Transient increases of synchronized neural activity during movement preparation: influence of cognitive constraints

The ability to prepare movement is an essential requirement for the control of goal-directed actions. It allows us to respond in an adaptable and swift manner to environmental conditions. In the present study, we manipulate cognitive context, by means of response probability, to modify the degree of movement preparation in a delayed cueing task performed with the right hand, and evaluate the neural dynamics (EEG coherence) and behavioural output (reaction time). Task-related coherence was stronger over the contralateral hemisphere. In particular, coherence between the left sensorimotor area and frontal (C3-F3, C3-FC3) and parietal (C3-P3) regions was increased during right-hand movement preparation as compared to rest in the alpha frequency band (8–12 Hz). Reducing response probability diminished the degree of functional coupling between C3-F3 and C3-FC3, and was associated with a prolonged reaction time. These findings suggest an association between neural dynamics and behavioural performance and emphasize that response predictability biases information processing in goal-oriented behaviour.     

Cortico-cortical coupling patterns during dual task performance

We investigated the neural correlates of dual task performance using EEG coherence as a measure of the functional coupling between cortical regions. Nine healthy participants performed a rhythmical movement with the right hand and an isometric contraction with the left hand, either initiated simultaneously or successively. EEG data revealed that dual task performance was associated with stronger coherence in left hemispheric and mesial areas than the sum of the tasks performed separately in the beta (>12–30 Hz), but not alpha (8–12 Hz), band. This effect was more pronounced when the two assignments were initiated simultaneously, as opposed to successively. The data demonstrate that the pattern of cortico-cortical coupling during bimanual actions is not just the sum of that associated with its component parts, but is increased according to coordinative demands and processing load.     

Influence of working memory on patterns of motor related cortico-cortical coupling

Working memory is implicated in various higher-order cognitive operations. We hypothesized that the availability of a temporal representation in working memory would limit the extent of cortico-cortical coupling necessary to undertake a self-paced rhythmic movement. To this end we examined modulations in cortico-cortical interactions as determined by EEG coherence during a delay interval and subsequent movement reproduction. Right hand movement was initially paced by a metronome beat every 0.9 s, followed by a delay interval, after which hand movement was repeated in an unpaced manner. Movement reproduction after a long (22.5 s, corresponding to 25 movement cycles) compared to a short (5.4 s, corresponding to 6 movement cycles) delay interval was associated with an increased degree of functional coupling in the beta frequency band (12–30 Hz) of the left (movement-driving) hemisphere (F3-FC3, F3-C3 and F3-P3 connections) as well as mesial regions (FCz-FC3, FCz-C3 and Cz-FC3 connections) even though overall behavioral characteristics were not influenced. In addition, analysis of the EEG coherence in the delay period revealed a bilateral frontal network (F3-F4, F3-FC4, F4-FC3 and FC3-FC4 connections). Activity in the latter tended to be synchronized in the theta band (4–8 Hz) and was significantly less strong at 22.5 s than 5.4 s. These data suggest that working memory may be partly subserved by synchronization in a bilateral frontal network and may provide an intrinsic contextual influence that shapes the pattern of cortico-cortical interaction during a given task.     

Persistent effects of high frequency repetitive TMS on the coupling between motor areas in the human

Repetitive transcranial magnetic stimulation (rTMS) shows promise as a treatment for various movement and psychiatric disorders. How rTMS may have persistent effects on cortical function remains unclear. We hypothesised that it may act by modulating cortico-cortical connectivity. To this end we assessed cortico-cortical coherence before and after high frequency rTMS of the motor cortex. Sixteen healthy subjects received a single train (5 Hz, active motor threshold, 50 stimuli) of rTMS to the left motor hand area. Spectral power and coherence estimates were calculated between different EEG signals at rest and while muscles of the distal upper limb were tonically contracted. Repetitive TMS over the left motor hand area caused a significant decrease in the intrahemispheric EEG-EEG coherence between motor and premotor cortex in the 10.7–13.6 Hz (upper alpha band) lasting a few minutes after stimulation. There was no significant change in interhemispheric EEG-EEG coherence between motor areas. Thus, high frequency rTMS of the motor cortex decreases ipsilateral cortico-cortical intrahemispheric in the upper alpha band. Electronic Publication     

Field dependence, laterality and the EEG

There is evidence that an individual's 'cognitive style' is related to lateralization of function in the brain, and that this in turn is associated with characteristic EEG coherence spectra. We tested the hypothesis that field dependence (a measure of cognitive organization) and hand preference (a measure of functional organisation) relate to EEG coherence measures in a specific way. The predicted associations were based on the proposal that right preferent individuals have a more specific, and left preferents a more diffuse, system of functional units in the cortex. The association between alpha band resting EEG coherence (sampled on two occasions for both hemispheres from 12 right and 12 left preferent individuals), field dependence (Nyborg's criterion of frame dependence on a rod and frame test), and laterality scores (questionnaire and manual performance), was measured by Kendall's coefficient of concordance (W). Significant associations support the proposed model except for coherence within the left preferents' right hemisphere. It is argued that the right hemisphere is more specifically organised in strong sinistrals than the general model would predict. These and other results support the use of EEC coherence measures in the study of cerebral functional organisation.     

