Back to Free Will
Free will is incompatible with the human nervous system.
Table of Contents
- What Free Will Looks Like
- McEvil Assassinates the Director
- Neuroscience Stuff
- Deterministic Network of Neurons
- Predicting Voluntary Actions
What Free Will Looks Like
People believe they have free will, that they can decide among different possible courses of action. Free will looks like this:
If people have free will, they can decide among multiple futures open to them. Thus, at time t I can choose future A and I can choose future B.
McEvil Assassinates the Director
McEvil assassinated the Director. Did he have free will?
Free will pulling the trigger
Here’s what free would look like for McEvil at time t as he was about to pull the trigger.
Motor neurons make McEvil’s finger bend
Motor neurons bring about bodily movements.
Thus motor neurons caused McEvil’s finger to bend.
- An upper motor neuron runs from the primary motor cortex of the brain to the spinal column, where it synapses on a lower motor neuron, which runs from the spinal column to the hand, where it synapses on the muscle controlling bending the finger.
- When McEvil bends his finger …
- The upper motor neuron fires
- Which causes the lower motor neuron to fire
- Which causes the lower motor neuron to release the neurotransmitter acetylcholine across the synapse with the muscle.
- Which causes the muscle to contract
- Which causes the finger to bend
Free will in McEvil’s brain
Therefore, to have had free will to bend or not bend his finger, McEvil must have had free will to cause or prevent motor neurons firing.
Here’s the problem. We know the conditions under which motor neurons, and neurons in general, fire and don’t fire. And those conditions are incompatible with free will.
- A neuron at rest has less electric charge inside than out. The difference is about -70 mV, meaning that the inside charge minus the outside charge = -70 mV. (mV = millivolt =1/1,000 of a volt)
- A neuron fires when the difference in electric charge reaches a threshold of about -60 mV due to the influx of neurotransmitters at its dendrites. At that point an action potential occurs: a reversed voltage (about +55 mV) quickly travels down the axon, releasing neurotransmitters at the axon terminals.
- The action potential in the diagram is the blue segment.
Suppose that Neurons A, B, and C synapse on the dendrites of the upper motor neuron (UMN) that, if it fires, causes McEvil’s index finger to pull inward.
Suppose also that:
- Neuron A releases an excitatory neurotransmitter, increasing the inside voltage of UMN +7 mV.
- Neuron B releases an excitatory neurotransmitter, increasing the inside voltage of UMN +3 mV.
- Neuron C releases an inhibitory neurotransmitter, decreasing the inside voltage of UMN -7 mV.
- If A and B simultaneously fire, while C doesn’t, the inside voltage of UMN increases to -70 + 7 + 3 = -60, the threshold for making UMN fire
- Any other other combination of A, B, and C firing or not firing, fails to make UMN fire.
- For example, if A, B, and C all fire the inside voltage of UMN increases to -70 + 7 + 3 -7 = -67, below the threshold.
A and B firing and C not firing cause UMN to fire, causing McEvil’s finger to bend inward.
McEvil did not have free will
- McEvil has free will to bend or not bend his index finger only if he has free will to cause or prevent UMN firing.
- But McEvil can’t prevent UMN from firing because at the time, as UMN is on the verge of firing:
- Presynaptic neurons A and B have already fired and C has not.
- McEvil can’t change the past.
- So McEvil can’t prevent A and B from firing or make C fire.
- So McEvil can’t do anything to prevent UMN from firing.
- The argument applies not only to motor neurons but to any neuron whatever. So it doesn’t do any good to point to some other neuron and say that’s where McEvil had free will.
So McEvil could not have refrained from pulling the trigger. He did not have free will.
McEvil bears no moral responsibility
- A person is morally responsible for something he does only if he could have avoided doing it.
- McEvil could not have avoided pulling the trigger, killing the Director.
- Therefore McEvil is not morally responsible for assassinating the Director, meaning that he doesn’t deserve to be punished.
- “One important structure in the frontal lobe is the precentral gyrus, which constitutes the primary motor region of the brain. When parts of the gyrus are electrically stimulated in conscious patients (under local anesthesia), they produce localized movements on the opposite side of the body that are interpreted by the patients as voluntary.”
Deterministic Network of Neurons
- Nodes are neurons
- Arrow means synapses on
- Root node (with no arrow pointing away) fires because of its three presynaptic neurons.
- Those neurons fire because of their presynaptic neurons. And so on.
- Leaf nodes (with no arrows pointing to them) fire because of sensory organs
Predicting Voluntary Actions
- One kind of support for Neural Determinism would be experiments in which scientists predict voluntary actions based on prior brain activity.
- Several academic papers have reported such predictions
- “Time of conscious intention to act in relation to onset of cerebral activity (readiness-potential). The unconscious initiation of a freely voluntary act,” Brain 106, Sept 1983, by Libet B, Gleason CA, Wright EW, Pearl DK
- “Unconscious determinants of free decisions in the human brain,” Nature Neuroscience, April 2008, by Chun Siong Soon, Marcel Brass, Hans-Jochen Heinze, John-Dylan Haynes
- “Internally generated preactivation of single neurons in human medial frontal cortex predicts volition,” Neuron, Feb 2011, by Fried I1, Mukamel R, Kreiman G.
- Unconscious determinants of free decisions in the human brain, Nature Neuroscience, April 2008, by Chun Siong Soon, Marcel Brass, Hans-Jochen Heinze, John-Dylan Haynes
- There has been a long controversy as to whether subjectively ‘free’ decisions are determined by brain activity ahead of time. We found that the outcome of a decision can be encoded in brain activity of prefrontal and parietal cortex up to 10 s before it enters awareness. This delay presumably reflects the operation of a network of high-level control areas that begin to prepare an upcoming decision long before it enters awareness.
- The conscious decision to push the button was made about a second before the actual act, but the team discovered that a pattern of brain activity seemed to predict that decision by as many as seven seconds. Long before the subjects were even aware of making a choice, it seems, their brains had already decided.
- “The will has also recently become a target of empirical study in neuroscience and cognitive psychology. Benjamin Libet (2002) conducted experiments designed to determine the timing of conscious willings or decisions to act in relation to brain activity associated with the physical initiation of behavior. Interpretation of the results is highly controversial. Libet himself concludes that the studies provide strong evidence that actions are already underway shortly before the agent wills to do it. As a result, we do not consciously initiate our actions, though he suggests that we might nonetheless retain the ability to veto actions that are initiated by unconscious psychological structures. Wegner (2002) amasses a range of studies (including those of Libet) to argue that the notion that human actions are ever initiated by their own conscious willings is simply a deeply-entrenched illusion and proceeds to offer an hypothesis concerning the reason this illusion is generated within our cognitive systems. Mele (2009) and O’Connor (2009b) argue that the data adduced by Libet, Wegner, and others wholly fail to support their revisionary conclusions.”