Alpha Band Amplitudes Research Articles

High-alpha band synchronization across frontal, parietal and visual cortex mediates behavioral and neuronal effects of visuospatial attention

Visuospatial attention prioritizes processing of attended visual stimuli. It is characterized by lateralized alpha-band (8–14 Hz) amplitude suppression in visual cortex and increased neuronal activity in a network of frontal and parietal areas. It has remained unknown what mechanisms coordinate neuronal processing among frontoparietal network and visual cortices and implement the attention-related modulations of alpha-band amplitudes and behavior. We investigated whether large-scale network synchronization could be such a mechanism. We recorded human cortical activity with magnetoencephalography (MEG) during a visuospatial attention task. We then identified the frequencies and anatomical networks of inter-areal phase synchronization from source localized MEG data. We found that visuospatial attention is associated with robust and sustained long-range synchronization of cortical oscillations exclusively in the high-alpha (10–14 Hz) frequency band. This synchronization connected frontal, parietal and visual regions and was observed concurrently with amplitude suppression of low-alpha (6–9 Hz) band oscillations in visual cortex. Furthermore, stronger high-alpha phase synchronization was associated with decreased reaction times to attended stimuli and larger suppression of alpha-band amplitudes. These results thus show that high-alpha band phase synchronization is functionally significant and could coordinate the neuronal communication underlying the implementation of visuospatial attention.

Neural oscillations associated with auditory duration maintenance in working memory

The neural representation of auditory duration remains unknown. Here, we used electroencephalogram (EEG) recordings to investigate neural oscillations during the maintenance of auditory duration in working memory (WM). EEG analyses indicated that the auditory duration length was not associated with changes in the theta band amplitude, whereas the alpha band amplitudes during 3-s and 4-s auditory duration conditions were lower than during the 1-s and 2-s conditions. Moreover, the alpha band amplitude and accuracy were positively correlated in the 2-s duration condition. We also found that the neural representation of auditory duration is segmented, with a critical threshold point of approximately 2 s, which is shorter than that for visual duration (3 s). The results emphasised the involvement of the alpha band in auditory duration maintenance in WM. Our study’s findings indicate that different internal representations of auditory durations are maintained in WM below and above 2 s from the perspective of electrophysiology. Additionally, the critical threshold point is related to the sensory modality of duration.

Resting state intrinsic EEG impacts on go stimulus-response processes.

Neuropsychological research and practice rely on cognitive task performance measures as indicators of brain functioning. The neural activity underlying stimulus-response processes can be assessed with ERPs, but the relations between these cognitive processes and the brain's intrinsic resting state EEG activity are less understood. This study focused on the neurocognitive functioning of 20 healthy young adults in an equiprobable go/no-go task to map the ERP correlates of behavioral responses and examine contributions of the resting state intrinsic EEG to task-related outcomes. Continuous EEG was recorded during pretask eyes-closed (EC) and eyes-open (EO) conditions, and in the subsequent task. Delta, theta, alpha, and beta band amplitudes were assessed for the EC state and also for the reactive change to EO. Go/no-go ERPs were submitted to temporal principal components analysis, where the P2, N2, P3, and slow wave components of interest were extracted. The performance measure of reaction time (RT) variability was positively correlated with no-go and go errors, and also with go P2 amplitude, linking these to stimulus discrimination efforts involved in appropriate response selection. An N2c-P3b pairing was enhanced for shorter mean RTs, supporting their involvement in the decision to execute a response. A stepwise regression model identified EC midline delta as a predictor of P3b positivity, highlighting the relevance of delta in the neural mechanisms of attentional processes. These findings clarify the electrophysiology underlying decision-making processes in executive function, and provide a platform for further research assessing performance outcomes in larger samples and in developmental/clinical contexts.

Alpha-band rhythm suppression during memory recall reflecting memory performance.

Alpha-band rhythm is thought to be involved in memory processes, similarly to other spontaneous brain rhythms. Ten right-handed healthy volunteers participated in our proposed sequential short-term memory task that provides a serial position effect in accuracy rate. We recorded alpha-band rhythms by magnetoencephalography during performance of the task and observed that the amplitude of the rhythm was suppressed dramatically in the memory recall period. The suppressed region was estimated to be in the occipital lobe, suggesting that alpha-band rhythm is suppressed by activation of the occipital attentional network. Additionally, the alpha-band suppression reflected accuracy rate, that is, the amplitude was suppressed more when recalling items with higher accuracy rate. The sensors with a significant correlation between alpha-band amplitude and accuracy rate were located widely from the frontal to occipital regions mainly in the right hemisphere. The results suggests that alpha-band rhythm is involved in memory recall and can be index of memory performance.

