Possible involvement of the vagus nerve in monitoring plasma catecholamine levels

In their article Miyashita and Williams (Neurobiology of Learning and Memory 2006, 85, 116-124) describe the effect of peripheral administration of epinephrine on neural discharge in vagal afferent fibers. It seems that described data supports the hypothesis of the vagus nerve participation in monitoring plasma catecholamine levels and consequently modifying brain functions. However, do these results indicate indeed that afferent vagus nerve pathways are activated by circulating epinephrine? Catecholamines influence virtually all tissues and many functions. Vagus nerve participates significantly in monitoring of those effects. Therefore epinephrine-induced increases of afferent vagus nerve activity described by Miyashita and Williams may reflect not only exclusive activation of beta-adrenergic receptors but also an activation of other types of receptors on vagal sensory nerve endings, e.g., mechanosensors, chemoreceptors, and osmosensors. Discussion is focused on the possibility that the increase in afferent vagus nerve activity may reflect activation of mechanoreceptors of the vagus nerve endings in the epinephrine-activated heart.     

Similar changes in muscle fiber phenotype with differentiated consequences for rate of force development: Endurance versus resistance training

Resistance training has been shown to positively affect the rate of force development (RFD) whereas there is currently no data on the effect of endurance training on RFD. Subjects completed ten weeks of either resistance training (RT, n = 7) or endurance cycling (END, n = 7). Pre and post measurements included biopsies obtained from m. vastus lateralis to quantify fiber phenotype and fiber area and isokinetic dynamometer tests to quantify maximal torque (Nm) and RFD (Nm/s) at 0–30, 0–50, 0–100 and 0–200 ms during maximal isometric contraction for both knee extensors and flexors. Both groups increased the area percentage of type IIa fibers (p < .01) and decreased the area percentage of type IIx fibers (p = .05), whereas only RT increased fiber size (p < .05). RT significantly increased eccentric, concentric and isometric strength for both knee extensors and flexors, whereas END did not. RT increased 200 ms RFD (p < .01) in knee flexor RFD and a tendency towards an increase at 100 ms (p < .1), whereas tendencies towards decreases were observed for the END group at 30, 50 and 100 ms (p < .1), resulting in RT having a higher RFD than END at post (p < .01). In conclusion, resistance training may be very important for maintaining RFD, whereas endurance training may negatively impact RFD.     

The development of attention to simple and complex visual stimuli in infants: Behavioral and psychophysiological measures

The study of visual attention in infants has used presentation of single simple stimuli, multi-dimensional stimuli, and complex dynamic video presentations. There are both continuities and discontinuities in the findings on attention and attentiveness to stimulus complexity. A continuity is a pattern of looking that is found in the early part of infancy that remains throughout adulthood. A discontinuity is an emerging sensitivity to the content of the information in the stimulus presentations and alterations in patterns of attention based upon stimulus comprehensibility. The current paper reviews some of these findings with particular application to complex video presentations.     

Young adult couples’ behavioral and physiological responses to the infant simulator: A preliminary illustration of coparenting

This exploratory application of the infant simulator with two couples is designed to illustrate individual reactivity and coparenting behaviors in young couples in serious relationships who do not yet have children. A 35-min protocol with standardized onsets and offsets of inconsolable baby cries was used to capture partner’s individual behavioral and physiological responses as well as the couple’s joint efforts to soothe the crying baby. Task feasibility was demonstrated by couples’ persistent and wide-ranging efforts to calm the baby including rocking, feeding, changing, talking to the baby, and singing. Within-person fluctuations in ongoing heart rate (HR) and electrodermal activity (EDA) through the protocol suggested evidence of heightened physiological reactivity during baby crying compared to silence. During bouts of crying, higher HR also was evidenced when participants took the lead in caregiving as contrasted with assisting or busying themselves in another task. Behavioral observations indicated that this task elicited examples of coparenting behaviors including cooperation, support, undermining, and negotiating the division of labor. These preliminary pilot data demonstrate the potential of infant simulator paradigms with couples who are not yet pregnant but envision being future parents, and set the stage for future research to identify how individual and couple characteristics might impact reactions to shared baby caregiving.     

