Preparing for hard times: Scalp and intracranial physiological signatures of proactive cognitive control

Based on reward and difficulty information, people can strategically adjust proactive cognitive control. fMRI research shows that motivated proactive control is implemented through fronto‐parietal control networks that are triggered by reward and difficulty cues. Here, we investigate electrophysiological signatures of proactive control. Previously, the contingent negative variation (CNV) in the ERPs and oscillatory power in the theta (4–8 Hz) and alpha band (8–14 Hz) have been suggested as signatures of control implementation. However, experimental designs did not always separate control implementation from motor preparation. Critically, we used a mental calculation task to investigate effects of proactive control implementation on the CNV and on theta and alpha power, in absence of motor preparation. In the period leading up to task onset, we found a more negative CNV, increased theta power, and decreased alpha power for hard versus easy calculations, showing increased proactive control implementation when a difficult task was expected. These three measures also correlated with behavioral performance, both across trials and across subjects. In addition to scalp EEG in healthy participants, we collected intracranial local field potential recordings in an epilepsy patient. We observed a slow‐drift component that was more pronounced for hard trials in a hippocampal location, possibly reflecting task‐specific preparation for hard mental calculations. The current study thus shows that difficulty information triggers proactive control in absence of motor preparation and elucidates its neurophysiological signatures.     

EEG activity during the verbal-cognitive stage of motor skill acquisition

This study examined changes in EEG activity associated with motor performance during the verbal-cognitive stage of skill learning. Participants (n = 14) were required to practice a sequential finger tapping task. EEG activity was recorded both before and after short-term practice, during finger tapping and during two control conditions. EEG power (Fz, Cz, Pz, T3, T4) and coherence (T3-Fz, T4-Fz, Fz-Cz, Fz-Pz) were computed for the theta (4-8 Hz), slow alpha (8-10 Hz), fast alpha (10-12 Hz), slow beta (12-20 Hz), and fast beta (20-28 Hz) bandwidths. Changes in motor performance were rapid during the very early stages of practice and then slowed in accord with the law of practice. These changes were accompanied by increases of theta power at Fz and beta coherence at T4-Fz, suggesting that progression through the verbal-cognitive stage of a sequential finger tapping task is accompanied by more narrowed attention and improved mapping between the stimuli and the finger movements.     

Theta EEG neurofeedback benefits early consolidation of motor sequence learning

Procedural learning is subject to consolidation processes believed to depend on the modulation of functional connections involved in representing the acquired skill. While sleep provides the most commonly studied framework for such consolidation processes, posttraining modulation of oscillatory brain activity may also impact on plasticity processes. Under the hypothesis that consolidation of motor learning is associated with theta band activity, we used EEG neurofeedback (NFB) to enable participants to selectively increase either theta or beta power in their EEG spectra following the acquisition phase of motor sequence learning. We tested performance on a motor task before and after training, right after the NFB session to assess immediate NFB effects, 1 day after NFB to assess interaction between NFB effects and overnight sleep‐dependent stabilization, and 1 week after the initial session, to assess the effects of NFB on long‐term stabilization of motor training. We also explored the extent of the influence of single‐electrode NFB on EEG recorded across the scalp. Results revealed a significantly greater improvement in performance immediately after NFB in the theta group than in the beta group. This effect continued for testing up to 1 week following training. Across participants, post‐NFB improvement correlated positively with theta/beta ratio change achieved during NFB. Additionally, NFB was found to cause widespread band‐power modulation beyond the electrode used for feedback. Thus, upregulating postlearning theta power may yield contributions to the immediate performance and subsequent consolidation of an acquired motor skill.     

