Ratio Between Sensitive Strength to Light Information and Coupling Strength Affects Entrainment Range of Suprachiasmatic Nucleus

The suprachiasmatic nucleus(SCN), an endogenous clock in the brain of the mammals, regulates the physiological and behavioral activities according to the natural 24 h light-darkness cycle. Animals can also entrain themselves to non 24 h light-darkness cycles. The range of the periods which the animal can entrain to is called entrainment range. Previous studies have found that the entrainment range depends on the coupling strength and the sensitive strength to the light for the SCN neurons. However, the effect of the interplay between these two strengths on the entrainment range has not been examined. In the present study, we examine the effect of the ratio of the sensitive strength to the coupling strength on the entrainment range. We find that there is a parabolic-like relationship between the entrainment range and the ratio, and the largest entrainment range is obtained with a suitable ratio. Interestingly,the value of this suitable ratio is related to the comparison in the intrinsic amplitudes between the light information sensitive neurons and the light information insensitive neurons. Our finding will shed light on the interplay between the sensitive strength to the light information and the coupling strength, and the understanding for the diversity of the entrainment range among various species.