Carlos A. Comperatore

Subcortical and cortical components of the MLR generating system

The contributions of the auditory thalamo-cortical pathway, mesencephalic reticular formation, and inferior colliculus to the surface recorded auditory middle latency response (MLR) were assessed by selective inactivation of these areas with lidocaine. Evoked responses were recorded simultaneously from these areas and from the cortical surface. Lidocaine-induced changes were compared across recording sites. In the guinea pig, surface components measured from over the temporal lobe (waves A, B and C) and the midline (waves M- and M+) have been previously shown to reflect the activity of two distinct generating mechanisms. Effects of lidocaine injections corresponded to selective changes in components from these two systems. Injections in the medial geniculate body (MGB) were associated with total disruption of surface potentials measured over the temporal lobe, auditory cortex (AC) responses, and local activity in MGB. Thus the thalamo-cortical pathway appears to be important for the generation of MLRs recorded from the surface of the temporal lobe. These injections generally did not alter the surface midline responses or activity obtained from either the mesencephalic reticular formation (mRF) or the inferior colliculus (IC). Lidocaine injections within AC did not alter the basic response morphology of surface potentials, nor were significant changes measured within AC. Lidocaine injections into the mRF produced changes in all surface temporal potentials, the M+ midline surface potential, and in local potentials recorded from MGB and mRF. Injections into the IC changed surface and subcortical responses at all sites. This was the only injection to affect activity at the latency of surface midline wave, M-1. This wave may be the animal analogue for human wave Na. Control experiments indicated that the effects observed were specific to the neural inactivation of target areas. The MLR generating system appears to consist of contributions and interactions from multiple areas including the auditory thalamo-cortical pathway, mRF and IC. The animal model and experimental strategy described appear promising for linking the contributions from specific brain areas to surface MLR waves.

Effects of vagotomy on entrainment of activity rhythms to food access

Subdiaphragmatic vagotomy had little effect on anticipatory wheel running in rats maintained on 4 hr of food access per day. In ad lib conditions, sections of the anterior trunk of the vagus reduced total activity, but did not substantially affect its nocturnal distribution. During restricted feeding, rats with anterior trunk sections showed amounts of anticipatory wheel running comparable to controls, while vagotomized rats with suprachiasmatic nucleus (SCN) lesions showed a reduced amount of activity. After the posterior trunk was sectioned, as well, or after combined sections, there was little change in the amount of anticipatory activity but a significant increase (1 hr) in the duration. In control rats, the duration of anticipatory activity showed a nonsignificant decrease over 50 days on restricted feeding. Neither the vagus nerve, nor the SCN, are essential for the entrainment of activity to restricted feeding.

Entrainment of Duodenal Activity to Periodic Feeding

The electrical activity of the antrum and proximal duodenum was recorded simul taneously with bar pressing for food in various feeding conditions. During restricted feeding (RF; food available from 1200 to 1600 hr; lights-on from 0800 to 2000 h), large-amplitude slow potentials of duodenal origin were observed 3-5 hr preceding food access. These potentials occurred in short trains at irregular intervals of approximately 1 min and appeared to be associated with the active phase of the migrating motility complex. At least 8-10 days on RF were required before these irregular contractions (ICs) reliably preceded food access. The distribution of ICs showed a circadian variation during food deprivation, and transients lasting 4-6 days were observed in response to 6- or 8-hr phase delays of food access. These observations suggest that ICs are modulated by a circadian mechanism. On the average, the increase in ICs occurred about 2 hr earlier than bar pressing in anticipation of food, and there was no specific relation between individual ICs and bar pressing. However, bar pressing frequently occurred 0.5 min or longer after an increase in electromyogram (EMG) amplitude. Unreinforced bar pressing was never observed during a quiescent EMG.

MLRs in children are consistently present during wakefulness, stage 1, and REM sleep

Auditory middle latency responses (MLRs) were recorded continuously from normal children, ages 4 to 9 years, during natural sleep. Concurrently obtained EEG recordings were used to determine stages of sleep. Wave Pa was consistently present during wakefulness, alpha, stage 1, and REM sleep. Wave Pa detectability was poor during stage 4 sleep. The probability of obtaining wave Pa during stage 4 increased systematically with age. During stages 2 and 3, Pa detectability was variable. The inconsistency of MLRs in children currently limits their clinical use. These data indicate that the occurrence of MLRs in children is not haphazard, and that the MLR in children can be reliably obtained during certain states of arousal. A straightforward clinical application of these findings is that efforts to obtain MLRs be concentrated during periods favorable for recording the response. We suggest practical strategies for detecting optimal sleep stages.

Melatonin and the reduction or alleviation of stress

Abstract: In a double blind and placebo controlled study designed to investigate the effect of melatonin administration at 13:00 hr on menstrual characteristics, prolactin, and premenstrual syndrome‐like symptoms during simulated eastward travel, it was noted that melatonin reduces or alleviates the stress associated with the simulated travel. Bright lights were utilized to simulate eastward movement across six time zones. Melatonin (10 mg) was given to healthy females for 5 consecutive days during the late follicular and early luteal phases of the menstrual cycle. Hourly blood samples, used for analysis of melatonin and prolactin levels, were obtained for 24 hr before entering the dose administration phase of the study and again on the last dose day. Volunteers also completed a profile of moods state questionnaire upon waking on each of 8 days which overlapped the in‐house dose administration days. The placebo group showed a prolactin peak at 13:00 hr (dose time) on the last dose day/blood draw, while the melatonin group showed a prolactin peak at 15:00 hr. The prolactin peak at 13:00 hr is likely the result of stress, since stress is known to elicit the release of prolactin. The peak at 15:00 hr in the melatonin group was likely elicited by the administration of melatonin. Stress reduction in the melatonin group was supported by results from the profile of moods state questionnaire. The melatonin group consistently demonstrated scores indicative of less stress.

Design standards considerations and the effective prevention of operator fatigue

In this chapter, we explore the need to develop specific guidance, tailored to consumers of fatigue risk management systems, outlining how to verify that program elements effectively control the incidence of operator fatigue. We advance the notion that without independent proof of efficacy, consumers are left to assume that program implementation and sustainment costs actually yield the desired results. Lacking this information perpetuates losses associated with fatigue-related performance degradation, health issues, and mishaps. Inspection and verification protocols require objective evidence, beyond surveys, to demonstrate that fatigue management program elements control the incidence of operator fatigue in the workplace. Scientific and technological advances facilitate the evaluation of fatigue management programs and the use of objective techniques to test circadian rhythm stability and alertness. However, consumers are yet to incorporate these test protocols and technological advances in their safety management system assurance infrastructure. The prevailing assumption has been that scientific tests and methodologies are beyond the reach of the consumer and fall in the purview of scientists and fatigue management professionals. We propose the use of the design basis plan in safety management systems as the assurance infrastructure to associate program inspection elements, fatigue leading indicators, and specific standards with compulsory review and approval activities. These assurance activities not only provide objective means to identify fatigue management program elements that fail to control the incidence of operator fatigue but also enable consumers to proactively implement necessary modifications. Keywords: Driver distraction; Language: en