Paradoxical lateralization of brain potentials during imagined foot movements

Rhythmic entrainment of slow brain activity preceding leg movements

OBJECTIVE

The time course of the contingent negative variation (CNV) as well as beta-power are known to entrain to regular task rhythms, revealing implicit anticipatory timing. Thus far, these effects have been established for manual responses only. Here we investigate entrainment preceding leg movements.

METHODS

High-density EEG was recorded while participants were standing and responded to series of rhythmically presented arrow stimuli by making brisk leg movements. The standard interval between reaction stimuli differed between series and was either 1500 or 2000 ms. Each series' final interval was 1750 ms, representing a timing perturbation.

RESULTS

Entrainment was manifested in the CNV time course, where the maximum amplitude was reached just before the next stimulus was presented. The pattern of beta-(de)synchronization similarly entrained to the task rhythm. CNV scalp topographies suggested effector dependency of the entrainment-induced CNV.

CONCLUSION

We demonstrate that lower limb motor control, like upper limb control, readily entrains to a regular task rhythm.

SIGNIFICANCE

These findings are relevant to Parkinson's disease (PD), where problems are found in rhythm processing and temporal preparation. Investigation of the neural correlates of leg movement entrainment is important in view of presumed relations between entrainment and cueing of gait in PD.

Classifying EEG signals preceding right hand, left hand, tongue, and right foot movements and motor imageries

OBJECTIVE

To use the neural signals preceding movement and motor imagery to predict which of the four movements/motor imageries is about to occur, and to access this utility for brain-computer interface (BCI) applications.

METHODS

Eight naïve subjects performed or kinesthetically imagined four movements while electroencephalogram (EEG) was recorded from 29 channels over sensorimotor areas. The task was instructed with a specific stimulus (S1) and performed at a second stimulus (S2). A classifier was trained and tested offline at differentiating the EEG signals from movement/imagery preparation (the 1.5-s preceding movement/imagery execution).

RESULTS

Accuracy of movement/imagery preparation classification varied between subjects. The system preferentially selected event-related (de)synchronization (ERD/ERS) signals for classification, and high accuracies were associated with classifications that relied heavily on the ERD/ERS to discriminate movement/imagery planning.

CONCLUSIONS

The ERD/ERS preceding movement and motor imagery can be used to predict which of the four movements/imageries is about to occur. Prediction accuracy depends on this signal's accessibility.

SIGNIFICANCE

The ERD/ERS is the most specific pre-movement/imagery signal to the movement/imagery about to be performed.

Changes in cortical relative power in patients submitted to a tendon transfer: a pre and post surgery study

The aim of this study is analyze possible modifications in the cerebral cortex, through quantitative electroencephalography (qEEG) in patients submitted to a tendon transfer procedure (posterior tibialis) by the Srinivasan's technique. Four subjects (2 men and 2 women), 49.25 age average (SD +/ 21.4) were studied. All subjects have been through surgical procedure due to leprosy and had, at least, two years of drop foot condition. The qEEG measured the electrocortical activity (relative power) between 8 and 25 Hz frequencies pre and post surgery. A paired t test analyzed all data (p< or =0,05). The results show significant alterations in the alpha relative power, electrodes F7 (p=0.01) and F8 (p=0.021). Altogether, based on findings of the current literature, we can conclude that the tendon transfer procedure suggests electrocortical alterations sensitive to specific qEEG bands.

The beat goes on: rhythmic modulation of cortical potentials by imagined tapping

A frequency analysis was used to tag cortical activity from imagined rhythmic movements. Participants synchronized overt and imagined taps with brief visual stimuli presented at a constant rate, alternating between left and right index fingers. Brain potentials were recorded from across the scalp and topographic maps made of their power at the alternation frequency between left and right taps. Two prominent power foci occurred in each hemisphere for both overt and imagined taps, one over sensorimotor cortex and the other over posterior parietal cortex, with homologous foci in opposite hemispheres arising from oscillations 180 degrees out of phase. These findings demonstrate temporal isomorphism at a neural level between overt and imagined movements and illustrate a new approach to studying covert actions.