Motor sequence learning increases sleep spindles and fast frequencies in post-training sleep

STUDY OBJECTIVES: To investigate polysomnographic (PSG) sleep and NREM sleep characteristics, including sleep spindles and spectral activity involved in offline consolidation of a motor sequence learning task. DESIGN: Counterbalanced within-subject design. SETTING: Three weekly visits to the sleep laboratory. PARTICIPANTS: Fourteen healthy participants aged between 20 and 30 years (8 women). INTERVENTIONS: Motor sequence learning (MSL) task or motor control (CTRL) task before sleep. MEASUREMENTS AND RESULTS: Subjects were trained on either the MSL or CTRL task in the evening and retested 12 hours later the following morning on the same task after a night of PSG sleep recording. Total number and duration of sleep spindles and spectral power between 0.5 and 24 Hz were quantified during NREM sleep. After performing the MSL task, subjects exhibited a large increase in number and duration of sleep spindles compared to after the CTRL task. Higher sigma (sigma; 13 Hz) and beta (beta; 18-20 Hz) spectral power during the post-training night's sleep were also observed after the MSL task. CONCLUSIONS: These results provide evidence that sleep spindles are involved in the offline consolidation of a new sequence of finger movements known to be sleep dependent. Moreover, they expand on prior findings by showing that changes in NREM sleep following motor learning are specific to consolidation (and learning), and not to nonspecific motor activity. Finally, these data demonstrate, for the first time, higher fast rhythms (beta frequencies) during sleep after motor learning.     

Reduction of EEG power during expectancy periods in humans

The contingent negative variation (CNV), and the associated event-related desynchronization (ERD) on motor areas and sensory areas, and increase of alpha in the ipsilateral to the cued stimulus side, are different brain signals that reflect motor, sensory, and cognitive activations related to the expectancy of the next stimulus. However, the possibility of an overall change in EEG oscillatory activity during expectancy periods has not been directly addressed. The present report tests whether the background oscillatory activity is modulated by a warning signal. During the expectancy period, the power spectral density (PSD) between 0 and 42.9 Hz--including delta, theta, alpha, beta, and gamma--decreased with respect to the baseline. These results suggest that during expectancy periods there is a generalised decrease in the oscillatory activity, and that reduction of the EEG power would facilitate the phasic and oscillatory neural activities triggered by the next target stimulus.     

Differential cortical activation during observation and observation-and-imagination

The activity of the brain during observation or imagination of movements might facilitate the relearning of motor functions after stroke. The present study examines whether there is an additional effect of imagination over observation-only. Eight healthy subjects observed and observed-and-imagined a movement of a hand; 64-channel EEG was used to measure brain activity. The synchronization of the theta (4–8 Hz), alpha (8–13 Hz) and beta (13–25 Hz) frequency bands was calculated and plotted in topoplots. The temporal changes of the sensorimotor area (C3, C4) and the centro-parietal cortex (Pz) were analyzed in the two experimental conditions. During observation-and-imagination, a significant larger desynchronization (p = 0.004) in the sensorimotor area was found compared to observation-only in all electrodes and frequency bands. In addition, temporal differences were found between observation and observation-and-imagination in the alpha frequency bands. During observation-and-imagination, modulations of EEG rhythms were stronger than during observation-only in the theta, alpha and beta frequency bands and during almost the whole activity fragment. These findings suggest an additive effect of imagination to observation in the rehabilitation after stroke.     

Distinct patterns of brain oscillations underlie two basic parameters of human maze learning.

We examine how oscillations in the intracranial electroencephalogram (iEEG) relate to human maze learning. Theta- band activity (4-12 Hz in rodents; 4-8 Hz in humans) plays a significant role in memory function in rodents and in humans. Recording intracranially in humans, we have reported task-related, theta-band rhythmic activity in the raw trace during virtual maze learning and during a nonspatial working memory task. Here we analyze oscillations during virtual maze learning across a much broader range of frequencies and analyze their relationship to two task variables relevant to learning. We describe a new algorithm for detecting oscillatory episodes that takes advantage of the high signal-to-noise ratio and high temporal resolution of the iEEG. Accounting for the background power spectrum of the iEEG, the algorithm allows us to directly compare levels of oscillatory activity across frequencies within the 2- to 45-Hz band. We report that while episodes of oscillatory activity are found at various frequencies, most of the rhythmic activity during virtual maze learning occurs within the theta band. Theta oscillations are more prevalent when the task is made more difficult (manipulation of maze length). However, these oscillations do not tend to covary significantly with decision time, a good index of encoding and retrieval operations. In contrast, lower- and higher-frequency oscillations do covary with this variable. These results suggest that while human cortically recorded theta might play a role in encoding, the overall levels of theta oscillations tell us little about the immediate demands on encoding or retrieval. Finally, different patterns of oscillations may reflect distinct underlying aspects of memory function.     

