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.

Perception and understanding of dispositions and intentions of others through their actions are of immense importance for adaptive daily-life behavior and social communication. Here we ask whether, and, if so, how this ability is impaired in adolescents who were born premature and suffer early periventricular damage, periventricular leukomalacia (PVL) that affects brain connectivity. The visual event arrangement (EA) task was administered to PVL patients and two control groups, premature-born and term-born adolescents without brain abnormalities on a magnetic resonance imaging scan. Performance on the EA task was significantly lower in PVL patients as compared with controls. No difference was found between premature-born participants without lesions and term-born controls. Performance on the EA task was inversely related to the volumetric extent of lesions in the parieto-occipital regions of both hemispheres and, in particular, to the right temporal periventricular lesions. Whereas our earlier work reveals that compromised visual processing of biological motion, impairments in visual navigation, and other visual-perceptual disabilities in PVL patients are associated with parieto-occipital lesions, difficulties in the visual EA task solely are specifically linked to the right temporal periventricular lesions. For the first time, we show that the severity of the right temporal PVL can serve as a predictor of the ability for perception and understanding of others' actions. We assume that impairments in this ability in PVL patients are caused by disrupted brain connectivity to the right temporal cortex, a key node of the social brain.

Brain activation during executed (EM) and imagined movements (IM) of the right and left hand was studied in 10 healthy right-handed subjects using functional magnetic resonance imagining (fMRI). Low electromyographic (EMG) activity of the musculi flexor digitorum superficialis and high vividness of the imagined movements were trained prior to image acquisition. Regional cerebral activation was measured by fMRI during EM and IM and compared to resting conditions. Anatomically selected regions of interest (ROIs) were marked interactively over the entire brain. In each ROI activated pixels above a t value of 2.45 ( p < 0.01) were counted and analyzed. In all subjects the supplementary motor area (SMA), the premotor cortex (PMC), and the primary motor cortex (M1) showed significant activation during both EM and IM; the somatosensory cortex (S1) was significantly activated only during EM. Ipsilateral cerebellar activation was decreased during IM compared to EM. In the cerebellum, IM and EM differed in their foci of maximal activation: Highest ipsilateral activation of the cerebellum was observed in the anterior lobe (Larsell lobule H IV) during EM, whereas a lower maximum was found about 2-cm dorsolateral (Larsell lobule H VII) during IM. The prefrontal and parietal regions revealed no significant changes during both conditions. The results of cortical activity support the hypothesis that motor imagery and motor performance possess similar neural substrates. The differential activation in the cerebellum during EM and IM is in accordance with the assumption that the posterior cerebellum is involved in the inhibition of movement execution during imagination.