Alpha spectral power and coherence in the patients with mild cognitive impairment during a three-level working memory task

Objective: The functional relationship between calculated alpha band spectral power and inter-/intra-hemispheric coherence during a three-level working memory task of patients with mild cognitive impairment (MCI) was investigated. Methods: Subjects included 35 MCI patients according to the DSM-IV criteria (mean age: 62.3, SD: 6.5) and 34 healthy controls (mean age: 57.4, SD: 4.0) were selected from the community at large. All subjects performed a simple calculation and recall task with three levels of working memory load while electroencephalograph (EEG) signal was recorded. The spectral EEG power was computed over alpha1 (8.0～10.0 Hz) and alpha2 (10.5～13.0 Hz) frequency bands and was compared between rest stage and working memory processing stage by two-way ANOVA. Post hoc testing analyzed the differences between each two levels of working memory load during task processing. The inter-hemisphere EEG coherence of frontal (F3-F4), central (C3-C4), parietal (P3-P4), temporal (T5-T6) as well as occipital (O1-O2) was compared between MCI patients and normal controls. The EEG signals from F3-C3, F4-C4, C3-P3, C4-P4, P3-O1, P4-O2, T5-C3, T6-C4, T5-P3 and T6-P4 electrode pairs resulted from the intra-hemispheric action for alpha1 and alpha2 frequency bands. Result: There was significantly higher EEG power from MCI patients than from normal controls both at rest and during working memory processing. Significant differences existed between rest condition and three-level working memory tasks (P<0.001). The inter-and intra-hemispheric coherence during working memory tasks showed a "drop to rise" tendency compared to that at rest condition. There was significantly higher coherence in MCI patients than in the controls. When task difficulties increased, the cortical connectivity of intra-hemispheric diminished while the inter-hemispheric connectivity dominantly maintained the cognitive processing in MCI patients. Conclusion: The results of the present study indicate that the alpha frequency band may be the characteristic band in distinguishing MCI patients from normal controls during working memory tasks. MCI patients exhibit greater inter-hemispheric connectivity than intra-hemispheric connectivity when memory demands increase. MCI patients mobilize a compensatory mechanism to maintain the processing effectiveness while the processing efficiency is reduced.     

Abnormal cortical functional connections in Alzheimer＇s disease： analysis of inter- and intra-hemispheric EEG coherence

To investigate inter- and intra-hemispheric electroencephalography (EEG) coherence at rest and during photic stimulation of patients with Alzheimer‘s disease (AD). Thirty-five patients (12 males, 23 females; 52-64 y) and 33 sex- and age-matched controls (12 males, 21 females; 56-65 y) were recruited in the present study. EEG signals from C3-C4, P3-P4, TS-T6 and O1-O2 electrode pairs resulted from the inter-hemispheric action, and EEG signals from C3-P3, C4-P4, P3-O1, P4-O2, C3-O1, C4-O2, TS-O1 and T6-O2 electrode pairs resulted from the intra-hemispheric action. The influence of inter- and intra-hemispheric coherence on EEG activity with eyes closed was examined, using fast Fourier transformation from the 16 sampled channels. The frequencies of photic stimulation were fixed at 5, l0 and 15 Hz, respectively. The general decrease of AD patients in inter- and intra-hemispheric EEG coherence was more significant than that of the normal controls at the resting EEG, with most striking decrease observed in the alpha-1 (8.0-9.0 Hz) and alpha-2 (9.5-12.5 Hz) bands. During photic stimulation, inter- and intra-hemispheric EEG coherences of the AD patients having lower values in the alpha (9.5-10.5 Hz) band than those of the control group. It suggests that under stimulated and non-stimulated conditions, AD patients had impaired inter- and intra-hemispheric functional connections, indicating failure of brain activation in alpha-related frequency.     

