EEG, auditory evoked potentials and evoked rhythmicities in three-year-old children

ECG Approximate Entropy in the Elderly during Cycling Exercise

Approximate entropy (ApEn) is used as a nonlinear measure of heart-rate variability (HRV) in the analysis of ECG time-series recordings. Previous studies have reported that HRV can differentiate between frail and pre-frail people. In this study, EEGs and ECGs were recorded from 38 elderly adults while performing a three-stage cycling routine. Before and after cycling stages, 5-min resting-state EEGs (rs-EEGs) and ECGs were also recorded under the eyes-open condition. Applying the K-mean classifier to pre-exercise rs-ECG ApEn values and body weights revealed nine females with EEG power which was far higher than that of the other subjects in all cycling stages. The breathing of those females was more rapid than that of other subjects and their average heart rate was faster. Those females also presented higher degrees of asymmetry in the alpha and theta bands (stronger power levels in the right frontal electrode), indicating stressful responses during the experiment. It appears that EEG delta activity could be used in conjunction with a very low ECG frequency power as a predictor of bursts in the heart rate to facilitate the monitoring of elderly adults at risk of heart failure. A resting ECG ApEn index in conjunction with the subject's weight or BMI is recommended for screening high-risk candidates prior to exercise interventions.

Conscious and Non-conscious Representations of Emotional Faces in Asperger's Syndrome

Several neuroimaging studies have suggested that the low spatial frequency content in an emotional face mainly activates the amygdala, pulvinar, and superior colliculus especially with fearful faces(1-3). These regions constitute the limbic structure in non-conscious perception of emotions and modulate cortical activity either directly or indirectly(2). In contrast, the conscious representation of emotions is more pronounced in the anterior cingulate, prefrontal cortex, and somatosensory cortex for directing voluntary attention to details in faces(3,4). Asperger's syndrome (AS)(5,6) represents an atypical mental disturbance that affects sensory, affective and communicative abilities, without interfering with normal linguistic skills and intellectual ability. Several studies have found that functional deficits in the neural circuitry important for facial emotion recognition can partly explain social communication failure in patients with AS(7-9). In order to clarify the interplay between conscious and non-conscious representations of emotional faces in AS, an EEG experimental protocol is designed with two tasks involving emotionality evaluation of either photograph or line-drawing faces. A pilot study is introduced for selecting face stimuli that minimize the differences in reaction times and scores assigned to facial emotions between the pretested patients with AS and IQ/gender-matched healthy controls. Information from the pretested patients was used to develop the scoring system used for the emotionality evaluation. Research into facial emotions and visual stimuli with different spatial frequency contents has reached discrepant findings depending on the demographic characteristics of participants and task demands(2). The experimental protocol is intended to clarify deficits in patients with AS in processing emotional faces when compared with healthy controls by controlling for factors unrelated to recognition of facial emotions, such as task difficulty, IQ and gender.

Auditory evoked potential response and hearing loss: a review

Hypoacusis is the most prevalent sensory disability in the world and consequently, it can lead to impede speech in human beings. One best approach to tackle this issue is to conduct early and effective hearing screening test using Electroencephalogram (EEG). EEG based hearing threshold level determination is most suitable for persons who lack verbal communication and behavioral response to sound stimulation. Auditory evoked potential (AEP) is a type of EEG signal emanated from the brain scalp by an acoustical stimulus. The goal of this review is to assess the current state of knowledge in estimating the hearing threshold levels based on AEP response. AEP response reflects the auditory ability level of an individual. An intelligent hearing perception level system enables to examine and determine the functional integrity of the auditory system. Systematic evaluation of EEG based hearing perception level system predicting the hearing loss in newborns, infants and multiple handicaps will be a priority of interest for future research.