Modafinil augments oscillatory power in middle frequencies during rule selection

Control‐related cognitive processes are associated with cortical oscillations and modulated by catecholamine neurotransmitters. It remains unclear how catecholamine systems modulate control‐related oscillations. We tested modafinil effects on rule‐related 4–30 Hz oscillations, with double‐blind, placebo‐controlled (within‐subjects) testing of 22 healthy adults, using EEG during cognitive control task performance. EEG data underwent time‐frequency decomposition with Morlet wavelets to determine power of 4–30 Hz oscillations. Modafinil enhanced oscillatory power associated with high‐control rule selection in theta, alpha, and beta ranges, with a frontotemporal topography and minimal effects during rule maintenance. Augmentation of catecholamine signaling enhances middle‐frequency cortical oscillatory power associated with rule selection, which may subserve diverse subcomponent processes in proactive cognitive control.     

Theta‐ and alpha‐power enhancements in the electroencephalogram as an auditory delayed match‐to‐sample task becomes impossibly difficult

Recent studies have related enhancements of theta‐ (∼4–8 Hz) and alpha‐power (∼8–13 Hz) to listening effort based on parallels between enhancement and task difficulty. In contrast, nonauditory works demonstrate that, although increases in difficulty are initially accompanied by increases in effort, effort decreases when a task becomes so difficult as to exceed one's ability. Given the latter, we examined whether theta‐ and alpha‐power enhancements thought to reflect effortful listening show a quadratic trend across levels of listening difficulty from impossible to easy. Listeners (n = 14) performed an auditory delayed match‐to‐sample task with frequency‐modulated tonal sweeps under impossible, difficult (at ∼70.7% correct threshold), and easy (well above threshold) conditions. Frontal midline theta‐power and posterior alpha‐power enhancements were observed during the retention interval, with greatest enhancement in the difficult condition. Independent component‐based analyses of data suggest that theta‐power enhancements stemmed from medial frontal sources at or near the anterior cingulate cortex, whereas alpha‐power effects stemmed from occipital cortices. Results support the notion that theta‐ and alpha‐power enhancements reflect effortful cognitive processes during listening, related to auditory working memory and the inhibition of task‐irrelevant cortical processing regions, respectively. Theta‐ and alpha‐power dynamics can be used to characterize the cognitive processes that make up effortful listening, including qualitatively different types of listening effort.     

Neural co-activation as a yardstick of implicit motor learning and the propensity for conscious control of movement

Two studies examined EEG co-activation (coherence) between the verbal-analytical (T3) and motor planning (Fz) regions during a golf putting task. In Study 1, participants with a strong propensity to consciously monitor and control their movements, determined psychometrically by high scores on a movement specific Reinvestment Scale, displayed more alpha2 T3-Fz co-activation than participants with a weak propensity. In Study 2, participants who practiced a golf putting task implicitly (via an errorless learning protocol) displayed less alpha2 T3-Fz co-activation than those who practiced explicitly (by errorful learning). In addition, explicit but not implicit motor learners displayed more T3-Fz co-activation during golf putting under pressure, implying that verbal-analytical processing of putting movements increased under pressure. These findings provide neuropsychological evidence that supports claims that implicit motor learning can be used to limit movement specific reinvestment.     

