It has been suggested that sensory mismatch induces motion sickness, but its neural mechanisms remain unclear. To investigate this issue, theta waves in the hippocampal formation (HF) were studied during sensory mismatch by backward translocation in awake rats. A monopolar electrode was implanted into the dentate gyrus in the HF, from which local field potentials were recorded. The rats were placed on a treadmill affixed to a motion stage translocated along a figure 8-shaped track. The rats were trained to run forward on the treadmill at the same speed as that of forward translocation of the motion stage (a forward condition) before the experimental (recording) sessions. In the experimental sessions, the rats were initially tested in the forward condition, and then tested in a backward (mismatch) condition, in which the motion stage was turned around by 180 degrees before translocation. That is, the rats were moved backward by translocation of the stage although the rats ran forward on the treadmill. The theta (6-9 Hz) power was significantly increased in the backward condition compared with the forward condition. However, the theta power gradually decreased by repeated testing in the backward condition. Furthermore, backward translocation of the stage without locomotion did not increase theta power. These results suggest that the HF might function as a comparator to detect sensory mismatch, and that alteration in HF theta activity might induce motion sickness.

No abstract

Purpose This study aimed to explore the association between sleep quality and subjective fatigue in nurses who performed rotational-shift work. Methods A cross-sectional survey was conducted and included nurses working day and night shifts (n = 35) at Toyama University Hospital in Japan. To examine the influence of sleep quality on subjective fatigue, participants were categorized as poor (n = 23) or good (n = 12) sleepers. They assessed their own sleep status using the St Mary's Hospital Sleep Questionnaire and subjective fatigue following shift changes (holiday to day shift, day shift to day shift, before night shift, after night shift, and day shift to holiday). Results Poor sleepers' State-Trait Anxiety Inventory scores were higher relative to those of good sleepers. Moreover, good sleepers recovered from subjective fatigue after sleep following all shift changes. Poor sleepers' subjective fatigue also reduced after sleep following 'before night shift', 'after night shift', and 'day shift to holiday' shift changes but not 'holiday to day shift' or 'day shift to day shift' shift changes. Sleep duration was stable across shift changes in good sleepers, and poor sleepers' sleep durations were significantly longer following 'before night shift', 'after night shift', and 'day shift to holiday' shift changes relative to those following 'holiday to day shift' and 'day shift to day shift' shift changes. Conclusions The results suggested that poor sleepers' subjective fatigue following 'before night shift', 'after night shift', and 'day shift to holiday' could be reduced by increasing sleep duration, indicating that it is important to ensure sufficient sleep duration to improve all nurses' sleep quality and reduce poor sleepers' subjective fatigue. Furthermore, sufficient relaxation at bedtime and the reduction of anxiety are important in maintaining good sleep quality.

No abstract