  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.
