UC Santa Barbara

The brain's computational functions, from information synthesis and memory recall to consciousness, remain largely enigmatic. Despite great scientific effort, the mechanisms behind information storage, computation, and readout within the brain are still not well understood. Because of the warm, crowded nature of biological systems, it has traditionally been thought that quantum states would rapidly decohere and be unsuitable for biological information storage. Recently, the "Quantum Brain theory" has proposed the potential for a quantum information network in the brain that could maintain and process quantum information on timescales relevant to brain function. Within the framework of this theory, quantum information is stored in the collective phosphorus spin states of nanometric calcium phosphate clusters known as Posner molecules. The pair binding of these Posner molecules is postulated to be impacted by the collective phosphorus spin states, allowing for a unique quantum state to biochemical signal transduction mechanism. Given that this theory puts forward a uniquely possible method for quantum information processing in the brain, experimental validation or refutation of the theory would be an important step towards an understanding of brain function. This thesis presents experimental results aimed at testing the possibility of this Quantum Brain theory. We show that Posner molecules are stable in simulated body fluids, and uncover a differential lithium isotope effect on the growth of calcium phosphate. This isotope effect provides a link between nuclear spin states and calcium phosphate binding dynamics, and can be connected to in vivo lithium isotope effects in mitochondria. We also uncover spectroscopically 'dark state' phosphate assemblies after measuring unexpected 31P NMR signals, revealing that phosphate solution behavior and 31P nuclear spin dynamics are much more complex than previously predicted. These results verify key predictions of the Quantum Brain theory, indicating the possibility of quantum information processing in the brain, while also progressing our understanding of the complex solution phase space of calcium phosphate.