Glossary of Key Terms Autonomic nervous system: part of the peripheral nervous system (nerves) which controls much of our involuntary behaviour, such as our heart-rate, breathing-rate, and blood pressure. Circadian rhythm: a regular, repeating pattern with a 24-hour cycle, for example, the 24-hour sleep–wake cycle. Genome lag: the notion that some behaviour is not adaptive because genetic changes over thousands of generations have proceeded much slower than changes in our environment. Infradian rhythm: a regular, repeating pattern with a cycle that is longer than 24 hours, for example, the human monthly menstrual cycle. Jet lag: the adverse effects experienced from crossing time zones so that the body’s internal clock and local time in the new environment mismatch. Micro-sleep: Minute catnaps or very small instants of sleep during awake periods; the instants of micro- sleep are so shortlived that the person is not aware of them. NREM: non-rapid eye movements where the eyes are still during one type of sleep. Orexins: neuropeptide hormones involved in the stimulation of hunger, as well as of energy expenditure and wakefulness; also called hypocretins. Parasympathetic nervous system: the division of the autonomic nervous system which, when activated, makes us “rest and digest”, in other words calm down, slow down, and relax. (See also sympathetic nervous system; autonomic nervous system). Phototherapy: therapy using bright light, usually as closely similar as possible in wavelength to sunlight, to improve mood, for example for sufferers of seasonal affective disorder. PMS: pre-menstrual syndrome is a condition in many women in the days preceding their monthly period when mood and emotional swings can develop. REM: rapid eye movements which occur in one type of sleep. SAD: seasonal affective disorder is a mood disorder, a form of clinical depression in which the sufferer develops low mood with the onset of autumn and falling light levels, only improving in mood in late spring when light levels rise again. Sympathetic nervous system: the division of the autonomic nervous system that stimulates the body into “fight or flight”, in other words prepares it for sudden action. Among the effects are faster heart- and breathing-rates, and more glucose in the blood. (See also parasympathetic nervous system; autonomic nervous system). Ultradian rhythm: a regular pattern with a cycle of less than 24 hours, for example, the NREM/REM sleep cycles in a night’s sleep. Zeitgeber: An environmental factor (for example, light) that can act as a time cue.