*2.1. Assessment of Sleep Deprivation*

Before the fMRI examinations, all participants completed a questionnaire inquiring about the length of sleep the previous night, the amount of time elapsed since last waking up, the number and length of naps in the last 24 h prior to the fMRI, and potential problems with maintaining awareness during the fMRI scanning session. The effects of sleep deprivation and drowsiness were assessed using the Sleep Deficiency Effects Scale (the CHICa scale) [15]. This self-report tool enables the measurement of four components of an individual's fatigue resulting from sleep deprivation, and its results are grouped into four subscales; i.e., impaired thermoregulation (cold subscale), disrupted appetite (hunger subscale), affective problems (irritation subscale), and decreased level of cognitive functioning (cognitive attenuation subscale). Finally, the symptoms of fatigue were also assessed using the Polish version of the Japanese Questionnaire (named as the Assessment of the Current Well-Being) [16,17]. This questionnaire evaluates the symptoms of fatigue based on three groups of symptoms; i.e., (1) decreased activity (e.g., sleepiness, weariness, heaviness of the body), (2) weakened motivation (e.g., irritability, inability to concentrate, apathy), and (3) physical fatigue (e.g., trembling of the limbs, back pain), as well as a general score indicating an overall level of fatigue.