Alpha neurofeedback training improves SSVEP-based BCI performance

Objective. Steady-state visual evoked potential (SSVEP)-based brain-computer interfaces (BCIs) can provide relatively easy, reliable and high speed communication. However, the performance is still not satisfactory, especially in some users who are not able to generate strong enough SSVEP signals. This work aims to strengthen a user’s SSVEP by alpha down-regulating neurofeedback training (NFT) and consequently improve the performance of the user in using SSVEP-based BCIs. Approach. An experiment with two steps was designed and conducted. The first step was to investigate the relationship between the resting alpha activity and the SSVEP-based BCI performance, in order to determine the training parameter for the NFT. Then in the second step, half of the subjects with ‘low’ performance (i.e. BCI classification accuracy <80%) were randomly assigned to a NFT group to perform a real-time NFT, and the rest half to a non-NFT control group for comparison. Main results. The first step revealed a significant negative correlation between the BCI performance and the individual alpha band (IAB) amplitudes in the eyes-open resting condition in a total of 33 subjects. In the second step, it was found that during the IAB down-regulating NFT, on average the subjects were able to successfully decrease their IAB amplitude over training sessions. More importantly, the NFT group showed an average increase of 16.5% in the SSVEP signal SNR (signal-to-noise ratio) and an average increase of 20.3% in the BCI classification accuracy, which was significant compared to the non-NFT control group. Significance. These findings indicate that the alpha down-regulating NFT can be used to improve the SSVEP signal quality and the subjects’ performance in using SSVEP-based BCIs. It could be helpful to the SSVEP related studies and would contribute to more effective SSVEP-based BCI applications.

Alpha-band Amplitude During Memory Encoding Is an Index of Memory Performance

Alpha-band Amplitude During Memory Encoding Is an Index of Memory Performance

Neural dynamics in motor preparation: From phase-mediated global computation to amplitude-mediated local computation

Oscillatory activity plays a critical role in the brain. Here, we illustrate the dynamics of neural oscillations in the motor system of the brain. We used a non-directional cue to instruct participants to prepare a motor response with either the left or the right hand and recorded electroencephalography during the preparation of the response. Consistent with previous findings, the amplitude of alpha-band (8–14Hz) oscillations significantly decreased over the motor region contralateral to the hand prepared for the response. Prior to this decrease, there were a number of inter-regional phase synchronies at lower frequencies (2–4Hz; delta band). Cross-frequency coupling was quantified to further explore the direct link between alpha amplitudes and delta synchrony. The cross-frequency coupling of showed response-specific modulation, whereby the motor region contralateral to the preparation hand exhibited an increase in coupling relative to the baseline. The amplitude of alpha oscillations had an unpreferred and a preferred delta phase, in which the amplitude was modulated negatively and positively, respectively. Given the amplitude of alpha-band oscillations decreased over the analyzed period, the alpha amplitude might be down-regulated by the phase–amplitude coupling, although we do not have direct evidence for that. Taken together, these results show global-to-local computation in the motor system, which started from inter-regional delta phase synchrony and ended at an effector-specific decrease in the amplitude of alpha-band oscillations, with phase–amplitude coupling connecting both computations.

Occipitoparietal alpha-band responses to the graded allocation of top-down spatial attention.

The voluntary, top-down allocation of visual spatial attention has been linked to changes in the alpha-band of the electroencephalogram (EEG) signal measured over occipital and parietal lobes. In the present study, we investigated how occipitoparietal alpha-band activity changes when people allocate their attentional resources in a graded fashion across the visual field. We asked participants to either completely shift their attention into one hemifield, to balance their attention equally across the entire visual field, or to attribute more attention to one-half of the visual field than to the other. As expected, we found that alpha-band amplitudes decreased stronger contralaterally than ipsilaterally to the attended side when attention was shifted completely. Alpha-band amplitudes decreased bilaterally when attention was balanced equally across the visual field. However, when participants allocated more attentional resources to one-half of the visual field, this was not reflected in the alpha-band amplitudes, which just decreased bilaterally. We found that the performance of the participants was more strongly reflected in the coherence between frontal and occipitoparietal brain regions. We conclude that low alpha-band amplitudes seem to be necessary for stimulus detection. Furthermore, complete shifts of attention are directly reflected in the lateralization of alpha-band amplitudes. In the present study, a gradual allocation of visual attention across the visual field was only indirectly reflected in the alpha-band activity over occipital and parietal cortexes.

