Cerebral potentials during skilled slow positioning movements.

Movement-related potentials recorded from the scalp of man were investigated in two skilled positioning tasks, requiring flexions at different joints of the upper extremities. The average response time was approximately 1 sec. Subjects paced their movements themselves and performed without visual control or other external cues. After each trial a delayed visual feedback was given. It was found that the negative potential shift prior to the EMG onset, the 'Bereitschaftpotential', is followed by a persisting negativity during the execution of the action until the target position is reached. Approximately at this point a positive-going deflection appears. This 'goal-directed movement potential' is composed of at least two components: (a) a widely distributed, centrally dominant negativity, and (b) a smaller negative wave over the sensorimotor cortex contralateral to the responding limb. Small variations in response force do not influence the amplitude of the potentials. A negative shift in anticipation of the visual feedback has a topography different from the movement-related potentials, being predominant over the right hemisphere independent of the hand used

Hemispheric asymmetry of feedback-related potentials in a positioning task: comparison of right- and left-handed subjects.

Previous research has demonstrated that delayed nonverbal information feedback (IF) about the correctness of a positioning movement is preceded by a contingent negative variation (CNV) which is larger over the right hemisphere independent of movement side. It was hypothesized that this asymmetry is a manifestation of functional hemispheric specialization, and that, therefore, the distribution of the differences between CNV amplitude measures of the two hemispheres should be different in right-handed and left-handed subjects. The latter group should show a mean asymmetry score closer to zero, and a larger between-subject variance of the asymmetry scores. The present investigation was intended to test these assumptions in samples of rigorously defined right-handers (n = 12) and left-handers (n = 8). The results revealed the expected group differences of the CNV asymmetry scores. In addition, the P1-N1 peak-to-peak amplitude of the IF-evoked potentials was similarly lateralized as the pre-IF CNV and showed the same group differences. In contrast, the handedness groups did not differ in the contralateral lateralization of the movement-related potential shift in the same task.

Contingent negative variation and alpha attenuation responses in children with different abilities to concentrate.

In three paralleled groups, each of seven children (age, 11 years) with reliable high, average and low ability to concentrate, measured by psychological tests, the contingent negative variation (CNV) and the concomitant alpha attenuation responses were studied in warned reaction time experiments. Stimuli were tone (S1) and patterned light (S2). In half of the trials, S2 was a square, in the other half a triagle, stimuli being projected in random order onto the fixation point. In two experiments the children had to react (a) to each type of S2, and (b) selectively to one type of S2. Significant group differences were found. In comparison to the children with low ability to concentrate, the children with average and especially those with high ability to concentrate showed: (1) stronger central occipital alpha attenuation responses to the warning stimulus, but no differences in the early CNVs; (2) more occipital alpha reduction and enhanced development of central negativity before the imperative stimulus; (3) task-specific modulation of these responses, i.e. larger pre-S2 rise in negativity in the simple reaction task, and stronger pre-S2 reduction of alpha amplitudes in the discriminative reaction task.

Late components of average evoked potentials in children with different abilities to concentrate.

Three matched groups, each of seven 11-year-old children with good, average and poor ability to concentrate were selected. Evoked potentials and EEG alpha amplitude changes after visual imperative stimuli were studied in warned reaction time experiments. The children with poor ability to concentrate (compared with the other groups) showed longer latencies of the P2 component and reduced amplitudes of the P2-N2 deflection at the vertex. Similar, although attenuated, effects were found in the Fz derivation. No group effects could be established for Oz. These findings are discussed in relation to group differences in pre-stimulus negativity and alpha attenuation, as reported in a previous paper.

Hyperactive behavior and EEG arousal reactions in children.