A Comparative EEG Study in Normal and Autistic Children

We report here a comparative analysis of spectral power and mean coherence in the alpha, beta, and gamma rhythms in children aged 5–7 years, both normal and with early childhood autism, at rest and in conditions of a cognitive task (counting). In baseline conditions, both healthy children and those with autism showed a marked frontal-occipital alpha gradient. The cognitive task led to increases in the spectral power of the alpha1 range and its displacement into the left hemisphere without any alteration of alpha2; the task also produced a marked increase in spectral power in the alpha3 range. In healthy children, the cognitive task, as compared with baseline conditions, produced significant increases in the spectral power and coherence of the rapid rhythms in the central and frontal areas of the left hemisphere. In patients with early childhood autism, there was a right-sided predominance of spectral power in the alpha range both in baseline conditions and during the cognitive task. Baseline gamma-range spectral power in early childhood autism had greater values than in normal children and did not change during the cognitive task.     

Lateral Specialization of Cognitive Mode: II. EEG Frequency Analysis

This study reports a frequency analysis of hemispheric EEG asymmetries in normal subjects performing cognitive tasks. Language and arithmetic tasks were expected to engage primarily the left hemisphere; spatial and musical tasks were expected to engage primarily the right hemisphere. Both motor and non-motor tasks were used, e.g. writing a letter and composing a letter mentally. Recordings from temporal leads (T₃,T₄) and parietal leads (P₃,P₄) referred to the vertex C_z were subjected to discrete Fourier transforms; ratios of power from homologous leads (T₄/T₃, P₄/P₃) were computed in conventional frequency bands. These ratios (right/left) are significantly higher in verbal and arithmetic tasks than in spatial tasks primarily in the alpha band; the beta and theta bands show this effect less consistently. The delta band shows no such systematic effect of cognitive mode. Considering the alpha band alone reveals a task dependence of the asymmetry 2–5 times greater than we reported earlier for whole band power (1–35 Hz). Whenever a significant task dependence of asymmetry appears in any band, it is in the same direction: the hemisphere primarily engaged in the cognitive activity develops proportionately less power. The requirement of motor output increases the task dependence of alpha asymmetry and lowers alpha power levels.     

Cortico-cortical networks in patients with ideomotor apraxia as revealed by EEG coherence analysis

We sought to determine whether coherent networks which circumvent lesioned cortex are seen in patients with ideomotor apraxia (IMA) while performing tool-use pantomimes. Five normal subjects and five patients with IMA (three patients with corticobasal degeneration and two with left hemisphere stroke) underwent 64-channel EEG recording while performing three tool-use pantomimes with their left hand in a self-paced manner. Beta band (20-22 Hz) coherence indicates that normal subjects have a dominant left hemisphere network responsible for praxis preparation, which was absent in patients. Corticobasal degeneration patients showed significant coherence increase between left parietal-right premotor areas. Left hemisphere stroke patients showed significant coherence increases in a right parietofrontal network. The right hemisphere appears to store useable praxis representations in IMA patients with left hemisphere damage.     

Stability of EEG Laterality Effects

Task related interhemispheric asymmetries of ongoing EEG activity (alpha band) were tested for stability across three separate occasions. Seven cognitive tasks, presumed to differentially engage either the left or right cerebral hemisphere, were presented to 6 subjects. Involvement with the tasks was determined by evaluation of performance and with a subjective report on degree of involvement. Bilateral EEG was recorded over the parietal areas referenced to an ipsilateral ear, vertex and a central placement, on separate channels. Spectral intensity estimates of 8–13 Hz activity were used to form left/right ratios for determination of asymmetry. Intra-subject stability of alpha band activity was found to improve with the establishment of task validity and to be related to the electrode placement used.     

EEG power changes during a multiple level memory retention task.

