Luiz Pessoa

The Entangled Brain is a well-written, smooth read - but that doesn't make it a good book. There are 3 issues that stand-out.

1) The subtitle is TOTALLY misleading. This book hardly is about perception, cognition and emotion: Pessoa instead makes the case that the (distinct) brain areas that are generally considered to be responsible for perception, cognition and emotion are highly entangled, and that they cannot be "neatly disassembled into a set of independent parts". If you are looking for specific examples of how certain emotions influence perception, or vice versa, or how perception influences cognition, etc., look elsewhere. There hardly are any examples to be found in the book. What Pessoa provides is essentially a long list of nerve connections between the basal ganglia, the thalamus, the frontal lobe, the pallial amygdala, the ventral striatum, the superior collictulus, etc., etc.

By doing so, Pessoa does give a good overview of brain anatomy, and covers a bit of history of brain science too - with classical examples like Phineas Gage, Broca's Tan Tan, and a fair amount of others. I also have to stress he convincingly demonstrates his main thesis: the brain as an highly integrated organ, a very complex system with all kinds of loops, feedback and feedforward connections. If you want to know more about the specifics of that, this book might be for you.

2) It is unclear who he argues against. Pessoa often writes about neuroscientists that look at the brain as if it consists of fairly separate building blocks, with one area responsible for language, another for emotion, another for memory, etc. But he never names any recent papers or books that do so - he only refers to the New York Times archive twice, to show how a certain part of the brain is (was?) used in a newspaper. I'm just an amateur science lover, having read a couple of books about brains and the likes - check out my list of reviewed non-fiction to find out which - but from what I can gather, the opinion of Pessoa isn't really contested, and the fact that the brain is a complex neural network is pretty standard fare - even in the New York Times. I could be wrong here, but either way it would have been better if Pessoa had added specific sources.

3) Pessoa tries to argue against reductionism and the brain as a mere causal input-output organ. But he fails twice.

As for reductionism, he argues that a functioning brain can't be reduced to smaller components. I agree: you need all the components of the brain to have a healthy, functioning brain. BUT that does not make reductionism as a philosophical undertaking invalid: it just shows that to understand certain complex systems, you don't need to reduce things totally to its lowest possible level. Maybe that's why some reductionist tend to speak of 'mechanism' instead, and Pessoa admits the brain functions in a "mechanistic" way, "in the sense that all parts function according to the standard rules of chemistry and physics."

Because, what is often at stake in these debates is the principle of causality, as some scientists want to uphold the idea that the human brain (and so humans too) can somehow escape causality - like Pessoa in a way tries with the notion of "emergent" behavior. 'Emergence' refers to properties that are not present at the lower levels - but that's not what reductionist try to argue: no-one claims every property is found at every lower level. For if we can escape causality, we are free, but if we can't, the freedom of the will becomes a problematic notion. Pessoa never talks about free will in this book, but does try to stress the human brain as a flexible organ, responsible for flexible behavior, behavior that's "emergent" & "complex" - yet no-one that argues against free will claims that our behavior is not complex, or not situationally flexible, or not emergent from our protein brain.

When Pessoa tries to show that behavior is emergent and complex, and not just the result of input-output causality, this is where he fails too. He admits the brain can be thought of as a circuit in between sensory and motory cells. But his notion of input is misguided. Consider this crucial passage on page 153-154, under the telling heading "Decoupling Sensory Signals from Motor Responses":

"In chapter 3, we discussed a circuit involved in both defensive and appetitive behaviors centered on the optic tectum/superior collicus of the mid-brain. This system is extremely important across vertebrates. In rodents, it helps the animal decide if it should flee when movement is detected overhead or possibly approach and explore further if the movement is in the lower visual field. But the animal's behavior is flexible and not fixed by the input - the context in which it occurs, encompassing both external and internal worlds, is critical."

The problem with this part is that the context obviously is part of the input too. You cannot argue for the brain to be an entangled system, and then consider the input to the optic tectum to be only some visual input. The body's internal state (all kinds of sensors measuring appetite, hormone levels, pain, fatigue, etc.) offers constant, diverse inputs into the brain as a system, influencing how its subsystems operate. The same goes for the context, the "external" world: obviously the input is not limited to vision of some movement in the lower visual field. There's the other visual input, but simultaneously also input of all other senses (sound, temperature, tactile, smell, taste,...). On top of that, the brain is a system that evolves over time, something Pessoa does admit, coincidentally on the next page: the system learns. So also input (of whatever kind) received in the past, should be considered as well.

All that makes a sentence like "the animal's behavior is flexible and not fixed by the input" highly misleading. Pessoa here talks about one specific form of input (vision in the lower field) but the gist of his argument gets him to the "decoupling of sensory signals from motor responses", as if the brain somehow overcomes causality.

On page 218 he even goes as far as suggesting there might not be a close link between brain and behavior: "Now, when researches study the rat's brain under such conditions, a close relationship between brain and behavior is established. But as Paré and Quirk warn, the tight link might be apparent insofar as it would not hold under more general conditions. Neuroscience is experiencing a methodological renaissance."

In the final chapter, we get the following, a bit baffling statement on page 221: "In considering the benefits of such ubiquitous mixing of sensory and motor information, the investigators [Stringer et al. 2019] ventured that behaving effectively depends on the combination of sensory data, ongoing motor actions, and internal-state variables."

To which I would say: no shit, Sherlock. Notice again that ongoing motor actions and internal-state variables are decoupled from sensory data, while I would argue that also motor action and internal-state variables are very much part of our sensory data. In trying to (justifiably) break down the walls between brain regions, Pessoa keeps up some other walls that are conceptually just as problematic.

Let's consider a final passage, on page 212, in a chapter about unlearning fear:

"The decision to take flight is not just triggered by threat detection and involves computations that rely on multiple external and internal variables. Together, escape behaviors are far from simple stimulus-driven, stereotypical reactions. The mechanisms involved engage specialized circuits refined by eons of evolutionary times."

I get it, behaviorism and conditioning are a bit creepy. Scientists want to get away from Watson and Thorndike. But why even add the words "stimilus-driven" in the above part? True: real life rat or mice behavior is complex, not-stereotypical, not the same as in a 40 x 40 x 40 cm white laboratory box. But are "multiple external and internal variables" really no part of the brain's input? Aren't those variables stimuli too? Yes they are. Again, Pessea singles out on specific stimulus (predator detection), points at the fact that stuff is more complex, and then uses that cast doubt on the entire idea of "stimulus-driven" input behavior, as if the additional complexity isn't part of the input/stimulus.

All and all, a disappointing read.

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