At 12:23 18/08/02 -0700, you wrote: >Greetings, Keith, > >I agree with Ray's "Wow!" >I must have missed the fling <smile> -- could you take a couple of minutes >to summarize what Probram's 'holographic' model suggested? Apologies for >not already having some acquaintance with it -- my library is a couple of >thousand miles from here. > >Thanks, >Lawry
Lawry, I can't tell you much about Pribram's holographic suggestion because it was never worked out in any detail at all. It was just a interesting hypothesis because holographs had not long been invented and it seemed like an exciting possibility for the brain which at that time was still largely mysterious, micro-electrode probes not having been developed. The holographic idea only had flimsy evidence based on earlier experiments on mice and rats which showed that a learned act seemed to be scattered over the most of the perceptual processing areas of the brain, because excisions of cortical tissue had to be very extensive indeed before the learned act finally vanished from the repertoire. It was supposed, therefore, that originally there were multiple copies of the learned act scattered over large parts of the cortex and, even when very few remained (perhaps even only one!), then the full performance of the act could be resurrected in rather the same way that a holographic image can be resurrected from very small parts of the whole. However, the mice experiments were pretty crude. Parts of the learned act are indeed to be found in different parts of the brain but only specialised aspects of it, and if a few of those parts are excised then the other parts can still associate together and perform the act (albeit less skilfully). Had the experimenters excised certain other very precise areas of the brain -- namely the motor strip that gathers together and synthesises all the specialised aspects of the act and instructs the muscles to perform the act as an integrated whole -- then the learned act could not be performed at all. Indeed, over time, because the specialised parts of the original memory of the learned act could never again "complete the circuit", as it were, the synapses would weaken and the neuronal cells that were dedicated to the particular act would die from disuse. Here's another example based on the "grannie cell" approach. You and I will have multiple instances of the concept of tomato scattered all over our cortex, each with varying proportions of perceptual speciality and at different levels of processing according to the inputs that are usually involved when faced with a tomato and eating it or even throwing it at your least favourite politician (visual, taste, tactility, etc.) However, it would be possible that if either of us had a small stroke in a microscopically small area of the Wernicke's areas of the brain (perhaps only involving two or three cells perhaps) then the ability to utter the word "tomato" will have gone for good. You would be able to remember that a tomato was pleasant to eat. You would be able to choose a tomato from a pile of other fruit when asked to. But if you were asked the name of a tomato sitting on a plate in front of you would not be able to answer. You would not even "know" the answer. You would shake your head in puzzlement as though you'd never seen one before. However, if you were then instructed: "Pick up the tomato from the plate", you would be able to do so instantly. (This is similar to experiences that occur to tens of thousands of people every year when they have had minor strokes so it is not a fanciful example.) So this example is an attempt to describe the phenomenon that some thought was holographic. Does this satisfy? Keith ---------------------------------------------------------------------------- -------------- Keith Hudson,6 Upper Camden Place, Bath BA1 5HX, England Tel:01225 312622/444881; Fax:01225 447727; E-mail: [EMAIL PROTECTED] ________________________________________________________________________
