Daily Brain Snack: Why You Have a Split Brain
Your two hemispheres increase cognitive capacity in many tasks - but always operate together.
Aren’t many of the ideas around our split brain myths?
Yes, indeed, exactly. In fact my most popular article of all time (across all platforms) is about the myth of hemisphere specialisation.
In the above article I outline some of the history of the myth but also debunk it.
But why do we have two hemispheres then?
Yes, that is an obvious point, isn’t it? We clearly have two hemispheres and biology doesn’t do this type of thing by chance, so there must be a very good reason (which I also approach in the above article). This is precisely what Scott Brincat and Earl Miller outline in a paper just out.
So what is the reason then?
Well, they first of all point out as I and many others have that those mythical ideas of the left is analytical and the right is creative are 99% junk. We use the whole brain for all complex tasks. But one key feature is that visual and bodily coordination is clearly separated. And the reason that two hemispheres is better than one is that it optimises cognitive capacity. Specifically in spatial dimensions.
Please explain!
For us human beings, and all other animals, processing what is happening in the environment is incredibly important. If stone-age Andy is out hunting and focusing on a deer it would be great to have effective processing for objects or other animal that come from a different direction e.g a lion that may threaten me. This is more efficient if I have two hemispheres.
Basically separation of some tasks enables more efficient processing. This also applies to other ares such as working memory and attention that is important in all areas in life, from school, to walking down the street, to business contexts.
But what happens when something moves from left to right - this must go across two hemispheres then?
Yes, so if we have two objects in the left and right fields of vision they will be processed by the separate hemispheres, but if something moves across, it will indeed be handed off to the other hemisphere. And interestingly this has indeed been observed and described by Brincat and Miller - what actually happens is that we can track the movement across the hemispheres and when it is about to pass over to another hemisphere this already pre-activates (this is our predictive brain in action). However, this has a small processing cost i.e. we momentarily need higher processing power and attention may drop slightly.
So, what do the hemisphere do?
The hemispheres both split and share processing for the most effective outcome. Anything complex that we do such as creativity, or speaking, and writing, is a complex interplay between both hemispheres. Single-sided activity and sensory processing is independent but even then our hemispheres are coordinating.
Rather than think of what hemispheres do, think that separation increases cognitive capacity but requires coordinative ability. That applies in many domains in life.
Reference
Scott L. Brincat, Earl K. Miller.
Cognitive independence and interactions between cerebral hemispheres.
Neuropsychologia, 2025; 212: 109153
DOI: 10.1016/j.neuropsychologia.2025.109153