T. Elbert

EEG and slow cortical potentials in anticipation of mental tasks with different hemispheric involvement

Mental arithmetic is supposed to be processed by the left hemisphere, while pattern matching has been considered to be processed by the right hemisphere. These different mental tasks were presented to 16 right-handed male subjects. As a variable task difficulty was varied for the two task categories. The task presentations were preceded by 6 sec warning stimuli which indicated the level of difficulty of the task. EEG and slow cortical potentials (SCPs) were recorded from temporal and precentral leads of both hemispheres. The reference was noncephalic. During the anticipation interval beta-activity was enhanced above the hemisphere primarily involved in the particular task. SCPs failed to show a comparable clear pattern. A late negative component showed task-dependent asymmetries prior to easy tasks, but not prior to difficult tasks.

EEG and slow brain potentials during anticipation and control of painful stimulation

Cerebral responses in anticipation of painful stimulation and while coping with it were investigated in a fakir and 12 male volunteers. Experiment 1 consisted of 3 periods of 40 trials each. During period 1, subjects heart one of two acoustic warning stimuli of 6 sec duration signalling that either an aversive noise or a neutral tone would be presented at S1 offset. During period 2, subjects were asked to use any technique for coping with pain that they had ever found to be successful. During period 3, the neutral S2 was presented simultaneously with a weak electric shock and the aversive noise was presented simultaneously with a strong, painful shock, again under pain copying instructions. EEG activity within the theta band increased in anticipation of aversive events. Theta peak was most prominent in the fakirs EEG. A negative slow potential shift during the S1-82 interval was generally more pronounced in anticipation of the aversive events that the neutral ones, even though no overt motor response was required. Negativity tended to increase across the three periods, opposite to the usually observed diminution. In Experiment 2, all subjects self-administered 21 strong shock-noise presentations. The fakir again showed more theta power and more pronounced EEG negativity after stimulus delivery compared with control subjects. Contrary to the controls, self-administration of shocks evoked a larger skin conductance response in the fakir than warned external application.

Effect of an ACTH 4–9 analog on human cortical evoked potentials in a constant foreperiod reaction time paradigm

Abstract Thirty male volunteers, receiving either 40 mg ACTH 4–9 analog (Org 2766) or 40 mg placebo in a double-blind setting, participated in an experiment which investigated cortical evoked potentials, slow cortical potentials, EEG power spectrum, heart rate and response speed within a constant foreperiod reaction time paradigm. EEG was recorded frontally, precentrally and parietally. Subjects receiving Org 2766 responded significantly faster than placebo controls. Larger or advanced evoked potential components, a smaller late slow wave component, a tendency for more activity in lower alpha range and more pronounced decrease in mean heart rate across trials were found in peptide subjects as compared to placebo controls. These results suggest an effect of Org 2766 on cortical processes associated with early stimulus selection and processing.

Slow Cortical Potentials and Response Speed

Publisher Summary This chapter discusses slow cortical potentials and response speed. The relationship between slow cortical potentials (SCPs) and response speed is investigated by training subjects to induce different potential shifts of SCPs. Previous results had demonstrated that human subjects are able to achieve instrumental control over SCPs by a biofeedback procedure by which they learned to change their cortical potentials toward more or less negativity depending on signal tones. Two groups of 10 right-handed male student volunteers are investigated. Subjects get monetary gratuity depending on their success in the feedback task. Results demonstrate that instrumental control of SCPs is achieved by biofeedback training. They, furthermore, suggest that the visual, spatial feedback may be processed and stored in the right hemisphere (C4) that may result in larger amplitudes recorded from C4 and in larger differences between the required polarities in group 1 (C4 feedback). Differences between the trials with required negativity and positivity are maintained and even enlarged during reaction time trials without feedback. And finally, larger negative shifts resulted in shorter response latencies compared to less negative shifts.