How reliable are psychiatric diagnoses?

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This post, which mostly provides useful citations, was originally written as an answer to the following Quora question:

Is ADHD one of the only psychiatric conditions that can be diagnosed objectively?

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How many minds can one organism have? (Answer: One.)

I was asked this question on Quora:

Do the two halves of the brain have wills of their own? Can they dislike each other or fight?

Here’s my answer:

It’s very difficult to define what exactly the will is in neuroscientific terms. It seems best to reserve this word for the whole organism, rather than some part of it.

Some philosophers would say that attributing will to some sub-component of an organism is an example of the “mereological fallacy”. It’s like saying the stomach eats, or the brain thinks, or the legs walk. We use these kinds of phrases as a kind of poetic shorthand, but only a complete organism can be said to eat, think, or walk.

In the case of the two hemispheres, we also know that the left brain right brain story — that one is “rational” and the other “holistic/artistic” — is wildly misguided. Some neural processes are lateralized, but most normal tasks that humans perform require close integration and communication between the hemispheres.

But we do have to make sense of a common experience — being “in two minds” about something. Most people know what it is like to be in a conflicted state — multiple goals or biases seem to be tugging at us. Clearly decision-making involves a sort of “parliamant” in the brain, in which multiple vested interests vie to enact legislation that suits them. 🙂

But the parliament metaphor should not be taken too seriously. There is little to be gained in anthropomorphizing neurons or groups of neurons. Neural ensembles might sometimes seem to behave as if they have a will, but that idea will not really help us understand decision-making, or the subjective feeling of having a will.

So brain areas don’t have likes or dislikes — organisms do, and brain areas mediate the processes by which these likes and disliked become manifest.

For more on the problems with anthropomorphizing neural processes, see these two essays I wrote:

Persons all the way down: On viewing the scientific conception of the self from the inside out | 3 Quarks Daily (This essay is partly a gentle critique of the Pixar movie Inside Out.)

Me and My Brain: What the “Double-Subject Fallacy” reveals about contemporary conceptions of the Self | 3 Quarks Daily (This essay explores the tendency of people, including neuroscientists, to think of the brain is a separate agent from the person as a whole.)

I admit that it is often fun to anthropomorphize neurons, which is what I do in the essay below. I paint a picture of a neural city and a neural economy, complete with start-ups and investors. 🙂

Be Careful What You Wish For: Some Wild Speculation on Goodhart’s Law and its Manifestations in the Brain | 3 Quarks Daily

Further reading

Yohan John’s answer to Is the left brain and right brain concept a myth, or is it true?

Yohan John’s answer to What happens to consciousness when the brain’s two cerebral hemispheres are disconnected?

A Clockwork Orange? (A brief musing on the concept of a neural “code”)

I was asked this question on Quora:

Are there many layers of neural codes from the human retina to the optic nerve and the optic nerve to the brain, or are they essentially same signals relayed?

Here’s how I responded:

Here’s a question: in a system composed of clockwork, is there a “code”?

I ask this because I find that the “code” metaphor is often misleading when thinking about biology. Codes are composed of symbols. But it is not clear that neurons communicate using symbols.

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“Are thoughts just a bunch of electrical and chemical signals being tossed around inside the brain, or is there more to it than that?”

“In our world,” said Eustace, “a star is a huge ball of flaming gas.”

“Even in your world, my son, that is not what a star is but only what it is made of…”

The Voyage of the Dawn Treader, CS Lewis

I really like the quote above, which is from the Chronicles of Narnia. It raises a neat little metaphysical question:

Why do we assume that what a thing is made up of is what a thing is?

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What are emotions?

What indeed?

My research is on cognitive-emotional interaction, so I suppose I am qualified to answer this question. 🙂

But my answer cannot be the answer, since there is actually no consensus among scientists concerning the definition of emotions.

[Illustration of grief from Charles Darwin’s book The Expression of the Emotions in Man and Animals.]

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Inhibition and Excitation: the Yin and Yang of the Brain

Do excitatory and inhibitory neurons make binary logic in the brain?

Not really. But it’s a good question because we learn a lot when we try to answer it.

First, we have to clarify what the words ‘excitatory’ and ‘inhibitory’ mean.

  • Excitation is the process by which a neuron’s membrane potential (or voltage) increases. If excitation is sufficient, a neuron will produce an action potential.
  • Inhibition is the process by y which a neuron’s membrane potential (or voltage) decreases. If a neuron is already firing, then if it receives enough inhibition, it will stop firing.

So the statement “If some neurons are excitatory meaning they will fire and some inhibitory meaning they won’t” is not quite right. All neurons, whether excitatory or inhibitory, can fire, but only if they receive adequate excitation. If an inhibitory neuron fires, it can reduce the voltage of other neurons, whether they are excitatory or inhibitory. Excitation is the accelerator for all neurons. Inhibition is the brake for all neurons.

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