Chronobiology is a field of science that examines periodic (cyclic) phenomena in living organisms and their adaptation to solar and lunar related rhythms.

These cycles are known as biological rhythms.

A biological rhythm is a self-sustaining oscillation of endogenous origin.

period levelAmplitud

ePhase

The circadian rhythm can further be broken down into routine cycles during the day:

Diurnal

Nocturnal

Crepuscular

Social zeitgebe

rs

Zeitgebers

“time giver”

Entrainment

Sleep wake cycle is the master output rhythm of the circadian clock

controls REM sleep and the ratioof NREM/REM sleep.

controls NREM sleep

SCN

MT2

MT1

phase-shifting and entrainmenteffects of melatonin.

Inhibits he electrical activity ofSCN neurons

Melatonin

Retinal Ganglion cells

Suprachiasmatic Nucleus

Ventral Subparaventricular zone of the hypothalamus

Dorsomedial Hypothalamus

VLPO(ventrolateral preoptic

area)

Sleep

LHA

Arousal

Sleep changes as markers for depression

depressed patients show a reduction in the absolutenumber of delta waves during the first NREM

depressed patients show a reduction in decrease in delta activity throughout the night

sleep abnormalities in the first degree relatives of depressed patients suggests that these sleep changes can be viewed as “markers” of depression

patients with decreased REMOL prior to treatment are prone of developing subsequent episodes of depression and experiencing rapid relapses after remission

There are two theoretical ways:

the older the person, the more the

tendency to have a ‘‘morningness

’’

depressed patients reported significantly more ‘‘eveningness’’ than age- and sex-matched controls

morning type might be protective

against depression

whereas ‘‘eveningness’’

might cause increased

vulnerability

‘‘eveningness–morningness’’

dimension

Dawn simulation therapy

Refractory

unipolar

depression

Bipolar depres

sion

Antepartum

depression

Ttt of choic

e

Valproate

Lithium

Agomelatin

e

Melatonin

MT2 recept

or agonist

5 HT2C antagonist

MT1 recepto

r agonist

25 mg/day

P450 syste

m