Event-Related Desynchronization of Spontaneous Rhythm Caused by Anticipation of Collision

Event Abstract Back to Event Event-Related Desynchronization of Spontaneous Rhythm Caused by Anticipation of Collision Gakuto Aoyama1*, Koichi Yokosawa1, Shinya Kuriki2 and Makoto Takahashi1 1 Hokkaido University, Japan 2 Tokyo Denki University, Japan Animals, including human beings, subconsciously evade collisions. We have been investigating endogenous brain activity by MEG when humans anticipate a collision or intend to take evasive action. A form that expands rapidly while maintaining shape is recognized as a collision [1]. We presented participants with a collision-simulating image with a prior cue signal. Here we report results showing how spontaneous brain activity is modified by anticipation of a collision. MEG signals were recorded with a 76-ch helmet system (Elekta-Neuromag, custom-type) from 11 healthy male volunteers (24.9±3.9 years old). Each participant was presented with a visual collision-simulating stimulus in which a black indeterminate form expanded on a grey background in 170 ms (A: collision stimulus). As controls, two kinds of stimuli were presented. One was a uniform background, the brightness of which decreased with time to darkness (B: darkening stimulus), and the other was the black indeterminate form that changed in size in a random manner (C: random stimulus). A cue stimulus was given visually two seconds before each (A, B, or C) stimulus to enable the participant to anticipate the coming stimulus. One experimental session included 120 epochs per stimulus, in random order. Amplitude of spontaneous alpha band (8-13 Hz) rhythm decreased just after the onset of each stimulus and increased dramatically 400 ms later. The most notable result was that the amplitude of alpha rhythm before the collision stimulus (A) was significantly smaller than that before each control stimulus (B or C) (p<0.05) during the period between cue and stimulus. This result suggests that spontaneous brain activity in the alpha band is reduced by anticipating a negative (dangerous) event, possibly to prepare evasive action.

Functional characteristics of the brain and cognitive functions in patients with autonomic dysfunction combined with clinically apparent asthenia

Twenty six patients with autonomic dysfunction combined with clinically apparent asthenia and 22 healthy control subjects were examined with the use of clinico-neurologic, psychometric, neuropsychological and neurophysiological methods of investigation. Electrophysiologically, compression spectral analysis of EEG and auditory event-related potentials Р300 were used. The patients differed significantly from controls by the reduced attention selectivity, stability and switching, as well as by depression of short-term memory on words and digits. The patients group was also characterized by significantly lower Р300 wave amplitude and spectral power of EEG alpha band in the occipital areas of both hemispheres, in the posterior frontal, the central and the parietal areas of the right hemisphere, as well as by significantly higher spectral power of EEG theta band in the right frontal, the left parietal and the central areas of both hemispheres. One may conclude hat changes of spontaneous and evoked electrical activity of the brain in patients with an asthenia reflect the decrease in general level of brain functional activity owing to abnormal adjusting influences of the limbic-reticular structures. In this case a sufficient flow of cortical activation, necessary for the optimal information processing and maintenance of an adequate level of the directed attention and short-term memory, can not be generated.

Hypnotizability-related EEG alpha and theta activities during visual and somesthetic imageries

Hypnotizability is a cognitive multidimensional trait that involves peculiar imagery characteristics. Subjects with high- (Highs) and low (Lows)-susceptibilities to hypnosis have shown different levels of skill at visual and somesthetic-guided imageries performed during upright stance. The aim of this experiment is to study the modulation of the EEG alpha and theta band amplitude during guided visual and somesthetic imageries in Highs and Lows, as these rhythms are responsive to the cognitive activities involved in mental imagery. Our results show that, at variance with standing subjects, subjects in both groups in a semi-reclined position report higher vividness and lower effort for visual than for somesthetic imagery. EEG patterns however are different between the two groups. Highs exhibit a more widespread alpha desynchronization and slightly different EEG patterns during visual and somesthetic imageries, while Lows show segregated alpha- and theta-desynchronization, without any difference between the tasks. Our results indicate that different, hypnotizability-related cognitive strategies, that are revealed by differences in EEG modulation, are responsible for the similar subjective experience associated with visual and somesthetic imageries in Highs and Lows. In addition, in both groups higher order mental representation of different sensory modalities might be subserved by a unique integrated neural network.

