Morgan et al

• • the researcher bred hamsters so that their circadian rhythms were 20 hours, rather than the usual 24-hour cycle
• • SCN neurons from the 20-hour hamsters were transplanted into the brains of normal hamsters,
• • the hamsters with transplanted SCN neurons went on to follow the same irregular 20-hour circadian rhythm as the original 20-hour cycle hamsters
• thus, the transplanted SCN had imposed its irregular pattern onto the hamsters
• • the researcher concluded that the SCN is a significant endogenous pacemakers which is crucial to the proper functioning of circadian rhythms
• these findings also demonstrate the importance of exogenous zeitgebers to the sleep-wake cycle (endogenous pacemakers and exogenous zeitgebers work hand-in-hand)