Friday, June 22, 2018

On Desire 2018. Part 48: The Biology of Action

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We have reached the scariest part of the series for some desirists.

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Particularly for those people who value some empirical evidence in their philosophy.

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Chapters 8 and 9 of The Nature of Desire bring forth empirical evidence.

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The topic of discussion for the next few posts is: Schroeder, Timothy, (2017), “Empirical Evidence against a Cognitivist Theory of Desire and Action", In Deonna J. & Lauria F. (eds). The Nature of Desire. Oxford University Press.)

Schroeder's argument is that the biology of intentional action is more compatible with neo-Humeanism than it is with the various theories that interpret desires as cognitive states - beliefs or judgments that something is good or that one has a reason to perform some action. Specifically, the biology of action suggests that there are two inputs into intentional action - a cognitive input from the parts of the brain that are associated with beliefs and judgments, and an affective input that words through the reward system and dopamine production. This is more compatible with the neo-Humean system.

So . . . how does the brain work?

Schroeder provides us with a causal map. Note that he presents this map after a long discussion of the empirical research. This is not a map drawn while sitting at the philosopher's armchair. It is drawn while standing in the neuroscientist's laboratory.

One reasonable interpretation of the neuroscientific account might go as follows: one senses the world and makes judgments about it. These sense experiences and judgments are realized in the unimodal sensory and multimodal association cortex. They cause possible basic or primitive actions to be primed, with the priming of more complex possible actions (say, strumming a guitar) causing the priming of the less complex possible actions that are required (say, shaping one’s hand in a certain way, moving one’s arm, etc.). These primed actions can be commanded by clusters of neurons found in the motor hierarchy, naturally. Primed possible actions existing at a given time are typically more numerous than the actions one actually performs or would wish to perform. Thus, primed possible actions are all chronically suppressed, this being the role of the motor BG. At the same time as possible actions become primed, one’s experiences and judgments cause a response in one’s reward system. This response combines, in the motor BG, with one’s experiences and judgments. And this combination of experiences, thoughts, and reward signals in the motor BG causes a release of some of the primed possible actions.

Fine. What does this mean in English?

Here you area, reading this post . . . I assume . . . perceiving the world, assessing what you read, saying things to yourself like, "Hey, that finally makes sense?" and "How can anybody believe something as stupid as what this guy is putting on his blog?" But, are you going to keep reading? Are you going to go to the kitchen and get a piece of that chocolate cake? Are you going to write a comment?

As you perceive the world, your brain cues up a whole gaggle of actions compatible with those perceptions. It cues up a set of actions that would involve continued reading, a set of actions associated with going to the kitchen for some chocolate cake. A set of actions that are involved in making a comment. All of these are nominated for the action in question.

If all of these actions go through the gate, then you end up doing a whole lot of different actions at once. You can't do them all at once - it is physically impossible to do so. Normally, your brain will pick one of the nominees and say, "That one." And then you do it.

Sometimes, there is a specific type of action that leaks through the gate. It is usually a simple action. In most cases it is a part of an action - the utterance of a particular word or a simple muscle action such as a wink or a twitch. This is Tourette Syndrome. The behavioral oddities are commonly called "tics". The person afflicted with Tourette Syndrome report being "alienated" from these actions - they come from someplace else. They are not chosen. Whereas the action that is selected to make it through the gate is the action that is chosen - and, thus, it is the action that belongs to the agent.

So, what about this "choosing" of various queued up actions? How does that work?

Well, that comes by means of a dopamine signal that enters through the reward system. This signal selects one of the various act alternatives and says, "Do that one." If this signal is weak, an individual will choose an action, by find it difficult to execute the action. If the signal is stopped altogether, then the agent cannot act - no act is chosen - even though the agent wants to act. This is Parkinson's Disease.

Schroeder's description of the reward system and its effect on actions lacked detail. He wrote:

The [orbitofrontal cortex] has fairly stable, though not immutable, long-term dispositions to discriminate between [its] input signals. In response to some, nothing happens. In response to others, a signal is sent along the affective [basil ganglia].

The signal that is "sent along" is the signal that is relevant to selecting the action that gets let through the gate.

Schroeder does not say anything to this effect, but it seems that these "stable, though not immutable, long-term dispositions" seem to have a close relationship to what I have been calling desires. Desires, as I have described them, are certainly stable and long-term but malleable, and are used in selecting actions. However, nothing in Schroeder's description suggests assigning a value to a proposition being true. So, this may mean absolutely nothing. This is simply something to be filed away - perhaps it will be useful later.

One of Schroeder's comments that I am particularly curious about is this:

In addition to a reward system, the brain almost certainly also contains a distinct punishment system. Its existence may be inferred from such facts as that intuitively rewarding stimuli and intuitively punishing stimuli cause distinct but similarly located responses in OFC and distinct but similarly located responses in the affective BG, and from the fact that there are special brain chemicals particularly released in animals like us under punishing conditions and causing, e.g., freezing behavior in rats. Unfortunately, the effects of the punishment system on behavior can only be inferred by analogy to the effects of the reward system, as there is as yet no clear identification of the punishment system’s output structure.

I have long wanted to know something about the punishment system but, so far, have only been able to find information on the reward system. This is my first confirmation of the hypothesis that it works in a way similar to the reward system.

This actually is not a lot to go on - but it is more than I had. Schroeder used this to argue against cognitivist theories of desire by showing that the way the brain actually works a signal from the affective parts of the brain - the reward system - are used to choose action. This is not a part of the brain that is associated with beliefs and perceptions. So, theories that claim that a desire is to be understood as a belief or a perception are going to have problems matching their theories to the empirical fact. A neo-Humean, such as myself, will not have such problems.

So, it seems, I can breathe a sigh of relief . . . so far.

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