Large-scale cortical correlation structure of spontaneous oscillatory activity

Little is known about the brain-wide correlation of electrophysiological signals. We found that spontaneous oscillatory neuronal activity exhibited frequency-specific spatial correlation structure in the human brain. We developed an analysis approach that discounts spurious correlation of signal power caused by the limited spatial resolution of electrophysiological measures. We applied this approach to source estimates of spontaneous neuronal activity reconstructed from magnetoencephalography. Overall, correlation of power across cortical regions was strongest in the alpha to beta frequency range (8–32 Hz) and correlation patterns depended on the underlying oscillation frequency. Global hubs resided in the medial temporal lobe in the theta frequency range (4–6 Hz), in lateral parietal areas in the alpha to beta frequency range (8–23 Hz) and in sensorimotor areas for higher frequencies (32–45 Hz). Our data suggest that interactions in various large-scale cortical networks may be reflected in frequency-specific power envelope correlations.     

Slow brain potential and oscillatory EEG manifestations of impaired temporal preparation in Parkinson's disease

Performance in behavioral tasks is influenced by temporal expectations shaped by the temporal structure of the task. Such implicit temporal preparation is reflected in slow brain potentials and electroencephalographic oscillations and is attributed to interval timing mechanisms that probably depend on intact basal ganglia function. We investigated implicit timing in Parkinson's disease using a choice reaction task with two temporally regular stimulus presentation regimes, both including occasional deviant interstimulus intervals. Control subjects, but not patients, demonstrated temporal preparation in the form of an adjustment in time course of slow brain potentials to the duration of the interstimulus interval. However, in both groups, timing perturbations were accompanied by a slow brain potential amplitude drop at the time of expected stimulus occurrence, demonstrating intact representation of time in patients. In patients, oscillatory activity in beta and alpha bands showed attenuated preparatory desynchronization and reduced postmovement event-related synchronization, reflecting abnormal engagement and disengagement of sensorimotor and parietal areas. The results demonstrate profoundly deficient temporal preparation with preserved encoding of temporal information, a dissociation that may be explained by impaired dopamine-dependent motor learning. The results are discussed in the context of recent work on oscillatory activity in the basal ganglia.     

基于有限元方法的 theta 节律能量与导电媒质关系的研究

目的在认知功能研究中,与认知有很大关系的theta(4~12 Hz)节律的能量分析受到很多关注,该仿真研究了一个脑区theta能量与组织电特性的关系以深入了解theta能量所表达的物理意义。方法文章利用了COMSOL Multiphysics(FEMLAB)所提供的有限元方法 (finite element method,FEM)仿真了正弦振荡(4~8 Hz)的偶极子电流所形成的场电位(field potential,FP),分析了theta能量随导电媒质电导率特性变化的规律。结果 (1)Theta能量可随电导率的增大而减小,但随着各向异性的增强却没有下降。(2)与各向同性媒质对照,各向异性媒质的能量有变大可能。(3)偶极子电流的振幅和频率都对theta能量有影响。结论 Theta能量与导电媒质的特性和偶极子电流的特性均有关。     

Alpha power and coherence primarily reflect neural activity related to stages of motor response during a continuous monitoring task

Previously, EEG theta (4-6 Hz) was related to goal conflict resolution [Moore, R.A., Gale, A., Morris, P.H., Forrester, D., 2006. Theta phase locking across the neocortex reflects cortico-hippocampal recursive communication during goal conflict resolution. Int. J. Psychophysiol. 60, 260-273] in the context of theory linked with animal hippocampal theta [Gray, J.A., McNaughton, N., 2000. The Neuropsychology of Anxiety: An Enquiry into the Functions of the Septo-Hippocampal system, 2nd ed, Oxford University Press, Oxford]. Here, the hypothesis that human EEG alpha (8-12 Hz) may also be a natural analogue to animal hippocampal theta is tested. Participants engaged in a monitoring task where the object was to press a response key immediately after presentation of 4 individual, non-repeating, single integer odd digits. These were presented amongst a continuous stream of single integer digits and Xs. EEG recorded in the earlier study were reanalysed; this time extracting alpha power and coherence from the same 34 participants. Alpha had a different profile to theta and was not primarily related to goal conflict. Low alpha (8-10 Hz) coherence consistently increased at electrodes close to primary sensorimotor cortex; particularly during response execution and response inhibition. The coherence analysis revealed that high alpha (10-12 Hz) related to response execution. Supplementary analyses demonstrated widespread high alpha coherence increase during response execution, inhibition and preparation. These data were discussed within the context of motor driven 'classic alpha' and Rolandic mu. A coherence profile which differentiated response execution and response inhibition was proposed to reflect a working memory network which was activated during response execution. Also, alpha power (8-12 Hz) reduced at several central electrodes during response execution. This reflected classic Rolandic mu response. Participants displaying a predicted low alpha power trend had the fastest response times; this was linked with traditional views of low alpha's functional significance.     