AUDITORY ON- AND OFF-RESPONSES AND ALPHA OSCILLATIONS IN THE HUMAN EEG

In the present study, the wide band alpha and sub-bands of alpha in the auditory on- and off-responses to different stimulation frequencies were evaluated. Auditory on- and off-responses of 12 healthy volunteers (average 17 years old) were recorded from five locations (Fz, Cz, Pz, P3, and P4). The auditory stimuli of 80 dB SPL and 1000 ms duration were delivered at six different stimulation frequencies (f1-f6; 0.2, 0.6, 1, 2, 3, and 4 kHz, respectively). In using individual alpha frequency (IAF) as individual anchor point, wide band alpha and three different alpha frequency sub-bands with a bandwidth of 2 Hz each were defined: lower-1 alpha, lower-2 alpha, and upper alpha. The Root Mean Square (RMS) values of the alpha frequency bands were computed for two time periods: +/- 3 sd around the mean peak latency of the auditory on-responses (t1-on and t2-on) and a time window of the same length of the auditory off-responses (t1-off and t2-off). The alpha RMS values of both on- and off- responses showed significant differences between t1 and t2 periods on wide band, lower-1 and lower-2 alpha bands, especially at 0.2, 0.6, 1, 2, and 3 kHz stimulation frequencies in all recording places. Amplitudes in anterior locations (Fz, Cz) were higher than the others. These observations may provide a preliminary but nonetheless important understanding of how information may be processed in the brain.

Darwin's evolution theory, brain oscillations, and complex brain function in a new "Cartesian view"

Comparatively analyses of electrophysiological correlates across species during evolution, alpha activity during brain maturation, and alpha activity in complex cognitive processes are presented to illustrate a new multidimensional "Cartesian System" brain function. The main features are: (1) The growth of the alpha activity during evolution, increase of alpha during cognitive processes, and decrease of the alpha entropy during evolution provide an indicator for evolution of brain cognitive performance. (2) Human children younger than 3 years are unable to produce higher cognitive processes and do not show alpha activity till the age of 3 years. The mature brain can perform higher cognitive processes and demonstrates regular alpha activity. (3) Alpha activity also is significantly associated with highly complex cognitive processes, such as the recognition of facial expressions. The neural activity reflected by these brain oscillations can be considered as constituent "building blocks" for a great number of functions. An overarching statement on the alpha function is presented by extended analyzes with multiple dimensions that constitute a "Cartesian Hyperspace" as the basis for oscillatory function. Theoretical implications are considered.

Auditory processing indexed by stimulus-induced alpha desynchronization in children

By means of magnetoencephalography (MEG), we investigated event-related synchronization and desynchronization (ERS/ERD) in auditory cortex activity, recorded from twelve children aged four to six years, while they passively listened to a violin tone and a noise-burst stimulus. Time-frequency analysis using Wavelet Transform was applied to single-trials of source waveforms observed from left and right auditory cortices. Stimulus-induced changes in non-phase-locked activities were evident. ERS in the beta range (13-30 Hz) lasted only for 100 ms after stimulus onset. This was followed by prominent alpha ERD, which showed a clear dissociation between the upper (12 Hz) and lower (8 Hz) alpha range in both left and right auditory cortices for both stimuli. The time courses of the alpha ERD (onset around 300 ms, peak at 500 ms, offset after 1500 ms) were similar to those previously found for older children and adults with auditory memory related tasks. For the violin tone only, the ERD lasted longer in the upper than the lower alpha band. The findings suggest that induced alpha ERD indexes auditory stimulus processing in children without specific cognitive task requirement. The left auditory cortex showed a larger and longer-lasting upper alpha ERD than did the right auditory cortex, likely reflecting hemispheric differences in maturational stages of neural oscillatory mechanisms.

