Fig. 2:

Transients and Aftereffects. Transients (blue bars) can be caused by various treatments, such as the release of the animal into constant conditions (A) or a shift in the lighting regime (B). These transients usually persist for several days depending on the strength of the provoking signal. The white and black bar at the top of the scheme depicts light (12 h) and darkness (12 h), respectively. (C) An animal kept in constant darkness (DD) displays a stable free-running rhythm with a period length τ₁ before it is subjected to a light pulse. This pulse leads to a phase shift and often provokes τ₂, which is different from τ₁, as an aftereffect. If the animal is left in DD long enough after this treatment, it will again display its old period length τ₁. The red regression lines are drawn through the onsets before and after the light pulse to determine τ₁ and τ₂, respectively. The black bar at the top of the scheme represents constant darkness (24 h) conditions. DD, constant darkness; LD, light-dark cycle.