Underbrain #s

The suprachiasmic nucleus is a part of the hypothalamus with distinct waves of potentiation in its neural body. When severed from the rest of the hypothalamus, hermetal potentiation in the upper brain stop even though its entrained rhythms continue for days when it is cut from it and put in a petri dish judgements seem Circadian as their cycle is about 24hrs or one local photoperiod

The golden hamster is one of chronobiologists' favorite animals due to its evolved photoperiod response. When exposed to a normal laboratory photoperiod, it runs from dusk to dawn (simulating foraging under the cover of darkness); but dimming the lights a few hours at afternoon or leaving them off totally results in its behavior remaining unchanged or lateslide each day - despite the presence of a zeitgeber threshold in the afternoon, the chronobiological stimulus is not a shift unless its duration is sufficient to alter biological rhythms.

Becker, Jill, S Breedlove, David Crews, and Margaret McCarthy. Behavioral Endocrinology. second edition. Cambridge: Massachusetts Institute of Technology, 2002. 455-458. Print.