Occipital midline EEG and subjective rating of task difficulty as indices of mental task strain

Three measures of mental task strain, namely performance level, occipital midline beta-2 (Oz beta 2) amplitude and subjective rating of task difficulty, were taken in 34 healthy male students aged 19-24 years as they performed either a paced or a self-paced calculating task for 4 h. The performance levels were so constant throughout the work periods that they were of no use in evaluating mental task strain. The Oz beta 2 amplitudes increased significantly with the execution of both tasks, and a significant increase took place during the self-paced task work periods. From this, a critical value of Oz beta 2 amplitude for a heavy task strain was estimated to be about 3.5 microV (the difference between the values at work and at rest). The subjective ratings of task difficulty rose linearly with work time in both tasks. The subjective task strain attributable to work time was found to exceed the critical level long before the objective measure. In addition, other results suggest that the Oz beta 2 activity attributable to task execution is related to the capacity for achieving the task.     

Adaptation to the complexity of a task (a P300 study)

In numerous studies the P300 component of the event-related brain potential (ERP) has been shown to occur in connection with stimulus evaluation processes. 10 healthy right-handed volunteers (3 women, 7 men) aged from 25 to 30 years (mean age 27.8 years) participated in the experiments. One of 5 equiprobably occurring two-letter strings appeared on the screen always at the same central location. The strings informed the subjects about the difficulty of subsequently presented mental arithmetic tasks. After the letter strings vanished from the screen the subjects were to press the space-bar whereby a mental arithmetic task was presented corresponding in difficulty to the preceding message. The EEG was recorded by means of Ag/AgCl electrodes from frontal (F zeta), central (C zeta) and parietal (P zeta) midline electrodes referenced to linked earlobes. EEG and EOG were sampled 1200 ms, starting 200 ms prior to string onset. P300 peak latencies, peak amplitudes and areas in the time range 300 to 900 ms were measured in ERPs averaged selectively for the 5 strings. The main finding was that the P300 amplitude in ERPs to the 5 different strings varied in a U-shaped trend as a function of announced task difficulty. This result gives further evidence that the P300 amplitude reflects distance between incoming information and current adaptation level at the inferred internal dimension, i.e. task difficulty in this experiment.     

Changes of slow and steady brain potentials during complex tasks

Recordings of slow potentials and changes of steady level of the EEG in man during manual and mental tasks show that an increase in mental load (as determined by the difficulty of the task) is accompanied by an increase in negativity at midline electrodes. It is suggested that this negativity is due to cortical excitation that facilitates performance.     

The Primary Visual Cortex Is Differentially Modulated by Stimulus-Driven and Top-Down Attention

Selective attention can be focused either volitionally, by top-down signals derived from task demands, or automatically, by bottom-up signals from salient stimuli. Because the brain mechanisms that underlie these two attention processes are poorly understood, we recorded local field potentials (LFPs) from primary visual cortical areas of cats as they performed stimulus-driven and anticipatory discrimination tasks. Consistent with our previous observations, in both tasks, we found enhanced beta activity, which we have postulated may serve as an attention carrier. We characterized the functional organization of task-related beta activity by (i) cortical responses (EPs) evoked by electrical stimulation of the optic chiasm and (ii) intracortical LFP correlations. During the anticipatory task, peripheral stimulation that was preceded by high-amplitude beta oscillations evoked large-amplitude EPs compared with EPs that followed low-amplitude beta. In contrast, during the stimulus-driven task, cortical EPs preceded by high-amplitude beta oscillations were, on average, smaller than those preceded by low-amplitude beta. Analysis of the correlations between the different recording sites revealed that beta activation maps were heterogeneous during the bottom-up task and homogeneous for the top-down task. We conclude that bottom-up attention activates cortical visual areas in a mosaic-like pattern, whereas top-down attentional modulation results in spatially homogeneous excitation.     

