimuli relative to controls. Significant correlations were also found between alpha power, Go-trial RT and errors. We conclude that abnormal activity in the structures damaged in this group may render such patients less capable of maintaining a state of alpha desynchronisation compared to controls, resulting in poorer performance on the task.

Phase-locked alpha and theta oscillations generate the P1–N1 complex and are related to memory performance

An oscillatory phase resetting model is presented and data are reported which indicate that early components of the event-related potential are due to the superposition of evoked oscillations. The following hypotheses were tested and could be confirmed: (i) theta and alpha show a significant increase in phase locking during the time window of the P1 and N1 as compared to a prestimulus reference, (ii) the dynamics of event-related changes in evoked theta and alpha power obey the same principles as are known from event-related de-/synchronization research, and (iii) latency measures of the P1-N1 complex are negatively correlated with individual alpha frequency. In addition, we have found that theta phase locking is larger during encoding than recognition and that good memory performers show a larger increase in theta and alpha phase locking during recognition in the time window of the N1. Our general conclusion is that the P1-N1 complex is generated primarily by evoked alpha and theta oscillations reflecting the synchronous activation of a working- and semantic memory system.

Estimation of Nonstationary EEG With Kalman Smoother Approach: An Application to Event-Related Synchronization (ERS)

An adaptive spectrum estimation method for nonstationary electroencephalogram by means of time-varying autoregressive moving average modeling is presented. The time-varying parameter estimation problem is solved by Kalman filtering along with a fixed-interval smoothing procedure. Kalman filter is an optimal filter in the mean square sense and it is a generalization of other adaptive filters such as recursive least squares or least mean square. Furthermore, by using the smoother the unavoidable tracking lag of adaptive filters can be avoided. Due to the properties of Kalman filter and benefits of the smoothing the time-frequency resolution of the presented Kalman smoother spectra is extremely high. The presented approach is applied to estimation of event-related synchronization/desynchronization (ERS/ERD) dynamics of occipital alpha rhythm measured from three healthy subjects. With the Kalman smoother approach detailed spectral information can be extracted from single ERS/ERD samples.

Sensitivity of human EEG alpha band desynchronization to different working memory components and increasing levels of memory load

Event-related alpha band desynchronization is frequently used to analyze spatiotemporal cortical activation patterns during the performance of cognitive tasks. In the present paper the sensitivity of alpha band desynchronization to increasing levels of cognitive load and to different cognitive working memory components is investigated. A 27-channel electroencephalogram of 62 participants while solving (a) a short-term memory and (b) a working memory task (dual task), each with five levels of memory load, was analyzed. We found (a) a linearly increasing desynchronization in the upper alpha band with ascending cognitive load, and (b) evidence of the involvement of distinguishable cognitive components (storage and controlled attention) in the memory tasks.

Anoxic-ischemic alpha coma: prognostic significance of the incomplete variant

The prognostic significance of post-anoxic-ischemic alpha coma (AC) is controversial. We recorded somatosensory evoked potentials (SEPs) and performed serial electroencephalography (EEG) in a 60-year-old woman in coma after cardiac arrest. The first EEG was recorded after 48 hours (GCS=5; E1-V1-M3); brain-stem reflexes were preserved. The EEG pattern showed monotonous alpha frequencies (10-11 Hz) with posterior predominance; acoustic and noxious stimuli evoked EEG reactivity. Early cortical SEPs (72 h) were normal. On the fifth day (GCS=8; E4-V1-M3), the EEG alpha pattern was replaced by a diffuse delta activity; rhythmic theta changes appeared spontaneously or in response to stimuli. The patient regained consciousness on the tenth day and EEG showed posterior theta activity (6-7 c/s) partially reactive to stimuli. At the 6-month follow-up, cognitive evaluation showed mild dementia. Recent studies identified two forms of AC. Patients with complete AC have an outcome that is almost invariably poor. Conversely, incomplete AC (posteriorly accentuated alpha frequency, reactive and with SEPs mostly normal) reflects a less severe degree of anoxic-ischemic encephalopathy. The case we report should be classified, according to the SEPs and EEG features, as incomplete AC. The fact that the patient has regained consciousness, even if with residual cognitive impairment, confirms the need to distinguish this variant from complete AC.

Subjective sleepiness correlates negatively with global alpha (8-12 Hz) and positively with central frontal theta (4-8 Hz) frequencies in the human resting awake electroencephalogram

Subjective sleepiness is part of the system controlling the decision to go to sleep in humans. Extended periods of waking lead to increased sleepiness, as well as to changes in cortical electroencephalogram (EEG) during waking. We investigated the association of sleepiness and awake EEG spectra during 40 h of wakefulness using multi-electrode EEG recordings for full coverage of the scalp. We found: (1). strong negative correlations of alpha (8-12 Hz) power with subjective sleepiness at all scalp locations, suggesting a negative association between sleepiness and general cortical activation; and (2). positive correlations of theta (4-8 Hz) power with subjective sleepiness with a focus on frontal locations, suggesting additional location specific associations between sleepiness and cortical activation. These findings support the notion that sleepiness is directly represented in the awake EEG.

Kognitive Prozesse und dynamische Zeitstrukturen. Vorstellung eines Meßgerätes zur Untersuchung der Mikro-Vigilanz-Shift-(MVS-)Hypothese. Cognitive Processes and Dynamical Time Structures. Introduction of a Method for Testing the Microvigilance Shift (MVS) Hypothesis

The psychophysiological measuring method for the determination of the auditory order threshold (OT) is steadily gaining in importance, both for the diagnosis and treatment of speech disorders. Observed intraindividual variability of (macro-) vigilance led to the hypothesis of discontinuous cognitive processing in the central nervous system. The base for the variability of microvigilance is hypothesized to be in the phase difference of the alpha rhythm. To test for this hypothesis, we developed an EEG-comparator, which allows for a phase-dependent triggering of external stimuli. In direct comparison with stochastic (i.e. non-phase-dependent) stimulus presentation, the threshold in phase-dependent OT-testing is distinctly lower. Optimal results occurred at phase angels of phi = 90 degrees and phi = 270 degrees. Our findings support the hypothesis of a correlation between alpha rhythm and vigilance processes. Furthermore, there seems to be evidence that memory processes go with changes in vigilance, and in this context the alpha phase correlation seems to be important.