The strength of anticipatory spatial biasing predicts target discrimination at attended locations: a high‐density EEG study

Cueing relevant spatial locations in advance of a visual target results in modulated processing of that target as a consequence of anticipatory attentional deployment, the neural signatures of which remain to be fully elucidated. A set of electrophysiological processes has been established as candidate markers of the invocation and maintenance of attentional bias in humans. These include spatially-selective event-related potential (ERP) components over the lateral parietal (around 200-300 ms post-cue), frontal (300-500 ms) and ventral visual (> 500 ms) cortex, as well as oscillatory amplitude changes in the alpha band (8-14 Hz). Here, we interrogated the roles played by these anticipatory processes in attentional orienting by testing for links with subsequent behavioral performance. We found that both target discriminability (d') and reaction times were significantly predicted on a trial-by-trial basis by lateralization of alpha-band amplitude in the 500 ms preceding the target, with improved speed and accuracy resulting from a greater relative decrease in alpha over the contralateral visual cortex. Reaction time was also predicted by a late posterior contralateral positivity in the broad-band ERP in the same time period, but this did not influence d'. In a further analysis we sought to identify the control signals involved in generating the anticipatory bias, by testing earlier broad-band ERP amplitude for covariation with alpha lateralization. We found that stronger alpha biasing was associated with a greater bilateral frontal positivity at approximately 390 ms but not with differential amplitude across hemispheres in any time period. Thus, during the establishment of an anticipatory spatial bias, while the expected target location is strongly encoded in lateralized activity in parietal and frontal areas, a distinct non-spatial control process seems to regulate the strength of the bias.

Coherent oscillatory networks supporting short-term memory retention

Accumulating evidence suggests that top-down processes, reflected by frontal-midline theta-band (4–8 Hz) electroencephalogram (EEG) oscillations, strengthen the activation of a memory set during short-term memory (STM) retention. In addition, the amplitude of posterior alpha-band (8–13 Hz) oscillations during STM retention is thought to reflect a mechanism that protects fragile STM activations from interference by gating bottom-up sensory inputs. The present study addressed two important questions about these phenomena. First, why have previous studies not consistently found memory set-size effects on frontal-midline theta? Second, how does posterior alpha participate in STM retention? To answer these questions, large-scale network connectivity during STM retention was examined by computing EEG wavelet coherence during the retention period of a modified Sternberg task using visually-presented letters as stimuli. The results showed (a) increasing theta-band coherence between frontal-midline and left temporal-parietal sites with increasing memory load, and (b) increasing alpha-band coherence between midline parietal and left temporal/parietal sites with increasing memory load. These findings support the view that theta-band coherence, rather than amplitude, is the key factor in selective top-down strengthening of the memory set and demonstrate that posterior alpha-band oscillations associated with sensory gating are involved in STM retention by participating in the STM network.

EEG alpha oscillations in the preparation for global and local processing predict behavioral performance

Visual attention can be directed either to the global features of a display or to the local elements that make up the display. We investigated whether oscillatory brain responses to globally or locally directed cue stimuli predict behavioral performance in subsequent target processing. Induced alpha band (8-12 Hz) amplitudes in the pre-stimulus interval were measured separately for the global and the local level, where individual trials were assigned to one of three groups according to the response speed towards incongruent stimuli. Fast responses to local features were associated with high alpha amplitudes in the right centro-parietal cortex, whereas fast responses to global forms were associated with high alpha in left centro-parietal cortex. For trials with slower responses, the pattern of hemispheric differences was diminished or even reversed. It is interpreted that the left and the right parietal cortex exert top-down control over hierarchical processing by inhibiting stimulus representations in one hemisphere.

