Table 1.

Effects of different abnormal light–dark cycles on circadian rhythm, sleep, arousal, and performance.

Conditions	Circadian	Sleep	Arousal	Cognitive
Constant light	↑ Internal period length (nocturnal)	?	↑ Or ↓ glucocorticoid (e.g., CORT) levels	↓ Spatial performance
	↑ mPER2 expression in suprachiasmatic nuclei (SCN)			↓ Contextual fear conditioning
	↓ SCN neuronal firing			↓ Passive avoidance
	↓ Amplitude in peripheral tissues			↓ Appetitive response timing
	Behavioral arrhythmia
Jet lag	↓ Locomotor/exploratory activity	↓ Total sleep	↑ CORT response to aversive stimuli	↓ Spatial performance
	Alter phase relationships between SCN and peripheral tissues	↑ Rapid-eye movement (REM) sleep		↓ Appetitive response timing
		Fragmented sleep		↓ Conditioned place preference
Non-24 h T-cyclesa	↑ Internal period length (nocturnal)	Desynchronize core body temperature and REM sleep	↑ CORT level	↓ Passive avoidance
		↑ Slow-wave activity (sleep)		↓ Spatial performance
		Alter θ and γ power (wake)		↓ Object-recognition performance
Dim light at night	↓ Locomotor/exploratory activity	↓ Amplitude in REM and non-rapid-eye movement rhythms	↓ CORT rhythm	↓ Spatial performance
	↓ Amplitude of activity rhythm			↑ Anxiety-related behavior
	↓ Amplitude of mPER1/2 rhythms			↑ Depression-related behavior
Disruptive Phase Shiftb	↓ Clock gene expression in SCN	↑ Daytime sleep	?	↓ Object-recognition performance
	Arrhythmia (activity, core body temperature, melatonin)			↓ Spatial alternation performance

^aT7, T20, or T22 cycles.

^bHamsters only.

↑ = Increase, ↓ = Decrease; ? = No published studies available. See text for details and references.