Still reading aloud to myself from Iain McGilchrist's book, The Master and his Emissary. I've made it all the way to p. 22. Yup, this is a good thing. This really slows me down, makes me think and feel, soaks info into the neurons way better than reading/skimming effortlessly/silently. Similar to walking through countryside on foot as opposed to driving through it. Makes the book feel alive, not mere "seen-ery."
You might think that as brains evolve to become larger, the interhemispheric connections would increase in tandem. But not at all. They actually decrease relative to brain size (Jänke and Steinmetz 2003 p 210-11). The bigger the brain, the less interconnected it is. Rather than taking the opportunity to increase connectedness, evolution appears to be moving in the opposite direction. (...) it turns out that the greater the brain asymmetry, too, the smaller the corpus callosum, suggesting that the evolution both of brain size and of hemispheric asymmetry went hand in hand with a reduction in interhemispheric connectivity (Hopkins and Marino 2003). And, in the ultimate case of the modern human brain, its twin hemispheres have been characterized as two autonomous systems (Friedman & Polson 1981 p. 18-19).
So, yay. Just ducky. As if it wasn't hard enough for the neotenous ape to become adult and wait 20 years for its brain to myelinate all the way throughout the cognitive-evaluative frontal lobes to gain executive function, we have two almost autonomous brains in there, in a way, taking two decades to ripen. Plus, they have to learn to get along with each other with fewer direct pathways available, are forced to externalize themselves so they can hear, see, feel each other, plus they prefer distinct modes of operation. Oh joy. No wonder being a human antigravity suit is not for sissies. Two whole brains to manage.
Just yesterday, I found this: Patients Reflect on Life with a Common Brain Malformation, by Daisy Yuhas:
"At least 1 in 4000 infants is born without a corpus callosum... “It’s a hidden disability,” says University of California Institute of Technology psychologist Lynn Paul. Many born without this structure go undiagnosed for years—only neuroimaging can confirm the agenesis, or failed development, of this brain area. Instead people are diagnosed with disorders such as autism, depression, or ADHD."(Depression, eh? Hmmn...)