EEG changes related to the amount of information held in memory during a 4-s retention period were studied. The predictability of the amount of information held in memory was varied. In the weighted condition, 60% of the trials contained only one item and the remaining 40% of the trials were evenly distributed between trials containing 3, 5, 7, or 8 items. In the random condition, the levels were equally represented and randomly presented. In the blocked condition the levels were equally represented but presented in five blocks containing only items from one of the levels. Initial widespread decreases in alpha band power were followed by increased activity in all three conditions. The more difficult of the five levels produced decreased alpha activity in more localized posterior left hemisphere sites. This suggests two alpha mechanisms, one associated with task engagement and the other related to the cognitive demands regardless of the presentation context. Theta band power increased over frontal scalp, and to a lesser extent over left parietal and temporal areas and bilateral occipital sites, during only the weighted condition. These changes were uniform over the entire retention period. Beta 2 activity was also influenced by the task difficulty and the time course of the retention period in the two conditions. Beta 2 activity resembled both alpha and theta in that in levels 1, 2 and 3 it acted like alpha with increasing power over time at numerous widespread sites while the higher difficulty levels showed higher power at the beginning of the retention period and then decreased.     

The Role of the Context of Cognitive Activity in the Recognition of Facial Emotional Expressions

The effects of the types of additional cognitive tasks (visuospatial or semantic) added to the context of experiments with a set to recognition of an emotionally negative facial expression were studied in healthy human subjects. Loading on working memory decreased the plasticity of the set: changes in the situation increased the number of erroneous recognitions of the facial expression. Differences were seen in the nature of erroneous recognitions (assimilative and contrast illusions) depending on the additional task. Analysis of coherence functions of cortical electrical potentials in the low-frequency alpha (8–10 Hz) and beta (14–20 Hz) ranges supported the hypothesis that increases in the loading on working memory lead to decreases in the involvement of the frontal mechanisms of selective attention in the formation and actualization of the set. This leads to slowing of the process of set shifting. Loading on working memory induced hemisphere asymmetry in prestimulus electrical activity: spatial synchronization of theta potentials significantly decreased in the right hemisphere and increased in the left. The functional significance of coherence connections in the theta range between the dorsolateral part of the prefrontal cortex and the temporal area in the right hemisphere for the process of set substitution is discussed.     

Correlation of alpha activity between the frontal and occipital cortex.

A method of modified coherence analysis was applied to the interpretation of EEG differences between the frontal and occipital cortex. This paper discusses a bidirectional communication model for the frontal and occipital cortex. Directed coherence method was used to analyze alpha activities over the scalp. The results show that both in the left and right hemisphere, slow waves in the alpha frequency band had high correlation in the frontal-occipital direction, and fast waves had high correlation in the occipital-frontal direction. It may suggest that the structure of information transmission is different for fast and slow waves of alpha rhythm.     

Coordinate processing during the left-to-right hand transfer investigated by EEG

Information about visuomotor tasks is coded in extrinsic, object-centered and intrinsic, body-related coordinates. For the reproduction of a trained task in mirror orientation with the opposite untrained hand, acquired extrinsic coordinates must be transformed. In contrast, intrinsic coordinates have to be modified during the execution of the originally oriented task. As shown recently, processes of coordinate transformations during the right-to-left hand transfer are associated with movement preparation and occur preferentially in the left hemisphere. Here, movement-related potentials, EEG power, and EEG coherence were recorded during the repetition of a drawing task previously trained by the nondominant left hand (Learned-task) and its execution in original and mirror orientation by the right hand (Normal- and Mirror-task). To identify EEG correlates of coordinate processing during intermanual transfer rather than effects due to the use of the right versus left hand, only those EEG data were analyzed which differed between the Normal- and Mirror-tasks. Whereas the Normal-task did not differ from the Learned-task in any of these predefined EEG parameters, beta coherence increased in the Mirror-task in the period ranging from 1 to 2 s after movement onset. These increases were especially prominent between hemispheres but were also observed symmetrically in the parieto-frontal electrode pairs of both hemispheres. Behavioral data revealed that the performance in the Learned- and both transfer tasks improved after left-hand training. Results of the present study indicate that coordinate transformation during the left-to-right hand transfer occurs in the phase of movement execution and affects predominantly extrinsic coordinates. Intrinsic coordinates are presumably mainly used in their original form. The modification of extrinsic coordinates is accompanied by increased information flow between both hemispheres; thereby inter-hemispheric connections—as mediated via the corpus callosum—seem to play a central role.     

