Plasticity

F. Frank LeFever flefever at ix.netcom.com
Tue Jun 2 23:16:03 EST 1998


I'm replying off top of my head without access to proper references
(they're at work), but want to encourage legitimate neuroscience
discussion in a forum which has been much abused by other nonsense
recently.

I don't think it is a matter of a neuron's changing its "behavioral
function"; rather, changes of connections among neurons.  Doubt a 
single neuron has a "behavioral function" (although of course there was
the famous hyppothetical "grandmother neuron"!)(i.e. the endpoint of
converging and increasingly specific visual stream inputs en route to
the infratemporal region).

Denervation studies and "paired stimulation" studies in the past few
years have shown reorganization of "cortical maps" with such
astonishing rapidity as to suggest "reprograming" in the sense of
altering synaptic biases in existing networks rather than formation of
new "connections" of a "hardwired" sort.  (All right, I'll  try to
recall the spelling without access to my files: Mezernich? One
researcher who has done a lot of this rapid plasticity work).

On the other hand, Ed Taub's monkeys (kidnapped from his Silver Springs
labs many years ago) did one last service: examination of their brains
LONG after posterior root section (i.e. denervation) showed extensive
reorganization, perhaps of the "hard-wired" sort--published in
_Science_ several years ago.  These were mature monkeys.

ASIDE: Ed was a friend of mine in grad school; I visited his lab and
saw monkeys used in his initial work.  It was impressive to watch them
direct movements to targets (e.g. to pick up a raisin without visual
guidance or somatosensory feedback!  And with very little deliberate
attention, being busy challenging other monkeys--eye contact, jutting
jaw, hoots, etc.).  I am happy that he has found a new start and that
he has been belatedly recognized  (e.g. by American Psychological
Assoociation) for his accomplishments.

Apparently some plasticity in adults is enhanced by noradrenergic
activity.

All for now!

F. Frank LeFever, Ph.D.
New York Neuropsychology Gropup






In <357373D7.267FBEBD at interlog.com> Brian Scott <brians at interlog.com>
writes: 
>
>Gernot S Doetsch wrote:
>> 
>>    Much has recently been written about the plasticity of adult 
>>brains. Following peripheral denervation or sensorimotor training, 
>>significant changes can occur in the response properties of cortical
>> neurons and the details of somatosensory and motor cortical maps. Do
>> such physiological changes mean that the sensory or motor function
of
>> the affected neurons has changed accordingly? Can the "behavioral 
>>function" of adult mammalian neurons ever change? If so, under what 
>>circumstances?
>
>I've read of neurons in the visual system becoming responsive to
auditory
>stimuli after denervation or sensory deprivation...details escape me. 
Something
>like synesthesia perhaps.  Does this count as a change in sensory
function?  
>
>-- 
>  Brian Scott          |  Bloorview Epilepsy Research Program
>  brians at interlog.com  |  University of Toronto, Canada




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