Discover Magazine has an interesting Carl Zimmer article on one of the most intriguing questions in neuroscience – why do we have two cortical hemispheres? And why are they not quite the same?
It turns out that the ‘brain of two halves’ is incredibly common in the animal kingdom and that many creatures also show the behavioural lateralisation that we most readily see in humans as someone being left or right handed.
But it’s no entirely sure why we, or indeed, or animal compatriots, have evolved this way, although various theories are kicking around:
David Stark of Harvard Medical School recently found additional clues about lateralization in his studies of 112 different regions in the brains of volunteers. He and his collaborators discovered that the front portions of the brain are generally less tightly synchronized across the hemispheres than are the ones in the back. It may be no coincidence that the highly synchronized back regions handle basic functions like seeing.
To observe the world, it helps to have unified vision. At the front of the hemispheres, in contrast, we weave together streams of thought to produce complex, long-term plans for the future. It makes sense that these areas of the brain would be more free to drift apart from their mirror-image partners.
Zimmer goes on to puncture the myth of ‘left brained’ and ‘right brained’ people, or indeed, thinking styles, erroneously labelled with these pseudoscientific terms.
While certain cognitive styles have been correlated to greater activation in the left or right hemisphere, to describe a whole class of problems of thinking methods like this is nonsensical because the two hemispheres of the brain work together.
It’s like claiming someone is a good cook solely because they come from Italy. The generalisation is so broad it just doesn’t apply to individual people or situations.
Anyway, the Discover article is an excellent whistle-stop tour through the curious world of brain lateralisation.
Link to Discover on the brain of two hemispheres (via @mocost).
Mind Hacks 
I find this particularly interesting: “The left hemisphere specializes in picking out the sounds that form words and working out the syntax of the words, for example, but it does not have a monopoly on language processing. The right hemisphere is actually more sensitive to the emotional features of language, tuning in to the slow rhythms of speech that carry intonation and stress.”
Could anyone recommend a reference to follow for this?
There is no one reference because it’s a huge area. However, picking out sounds that form words is classically associated with Wernicke’s area, and working out syntax is classically associated with Broca’s area, and a search for either one should turn up plenty of things.
The right hemisphere is more sensitive to prosody and a search for neuropsychology of prosody should do the trick.
Most good general neuropsych books should have plenty on this.
My favourites are Human Neuropsychology (ISBN 0131974521) and Fundamentals of Human Neuropsychology (ISBN 0716795868).
Interesting post. I do find the right-left hemisphere distinction useful, even if I agree that pop culture tends to oversimplify its meaning.
I find the work of Daniel Pink in this area particularly illuminating. His book A Whole New Mind is fascinating.
I recently wrote a blog post on the book’s implications for the current global economic crisis:
http://alanfurth.com/a-whole-new-mind-for-finance
I find the work of Daniel Pink in this area particularly illuminating. His book A Whole New Mind is fascinating.
I recently wrote a blog post on the book’s implications for the current global economic crisis:
http://alanfurth.com/a-whole-new-mind-for-finance
In biology there is not always a good answer to why something is the way it is, aside from, “because our ancestors were that way and at some point it offered a competitive advantage.” It is like asking why we are bilaterally symmetrical. It offered some evolutionary advantage in the distant past, and these relics constrain our development because the cost of being rid of them is too high. As the article discusses, our ancestors had that kind of brain, so we do too. It became part of our embryological development and we are stuck that way. The small asymmetries that have evolved in our brains must have helped us survive as a species, but offspring tend to not survive the kind of mutations necessary to evolve a totally different brain plan. There may be brain designs that are more efficient than our two-sided brain, but we can’t get there from here. Evolution does not always result in the most efficient or elegant design. Perhaps we survive despite our two-sided brain, not because of it.