Analysis of heart rate variability amongst cyclists under perceived variations of risk exposure

Cycling as a mode of travel provides an opportunity for many people to increase their levels of regular physical activity and contribute to their mental and physical health. Heart rate is often used as a means of measuring the intensity and energy expenditure of physical activity. However, heart rate is also linked to emotional factors such as anxiety and fear. Perceptions of risk due to external factors such as other road users and infrastructure may arouse such emotions in urban cyclists. The present study set out to investigate whether or not perceptions of risk among urban cyclists may lead to increased heart rates. Cyclists completed a test route in normal traffic conditions in Cork, Ireland and heart rates and self-reported risk ratings were recorded in real time. Evidence was found of a link between perceptions of risk and heart rates. This raises questions regarding the use of heart rate to estimate exercise intensity and energy expenditure during urban cycling. The perceptions of cyclists of their safety in relation to various road elements on familiar routes were also assessed, as well as specific events which they perceive to be high in risk. The results indicate that incidents involving car traffic and busy roads which offer no protection from interaction with car traffic are associated with greatest perceptions of risk.     

Transient cardiac responses to witnessing horrible events in young adult female exercisers and non-exercisers

ObjectivesIt has been proposed that regular exercisers may be less vulnerable to the effects of stress and better able to cope with aversive events than people who are sedentary, but findings have not been consistent. In the present study, physiological variables indicating specific relevant psychological processes were used to objectively assess women's responses to stressful events.Design and MethodNon-exercising (n = 56) and regularly exercising women (up to 4 h, n = 62, and more than 4 h per week, n = 50) were viewing an aversive film consisting of scenes of real injury and death, and their transient cardiac responses to sudden horrifying events happening to persons in the film were obtained, as well as changes of prefrontal-posterior coupling, measured by EEG.ResultsCompared to regularly exercising women, non-exercising women showed a clearly more pronounced second accelerative component of the transient heart rate response to the terrifying events, indicating greater sensitivity of the avoidance (defensive) motivational system and heightened sensitivity to aversive stimuli. Moreover, non-exercising women did not show the expected characteristic initial heart rate acceleration when the scene approached its fatal end, that is, more rigid responding, and EEG data indicated less susceptibility to affect-laden information at the perceptual level.ConclusionsThe findings support the notion of less adaptive coping with adverse events in sedentary compared to exercising women and add to the growing evidence suggesting a stress-buffering effect of regular exercise, therefore promoting resilience and resistance to the negative impact of stressor and trauma exposure.     

Electroencephalographic and autonomic alterations in subjects with frequent nightmares during pre-and post-REM periods

Abnormal arousal processes, sympathetic influences, as well as wake-like alpha activity during sleep were reported as pathophysiological features of Nightmare Disorder. We hypothesized that in Nightmare Disorder, wake-like cortical activity and peripheral measures linked to arousals would be triggered by physiological processes related to the initiation of REM periods. Therefore, we examined electroencephalographic (EEG), motor and autonomous (cardiac) activity in a group of nightmare (NM) and healthy control (CTL) subjects during sleep-state-transitions while controlling for the confounding effects of trait anxiety. Based on the second-nights’ polysomnographic recordings of 19 Nightmare Disordered (NM) and 21 control (CTL) subjects, we examined the absolute power spectra focusing on the alpha range, measures of heart rate variability (HRV) and motor (muscle tone) activity during pre-REM and post-REM periods, separately. According to our results, the NM group exhibited increased alpha power during pre-REM, but not in post-REM, or stable, non-transitory periods. While CTL subjects showed increased HRV during pre-REM periods in contrast to post-REM ones, NM subjects did not exhibit such sleep state-specific differences in HRV, but showed more stable values across the examined sleep stages and less overall variability reflecting generally attenuated parasympathetic activity during sleep-state-transitions and during stable, non-transitory NREM states. These differences were not mediated by waking levels of trait anxiety. Moreover, in both groups, significant differences emerged regarding cortical and motor (muscle tone) activity between pre-REM and post-REM conditions, reflecting the heterogeneity of NREM sleep. Our findings indicate that NM subjects’ sleep is compromised during NREM–REM transitions, but relatively stabilized after REM periods. The coexistence of sleep-like and wake-like cortical activity in NM subjects seems to be triggered by REM/WAKE promoting neural activity. We propose that increased arousal-related phenomena in NREM–REM transitions might reflect altered emotional processing in NM subjects.