EEG dynamics reflects the partial and holistic effects in mental imagery generation

Mental imagery generation is essential in the retrieval and storage of knowledge. Previous studies have indicated that the holistic properties of mental imagery generation can be evaluated more easily than the partial properties. However, the relationship between partial and holistic mental imagery generations has not been clearly demonstrated. To address this issue, we designed a task to investigate the changes in the spectrum of the electroencephalogram (EEG) during partial or holistic imagery generation. EEG signals were obtained from 18 healthy subjects, and a statistical measure of spectral dynamics between two EEG signals in per frequency band was performed. Additionally, a bicoherence spectrum analysis was used to detect the phase coupling within these two imagery conditions. Our results indicated that EEG of the partial imagery appeared earlier and stronger than that of the holistic imagery in the theta (5–8 Hz) range in a time window around 220 to 300 ms after cue onset, and a slight decrease in the alpha (8–12 Hz) band was observed at around 270 ms. The scalp topography of these changes in the theta and alpha bands distributed overall significantly in the frontal and central-temporal areas. The significant phase coupling within two conditions was remarkable at high frequency. From these results, we infer that there are complex relations between partial and holistic imageries. The generation of partial mental imagery is not a subprocess of holistic imagery, but it is relevant to holistic imagery and requires correct modification from the holistic information.     

EEG analysis of children with attention-deficit/hyperactivity disorder and comorbid reading disabilities

This study investigated electroencephalographic differences between two groups of children with attention-deficit/hyperactivity disorder, combined type, with reading disabilities (ADHD + RD) or without (ADHD) and typical control participants. Twenty participants were included in each group. All participants were between the ages of 8 and 12 years, and groups were matched on age and gender. The electroencephalographic (EEG) was recorded during an eyes-closed resting condition from 21 monopolar derivations, which were clustered into nine regions for analysis. The EEGs were Fourier-transformed to provide absolute and relative power estimates for the delta, theta, alpha, and beta bands. Ratio coefficients were also calculated for the theta/alpha and theta/beta ratios. Compared with controls, the clinical groups demonstrated the increased slow-wave and reduced fast-wave activity commonly reported in the ADHD literature. The ADHD + RD group had more relative theta, less relative alpha, and a higher theta/alpha ratio than the ADHD group. A number of hemispheric differences were also found in the delta and alpha bands. These results suggested that some of the EEG divergences found in the ADHD + RD group represent an electrophysiological component associated with the reading disability that is independent of the EEG divergences found in ADHD.     

Study on EEG power and coherence in patients with mild cognitive impairment during working memory task

To investigate the features of electroencephalography (EEG) power and coherence at rest and during a working memory task of patients with mild cognitive impairment (MCI). Thirty-five patients (17 males, 18 females; 52～71 years old) and 34 sex- and age-matched controls (17 males, 17 females; 51～63 years old) were recruited in the present study. Mini-Mental State Examination (MMSE) of 35 patients with MCI and 34 normal controls revealed that the scores of MCI patients did not differ significantly from those of normal controls (P＞0.05). Then, EEGs at rest and during working memory task with three levels of working memory load were recorded. The EEG power was computed over 10 channels: right and left frontal (F3, F4), central (C3,C4), parietal (P3, P4), temporal (TS, T6) and occipital (O1, O2); inter-hemispheric coherences were computed from five electrode pairs of F3-F4, C3-C4, P3-P4, T5-T6 and O1-O2 for delta (1.0～3.5 Hz), theta (4.0～7.5 Hz), alpha-1 (8.0～10.0 Hz), alpha-2 (10.5～13.0 Hz), beta-1 (13.5～18.0 Hz) and beta-2 (18.5～30.0 Hz) frequency bands. All values of the EEG power of MCI patients were found to be higher than those of normal controls at rest and during working memory tasks. Furthermore, the values of EEG power in the theta, alpha-1, alpha-2 and beta-1 bands of patients with MCI were significantly high (P＜0.05) in comparison with those of normal controls. Correlation analysis indicated a significant negative correlation between the EEG powers and MMSE scores. In addition, during working memory tasks, the EEG coherences in all bands were significantly higher in the MCI group in comparison with those in the control group (P＜0.05). However, there was no significant difference in EEG coherences between two groups at rest. These findings comprise evidence that MCI patients have higher EEG power at rest, and higher EEG power and coherence during working conditions. It suggests that MCI may be associated with compensatory processes at rest and during working memory tasks. Moreover, failure of normal cortical connections may be exist in MCI patients.     

