become lowered during wakefulness as they process information, making them more responsive, and so need to be adjusted back to preserve their signal-to-noise ratio. The down-state provided by K-complexes does this by reducing the strengths of synaptic connections that occur while an individual is awake. Further, the recovery from the down-state they induce allows that "cortical firing 'reboots' in a systematic order" so that memory engrams encoded during neuronal firing can be "repeatedly practiced and thus consolidated". Development They are present in the sleep of 5-month-old infants, and develop with age. Between 3 and 5 years of age a faster negative component appears and continues to increase until adolescence. Another change occurs in adults: before 30 years of age their frequency and amplitude is higher than in older people particularly those over 50 years of age. This parallels the decrease in other components of sleep such as sleep spindle density and delta power. Clinical Epilepsy In individuals with idiopathic generalized epilepsy, K-complex induced synchronization can trigger spike-and-wave discharges. This tends to happen most between the shift between waking and NREM, and between NREM and REM sleep. In autosomal dominant nocturnal frontal lobe epilepsy, K-complexes are almost invariably present at the start of seizures. Restless legs syndrome Individuals with restless legs syndrome have increased numbers of K-complexes and these are associated with (and often precede) leg movements. Dopamine enhancing drugs such as L-DOPA that reduce leg movements do not reduce the K-complex suggesting that they are primary and the leg movements secondary to them. Failure of such drugs to reduce K-complexes in spite of reducing the leg movements has been suggested to be why patients after such treatment still continue to complain of non-restorative sleep. Clonazepam is another treatment for RLS; like other benzodiazepines, it inhibits REM sleep by enhancing levels of GABA. This inhibition of REM sleep significantly decreases K-complex count, and unlike L-DOPA treatment, clonazepam studies report improvement in sleep restoration. Therefore, drugs that inhibit REM sleep also decrease K-complex count. Obstructive sleep apnea Obstructive sleep apnea syndrome is associated with inspiratory occlusions evoking fewer K-complexes during NREM sleep even though K-complexes are evoked normally to auditory stimuli and such individuals react normally to respiratory interruptions when awake. This suggests a link between such sleep apnea and a sleep specific blunted cortical response to respiratory problems. Notes Electroencephalography Sleep physiology