Implicit motor-sequence learning in humans following unilateral stroke: the impact of practice and explicit knowledge

Learning and memory are sub-served by two interrelated systems - explicit and implicit. Explicit memory involves facts, while one form of implicit memory involves perceptual-motor processes. The purpose of this series of experiments was to investigate the ability of individuals with stroke-related brain damage to demonstrate implicit motor-sequence learning and the relative impacts of (1) extended practice, or (2) explicit knowledge prior to practice. Implicit learning was severely impaired without explicit knowledge and even under conditions of extended practice. However, when explicit knowledge was provided prior to practice, participants with stroke demonstrated implicit motor-sequence learning. These data suggest that following unilateral stroke, providing explicit information about the task and sequence can attenuate implicit motor learning deficits.     

Cross‐modal distractors modulate oscillatory alpha power: the neural basis of impaired task performance

Unexpected novel sounds capture one's attention, even when irrelevant to the task pursued (e.g., playing video game). This often comes at a cost to the task (e.g., slower responding). The neural basis for this behavioral distraction effect is not well understood and is subject of this study. Our approach was motivated by findings from cuing paradigms suggesting a link between modulations in oscillatory activity and voluntary attention shifts. The current study tested whether oscillatory activity is also modulated by a task‐irrelevant auditory distractor, reflecting a neural signature of an involuntary shift of attention and accounting for the impaired task performance. We reanalyzed magnetoencephalographic data collected via an auditory‐visual distraction paradigm in which a task‐relevant visual stimulus was preceded by a task‐irrelevant sound on each trial. In 87.5% this was a regular sound (Standard); in 12.5% this was a novel sound (Distractor). We compared nonphase locked oscillatory activity in a time window prior to the visual target as a function of the experimental manipulation (Distractor, Standard). We found low power in the pretarget time window for Distractors compared to Standards in the alpha and beta frequency bands. Importantly, individual alpha power correlated with response speed on a trial‐by‐trial basis for the Distractor only. Sources were localized to the occipital cortex, and also to the parietal and supratemporal cortices. These findings support our hypothesis that the distractor‐related alpha power modulation indexes an involuntary shift of attention which accounts for the impaired task performance.     

Effects of feedback delay and agency on feedback‐locked beta and theta power during reinforcement learning

Feedback‐based learning initiated by dopamine (DA) cell firing is crucial for adaptive behavior. The nature and context of feedback can vary, however, affecting how feedback is processed. For example, the feedback‐related negativity (FRN) in the ERP in humans, which has been linked to the DA system, is reduced for delayed feedback and for observational compared to active learning. Recent research suggested that oscillations in the theta and beta band over the medio‐frontal cortex reflect distinct feedback processing mechanisms. In this study, we hypothesized that the power in both frequency bands is affected by feedback delay and agency. We thus investigated effects of feedback delay (1 s vs. 7 s) on induced theta and beta band power and the FRN in a probabilistic feedback learning task in two participant groups, one learning actively and one by observation. For theta and beta, a larger power difference between negative and positive feedback for immediate than delayed feedback was found, driven by positive feedback for beta and by negative feedback for theta, while no differential modulation by agency was seen for theta or beta power following positive and negative feedback. These results indicate that feedback‐locked beta and theta both reflect neural processes that are specific for the integration of feedback and recently preceding events, possibly linked to cognitive control and memory. With respect to the FRN amplitude, we could replicate previous findings of both delay and agency modulations, suggesting that the neural processes underlying feedback‐locked ERPs and theta and beta power modulations differ.     

