Travis Craddock

How molecular processes may contribute to information processing in the brain remains unresolved. Quantum biology offers a testable framework for examining whether quantum processes, such as spin dynamics, can influence cellular structures relevant to neural plasticity and cognition. We focus on microtubules, dynamic cytoskeletal polymers that regulate neuronal architecture and depend on a magnesium dependent assembly process. Recent experiments show that microtubule assembly responds jointly to weak magnetic fields and magnesium isotope substitution, with effects linked specifically to spin-bearing magnesium isotope. This pattern is consistent with a quantum biological process known as radical-pair spin dynamics, in which weak magnetic interactions and nuclear spins alter chemical reaction pathways. Specifically, results suggest the spin of magnesium affects a radical pair which may involve the spin of nearby phosphorous atoms. As microtubules contain ordered arrays of phosphorous containing nucleosides whose nuclei offer candidate spin degrees of freedom for biological information storage or processing, this suggests a possible manipulation of biological quantum information processing by magnetic fields. These findings identify the cytoskeleton as a plausible molecular interface through which quantum spin effects could influence neural organization and function. We outline experiments needed to identify the responsible chemical intermediates and test whether such effects extend from microtubules to neuronal plasticity and brain-level information processing.