Inter-hemispheric connections modulate splitting in a computational model of the bilateral SCN

Area of Science:

• Neuroscience
• Chronobiology
• Computational Biology

Background:

• Splitting, characterized by two rest/wake cycles, occurs in hamsters under constant light due to the desynchronization of the left and right suprachiasmatic nuclei (SCN).
• While the antiphase relationship within and between SCN hemispheres in split activity is known, the role of inter-hemispheric connections remains unclear.

Purpose of the Study:

• To investigate the influence of commissural projections connecting the left and right SCN on split and unsplit activity dynamics.
• To analyze the role of inter-hemispheric connections in the desynchronization of the SCN using a computational model.

Main Methods:

• Development of a 4-node computational model representing the core and shell of the bilateral SCN.
• Simulation of the model under various lighting conditions to measure period and phase relationships.
• Bifurcation analysis to characterize system dynamics and identify transition points between split and unsplit states.

Main Results:

• The bilateral SCN model exhibits spontaneous splitting unless entrained by light cycles or possessing excitatory inter-hemispheric connections.
• Constant light conditions had limited impact on transitions between split and unsplit activity.
• The strength and polarity of contralateral connections significantly influenced dynamical transitions, suggesting their importance over light intensity.

Conclusions:

• Excitatory inter-hemispheric connections are potentially vital for maintaining freerunning activity and preventing SCN desynchronization.
• Splitting behavior may be linked to the plasticity of inter-hemispheric connections within the SCN.
• Computational modeling provides insights into the neural mechanisms underlying circadian rhythm splitting.