EEG arousal reactions and parameters of spontaneous EEG activity were studied in two extreme groups of behavior problem children (11 hyperactives and 11 non-hyperactives), selected on the basis of a rating of motor restlessness the core symptom of the "hyperactivity syndrome". The EEG was recorded in three reaction time experiments: a tone light conditioning paradigm and two series with random stimulation. An automatic analysis of EEG parameters was employed to describe the time functions of alpha amplitudes in the single trial. The main findings are: 1. In periods free from stimulation, hyperactive children have higher alpha and beta amplitudes, more alpha waves and a smaller amount of beta waves. This indicates a lower state of EEG arousal in the hyperactives. 2. The amplitude reduction to tone (in the single trial) develops more slowly in the hyperactive group. This group difference increases over the experimental situations. 3. The arousal responses to tone, in terms of the level of maximum amplitude reduction, become comparably weaker in the hyperactives across the experiments. 4. Under all experimental conditions the hyperactives exhibit shorter arousal responses to the light stimulus than the non-hyperactive children. 5. Reaction time performance of the groups is clearly different, hyperactives showing the longer latencies. 6. Although conditional changes in the arousal reactions to both stimuli are reliably demonstrable in all children, the groups show no difference in the corresponding measures. These findings are discussed under the aspects of activation and of attention behavior of the subjects.

Cerebral potentials during smooth goal-directed hand movements in right-handed and left-handed subjects.

During smooth goal-directed hand movements a negative potential shift can be recorded from the human scalp. This goal-directed movement potential (GDMP) is preponderant over central areas with a maximum at the vertex and, over the motor cortex, contralaterally larger than ipsilaterally to the moving hand. In 11 right-handed and 6 left-handed subjects, the morphology and distribution of these potential shifts were studied in relation to task differences, moving hand and handedness. The results show a functional differentiation of two components of the GDMP: (1), a lateralized, slow negative wave, restricted to the precentral area and selectively varying with the hand used, and (2), a widespread, bilateral symmetrical component, selectively influenced by task-specific and individual factors. Two effects reflect an influence of the subject's handedness on the GDMP: (A) averaged for both hand conditions, there are larger amplitudes over the hemisphere contralateral to the dominant hand, and (b), averaged for both hemispheres, larger amplitudes result from using the non-dominant hand.

Scalp recorded slow potential shifts during isometric ramp and hold contractions in human subjects.

During voluntary isometric slow ramp contractions of the hand up to an internally defined target force level sustained negative potential shifts in the EEG were recorded from 6 human subjects. The potential shifts are composed of (a) a bilateral wide spread negativity with a maximum amplitude at the vertex, and (b) a smaller negative wave contralateral to the responding hand with a maximum over the respective motor area. Both components disappear during a voluntary isometric isotonic contraction when subjects have to maintain a stable force level for some seconds.

Somatosensory evoked potentials to mechanical disturbances of positioning movements in man: gating of middle-range components.

Somatosensory evoked potentials (SEPs) and EMG responses to mechanical disturbances of positioning movements of the index finger were recorded from normal subjects who performed smooth flexions against the constant load of a torque motor in order to reach a specified target zone. According to a random series 60% of the movements were disturbed by step increases or decreases of the load which subjects had to compensate for (movement condition, MC). As control procedures (a) the same stimuli were applied while the subject had to maintain a constant finger position against the same load (hold condition, HC), and (b) comparable mechanical stimuli were administered to the stationary relaxed finger (resting condition, RC). In MC and HC, the EMG responses consisted of a long-latency (53-61 msec) reflex component, and a 'voluntary' component (98-134 msec). In all 3 conditions, the sequential SEP deflections measured over the sensorimotor cortex included peaks P85 (ipsilateral), N150 (bilateral) and P220 (bilateral). A contralateral N90 component (onset latency 55-60 msec), present in HC and RC, was markedly reduced or absent in MC. Neither in the preceding nor in the consecutive SEP components were there any significant condition-dependent differences, though the N150 showed a trend to diminished amplitude in MC as well. The suppression of SEP components in MC is discussed in terms of efferent and afferent 'gating' actions exerted on the somatosensory input during movement.

Relationships between the late component of the contingent negative variation and the bereitschaftspotential.

The purpose of this study was to determine whether the late component of the contingent negative variation (CNV) in a S1-S2-respond paradigm shares critical features with the Bereitschaftspotential (BP) prior to self-paced voluntary movements. In a group of 8 subjects, the late CNV and the BP exhibited: (a) similar effects of response speed variation, (b) corresponding influences of subjective factors, and (c) a similar scalp distribution with the exception that the BP was much more lateralized. In contrast, no such relationships were found between early CNV and BP.