Inter-and intra-hemispheric EEG coherence in patients with mild cognitive impairment at rest and during working memory task

Objective： To assess functional relationship by calculating inter- and intra-hemispheric electroencephalography （EEG） coherence at rest and during a working memory task of patients with mild cognitive impairment （MCI）. Methods： The sample consisted of 69 subjects： 35 patients （n = 17 males, n = 18 females; 52-71 years old） and 34 normal controls （n = 17 males, n = 17 females; 51 -63 years old）. Mini-mental state examination （MMSE） of two groups revealed that the scores of MCI patients did not differ significantly from those of normal controls （P〉0.05）. In EEG recording, subjects were performed at rest and during working memory task. EEG signals from F3-F4, C3-C4, P3-P4, T5-T6 and O1-O2 electrode pairs are resulted from the inter-hemispheric action, and EEG signals from F3-C3, F4-C4, C3-P3, C4-P4, P3-O1, P4-O2, T5-C3, T6-C4, T5-P3 and T6-P4 electrode pairs are resulted from the intra-hemispheric action for delta （1.0-3.5 Hz）, theta （4.0-7.5 Hz）, alpha-1 （8.0-10.0 Hz）, alpha-2 （10.5-13.0 Hz）, beta-1 （13.5-18.0 Hz） and beta-2 （18.5-30.0 Hz） frequency bands. The influence of inter- and intra-hemispheric coherence on EEG activity with eyes closed was examined using fast Fourier transformation from the 16 sampled channels. Results： During working memory tasks, the inter- and intra-hemispheric EEG coherences in all bands were significantly higher in the MCI group in comparison with those in the control group （P〈0.05）. However, there was no significant difference in inter- and intra-hemispheric EEG coherences between two groups at rest. Conclusion： Experimental results comprise evidence that MCI patients have higher degree of functional connectivity between hemispheres and in hemispheres during working condition, It suggests that MCI may be associated with compensatory processes during working memory tasks between hemispheres and in hemispheres. Moreover, failure of normal cortical connections may exist in MCI patients.     

The event‐related low‐frequency activity of highly and average intelligent children

Using time‐frequency analysis techniques to investigate the event‐related low‐frequency (delta: 0.5–4 Hz; theta: 4–8 Hz) activity of auditory event‐related potentials (ERPs) data of highly and average intelligent children, 18 intellectually gifted children, and 18 intellectually average children participated the present study. Present findings show that intellectually gifted children had significantly larger delta activity than their normal peers in mismatch negativity (MMN) component, while in P3a component, which originates from stimulus‐driven frontal attention mechanisms during task processing, intellectually gifted children had both significantly larger delta and theta activities than their normal peers. The present findings further supported that low‐frequency brain activity could be regarded as the basis of intelligence and cognitive functions, and spectral EEG time‐frequency analysis technique should be used to explore some new aspects of brain activity relating to intelligence.     

改变音乐节拍对脑电功率谱变异的影响及其心理意义

目的旨在探索音乐节拍对大脑活动主要区域信息加工过程中的脑电波谱变异.方法采用自编的音乐播放软件给被试分别播放(42、65、120 BPM)3种音乐节拍的65 dB音乐,每种节拍曲目播放5 min,并采集16脑区的脑电信号进行离线分析.结果 (1)与安静状态相比播放音乐时被试在7个波段的脑电波谱功率显著降低;播放音乐时脑电波谱重心频率向低频段移动,表明疲劳程度增加;(2)改变音乐节拍显著降低α1波频段的功率而增加α2波频段的功率;(3)从频段功率占比看,加快音乐节拍节奏增加高频段脑电波活动,降低节拍节奏增加低频段活动而降低高频段脑电波活动.结论音乐节拍显著影响脑电波谱功率变异,65 BPM的中等节奏音乐有利于注意力集中和放松休息,120 BPM快节奏音乐有利于激活唤醒水平,加快运动,改变音乐节拍增加注意负荷,消耗更多的心理加工资源,其意义有待于进一步探索.     