Investigating neural efficiency of elite karate athletes during a mental arithmetic task using EEG

Neural efficiency is proposed as one of the neural mechanisms underlying elite athletic performances. Previous sports studies examined neural efficiency using tasks that involve motor functions. In this study we investigate the extent of neural efficiency beyond motor tasks by using a mental subtraction task. A group of elite karate athletes are compared to a matched group of non-athletes. Electroencephalogram is used to measure cognitive dynamics during resting and increased mental workload periods. Mainly posterior alpha band power of the karate players was found to be higher than control subjects under both tasks. Moreover, event related synchronization/desynchronization has been computed to investigate the neural efficiency hypothesis among subjects. Finally, this study is the first study to examine neural efficiency related to a cognitive task, not a motor task, in elite karate players using ERD/ERS analysis. The results suggest that the effect of neural efficiency in the brain is global rather than local and thus might be contributing to the elite athletic performances. Also the results are in line with the neural efficiency hypothesis tested for motor performance studies.     

Time to task failure and motor cortical activity depend on the type of feedback in visuomotor tasks

The present study aimed to elucidate whether the type of feedback influences the performance and the motor cortical activity when executing identical visuomotor tasks. For this purpose, time to task failure was measured during position- and force-controlled muscular contractions. Subjects received either visual feedback about the force produced by pressing a force transducer or about the actual position between thumb and index finger. Participants were instructed to either match the force level of 30% MVC or the finger position corresponding to the thumb and index finger angle at this contraction intensity. Subjects demonstrated a shorter time to task failure when they were provided with feedback about their joint position (11.5 ± 6.2 min) instead of force feedback (19.2 ± 12.8 min; P = 0.01). To test differences in motor cortical activity between position- and force-controlled contractions, subthreshold transcranial magnetic stimulation (subTMS) was applied while executing submaximal (20% MVC) contractions. SubTMS resulted in a suppression of the first dorsal interosseus muscle (FDI) EMG in both tasks. However, the mean suppression for the position-controlled task was significantly greater (18.6 ± 9.4% vs. 13.3 ± 7.5%; P = 0.025) and lasted longer (13.9 ± 7.5 ms vs. 9.3 ± 4.3 ms; P = 0.024) compared to the force-controlled task. The FDI background EMG obtained without stimulation was comparable in all conditions. The present results demonstrate that the presentation of different feedback modalities influences the time to task failure as well as the cortical activity. As only the feedback was altered but not the mechanics of the task, the present results add to the body of evidence that suggests that the central nervous system processes force and position information in different ways.     

Different neuroplasticity for task targets and distractors

Adult learning-induced sensory cortex plasticity results in enhanced action potential rates in neurons that have the most relevant information for the task, or those that respond strongly to one sensory stimulus but weakly to its comparison stimulus. Current theories suggest this plasticity is caused when target stimulus evoked activity is enhanced by reward signals from neuromodulatory nuclei. Prior work has found evidence suggestive of nonselective enhancement of neural responses, and suppression of responses to task distractors, but the differences in these effects between detection and discrimination have not been directly tested. Using cortical implants, we defined physiological responses in macaque somatosensory cortex during serial, matched, detection and discrimination tasks. Nonselective increases in neural responsiveness were observed during detection learning. Suppression of responses to task distractors was observed during discrimination learning, and this suppression was specific to cortical locations that sampled responses to the task distractor before learning. Changes in receptive field size were measured as the area of skin that had a significant response to a constant magnitude stimulus, and these areal changes paralleled changes in responsiveness. From before detection learning until after discrimination learning, the enduring changes were selective suppression of cortical locations responsive to task distractors, and nonselective enhancement of responsiveness at cortical locations selective for target and control skin sites. A comparison of observations in prior studies with the observed plasticity effects suggests that the non-selective response enhancement and selective suppression suffice to explain known plasticity phenomena in simple spatial tasks. This work suggests that differential responsiveness to task targets and distractors in primary sensory cortex for a simple spatial detection and discrimination task arise from nonselective increases in response over a broad cortical locus that includes the representation of the task target, and selective suppression of responses to the task distractor within this locus.     