Paradox lost? Exploring the role of alpha oscillations during externally vs. internally directed attention and the implications for idling and inhibition hypotheses

Although slow waves of the electroencephalogram (EEG) have been associated with attentional processes, the functional significance of the alpha component in the EEG (8.1-12 Hz) remains uncertain. Conventionally, synchronisation in the alpha frequency range is taken to be a marker of cognitive inactivity, i.e. 'cortical idling'. However, it has been suggested that alpha may index the active inhibition of sensory information during internally directed attentional tasks such as mental imagery. More recently, this idea has been amended to encompass the notion of alpha synchronisation as a means of inhibition of non-task relevant cortical areas irrespective of the direction of attention. Here we test the adequacy of the one idling and two inhibition hypotheses about alpha. In two experiments we investigated the relation between alpha and internally vs. externally directed attention using mental imagery vs. sensory-intake paradigms. Results from both experiments showed a clear relationship between alpha and both attentional factors and increased task demands. At various scalp sites alpha amplitudes were greater during internally directed attention and during increased load, results incompatible with alpha reflecting cortical idling and more in keeping with suggestions of active inhibition necessary for internally driven mental operations.

Modulation of θ/α frequency profiles of slow auditory-evoked responses in the songbird zebra finch

Spatiotemporal patterns of forebrain neural activity associated with auditory perception of biologically relevant complex acoustic stimuli can be conveniently studied in the songbird zebra finch. Here we present a time-frequency analysis of averaged slow auditory-evoked potentials (sAEPs) obtained at electrode locations overlying the main song control nucleus, high vocal center. Gabor spectrograms of these sAEPs show a prolonged response time course consisting of unimodal frequency peaks in the theta/alpha range (4-17 Hz). There is a stimulus-dependent modulation of the duration of the response and of the total number of its constituent frequency peaks, an effect that is bilateral in 75% of the birds and lateralized to the left side in the remaining 25%. Since the state of alertness of birds modulates these parameters along a similar continuum, these findings suggest that modulation of sAEP frequency profile may be dependent on attentional mechanisms. The presence and modulation of neurobiologically ubiquitous dominant frequency components also implicate the possible role of induced cerebral neuronal circuit oscillations in songbird auditory perception.

Intra- and inter-hemispheric coupling of electroencephalographic 8-13 Hz rhythm in humans and force of static finger extension

The coupling of electroencephalographic (EEG) 8-13 Hz oscillations during static right finger extension performed under four different force levels was analyzed in 12 right-handed subjects. Increases in force of static muscle contraction were accompanied by increases in the 8-13 Hz band coherence between the contralateral sensorimotor area (S1/M1) and the ipsilateral S1/M1, frontal and parietal cortex, between supplementary motor area and bilateral S1/M1, and between posterior parietal cortex and bilateral S1/M1. The results suggest increased functional coupling between primary and higher-order motor areas during increased motor effort.

Event-related alpha and theta responses in a visuo-spatial working memory task

OBJECTIVE

To explore the reactivity of the theta and alpha rhythms during visuo-spatial working memory.

METHODS

One hundred and seventy-four subjects performed a delayed response task. They had to remember the spatial location of a target stimulus on a computer screen for a 1 or a 4s retention interval. The target either remained visible throughout the entire interval (sensory trials) or disappeared after 150ms (memory trials). Changes in induced band power (IBP) in the electroencephalogram (EEG) were analyzed in 4 narrow, individually adjusted frequency bands between 4 and 12Hz.

RESULTS

After presentation of the target stimulus, a phasic power increase was found, irrespective of condition and delay interval, in the lower (roughly, 4-8Hz) frequency bands, with a posterior maximum. During the retention interval, sustained occipital-parietal alpha power increase and frontal theta power decrease were found. Most importantly, the memory trials showed larger IBP decreases in the theta band over frontal electrodes than the sensory trials.

CONCLUSIONS

The phasic power increase following target onset is interpreted to reflect encoding of the target location. The sustained theta decrease, which is larger for memory trials, is tentatively interpreted to reflect visuo-spatial working memory processes.

Source localization of MEG sleep spindles and the relation to sources of alpha band rhythms

OBJECTIVE

First, to determine the distribution of the estimated sources of sleep spindles, and alpha and mu rhythms based on whole-head magnetoencephalogram (MEG) recordings; second, to scrutinize the physiological relevance of the dipole fit algorithm in localizing on-going normal rhythmic activities.

METHODS

One hundred and fifty-one channels were used to record spontaneous MEG activity during wakefulness and superficial sleep in 4 normal subjects. The equivalent dipolar sources were estimated by a new 'dipole fit algorithm' and projected on the corresponding magnetic resonance images.

RESULTS

Equivalent dipoles of MEG spindles were distributed over the centro-parietal region. Those of alpha rhythms were concentrated around the occipito-parietal sulcus and those of mu rhythms were confined to the area around the central sulcus.

CONCLUSIONS

MEG sleep spindles, and alpha and mu rhythms have distinct spatial distributions of their equivalent dipolar sources. This demonstrates that various cortical regions that oscillate within the same frequency band have different spatial organizations and different functional aspects.