Neurodevelopmental Correlates of Theory of Mind in Preschool Children

Baseline electroencephalogram (EEG) data were collected from twenty-nine 4-year-old children who also completed batteries of representational theory-of-mind (RTM) tasks and executive functioning (EF) tasks. Neural sources of children's EEG alpha (6–9 Hz) were estimated and analyzed to determine whether individual differences in regional EEG alpha activity predicted children's RTM performance, while statistically controlling for children's age and EF skills. Results showed that individual differences in EEG alpha activity localized to the dorsal medial prefrontal cortex (dMPFC) and the right temporal–parietal juncture (rTPJ) were positively associated with children's RTM performance. These findings suggest that the maturation of dMPFC and rTPJ is a critical constituent of preschoolers' explicit theory-of-mind development.     

Electrophysiological correlates of dyslexic subtypes.

The construct validity of Boder's typology of dyslexia was investigated using quantified EEG. Thirty-nine children, ranging in age from 7-0 to 10-11, were recorded during a contextual reading task and at rest. During reading, children with dyslexia were expected to show increased theta and beta amplitude compared to nondisabled readers. These differences were expected in regions of presumed strength for each subtype as a sign of overengagement in task. Children with phonological deficits (dysphonetic dyslexia) were expected to adopt visuospatial processing strategies (right occipital-parietal activation), those with orthographic deficits (dyseidetic dyslexia) to emphasize phonetic strategies (left temporal-parietal activation). Results supported beta frequency differences in anticipated regions by subtype during the reading task. However, the direction of difference hypothesis was not supported. Decreased amplitudes in both groups with dyslexia compared to normally achieving readers suggest reconceptualization of the theoretical base for the Boder subtyping system.     

Neural Oscillation Reveals Deficits in Visuospatial Working Memory in Children With Developmental Coordination Disorder

The electroencephalographic (EEG) oscillations associated with visuospatial working memory (VSWM) were examined in children with developmental coordination disorder (DCD; 10–11 years; N = 29) and typically developing (TD) children (10–11 years; N = 29). Behaviorally, DCD showed poorer VSWM than TD, which coincided with the diminished ability of DCD in modulating neural oscillations. Furthermore, prestimulus oscillatory alpha activity was correlated with VSWM performance. The results suggest that children with DCD might have a reduced ability to encode and recognize new information, and in particular have difficulty in maintaining task‐relevant information, resulting in poorer VSWM. This study thus concludes that changes in oscillatory EEG activity reflect some of the problems leading to cognitive deficits in DCD.     

The Reflecting Brain: Reflection Competence in an Educational Setting Is Associated With Increased Electroencephalogram Activity in the Alpha Band

Teachers' ability to critically reflect classroom situations in relation to their own actions constitutes an important prerequisite to improve teaching performance and professional behavior. This study investigated electroencephalogram activity in the alpha band during a reflection task before and after training in a sample of preservice teachers. Reflection was associated with stable brain activity patterns over two separate time points of assessment. Increased alpha power during reflection of pedagogically relevant scenarios was found at occipital sites, especially in participants with higher reflection competence. This is consistent with prior studies that showed increased alpha power during mental imagery among other tasks. Training of reflection competence, administered in a subsample of participants, was accompanied by increased reflection performance, while no intervention‐related effects were found at the neurophysiological level. The findings of this study provide first preliminary evidence of increased alpha power at occipital sites as a neurophysiological indicator of reflections of pedagogically relevant educational scenarios.     

Mother–Child Interaction: Links Between Mother and Child Frontal Electroencephalograph Asymmetry and Negative Behavior

It is well accepted that parent–child interactions are bidirectional by nature, yet not much is known about the psychophysiological activity underlying these interactions. This study examined, during a parent–child interaction, how a child's negativity statistically predicted maternal frontal electroencephalograph (EEG) asymmetry and how a mother's negativity statistically predicted child frontal EEG asymmetry. Thirty‐four mother–child dyads participated in the study. Maternal and child behaviors and physiology were measured during a puzzle task. Results indicated that mothers whose children exhibited more challenging behaviors during the dyadic interaction displayed more right (relative to left) asymmetry, as did children whose mothers were high in negativity during the interaction. These findings suggest that mothers and children react to each other's signals not only behaviorally but also physiologically.     