Effect of bright light on EEG activities and subjective sleepiness to mental task during nocturnal sleep deprivation

The purpose of this study was to investigate the effect of the exposure to bright light on EEG activity and subjective sleepiness at rest and at the mental task during nocturnal sleep deprivation. Eight male subjects lay awake in semi-supine in a reclining seat from 21:00 to 04:30 under the bright (BL; >2500 lux) or the dim (DL; <150 lux) light conditions. During the sleep deprivation, the mental task (Stroop color-word conflict test: CWT) was performed each 15 min in one hour. EEG, subjective sleepiness, rectal and mean skin temperatures and urinary melatonin concentrations were measured. The subjective sleepiness increased with time of sleep deprivation during both rest and CWT under the DL condition. The exposure to bright light delayed for 2 hours the increase in subjective sleepiness at rest and suppressed the increase in that during CWT. The bright light exposure also delayed the increase in the theta and alpha wave activities in EEG at rest. In contrast, the effect of the bright light exposure on the theta and alpha wave activities disappeared by CWT. Additionally, under the BL condition, the entire theta activity during CWT throughout nocturnal sleep deprivation increased significantly from that in a rest condition. Our results suggest that the exposure to bright light throughout nocturnal sleep deprivation influences the subjective sleepiness during the mental task and the EEG activity, as well as the subjective sleepiness at rest. However, the effect of the bright light exposure on the EEG activity at the mental task diminishes throughout nocturnal sleep deprivation.     

Total activation change of visual and motor area due to various disturbances

Brain activation is affected by gradient acoustic noise and various disturbances as well as by other primary tasks. Therefore, we have studied the effects of various disturbances of two different levels of difficulty, that is, weak and strong difficulty levels for primary visual and motor tasks. In the case of visual task with motor and mental disturbances, we found it decreased as motor and mental disturbance difficulty-level increased, compared with the case of without motor and mental disturbances. To the contrary, in the case of motor activity, the total activation of motor cortex with weak and with strong mental disturbance increased as mental disturbance difficulty-levels increased. Therefore, one can conclude that when mental disturbance is added, the visual cortex and motor cortex have an opposite result and when the difficulty-level of the disturbance is increased, the primary tasks are affected more significantly. Although the current observation is preliminary and requires more careful experimental study, it appears that various disturbance effects on brain functions (such as motor and visual cortical responses) produce significant differences in data observations.     

Changes in the space-time organization of the bioelectrical activity of the human brain on completing the solution of a mental task

Changes in spatial-temporal organization of human bioelectrical brain activity were studied following formal completion of the process of solution of mental tasks of various complexity. It was shown that in the first seconds after the response, desynchronization took place of cortical potentials, identical to the one observed in the process of solution; at frequencies of alpha- and beta-2-rhythms, predominant decrease took place of parameters of spatial-temporal biopotentials conjunction as compared to the level of calm alertness. Dynamics of recovery of calm alertness EEG characteristics is determined by subjective complexity for the subject of previous activity and by the degree of his confidence in the correctness of the obtained result. The latter is determined by individual-typological properties of the subject.     

The mapping of brain biopotentials during the solving of a verbal task]

Reverse averaging of cortical potentials from the moment of the motor response followed the verbal task solving (anagram riddle) revealed some brain potentials correlations with the process of a decision making. In the case of task solving the negative frontal wave with the latency 900-400 ms from the motor response was recorded. Intracortical interaction mapping of this potential showed the regular patterns of cortical functional connections in different frequency ranges (alpha, beta). Successful solving of the task was characterized with predominant interaction foci topography in the frontal and left-temporal cortical areas in alpha band and parietal zones in beta. The absence of the task solution was characterized with the parieto-occipital interaction foci in alpha band and their frontal localization in beta.     

Event-related desynchronization (ERD) patterns during memory processes: effects of aging and task difficulty

Event-related desynchronization (ERD) was studied in 10 young (mean age = 19.1) and 10 older (mean age = 62.8) subjects during two recognition tasks: verbal and visuo-spatial. The difficulty of these tasks varied according to the difficulty to distinguish between targets and distractors. EEGs recorded from 29 electrodes were used to compute ERDs from 14 source derivations in 125 msec intervals. Thereafter, they were displayed as spatio-temporal maps. The results show that desynchronization was more widespread in the visuo-spatial compared to the verbal task. This was observed in the two age groups, although it was more pronounced in the young subjects. The effect of task complexity was also influenced by the kind of material to be remembered: more differences between the two levels of difficulty were observed during the verbal task.The results revealed significant influences of the task and time variables on the ERD patterns. A distinct time course of the desynchronization phenomenon was observed to be related to the kind of recognition task. Age and task complexity interacted with the other variables.     

