On 10 Feb 2004, Pollak, Edward wrote: > I had 2 questions from students the other day that I could not answer > hopefully you folks can help. > > 1) This is an old one to which I've never found a satisfactory > answer: Is there an adaptive significance to the contralateral > organization of the brain. If so, what is it? Or is it just a > peculiarity of neural development.
I've collected some information on this one, but no satisfactory answer. A post on another list (1998) quoted the following personal response from the neuropsychologist Jerre Levy; "Crossed regulation began in the vertebrate ancestors, who are represented today by primitve chordates, such as amphioxus, and was passed down to all their descendants. For multiple reasons, it's a lousy engineering plan, but vertebrates are stuck with what they inherited. Amphioxus automatically filters food from water that passes by its "mouth" and automatically exudes sperm or ova in response to seasonal changes in light. It has no capaicty for directed movement and no approach reflexes. Most of the time, its tail is buried in the sand of ocean shallows. It has one reflex: if poked or pushed on one side, it coils in the opposite direction (the coiling reflex). Thus, a stimulus on one side of the body elicits muscle contraction on the opposite half, which requires crossed comunication. The absence of approach reflexes means that a stimulus on one side of the body never has to elicit muscle contraction on the same side". I'm not sure I understand this speculation (which is what it is) but it seems to lay the blame as far back as amphioxus. Another poster pointed out that Steven Pinker in _How the Mind Works_ similarly fingers primitive chordates, although he calls it only an evolutionary "accident" which we all were subsequently stuck with, a concept which I do understand. I also have two references, neither of which I've looked at, although I still intend to, some day. Perhaps Ed will take a look at them and tell us what what they say. Kashalikar, S. (1988). An explanation for the development of decussations in the central nervous system. Medical Hypotheses, 26, 1- 8. Capozzoli, N. (1995). Why are vertebrate nervous systems crossed? Medical Hypotheses, 45, 471-475. Stephen ___________________________________________________ Stephen L. Black, Ph.D. tel: (819) 822-9600 ext 2470 Department of Psychology fax: (819) 822-9661 Bishop's University e-mail: [EMAIL PROTECTED] Lennoxville, QC J1M 1Z7 Canada Dept web page at http://www.ubishops.ca/ccc/div/soc/psy TIPS discussion list for psychology teachers at http://faculty.frostburg.edu/psyc/southerly/tips/index.htm _______________________________________________ --- You are currently subscribed to tips as: [EMAIL PROTECTED] To unsubscribe send a blank email to [EMAIL PROTECTED]
