I’m starting on a new book, entitled ‘The Entangled Brain: How Perception, Cognition, and Emotion are Woven Together” by Luiz Pessoa! Coming from a psychology background that didn’t have a strong emphasis on neuroscience, I’m excited to get deeper into and learn more about the study of the brain and how it relates to behaviour.
The choice of book is very intentional. One reason I started adopting an ecological approach to cognitive science was because of the realisation that for far too long, we have been studying the capacities of the mind isolated from the body and environment. The problem with this is that it doesn’t recognise how our brains are embodied, and that we as organisms are embedded within a context. We aren’t simply brains wandering about reacting to stimuli. Rather, we are brains-in-a-head-on-a-body-in-an-environment surrounded by a constant flux of rich information. In other words, instead of looking at individual bits and pieces, we have to look at the system as a whole.
The current state of neuroscience
In a similar manner, Pessoa recognises that the current state of neuroscience is headed in the wrong direction. Most of neuroscience takes what he calls a ‘divide-and-conquer’ approach to studying the brain. That is, given how complex the brain is, scientists have opted to split the brain up into different components, studying them each individually, before trying to fit them all back together as if putting back a jigsaw puzzle. For instance, the Brodmann map, first formulated by Korbinian Brodmann in 1908, represented a first attempt to divide each hemisphere of the brain into 50 different anatomical units, and is still widely used today. More recently, Glasser et al. (2016) released a paper that saw the cerebral cortex divided into 180 parts in each hemisphere.
And it’s not just about splitting the brain up just for the sake of it. More specifically, neuroscience takes a function-to-structure mapping approach, where a particular function can be attributed to a specific area or region of the brain. Pessoa provides some examples of this: the insula contributes to drug urges; the fusiform gyrus is involved in face perception, the prefrontal cortex enhances attention, the amygdala facilitates fear responses etc… So not only do we divide the brain up into different sub-components, but we also attribute function to unique components.
Brains as complex systems
What’s the problem with this? After all, is this not reminiscent of the mechanistic reductionist approach (which, for the most part, has served us well) to science advocated by Newton and Descartes? The issue here, according to Pessoa, is that it treats biology (and the brain) like physics or, even worse, engineering. What Pessoa is trying to get across here is, on my reading, that biological systems (and lots of complex systems, for that matter) are complex, and not complicated.
What’s the difference between these two terms? A space shuttle built by NASA is a complicated system. It has many different components that are combined in intricate ways that result in a functional spaceship. Crucially, these components are put together in such a manner that they interact in a linear and predictable way. Given a certain input, the operators know exactly what output they will get. If I press this button, I know that this part of the space shuttle fires up. If I push this throttle by a certain amount, I know that the engines will fire up to this amount. Complex systems, too, are made of simpler components. The main difference, however, is that their interactions are characterised by nonlinearity. As such, the lower-order interactions often give rise to unexpected or unpredictable higher-order behaviours that cannot be inferred from the properties of the lower-order components.
Do you see the issue now? We have been treating brains like complicated systems that consist of linear, straightforward interactions. But what if they are actually complex systems? Made up of networks of connectivity whose functional manifests cannot be tied down to an identifiable or consistent subcomponent? This is the main point that Pessoa is trying to put across – brains are complex systems that aren’t reducible to their individual components. You can’t study the brain by using the ‘divide-and-conquer’ strategy, for as Gestalt psychologists would put it, the whole is different from the sum of its parts.
Explanations in neuroscience
So, we’ve made the argument that the current trajectory of neuroscience isn’t very promising. We need to approach it from a complexity and system-based perspective instead. But before we move on, it’s still helpful to be aware of the current methods and conclusions of neuroscience.
Here, Pessoa points out that the central question of neuroscience is: How does the brain generate behaviour? How do we get from electrical impulses between neurons to sensing, feeling, perceiving, thinking, and acting? To answer this, neuroscience employs 3 primary methods of study: lesion studies look at changes to different capacities once a certain brain area is damaged; activity studies seek out brain signals while participants perform certain behaviours and functions; and manipulation studies temporarily enhance or silence brain signals before observing how this affects participants. Across these different methods, a conclusion is made about a specific part of the brain, in the form: area or circuit X is involved in behaviour Y.
At this point, Pessoa makes a worrying observation. Note the general conclusion made above. Now, look at the examples of function-to-structure mapping in the 4th paragraph. Have you noticed just how vague the relational verbs used are? Involved, contributed, facilitated, enhanced… Pessoa calls these filler terms, which, while making an association between a function and structure, actually tell close to nothing about how exactly a function results from a certain brain area! What are the exact mechanisms and processes involved? What parts are at play, and how do they interact? Despite pushing for a reductionistic function-to-structure approach to the brain sciences, neuroscience has actually achieved very little in terms of the question of ‘how-exactly’.
Correlation or causation?
While we continuously push for answers to causality, the results from neuroscience actually point more to correlation. Pessoa points us to an analogy provided by Ralph Adolphs and David Anderson. It’s pretty succinct, so I’ll leave the full quote here:
'We can predict whether a car is moving or not, and how fast it is moving, by “imaging” its speedometer. That does not mean that we understand how an automobile works. It just means that we’ve found something that we can measure that is strongly correlated with an aspect of its function. Just as with the speedometer, imaging [measuring] activity in the amygdala (or anywhere else in the brain), in the absence of further knowledge, tells us nothing about the causal mechanism and only provides a “marker” that may be correlated with an emotion.' (Adolphs and Anderson 2018, p. 31)
The point here is pretty clear. By imaging the brain using techniques such as fMRI, all we have done is establish a correlation between a particular behaviour and the activation of a particular brain region. Superficially, it seems like we’ve found the structural cause of a function. Except we haven’t. If a speedometer can ‘light up’ without being the cause behind a car’s movement, surely it remains possible that the amygdala can be activated without being the cause behind our fear responses!
The grim reality is that for all the results and progress we’ve made in neuroscience, there exists, according to Pessoa, a huge gulf (and not gap!) between what we know about the brain, and what popular science and the media would like us to think we know about the brain. All things considered, this is a timely reminder to everyone to be wary of any big and bold claims made in neuroscience, especially anything that definitively states that we have found the structural (brain) basis of a particular human capacity.
All hope is not lost, though! In the rest of the book, we’ll look deeper into how a systems-based approach to neuroscience can work. But first, the part we all dread, a whole section dedicated to neuroanatomy in chapter 2! :)
References
Adolphs, R., & Anderson, D. J. (2018). The Neuroscience of Emotion: a new synthesis. https://openlibrary.org/books/OL29367978M/Neuroscience_of_Emotion
Glasser, M. F., Coalson, T. S., Robinson, E. C., Hacker, C. D., Harwell, J., Yacoub, E., Ugurbil, K., Andersson, J., Beckmann, C. F., Jenkinson, M., Smith, S. M., & Van Essen, D. C. (2016). A multi-modal parcellation of human cerebral cortex. Nature, 536(7615), 171–178. https://doi.org/10.1038/nature18933
Pessoa, L. (2022). The entangled brain. In The MIT Press eBooks. https://doi.org/10.7551/mitpress/14636.001.0001
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