Sleepiness has been associated to several functional changes such as poor performance of postural control. Although several studies have identified this association, little is know about the postural control underlying mechanisms that sleepiness would be affecting. Considering that postural control demands an intricate relationship between sensory information and motor action, sleepiness would be affecting the mechanisms that regulate this relationship. Sensory information and motor action in postural control has been investigates through the moving room paradigm because one can manipulate a sensory input source and to observe the motor response such as body oscillation induced by the sensory manipulation. Using this paradigm, several studies have shown that changes in the sensory information and body sway changes occur with and without a conscious involvement of the participant, which could be affected by sleepiness Therefore, the aim of this study is to examine the effects of sleepiness in the sensory information and body sway relationship due to a moving room. Forty participants will constitute two groups: one group in which the participants will undergo a sleepiness period (SP) e one group in which sleep will be normal (NS). Both groups will be tested in two days. In the first day, participants will stay upright in a moving room, for four trials, each lasting 60 seconds. In the first trial, the room will remain motionless (baseline) but in the three remaining, the room will oscillated with frequency of 0,2 Hz, amplitude of 0,6 cm, and velocity of 0,6 cm/s. After this testing, participants of SP group will stay without sleep for the next 24 hours, whereas participants of the NS group will sleep from 7 to 9 hours. In the following day, participants will return to the laboratory and will perform eight trials. Firstly, all participants will perform four trials similar to the ones of the first day. In the fourth trials, half of the participants of each group will be exposed to a larger movement of the room: 0,2 Hz of frequency, 3,5 cm of amplitude, and 3,5 cm/s of velocity. In the remaining trials (3 last ones), the room will oscillated with small parameters again (0,2 Hz, 0,6 cm and 0,6 cm/s). The other half of the participants, in the fourth trial, will be told that the room will move and request to remain upright as still as possible. In the remaining trials, the room will oscillated with frequency of 0,2 Hz, 0,6 cm, and 0,6 cm/s. In all trial, body oscillation and moving room position will be obtained by using a motion analysis system. The magnitude of body sway will be verified by calculating the mean sway amplitude and the relationship between the moving room position and body sway will be investigated using the following variables: coherence, gain, phase, and position and velocity variability. Statistical analyses will involve ANOVAs and MANOVAs and will, initially, verify if the magnitude of body sway is affected by sleepiness. Following, analyses will test if sleepiness produces any change in the relationship between the room movement and body sway. Finally, analyses also will examine if sleepiness change adaptive behavior that occurs when the visual stimulus is altered, such as in the fourth trial of the second day, or when information about the movement of the room is provided to the participant.
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