Is the whole thing grounded?

The whole thing, in this case, is Iain McGilchrist’s hemisphere hypothesis. Jonathan Rowson,¹ says that McGilchrist reads very persuasively, but…when it comes to actually build on it you want to be sure that it’s not going to buckle under you.² I find Rowson’s conclusion highly relevant, not least because McGilchrist himself refers to the possibility that the whole thing may just be metaphorical and not necessarily grounded in the brain.³

All this raises a number of questions for me:

1. If each person’s brain develops differently, leading to unique lateralization in each individual,⁴ then how does this impact the hemisphere hypothesis?
2. What if the lateralization of brain function is much more dynamic than assumed by McGilchrist due to, for example, neuroplasticity?⁵
   I’m currently reviewing what McGilchrist writes about lateralization in his books The Master and His Emissary and in The Matter with Things. So far, I’ve learned that the lateralization changes with training (for artists and musicians), is different between males and females, depends upon sex hormones, and even depends on where a woman is in the menstruation cycle.
3. How common is anomalous lateralization? How do you know? Maybe most of us are anomalous in one way or another?
   Both dyslexia and handedness have something to do with the lateralization of brain function. One of my children, for example, is dyslexic. And up to 20% of the general population may have some degree of symptoms.⁶ My grandchild, still a baby, already shows a preference of using the left hand. Approximately 10% of the population is left-handed.⁷

So, how do I know that the hemishpere hypothesis really is grounded in the brain? Does it matter? Yes! If the hemisphere hypothesis turns out to be just a metaphor, then the claims based on the metaphor may be unjustified, that is the explanatory power is not to be found in the divided brain. As the saying goes, extraordinary claims require extraordinary evidence!

McGilchrist points to 5000 studies in support of the hemisphere hypothesis,⁸ but what is the quality of each one of those studies? And how do I, as a reader, know that McGilchrist’s conclusions actually are according to what the study shows? And, can those results be trusted? Unfortunately, I don’t know unless I review the research myself.

A few studies, with a few participants, on specific lateralizations do not provide overwhelming evidence whatever the outcome. What is more is that even if lateralizations are found, explaining their relevance for and relation to the claims of the hemisphere hypothesis is far from trivial. And when a lateralization is found it’s not necessarily a straightforward division according to the left and right hemispheres.⁹

It seems, so far, that the closer I look the shakier the ground becomes, but it might change, of course. McGilchrist uses language to make the point — and he uses it very well — but that, in itself, provides no grounding. Well-articulated opinions are still opinions!

Update 2024-09-25:
Text changed from “are wrong” to “may be unjustified, that is the explanatory power is not to be found in the divided brain”.

Update 2024-09-24:
Text updated for better readability. Notes updated with dates. Typos corrected.

Notes:
1. Jonathan Rowson is co-founder and Chief Executive of Perspectiva. Perspectiva Press is the publisher of Iain McGilchrist’s book The Matter with Things. Rowson has had a professional relationship with McGilchrist since 2011.
2. Perspectiva, “Iain McGilchrist & Rupert Read in Conversation: Are We in a War Against Life?”, 20230613, YouTube Video, 1:44:30, https://youtu.be/WvZ9-Y8MR0o?t=4049
3. Perspectiva, “Iain McGilchrist & Rupert Read in Conversation: Are We in a War Against Life?”, 20230613, YouTube Video, 1:44:30, https://youtu.be/WvZ9-Y8MR0o?t=3614
4. Lateralization of brain function, Wikipedia, last updated 20240913, accessed 20240923, https://en.wikipedia.org/wiki/Lateralization_of_brain_function
5. Neuroplasticity, Wikipedia, last updated 20240912, accessed 20240923, https://en.wikipedia.org/wiki/Neuroplasticity
6. Dyslexia, Wikipedia, last updated 20240820, accessed 20240923, https://en.wikipedia.org/wiki/Dyslexia
7. Handedness, Wikipedia, last updated 20240910, accessed 20240923, https://en.wikipedia.org/wiki/Handedness
8. Iain McGilchrist, The Master and His Emissary, 2019, Preface to the New Expanded Edition.
9. Michael Spezio, McGilchrist and hemisphere lateralization: a neuroscientific and metanalytic assessment.