Cognitive Style and Individual Differences in EEG Alpha During Information Processing

Abstract When presented with a task, it was hypothesised that different people tend to process the same information in different ways, using different areas of the brain, depending upon their cognitive style. The study used 15 adult subjects, who received the computer‐presented Cognitive Styles Analysis to assess their positions on two basic cognitive style dimensions: the Wholist‐Analytic and Verbal‐Imagery. In a computer‐presented task, subjects were asked to view words presented singly at a rate of two, five and 10 words/second and in pairs at five and 10 word‐pairs/second and to press a key when a word appeared which was in a target conceptual category (e.g. a fruit). The task comprised eight 30‐second trials. During the task, alpha band EEG was monitored at 15 locations. For the Wholist‐Analytic style, Analytics had, over all tasks, lower alpha power relative to the Wholists at all locations, and particularly posteriorly. With the Verbal‐Imagery dimension, there was style‐hemisphere effect, with Verbalisers having relatively more suppression on the left posterior temporal location T5 compared to right T6, and Imagers having the reverse. These results justify further exploration of the cerebral basis of individual differences in cognitive style.     

Preschool Children's Symbolic Representation of Objects through Gestures

To investigate the symbolic quality of preschoolers' gestural representations in the absence of real objects, 48 children (16 3-, 4-, and 5-year-olds) performed 2 tasks. In the first task, they were asked to pretend to use 8 common objects (e.g., "pretend to brush your teeth with a toothbrush"). There was an age-related progression in the symbolic quality of gestural representations. 3- and 4-year-olds used mostly body part gestures (e.g., using an extended finger as the toothbrush), whereas 5-year-olds used imaginary object gestures (e.g., pretending to hold an imaginary toothbrush). To determine if children's symbolic skill is sufficiently flexible to allow them to use gestures other than those spontaneously produced in the first task, in the second task children were asked to imitate, for each object, a gesture modeled by an experimenter. The modeled gesture was different from the one the child performed on the first task (e.g., if the child used a body part gesture to represent a particular object, the experimenter modeled an imaginary object gesture for that object). Ability to imitate modeled gestures was positively related to age but was also influenced by the symbolic mode of gesture. 3-year-olds could not imitate imaginary object gestures as well as body part gestures, suggesting that young preschoolers have difficulty performing symbolic acts that exceed their symbolic level even when the acts are modeled. Results from both tasks provide strong evidence for a developmental progression from concrete body part to more abstract imaginary object gestural representations during the preschool years.     

Detecting stable phase structures in EEG signals to classify brain activity amplitude patterns

Obtaining an electrocorticograms （ECoG） signal requires an invasive procedure in which brain activity is recorded from the cortical surface. In contrast, obtaining electroencephalograms （EEG） recordings requires the non-invasive procedure of recording the brain activity from the scalp surface, which allows EEG recordings to be performed more easily on healthy humans. In this work, a technique previously used to study spatial-temporal patterns of brain activity on animal ECoG was adapted for use on EEG. The main issues are centered on solving the problems introduced by the increment on the interelectrode distance and the procedure to detect stable frames. The results showed that spatial patterns of beta and gamma activity can also be extracted from the EEG signal by using stable frames as time markers for feature extraction. This adapted technique makes it possible to take advantage of the cognitive and phenomenological awareness of a normal healthy subject.     

