The brain-trigger design. A powerful tool to investigate brain-behavior relations

The enigma of infra-slow fluctuations in the human EEG

Spontaneous Infra-Slow Fluctuations (ISFs) of the human EEG (EEG-ISFs) were discovered 60 years ago when appropriate amplifiers for their recordings were designed. To avoid skin-related artifacts the recording of EEG-ISFs required puncturing the skin under the electrode. In the beginning of the 21st century the interest in EEG-ISFs was renewed with the appearance of commercially available DC-coupled amplified and by observation of ISFs of the blood oxygen level–dependent (BOLD) functional magnetic resonance imaging signal at a similar frequency. The independent components of irregular EEG-ISFs were shown to correlate with BOLD signals which in turn were driven by changes in arousal level measured by galvanic skin response (GSR), pupil size and HRV. There is no consensus regarding the temporal organization of EEG-ISFs: some studies emphasize the absence of peaks on EEG-ISFs spectra, some studies report prominent oscillations with frequency around 0.1 or 0.02 Hz, while some emphasize multiple discrete infraslow oscillations. No studies used parameters of EEG-ISFs as neuromarkers to discriminate psychiatric patients from healthy controls. Finally, a set of working hypotheses is suggested that must be tested in future research to solve the enigma of EEG-ISFs.

Arousal and attention: self-chosen stimulation optimizes cortical excitability and minimizes compensatory effort

Cortical excitability is assumed to depend on cortical arousal level in an inverted U-shaped fashion: Largest (optimal) excitability is usually associated with medium levels of arousal. It has been proposed that under conditions of low arousal, compensatory effort is exerted if attentional demands persist. People tend to avoid this resource-consuming top-down compensation by creating or selecting environmental conditions that provide sufficient bottom-up stimulation. These assumptions were tested in an attention-demanding dual-task situation: We combined a simulated driving task to induce three different arousal levels by varying stimulation (high vs. low vs. self-chosen) with a visual two-stimulus paradigm to assess cortical excitability by the initial contingent negative variation (iCNV) component of the event-related potential. Additionally, we analyzed the oscillatory power of the beta2 band of the electroencephalogram at anterior frontal sites, which is assumed to reflect low-arousal compensatory activity. The iCNV amplitude differed in all three arousal conditions as expected: It was highest in the condition of self-chosen stimulation and lowest in the low- and high-arousal conditions. Additionally, in the low-arousal condition, anterior frontal beta2 power was found to be significantly higher than in the other two conditions and correlated positively with subjective strain. This pattern of results suggests that subjects select medium levels of stimulation which optimize cortical excitability under attentional demand conditions. The elevated fronto-central beta2 power in the low-stimulation condition may indicate the involvement of the anterior cingulate cortex in compensating for reduced arousal by top-down stimulation of the noradrenergic arousal system.

Brain Slow Potentials and Postural Sway Behavior During Sharpshooting Performance

In the present study, the relation of preparatory brain slow potentials (SPs) to postural body sway during sharpshooting performance was examined. SPs from frontal, left-central, and right-central areas were recorded from 6 elite and 6 non-elite sharpshooters during a realistic simulated shooting task. A force platform technique was used in the recording of postural sway. The results showed that body sway, as indexed by sway amplitude and mean velocity, was associated with the concomitant SP changes. That relationship was dependent on the shooter's expertise level, however. The main finding among the elite shooters was that the reduced amplitude of body sway coincided with reduced frontal positivity, whereas in the non-elite shooters, the amplitude of sway and the mean sway velocity in the anteroposterior direction were typically accompanied by the lateralization of central negativity. Those findings offer some new insights for evaluating the functional significance of preparatory brain SPs associated with psychomotor processing in sharpshooting. The results from the present study also have implications for the understanding of the postural strategies employed by shooters of different expertise levels.