Psychophysiological characteristics of patients with alcohol epileptic syndrome

The relationship between ongoing occipital alpha rhythm (8–12 Hz) and the generation of visual evoked potentials (VEPs) has been discussed controversially. While the “evoked theory” sees no interaction between VEP generation and the alpha rhythm, the “oscillatory theory” (also known as “phase-reset theory”) postulates VEP generation to be based on alpha rhythm phase resetting. Previous experimental results are contradictory, rendering a straightforward interpretation difficult. Our approach was to theoretically model the implications of the evoked and oscillatory theory also incorporating stimulus-induced alpha-rhythm desynchronization. As a result, the model based on the oscillatory theory predicts alpha-band dependent VEP amplitudes but constant phase locking. The model based on the evoked theory predicts unaffected VEP amplitudes but alpha-band dependent phase locking. Subsequently, we analyzed experimental data in which VEPs were assessed in an “eyes open” and “eyes closed” condition in 17 subjects. For early components of the VEP, findings are in agreement with the evoked theory, i.e. VEP amplitudes remain unaffected and phase locking decreases during periods of high alpha activity. Late VEP component amplitudes (> 175 ms), however, are dependent on pre-stimulus alpha amplitudes. This interaction is contradictory to the oscillatory theory since this VEP amplitude difference is not paralleled by a corresponding difference in alpha-band amplitude in the affected time window. In summary, by using a model-based approach we identified early VEPs to be compatible with the evoked theory, while results of late VEPs support a modulatory but not causative role – the latter implied by the oscillatory theory – of alpha activity for EP generation.

Influence of ongoing alpha rhythm on the visual evoked potential

The relationship between ongoing occipital alpha rhythm (8–12 Hz) and the generation of visual evoked potentials (VEPs) has been discussed controversially. While the “evoked theory” sees no interaction between VEP generation and the alpha rhythm, the “oscillatory theory” (also known as “phase-reset theory”) postulates VEP generation to be based on alpha rhythm phase resetting. Previous experimental results are contradictory, rendering a straightforward interpretation difficult. Our approach was to theoretically model the implications of the evoked and oscillatory theory also incorporating stimulus-induced alpha-rhythm desynchronization. As a result, the model based on the oscillatory theory predicts alpha-band dependent VEP amplitudes but constant phase locking. The model based on the evoked theory predicts unaffected VEP amplitudes but alpha-band dependent phase locking. Subsequently, we analyzed experimental data in which VEPs were assessed in an “eyes open” and “eyes closed” condition in 17 subjects. For early components of the VEP, findings are in agreement with the evoked theory, i.e. VEP amplitudes remain unaffected and phase locking decreases during periods of high alpha activity. Late VEP component amplitudes (> 175 ms), however, are dependent on pre-stimulus alpha amplitudes. This interaction is contradictory to the oscillatory theory since this VEP amplitude difference is not paralleled by a corresponding difference in alpha-band amplitude in the affected time window. In summary, by using a model-based approach we identified early VEPs to be compatible with the evoked theory, while results of late VEPs support a modulatory but not causative role – the latter implied by the oscillatory theory – of alpha activity for EP generation.

Alpha reduction and event-related potentials, theta and gamma increase linked to letter selection

We examined evoked and induced modulations in theta, alpha and gamma oscillations, and also the P2 and late positive component of event-related potentials, during a visual discrimination task with target and nontarget letters. Results for target letters showed a decrease in the amplitude of alpha-band (10-11 Hz) activity and an increase in theta (4-7 Hz) and gamma (40-44 Hz) activities around 350 ms after stimulation. P2 and late positive component presented a higher amplitude to target than to repeated nontarget letters. Alpha reduction was inversely related to theta and late positive component increase. Moreover, gamma oscillation amplitude was directly related to theta amplitude. The findings suggest the importance of occipitoparietal alpha reduction for the development of task-related neuronal activity.