Motor sequence learning with the nondominant left hand

Whereas the human right hemisphere is active during execution of contralateral hand movements, the left hemisphere is engaged for both contra- and ipsilateral movements, at least for right-handed subjects. Whether this asymmetry is also found during motor learning remains unknown. Implicit sequence learning by the nondominant left hand was examined with the serial reaction time (SRT) task during functional brain imaging. As learning progressed, increases in brain activity were observed in left lateral premotor cortex (PMC) and bilaterally in supplementary motor areas (SMA), with the increase significantly greater in the left hemisphere. The left SMA site was similar to one previously identified with right-hand learning, suggesting that this region is critical for representing a sequence independent of effector. Learning with the left hand also recruited a widespread set of temporal and frontal regions, suggesting that motor skill learning with the nondominant hand develops within both cognitive and motor-related functional networks. After skill acquisition, subjects performed the SRT task with their right hands, and sequence transfer was tested with the original and a mirror-ordered sequence. With the original sequence, the stimulus sequence and series of response locations remained unchanged, but the finger movements were different. With the mirror-ordered sequence, the response sequence involved finger movements homologous to those used during training. Performance of the original and mirror sequence by the right hand was significantly better than with random stimuli. Mirror transformation of the sequence by the right hand was associated with a marked increase in regional activity in the left motor cortex, consistent with a role for sequential transformation at this level of the motor output pathway.     

Effects of normal aging on event-related desynchronization/synchronization during a memory task in humans

Event-related desynchronization (ERD) and event-related synchronization (ERS) of the 1-20Hz EEG frequencies were studied using wavelet transforms in young (n = 10, mean age 22) and elderly subjects (n = 10, mean age 65) performing an auditory Sternberg memory task with words as stimuli. In both age groups, encoding of the four-word memory set elicited ERS in the theta and alpha frequency range. Theta ERS, and ERD in the alpha and beta bands were observed during retrieval. During encoding, the elderly showed greater alpha ERS and smaller theta ERS. During retrieval, smaller alpha ERD and theta ERS was found in the elderly subjects. Also, in the elderly, beta ERD was elicited in the late time window during retrieval. The statistically significant differences between the age groups were more marked during retrieval than during encoding. The results indicate that although the two groups performed equally well behaviorally in the task and the elderly subjects were cognitively intact, normal aging affects oscillatory theta, alpha and beta responses particularly during retrieval from working memory. The ERD/ERS patterns of the elderly resemble those of children found in a recent study, which might suggest that those memory-related brain processes that evolve later in childhood are the first to be affected in older age.     

SSVEP and ERP measurement of cognitive fatigue caused by stereoscopic 3D

Characteristically within the resting brain there are slow fluctuations (around 0.1 Hz) of EEG and NIRS-(de)oxyhemoglobin ([deoxy-Hb], [oxy-Hb]) signals. An interesting question is whether such slow oscillations can be related to the intention to perform a motor act. To obtain an answer we analyzed continuous blood pressure (BP), heart rate (HR), prefrontal [oxy-Hb], [deoxy-Hb] and EEG signals over sensorimotor areas in 10 healthy subjects during 5 min of rest and during 10 min of voluntary finger movements. Analyses of prefrontal [oxy-Hb]/[deoxy-Hb] oscillations around 0.1 Hz and central EEG band power changes in the beta (alpha) band revealed that the positive [oxy-Hb] peaks preceded the central EEG beta (alpha) power peak by 3.6 ± 0.9 s in the majority of subjects. A similar relationship between prefrontal [oxy-Hb] and central EEG beta power was found during voluntary movements whereby the post movement beta power increase (beta rebound) is known to coexist with a decreased excitability of cortico-spinal neurons. Therefore, we speculate that the beta power increase ∼3 s after slow fluctuating [oxy-Hb] peaks during rest is indicative for a slow excitability change of central motor cortex neurons. This work provides the first evidence that initiation of finger movements at free will in relatively constant intervals around 10 s could be temporally related to slow oscillations of prefrontal [oxy-Hb] and autonomic blood pressure in the resting brain.