Function of circle of Willis

Area of Science:

• Neuroscience
• Evolutionary Biology
• Vascular Anatomy

Background:

• The circle of Willis (CW) has been theorized as a compensatory system for arterial occlusion for nearly 400 years.
• This long-standing theory, while accepted, faces challenges based on recent scientific observations and evolutionary perspectives.

Purpose of the Study:

• To critically re-evaluate the compensatory theory of the circle of Willis.
• To propose an alternative physiological function for the CW based on anatomical and evolutionary evidence.

Main Methods:

• Critique of the existing compensatory theory using arguments via negativa.
• Comparative analysis across species to assess evolutionary patterns.
• Evaluation of anatomical data regarding communicating artery size and prevalence.

Main Results:

• The current compensatory theory is challenged for being anthropocentric and implying evolutionary foresight.
• The CW's structure suggests a convergent evolutionary trait rather than a specific compensatory adaptation.
• Communicating arteries are often too small for significant blood flow and are frequently absent or underdeveloped.

Conclusions:

• The circle of Willis likely functions as a passive pressure-dissipating system, not primarily for compensation.
• Hemodynamic stress is managed by the CW transferring pressure and mitigating pulse wave arrival asymmetry.
• This passive role protects cerebral arteries and the blood-brain barrier from damaging forces.