A Developmental Investigation of Stop-Signal Inhibition

Abstract. The present study examined the development of response inhibition in the stop-signal task across child (8-13 years), young-adult (18-22 years), and middle-aged adult (29-47 years) groups through a dissociation of low- and higher-frequency ERP activity. Fifty-one subjects (n = 17 in each group) performed the stop-signal task, which consisted of a visual choice reaction time (RT) task and auditory stop-signals, while EEG was recorded. The original EEG data (0.01-30 Hz) was subsequently filtered to separate slow-wave (0.01-2 Hz) and residual (2-30 Hz) activity. Performance findings revealed that stop-signal reaction time (SSRT) decreased from the child to young-adult group and then showed a small increase in the middle-aged adult group. Original ERPs revealed decreasing N1 and N2 amplitudes and increasing P2 and P3 amplitudes across the scalp with increasing age for successful-stop trials. These developmental effects did not occur in the residual waveforms after removal of slow-wave activity. For failed-stop trials, a response-locked negative component, identified as the error-negativity (Ne), showed an age-related decrease in amplitude across the scalp in the residual, but not the original, waveform. The error-positivity (Pe) increased in amplitude with age in the original data, but this was accounted for by a positive slow-wave (PSW). Together, the findings suggest that underlying slow-wave activity accounts for a large number of developmental effects in the traditionally quantified ERP components, but may also obscure effects occurring in residual activity. These findings highlight the importance of dissociating low- and higher-frequency ERP activity in developmental research.

Event-related slow-wave activity in two subtypes of attention-deficit/hyperactivity disorder

OBJECTIVE

Previous time-frequency studies have indicated that event-related low-frequency activity has important effects on component topography and developmental effects in auditory event-related potentials (ERPs) of children and adolescents. This study investigated the influence of event-related slow-wave (SW) (0.01-2 Hz) activity in the group differences seen between children with and without attention-deficit/hyperactivity disorder (AD/HD) of different subtypes.

METHODS

Time-frequency analysis techniques were applied to auditory ERP data derived from children with AD/HD predominantly inattentive type (n = 30), AD/HD combined type (n = 30) and age-matched control subjects (n = 30).

RESULTS

Event-related early frontal negative and late posterior positive SW components were reduced in the AD/HD combined type group, but not AD/HD inattentive type group, relative to controls. The RESIDUAL ERPs, which represented event-related 2-12 Hz activity, showed clinical vs. control group differences in components that were similar in both AD/HD subtype groups.

CONCLUSIONS

The time-frequency results showed that event-related SW (0.1-2 Hz) activity contributes importantly to group differences between AD/HD and control children, and the pattern of group differences from controls for each of the AD/HD subtype groups, which are evident in raw ERPs. These results emphasise both the clinical and developmental importance of this form of analysis.

SIGNIFICANCE

This novel approach revealed additional specific information about stimulus processing and regional inhibition/activation in two AD/HD subtypes, relative to control subjects.

Age effects on visual EEG responses reveal distinct frontal alpha networks

OBJECTIVES

The present study aimed to describe the effect of aging on single-trial visual alpha responses.

METHODS

Visual evoked potentials were recorded at F3, Cz, P3, and O1 in 12 young (20-30-year-olds) and in 10 middle-aged adults (50-55-year-olds). Slow (7-10 Hz) and fast (10-15 Hz) alpha frequency bands were analyzed. Three parameters of single alpha responses were assessed for the 0-300 ms period after stimulus: (i) maximal single-sweep amplitude; (ii) phase-locking with stimulus, and (iii) enhancement of post-stimulus relative to pre-stimulus alpha activity.

RESULTS

Ongoing alpha activity at anterior sites was larger in middle-aged subjects. Age differences in response amplitude depended on the anterior shift of ongoing alpha activity. Over fronto-central areas, the phase-locking of fast alpha responses was significantly increased, whereas the phase-locking of slow alpha responses was decreased in middle-aged compared to young adults, independently of amplitude. In contrast to slow alpha responses, frontal and occipital fast alpha responses were interrelated.

CONCLUSIONS

These observations are in accordance with previous findings from the auditory modality implying that the age-related changes in frontal alpha oscillations are modality-independent. Slow and fast frontal alpha responses were affected differentially by the age, which might reflect the activations of functionally distinct alpha networks.

