Figure 3.

Results of numerical simulations of equations (4)-(7) with the parameters in Table 1. (a) Period $T_{sr}$ of independent SCN activity components under external light-dark cycles of varying period $T$ (in hours). The component at the field period $T$ is indicated in red open circles within the entrainment range and in gray circles outside the entrainment range. Red stars indicate the period of SCN activity at a second (dissociated) rhythm $T_{sr}$ . Black crosses are experimental data reported by Campuzano et al. (1998). The dashed horizontal line is the period of SCN oscillations ${\tau }_{DD}=24.84\mathrm{h}$ under dark-dark conditions (cue strength $F=0$ ), calculated from the mean value of equations (5) and (7) in the synchronized state. (b) Intensity of light-dark ( $F$ , hollow markers) and second rhythm ( $sr$ , solid makers) components of SCN activity, in the core ( $\upsilon$ , circles) and shell ( $d$ , squares). Vertical lines indicate the lower and upper bounds of the entrainment range, $LLE=23.26\mathrm{h}$ and $ULE=25.28\mathrm{h}$ , respectively. For comparison, the mean free-running periods of the shell and the core are ${\tau }_d=23.3\mathrm{h}$ and ${\tau }_{\upsilon }=25.1\mathrm{h}$ , respectively. (c) Dependence of the entrainment range (gray horizontal bars) on the difference between the free-running periods of core and shell, ${\tau }_{\upsilon }-{\tau }_d$ . Here, ${\tau }_{\upsilon }$ is fixed as ${\tau }_{\upsilon }=25.1\mathrm{h}$ (black dots) and ${\tau }_d$ (blue dots) varies. Abbreviation: LLE = lower limit of entrainment;SCN = suprachiasmatic nucleus; ULE = upper limit of entrainment.