Multimedia: Differences in cognitive processes observed with EEG

This study investigated the cognitive processes involved in learning information presented in multimedia and text format using electroencephalographic (EEG) measures. Thirty-eight students (19 gifted, and 19 average) learned material presented with text (text); text, sound, and picture (picture); and text, sound and video (video), while their EEG was recorded. Alpha power, which is inversely related to mental effort, was analyzed. For thetext presentation, the alpha power measures showed higher amplitudes (less mental activity) over the occipital and temporal lobes, and less alpha power (higher mental activity) over the frontal lobes. The results support the assumption that thevideo andpicture presentations induced visualization strategies, whereas thetext presentation mainly generated processes related to verbal processing. The results further showed that gifted students displayed less mental activity during all three formats of presentation. These differences were especially pronounced for thevideo format. No gender-related differences in EEG patterns related to the format of presentation were observed.     

Morphological and orthographic effects on hemispheric

We tested the effects of morphological and orthographic differences between English, Hebrew, and Arabic on the functioning of the two cerebral hemispheres. University students who were native speakers of each of the three languages performed a lateralized consonant-vowel-consonant (CVC) identification task. The stimuli were presented vertically in three conditions: left visual field (LVF), right visual field (RVF), and bilaterally (BVF). Three dependent measures were used: (1) exposure duration of the stimuli in order to achieve a 50% error rate, (2) total number of errors in each presentation condition and (3) the difference between errors on the first letter and errors on the last letter, a qualitative measure of sequential processing. Arabic readers required longer exposure durations of the syllables in order to achieve a 50% error rate than Hebrew readers, who in turn, required longer exposure durations than native English readers. Readers of all three languages evinced left hemisphere specialization for this linguistic task and a bilateral advantage. The qualitative patterns revealed that the Arabic and Hebrew speakers showed the same hemispheric difference pattern, that was different from the one shown by English readers, and that Arabic readers showed a qualitative pattern suggesting higher levels of sequential processes in both hemisphere than readers of Hebrew and English. We interpret this as reflecting the adaptation of hemispheric abilities to reading languages that differ in morphological structure and orthography.     

Effects of forced movements on learning: Findings from a choice reaction time task in rats

To investigate how motor sensation facilitates learning, we used a sensory–motor association task to determine whether the sensation induced by forced movements contributes to performance improvements in rats. The rats were trained to respond to a tactile stimulus (an air puff) by releasing a lever pressed by the stimulated (compatible condition) or nonstimulated (incompatible condition) forepaw. When error rates fell below 15%, the compatibility condition was changed (reversal learning). An error trial was followed by a lever activation trial in which a lever on the correct or the incorrect response side was automatically elevated at a preset time of 120, 220, 320, or 420 ms after tactile stimulation. This lever activation induced forepaw movement similar to that in a voluntary lever release response, and also induced body movement that occasionally caused elevation of the other forepaw. The effects of lever activation may have produced a sensation similar to that of voluntary lever release by the forepaw on the nonactivated lever. We found that the performance improvement rate was increased by the lever activation procedure on the incorrect response side (i.e., with the nonactivated lever on the correct response side). Furthermore, the performance improvement rate changed depending on the timing of lever activation: Facilitative effects were largest with lever activation on the incorrect response side at 320 ms after tactile stimulation, whereas hindering effects were largest for lever activation on the correct response side at 220 ms after tactile stimulation. These findings suggest that forced movements, which provide tactile and proprioceptive stimulation, affect sensory–motor associative learning in a time-dependent manner.     

sEMG feature analysis on forearm muscle fatigue during isometric contractions

In order to detect and assess the muscle fatigue state with the surface electromyography(sEMG) characteristic parameters,this paper carried out a series of isometric contraction experiments to induce the fatigue on the forearm muscles from four subjects,and recorded the sEMG signals of the flexor carpi ulnaris.sEMG's median frequency(MDF) and mean frequency(MF) were extracted by short term Fourier transform(STFT),and the root mean square(RMS) of wavelet coefficients in the frequency band of 5—45 Hz was obtained by continuous wavelet transform(CWT).The results demonstrate that both MDF and MF show downward trends within 1 min; however,RMS shows an upward trend within the same time.The three parameters are closely correlated with absolute values of mean correlation coefficients greater than 0.8.It is suggested that the three parameters above can be used as reliable indicators to evaluate the level of muscle fatigue during isometric contractions.