Event-related alpha oscillations in task processing

OBJECTIVES

Recent findings substantiate the view that electroencephalographic (EEG) alpha rhythm (7-13 Hz) is functionally involved in information processing. However, the association of alpha rhythms with cognitive brain processes is less well understood because both augmentation and suppression of alpha oscillations have been observed to accompany task performance. The present study evaluates the effect of task processing on event-related alpha oscillations at the level of single-sweep analysis.

METHODS

EEG was recorded from Fz, Cz and Pz electrodes in 10 subjects participating in two experimental sessions, in which auditory stimuli with equal physical parameters were presented under different instructions (passive and task). Separate measurements of single-sweep amplitude and phase-locking were performed and statistically analyzed for consecutive time windows in the poststimulus epoch.

RESULTS

Major results show that, during the cognitive task, the phase-locking of alpha oscillations at the frontal site is significantly increased for the time window of 500-1000 ms after stimulation.

CONCLUSIONS

The involvement of enhanced and synchronized frontal alpha activity in higher brain processes is strongly emphasized.

An investigation of the event-related slow-wave potential (0.01-2 HZ) in normal children

Previous research has indicated that the auditory ERPs of children are dominated by a frontal negative slow-wave. This paper outlines a preliminary attempt to separate event-related low-frequency activity from traditional ERP components as found in older subjects. An active auditory oddball task was completed by 30 normal children aged from 8 to 18 years, and ERPs to target and standard stimuli were derived. The original ERP files were digitally filtered to calculate separate ERPs containing only 0.01-2 Hz activity (termed the SW-ERP) or 2-12 Hz activity (termed the RESIDUAL ERP) for each subject. The SW-ERP was maximally correlated with the slow-wave factor from a principal components analysis of the original target and standard waveforms. The SW-ERPs to target stimuli contained an early negative component which showed an age-related decrease, and a late positive component which did not. The SW-ERP was found to be partly responsible for the differences in component amplitude and morphology between sites observed in the raw ERPs.

EEG theta and frontal alpha oscillations during auditory processing change with aging

The present study assessed the effect of age on time and frequency components of auditory evoked potentials in two groups of adults, young (18-30 years old) and middle-aged (50-55 years old). Averaged and single-sweep potentials were analyzed. Analysis of single alpha and theta responses was performed for 3 parameters - single-sweep amplitude, phase-locking, and enhancement. Significant age differences were revealed only at the level of single sweeps: (i) at the 3 mid-line locations (Fz, Cz, and Pz), middle-aged adults manifested theta phase-locking and enhancement which were significantly stronger than those in young adults; and (ii) in contrast, only over the frontal brain area were the alpha responses stronger in phase-locking and enhancement in the middle-aged than in young subjects. Thus, the analysis of frequency responses at the level of single sweeps enabled us to reveal age differences in simple auditory stimulus processing that were otherwise not detectable in the averaged potential. The results imply that the alpha response system may relate to frontal brain functioning during aging.

Developmental changes in the event-related EEG theta response and P300

Event-related potentials (ERPs) from 50 children (6-11 years) and 10 adults were elicited by auditory passive, and by rare target and frequent non-target stimuli, and analyzed in the time and frequency domains. The latency of the maximal theta response (or the theta frequency component of the ERP) was evaluated with respect to age and scalp topography effects. The major findings were: (1) The latency of the maximal theta response decreased with increasing age in children, although for each stimulus type and location adults had shorter latencies than the children. (2) The developmental time course of latency reduction depended on the electrode location, with the most prominent reduction occurring at 8 years at Cz, and no differences between children groups obtained for the frontal site. (3) Maximal theta response latency was strongly associated with the latency of the late parietal P400-700 (P3b) component in children. The results suggest that the developmental latency decrease in P300 processes originate from a decrease in the preceding theta-related processes and may reflect a speeding of cognitive stimulus evaluation.