A dose-response investigation of the benefits of napping in healthy young,middle-aged and older adults

Older adults experience more fragmented sleep, greater daytime sleepiness and, nap more often than younger adults. Little research has investigated the effects of napping on waking function in older adults. In the present study, waking cognitive performance was examined in 10 young (mean age = 28 years), 10 middle-aged (mean age = 42 years) and 12 older adults (mean age = 61 years) following 60-min, 20-min and no nap conditions. It was expected that the older adults would need a longer nap to accrue benefits. Napping led to improvements for all age groups in subjective sleepiness, fatigue and accuracy on a serial addition/subtraction task. Waking electroencephalogram (EEG) confirmed that the participants were more physiologically alert following naps. There were no age differences in subjective reports or cognitive tasks; however, older adults had higher beta and gamma in the waking EEG, suggesting that they needed increased effort to maintain performance. Overall, older adults had smaller P2 amplitudes, reflecting their difficulty in inhibiting irrelevant stimuli, and delayed latencies and smaller amplitude P300s to novel stimuli, reflecting deficits in their frontal lobe functioning. Although older adults did garner benefits from napping, there was no evidence that they required longer naps to experience improvement.

     

Learning new gait patterns is enhanced by specificity of training rather than progression of task difficulty

The use of motor learning strategies may enhance rehabilitation outcomes of individuals with neurological injuries (e.g., stroke or cerebral palsy). A common strategy to facilitate learning of challenging tasks is to use sequential progression – i.e., initially reduce task difficulty and slowly increase task difficulty until the desired difficulty level is reached. However, the evidence related to the use of such sequential progressions to improve learning is mixed for functional skill learning tasks, especially considering situations where practice duration is limited. Here, we studied the benefits of sequential progression using a functional motor learning task that has been previously used in gait rehabilitation. Three groups of participants (N = 43) learned a novel motor task during treadmill walking using different learning strategies. Participants in the specific group (n = 21) practiced only the criterion task (i.e., matching a target template that was scaled-up by 30%) throughout the training. Participants in the sequential group (n = 11) gradually progressed to the criterion task (from 3% to 30% in increments of 3%), whereas participants in the random group (n = 11) started at 3% and progressed in random increments (involving both increases and decreases in task difficulty) to the criterion task. At the end of training, kinematic tracking performance on the criterion task was evaluated in all participants both with and without visual feedback. Results indicated that the tracking error was significantly lower in the specific group, and no differences were observed between the sequential and the random progression groups. The findings indicate that the amount of practice in the criterion task is more critical than the difficulty and variations of task practice when learning new gait patterns during treadmill walking.     

Pain-related and cognitive components of somatosensory evoked potentials following CO2 laser stimulation in man

We recorded cortical potentials evoked by painful CO₂ laser stimulation (pain SEP), employing an oddball paradigm in an effort to demonstrate event-related potentials (ERP) associated with pain. In 12 healthy subjects, frequent (standard) pain stimuli (probability 0.8) were delivered to one side of the dorsum of the left hand while rare (target) pain stimuli (probability 0.2) were delivered to the other side of the same hand. Subjects were instructed to perform either a mental count or button press in response to the target stimuli. Two early components (N2 and P2) of the pain SEP demonstrated a Cz maximal distribution, and showed no difference in latency, amplitude or scalp topography between the oddball conditions or between response tasks. In addition, another positive component (P3) following the P2 was recorded maximally at Pz only in response to the target stimuli with a peak latency of 593 msec for the count task and 560 msec for the button press task. Its scalp topography was the same as that for electric and auditory P3. The longer latency of pain P3 can be explained not only by its slower impulse conduction but also by the effects of task difficulty in the oddball paradigm employing the pain stimulus compared with electric and auditory stimulus paradigms. It is concluded that the P3 for the pain modality is mainly related to a cognitive process and corresponds to the P3 of electric and auditory evoked responses, whereas both N2 and P2 are mainly pain-related components.     

