Capacity of conscious agents to perform genuine choices among future alternatives is a prerequisite for moral responsibility. Determinism that pervades classical physics, however, forbids free will, undermines the foundations of ethics, and precludes meaningful quantification of personal biases. To resolve that impasse, we utilize the characteristic indeterminism of quantum physics and derive a quantitative measure for the amount of free will manifested by the brain cortical network. The interaction between the central nervous system and the surrounding environment is shown to perform a quantum measurement upon the neural constituents, which actualize a single measurement outcome selected from the resulting quantum probability distribution. Inherent biases in the quantum propensities for alternative physical outcomes provide varying amounts of free will, which can be quantified with the expected information gain from learning the actual course of action chosen by the nervous system. For example, neuronal electric spikes evoke deterministic synaptic vesicle release in the synapses of sensory or somatomotor pathways, with no free will manifested. In cortical synapses, however, vesicle release is triggered indeterministically with probability of 0.35 per spike. This grants the brain cortex, with its over 100 trillion synapses, an amount of free will exceeding 96 terabytes per second. Although reliable deterministic transmission of sensory or somatomotor information ensures robust adaptation of animals to their physical environment, unpredictability of behavioral responses initiated by decisions made by the brain cortex is evolutionary advantageous for avoiding predators. Thus, free will may have a survival value and could be optimized through natural selection.

有意识的代理人在未来的选择中进行真正选择的能力是道德责任的先决条件。然而，弥漫在经典物理学中的决定论禁止自由意志，破坏了伦理学的基础，并排除了对个人偏见进行有意义的量化。为了解决这一僵局，我们利用了量子物理学特有的不确定性，并对大脑皮层网络表现出的自由意志量进行了定量测量。中枢神经系统与周围环境之间的相互作用显示为对神经成分进行量子测量，从而实现从产生的量子概率分布中选择的单个测量结果。替代物理结果的量子倾向的固有偏差提供了不同数量的自由意志，可以通过学习神经系统选择的实际行动过程获得的预期信息增益来量化自由意志。例如，神经元电脉冲会在感觉或躯体运动通路的突触中引起确定性的突触小泡释放，而不会表现出自由意志。然而，在皮质突触中，囊泡释放是不确定地触发的，每个尖峰的概率为 0.35。这使得大脑皮层拥有超过 100 万亿个突触，其自由意志量超过每秒 96 TB。尽管感觉或躯体运动信息的可靠确定性传输可确保动物对其物理环境的稳健适应，由大脑皮层做出的决定引发的行为反应的不可预测性在进化上有利于避免捕食者。因此，自由意志可能具有生存价值，并且可以通过自然选择进行优化。