Alpha response system in children: changes with age

Evoked and event-related brain potentials (Eps, ERPs) may be regarded as originating from the reorganization of the spontaneous EEG rhythms (Başar, 1980). Until now, no data is available about the development of the evoked frequency components in EPs and ERPs of children. The main objective of the present research was to study the alpha response system in 6-11-year-old children. We suggested that the ability to reorganize the alpha activity and produce repeatable alpha patterns after external stimulation might undergo developmental changes that could reflect certain changes in information processing with increasing age from childhood to adulthood. Fifty 6-11-year-old children divided into five age groups, and 10 young adults were studied in a passive and an odd-ball condition. Alpha responses in the auditory EPs and non-target ERPs at Fz, Cz and Pz were analyzed. The magnitude and phase-locking with stimulus of single alpha responses were evaluated in the first 300 ms of the post-stimulus epoch. An original method was applied to assess quantitatively the repeatability (phase-locking) of the evoked alpha oscillations. The magnitude and the phase-locking to stimulus were analyzed with respect to their dependence on the age and topography factors. Our main results show that the alpha responses in 6-11-year-old children are different from those in adults: (1) Adults had significantly lower amplitude and stronger phase-locking than children; (2) Adults had maximal alpha amplitudes and phase-locking over the vertex, whereas children displayed maximal responses over the parietal site; (3) The phase-locking of eldest (10-11-year-old) children was as strong as in adults. Whereas no difference existed between groups of children in alpha response amplitudes, a significant increase in phase-locking from 6 to 11 years was observed. Concerning the obtained results we suggest that (1) Alpha response system is functionally involved in 6-11-year-old children, though its development is not complete at the age of 11, the upper limit of our sample (2) With regard to their differential developmental time-courses, the magnitude and the phase-locking parameters might be suggested to relate to different functional aspects of the alpha response system. The applied original method makes it possible to analyze the phase-locking to stimulus (or phase-reordering) separately and independently from the amplitude (enhancement) of the frequency responses, thus providing for a deeper examination of the evoked frequency components.

Brain theta response predicts P300 latency in children

The present study assessed the relationship between stimulus-induced electroencephalographic (EEG) theta activity (4-7 Hz) and the endogenous component P300 of auditory event-related potentials (ERPs) using a developmental model. ERPs were recorded from 50 children (6-11 years old) for oddball target and frequent non-target stimuli and analysed in the time and frequency domains. The latency of the maximal theta response of the digitally filtered (4-7 Hz) ERPs was evaluated with respect to age and scalp topography effects. The maximal theta response latency at Cz and Pz decreased with increasing age and entirely predicted the developmental latency reduction of the parietal P400-700 (P3b) component in children.

Developmental changes in the alpha response system

Evoked and event-related brain potentials (ERPs) may be regarded as originating from the reorganization of the spontaneous EEG rhythms. The main objective of the present research was to study the alpha responses in 6-11 year old children to determine whether the ability to reorganize alpha activity after external stimulation demonstrates developmental changes that could reflect variations in information processing with increased age. A total of 50 children aged 6-11 years, divided into 5 age groups, and 10 young adults were assessed in a passive and an oddball condition. Alpha responses in the passive and non-target ERPs at Fz, Cz and Pz were analyzed to assess quantitatively the repeatability (phase-locking) of the evoked alpha oscillations. The alpha responses in 6-11 year old children were different from those in adults: (1) adults had significantly lower amplitude and stronger phase-locking than children; (2) adults had maximal alpha amplitudes and phase-locking over the vertex, whereas children displayed maximal responses over the parietal site; (3) the phase-locking of eldest (10-11 year old) children was as strong as in adults. These findings indicate that the alpha response system is functionally involved in 6-11 year old children, though its development is not complete at the age of 11, and the magnitude and the phase-locking parameters may relate to different functional aspects of the alpha response system. Thus, younger children do produce alpha responses during information processing, but are not able to engage this system as strongly as older children and adults.