The hemodynamic response of the alpha rhythm: An EEG/fMRI study

EEG was recorded during fMRI scanning of 16 normal controls in resting condition with eyes closed. Time variations of the occipital alpha band amplitudes were correlated to the fMRI signal variations to obtain insight into the hemodynamic correlates of the EEG alpha activity. Contrary to earlier studies, no a priori assumptions were made on the expected shape of the alpha band response function (ARF). The ARF of different brain regions and subjects were explored and compared. It was found that: (1) the ARF of the thalamus is mainly positive. (2) The ARFs at the occipital and left and right parietal points are similar in amplitude and timing. (3) The peak time of the thalamus is a few seconds earlier than that of occipital and parietal cortex. (4) No systematic BOLD activity was found preceding the alpha band activity, although in the two subjects with the strongest alpha band power such correlation was present. (5) There is a strong and immediate positive correlation at the eyeball, and a strong negative correlation at the back of the eye. Furthermore, it was found that in one subject the cortical ARF was positive, contrary to the other subjects. Finally, a cluster analysis of the observed ARF, in combination with a Modulated Sine Model (MSM) fit to the estimated ARF, revealed that within the cortex the ARF peak time shows a spatial pattern that may be interpreted as a traveling wave. The spatial pattern of alpha band response function represents the combined effect of local differences in electrical alpha band activity and local differences in the hemodynamic response function (HRF) onto these electrical activities. To disentangle the contributions of both factors, more advanced integration of EEG inverse modeling and hemodynamic response modeling is required in future studies.

Phase/amplitude reset and theta–gamma interaction in the human medial temporal lobe during a continuous word recognition memory task

We analyzed intracranial electroencephalographic (EEG) recordings from the medial temporal lobes of 12 epilepsy patients during a continuous word recognition paradigm, contrasting trials of correctly recognized repeated words (hits) and correctly identified new words (correct rejections). Using a wavelet-based analysis, we investigated how power changes and phase clustering in different frequency bands contribute to the averaged event-related potentials (ERPs). In addition, we analyzed the actual mean phases of the different oscillations. Our analyses yielded the following results: (1) power changes contributed significantly only to the late components of the ERPs (>400 ms) (2) earlier ERP components were produced by a stimulus-related broad-band phase and amplitude reset of ongoing oscillatory activity about 190 ms after stimulus onset that involved not only the theta band, but also covered alpha and lower beta band frequencies (3) phase and amplitude reset occurred during an epoch of increased phase entrainment over time that lasted for about two oscillation periods for all involved frequencies and was more pronounced for correct rejections than for hits. The broad-band phase and amplitude reset was observed for both hits and correct rejections, and therefore, did not appear to support a specific cognitive function, but rather to act as a general facilitating factor for the processes involved in this memory task. Further analyses of synchronization between oscillations and power changes in different frequency bands revealed a task-dependent modulation of gamma activity by the entrained theta cycle, a mechanism potentially related to memory encoding and retrieval in the rhinal cortex and hippocampus, respectively.

The Temporal Dynamics of Electroencephalographic Responses to Alpha/Theta Neurofeedback Training in Healthy Subjects

Background. It has been shown recently that accurate feedback of alpha and theta electroencephalographic (EEG) activity, as employed in the commonly used #8220alpha/theta protocol,#8221 induced linear increments in within-session theta-over-alpha ratios in comparison to non-contingent feedback in a healthy sample. These data verify that alpha/theta feedback can facilitate within-session operant control over the EEG signature targeted by the training protocol. However, it is neither known whether any between-session theta/alpha ratio changes do reliably occur, nor what kind of temporal dynamics between the alpha and theta band amplitudes characterise within-session and/or between-session theta/alpha ratio changes. Method. In order to address these issues, analyses of an extensive data set (n = 48) of alpha/theta training in healthy volunteers were carried out. Specifically, alpha, theta, and theta/alpha ratio EEG dynamics were contrasted between groups of subjects that engaged in 10 sessions of training at PZ (n = 28), five sessions of training at PZ (n = 10), and 10 sessions at FZ (n = 10). Results. For alpha/theta training at PZ, significant within-session increments in theta/alpha ratios were mediated by slightly less pronounced decrements in theta than in alpha activity during the sessions. The traditional alpha/theta protocol at PZ was nevertheless associated with significant theta activity increments across the training process. For training at FZ, no significant within- or between-session changes in theta, alpha, or theta/alpha ratio values were found, but a progressively higher rate of within-session theta/alpha ratio modulation was evident across sessions. Furthermore, in contrast to the PZ groups, any changes in theta/alpha ratio at FZ were mediated by increases in theta relative to alpha amplitudes. Conclusions. These data elucidate the dynamics underlying the within-session theta/alpha ratio increments associated with posterior alpha/theta training, and document an increase in theta activity across 10 sessions of training, offering further evidence for a neurophysiological impact of this training protocol. In addition, the contrasting EEG characteristics associated with frontal versus posterior alpha/theta training underline the heterogeneous nature of these frequency components across varying scalp sites.