Chewing has been shown to alleviate feelings of sleepiness and improve cognitive performance during the day. This study investigated the effect of chewing on alertness and cognitive performance across one night without sleep as well as the possible mediating role of cardiac autonomic activity. Fourteen adults participated in a randomized, counterbalanced protocol employing a chewing, placebo and caffeine condition. Participants completed tasks assessing psychomotor vigilance, tracking, grammatical reasoning, alertness and sleepiness each hour across the night. All participants received either placebo or caffeine (200 mg), while the chewing condition also chewed on a tasteless and odorless substance for 15 min each hour. Heart rate (HR), root mean square of the successive differences in R-R intervals on the ECG (RMSSD), and preejection period (PEP) were simultaneously recorded. Alertness and cognitive performance amongst the chewing condition did not differ or were in fact worse when compared with placebo. Similarly, measures of HR and RMSSD remained the same between these two conditions; however, PEP was reduced in the later part of the night in the chewing condition compared with a relative increase for placebo. Caffeine led to improved speed and accuracy on cognitive tasks and increased alertness when compared with chewing. Relative increases in RMSSD and reductions in HR were demonstrated following caffeine; however, no change in PEP was seen. Strong associations between cardiac parasympathetic activity and complex cognitive tasks, as well as between subjective alertness and simpler cognitive tasks, suggest a differential process mediating complex versus simple cognitive performance during sleep deprivation.

Psychophysiological responses are considered to be a mediating factor in the development of pathological gambling (PG) and PG has been associated with differential arousal levels during gambling. Yet little is known about the specific psychophysiological responses to wins and losses in PG. This study investigated heart rate (HR) and skin conductance responses (SCRs) during the Iowa Gambling Task (IGT) in an adult PG group (n=46) and a normal control (NC) group (n=47). Anticipatory psychophysiological reactions to disadvantageous and advantageous choices during the IGT and psychophysiological responses to wins and losses were measured. The PG group performed worse than the NC group on the IGT and exhibited lower anticipatory SCRs and HR decreases when pondering choices of disadvantageous card decks during the IGT. The PG group showed a decrease in HR after losses and wins, whereas the NC group showed a decrease in HR after losses, but an increase in HR after wins. Reward and punishment sensitivity as measured by the self-report BIS/BAS scale influenced IGT performance and psychophysiological responses, but in general these effects were similar for the PG group and the NC group. Lower anticipatory psychophysiological responses to disadvantageous choices in PG suggest impaired risk assessment in this group. Absence of a HR increase after wins possibly implies that reward sensitivity is decreased in PG. Because levels of reward and punishment sensitivity were associated with differential anticipatory HR responses to advantageous and disadvantageous decks, it would be advisable to include this taxonomy in studies on psychophysiological responses to rewards and losses.

Objective
Patterns of low autonomic arousal have consistently been related to delinquency and disruptive behavior disorders (DBD) in children and adolescents. Findings on another stress regulating mechanism, the hypothalamic pituitary adrenal (HPA) axis, have been inconsistent, which may partly be due to not considering specific stress reactivity measures. Therefore, the aim of the present study was to investigate the relationship between disruptive behavior in male adolescents and their HPA and autonomic reactivity to a standard public speaking task (PST).
Method
Responsivity to the PST of cortisol, heart rate (HR), skin conductance level (SCL) and self-reported negative feelings was measured, and compared between 12and14-year-old boys who attended a delinquency diversion program (DP), with and without DBD (DP+, n=22 and DP−, n=49, resectively), and matched normal controls (NC, n=30). DBD diagnoses were based on a structured psychiatric interview.
Results
The DP+ group, but not the DP− group, showed a significantly decreased cortisol and HR response during the PST as compared with the NC group. No significant effects were found for SCL. All subjects connoted the task negatively.
Conclusions
The results indicate that low cortisol and HR responsivity to stress may be a neurobiological marker for delinquent boys with DBD, but not for those without DBD. Directions for future research and clinical implications are discussed.

Recently, devices have become available that allow non-invasive measurement of stroke volume and cardiac output through ambulatory thorax impedance recording. If such recordings have adequate temporal stability, they offer great potential to further our understanding of how repeated or chronic cardiovascular activation in response to naturalistic events may contribute to cardiovascular disease. In this study, 24h ambulatory impedance-derived systolic time intervals, stroke volume and cardiac output were measured in 65 healthy subjects across an average time span of 3 years and 4 months. Stability was computed separately for sleep and daytime recordings. To avoid confounding by differences in posture and physical activity across measurement days, temporal stability was computed using sitting activities only. During the day intraclass correlations were moderate for stroke volume (.29–.46) and cardiac output (.33–.46) and good for systolic time intervals (.55–.81). When test–retest comparison was limited to two comparable days (two work days or two leisure days), correlations for both SV (.42–.46) and CO (.43–.50) improved. Conclusion: Moderate long-term temporal stability is found for individual differences in ambulatory stroke volume and cardiac output measured by impedance cardiography.

The purpose of the current study was to validate the change in thoracic impedance (dZ) derived respiratory signal obtained from four spot electrodes against incidental spirometry. Additionally, a similar validation was performed for a dual respiratory belts signal to compare the relative merit of both methods. Participants were 38 healthy adult subjects (half male, half female). Cross-method comparisons were performed at three (paced) respiration frequencies in sitting, supine and standing postures. Multilevel regression was used to examine the within- and between-subjects structure of the relationship between spirometric volume and the respiratory amplitude signals obtained from either dZ or respiratory belts. Both dZ derived respiratory rate and dual belts derived respiratory rate accurately reflected the pacing frequencies. For both methods, fixed factors indicated acceptable but posture-specific regression on spirometric volume. However, random factors indicated large individual differences, which was supported by variability of gain analyses. It was concluded that both the dZ and dual belts methods can be used for measurement of respiratory rate and within-subjects, posture-specific, changes in respiratory volume. The need for frequent subject-specific and posture-specific calibration combined with relatively large measurement errors may strongly limit the usefulness of both methods to assess absolute tidal volume and minute ventilation in ambulatory designs.