Alertness is the state of active attention by high sensory awareness such as being watchful and prompt to meet danger or emergency, or being quick to perceive and act. It is related to psychology as well as to physiology. A lack of alertness is a symptom of a number of conditions, including narcolepsy, attention deficit disorder, chronic fatigue syndrome, depression, Addison's disease, or sleep deprivation. Pronounced lack of alertness can be graded as an altered level of consciousness. States with low levels of alertness include drowsiness. The word is formed from "alert", which comes from the Italian "all'erta" (on the watch, literally, on the height; 1618). Wakefulness refers mainly to differences between the sleep and the wake state, including for modulation or stimulation of these pathways, and vigilance refers to sustained alertness and concentration but both terms are sometimes used synonymously with alertness. Physiological aspects People who have to be alert during their jobs, such as air traffic controllers or pilots, often face challenges maintaining their alertness. Research shows that for people "...engaged in attention-intensive and monotonous tasks, retaining a constant level of alertness is rare if not impossible." If people employed in safety-related or transportation jobs have lapses in alertness, this "may lead to severe consequences in occupations ranging from air traffic control to monitoring of nuclear power plants." Biological pathways Neurotransmitters that can initiate, promote, or enhance wakefulness or alertness are serotonin, (nor)epinephrine, dopamine (e.g. blockade of dopamine reuptake), glutamate, histamine and acetylcholine. Neuromodulators that can do so include neuropeptide orexin. Similarly inhibition or reduction of alertness-inhibiting mechanisms such as certain cytokines and adenosine (as with caffeine) may also increase alertness. Wakefulness depends on the coordinated effort of multiple brain areas. These are affected by neurotransmitters and other factors. Activating some specific neuronal populations was also found to increase wakefulness. Experiments indicate that none of these neurotransmitters or the neurons producing them are individually necessary for maintaining wakefulness. Research to map the wakefulness circuitry is ongoing. Beta power has been used as an indicator of cortical arousal or alertness by several studies. A study also measured alertness with EEG data. Drugs used to increase alertness Around the world, the stimulant adenosine receptor antagonist caffeine is widely used to increase alertness or wakefulness and improve mood or performance, typically in the form of drinks like green tea (where it is mixed with bioactive l-theanine), energy drinks (also containing high