Bimanual coordination affects motor task switching

Task-switching paradigms have generally been used to investigate cognitive processes involved in decision making or allocating attention. This work extended the task-switching paradigm into the motor domain in order to investigate the consequences of an unexpected environmental perturbation on reaction time and movement time. Typically, task-switching paradigms have investigated consequences of rearranging task sets from one trial to the next; this work explored rearranging planned movements within the context of a single trial. Of particular interest was how the motor system reorganizes coordination patterns when reaching amplitude congruency is manipulated between the two hands. Results for Experiment 1 and the far distance in Experiment 2 indicated that reaction time switch costs were the smallest during congruent task-switch trials, where reaching amplitudes between the two hands were the same. This implies that a planned movement parameter for one hand is accessible for the other hand in the circumstance of an unexpected task switch. However, the reversed congruency effects found for the near distance in Experiment 2 suggest that the ability to capitalize on stored parameter information to decrease reaction time is dependent on environmental factors and task instructions. Movement time results showed that even if a movement with one hand is aborted in mid-execution, it can still influence the performance of the other hand during a task switch. This suggests that bimanual coordination can affect prehensile performance even though only one hand has a goal to achieve.     

Asymmetric eeg changes as method actors generated emotions

Nine method actors recalled personal experiences to create emotional states of sexual arousal or depression. Electroencephalographic (EEG) data recorded from left and right frontal, central, parietal and occipital locations were spectrally analyzed for power in each major frequency band and for coherence among all pairs of channels. Contrasts between the emotion conditions showed less alpha power (greater activation) over the right hemisphere for sexual arousal than for depression. Analysis of coherence topography showed higher coherence in right central and posterior regions during the sexual arousal condition. These data are consistent with previous evidence of right hemisphere contribution to sexual arousal and suggest further that asymmetric patterns of brain activity may be associated with specific emotional states.     

Sex differences in EEG coherence during a verbal memory task in normal adults.

Coherence analysis was applied to the EEG of 15 female and 15 male subjects who had to memorise dichotically presented lists of concrete nouns. The EEG was recorded from 16 scalp electrodes placed in accordance with the 10/20 system. The results show significant gender-related differences in total coherence reactivity due to a greater increase of rest to task coherence in female than in male subjects. Women differed by showing higher coherence reactivity in the right hemisphere for all analysed (theta 1, theta 2, alpha 1, and alpha 2) frequency bands. They also had more extensive task-induced increases of interhemispheric coherence in theta bands in comparison with single changes in male subjects. In women these changes were mainly between the frontal electrodes of the left hemisphere paired with posterior electrodes of the other hemisphere. These findings indicate sex-related differences in functional cortical organisation during verbal memory tasks.     

The specificity of intrahemispheric EEG alpha coherence asymmetry related to psychological task

Male right handed subjects performed two parallel verbal and nonverbal memory tasks, known to be associated with the anterior temporal lobe, while EEG was recorded from temporal sites referred to either FZ or to linked mastoids. Intrahemispheric coherence and power in the alpha band were calculated. Coherence effects were observed, independent of reference site, which associated the right hemisphere and nonverbal tasks with increased coherence. These effects appear to be relatively specific to more anterior temporal electrode pairs, and confirm previous findings. Power effects demonstrated the difficulty of assessing task-dependent changes independent of reference site, and suggested that specific alpha enhancement may be observed with task involvement. The contribution of coherence analysis to the study of cerebral organisation is discussed.     

Increasing right hand dominance with age on a motor skill task

A standardized pegboard task was used to investigate changes in manipulative skill as a function of age in 119 right-handed subjects. The typical pattern of cognitive impairment in old age indicates a relative preservation of functions which depend on the integrity of the left hemisphere. In accord with these observations, we predicted that, with increasing age, right hand motor skills would be better preserved than left hand skills. We found this on initial exposure to the task (P less than 0.01); however, the phenomenon was masked by practice, because older subjects (over 60 years of age) derived more improvement to their left hand motor skill, as a result of practice, than they did to their right hand skill (P less than 0.05). The asymmetrical effects of ageing on motor skill may be relevant to the increasing prevalence of emotional lability and neurosis in the elderly, since emotional control is thought to be dependent on right hemisphere mechanisms.     

Interference asymmetry involving concurrent tasks performed by native American students

It is assumed that Native Americans are right‐hemisphere dominant and therefore need special teaching techniques. This study examined the language and spatial lateralization of monolingual English‐speaking Native American students by means of the cognitive‐manual dual‐task model. The results revealed the following asymmetric interference: greater right‐hand disruption while reading, greater left‐hand disruption while solving spatial problems, fewer words read while tapping with the right hand, and fewer spatial problems solved while tapping with the left hand. However, the “good” Native American students had normal (left‐hemisphere language/right‐hemisphere spatial) lateralization, whereas the “poor” students had atypical lateralization for righthanders, primarily involving both left‐hemisphere language and left‐hemisphere spatial function. The neurological consequence of crowding language and spatial processing into the same hemisphere is discussed. Two major conclusions are that the Native American students of this study were not right‐hemisphere dominant, and that nonnormal language/special lateralization resulted in learning problems, possibly suggesting a new subclassification within the special education/handicapping condition of learning disabilities.