Multivariate information-theoretic measures reveal directed information structure and task relevant changes in fMRI connectivity

The human brain undertakes highly sophisticated information processing facilitated by the interaction between its sub-regions. We present a novel method for interregional connectivity analysis, using multivariate extensions to the mutual information and transfer entropy. The method allows us to identify the underlying directed information structure between brain regions, and how that structure changes according to behavioral conditions. This method is distinguished in using asymmetric, multivariate, information-theoretical analysis, which captures not only directional and non-linear relationships, but also collective interactions. Importantly, the method is able to estimate multivariate information measures with only relatively little data. We demonstrate the method to analyze functional magnetic resonance imaging time series to establish the directed information structure between brain regions involved in a visuo-motor tracking task. Importantly, this results in a tiered structure, with known movement planning regions driving visual and motor control regions. Also, we examine the changes in this structure as the difficulty of the tracking task is increased. We find that task difficulty modulates the coupling strength between regions of a cortical network involved in movement planning and between motor cortex and the cerebellum which is involved in the fine-tuning of motor control. It is likely these methods will find utility in identifying interregional structure (and experimentally induced changes in this structure) in other cognitive tasks and data modalities.     

Use of frequency domain analysis of skin conductance for evaluation of mental workload

A specially designed mental task was performed by 16 subjects for frequency domain analysis of skin conductance (SC) to evaluate mental workload. The task was to memorize target letters, detect them within a 4 x 4 alphabet arrangement, and answer whether the number of targets contained in the arrangement corresponded to a randomly displayed number. As the number of target letters increased, the score for the card-sort NASA Task Load Index (CSTLX) and task performance increased significantly. The traditional parameter for the number of transient wave forms of SC response (SCR) and the height of its wave did not show any significant effect of task difficulty. In addition, SCRs were subjected to Fourier transformation and integration of the spectrum from 0.03 to 0.5 Hz. This frequency domain analysis enabled detection of small differences in mental workload that could not be detected by traditional amplitude domain analysis. Frequency-based analysis enables easy processing of physiological signals and is very effective in evaluating mental stress using SC recorded under actual environmental conditions such as the driving of a vehicle.     

Dynamics of the electroencephalogram during performance of a mental task

Dynamics of the EEG activity — during the performance of a mental task — was investigated by the nonstationary power spectrum method. The performance of the mental arithmetic is associated with suppression of the alpha wave. The suppression of the alpha wave is not as marked as the alpha blocking accompanying opening of the eyes. Alpha wave suppression during the mental task was nonsymmetric around the center frequency of the alpha wave, and lower frequency components were suppressed more than high frequency components. An explanation of these observations is proposed in terms of decrease in the periods of alpha prevalence during performance of mental tasks.     

Effects of Relaxing Music on Mental Fatigue Induced by a Continuous Performance Task: Behavioral and ERPs Evidence

The purpose of this study was to investigate whether listening to relaxing music would help reduce mental fatigue and to maintain performance after a continuous performance task. The experiment involved two fatigue evaluation phases carried out before and after a fatigue inducing phase. A 1-hour AX-continuous performance test was used to induce mental fatigue in the fatigue-inducing phase, and participants’ subjective evaluation on the mental fatigue, as well as their neurobehavioral performance in a Go/NoGo task, were measured before and after the fatigue-inducing phase. A total of 36 undergraduate students (18–22 years) participated in the study and were randomly assigned to the music group and control group. The music group performed the fatigue-inducing task while listening to relaxing music, and the control group performed the same task without any music. Our results revealed that after the fatigue-inducing phase, (a) the music group demonstrated significantly less mental fatigue than control group, (b) reaction time significantly increased for the control group but not for the music group, (c) larger Go-P3 and NoGo-P3 amplitudes were observed in the music group, although larger NoGo-N2 amplitudes were detected for both groups. These results combined to suggest that listening to relaxing music alleviated the mental fatigue associated with performing an enduring cognitive-motor task.