question- field potential & population spike

MGLinWS mglinws at aol.com
Fri Sep 22 19:30:39 EST 1995


I recently wrote:

:You should know that many of us consider these
:"spikes" to be essential to understanding the computations performed by
:neurons in places like the hippocampus and cerebral cortex, where much
:work on LTP has been done.  In fact, if an LTP-like process is involved
in
:neural plasticity, we may one day find proof for such a process through
:single-unit recording methods in behaving animals that demonstrate
changes
:in neural activity that parallel changes in behavioral performance (i.e.,
:learning).

hdvorak at cns.caltech.edu (Hannah Dvorak) responded:

:And, as you surely know, just this has been done by McNaughton and
:Wilson, who showed increases in correlated firing between place cells
:during maze running and again while the rats were sleeping after
:running the maze, and presumably "replaying" the memory of the maze
:in their sleep.  However, to the best of my knowledge it has not been
:shown that such a change in firing patterns is directly due to LTP.
:It's probably a more complicated network property (which, in my
:opinion, does make it more interesting).

The paper by McNaugton and Wilson was a wonderful demonstration of 
recent developments in many neuron recording.  However, I am not sure 
that the McNaugton and Wilson article "proved" anything, other
than showing that neurons are capable of firing in a correlated fashion 
during multiple behavioral states.  

I must admit that I chose the wrong words in my original statement.  
I said that "changes in neural activity that parallel changes in 
behavioral performance" might be evidence for learning and this 
evidence might be based on an LTP-like process.  An e-mail I received 
in response to my posting pointed out that I forgot that "correlation 
is not causation".  I agree!  Simple correlations between behavior and 
neural activity, or between pairs of neurons, before and after some 
behavior is learned is not "proof" of learning.  What we really need is 
proof that the change in neural activity PREDICTS the animal's state of 
learning.  (This is the best we can due.  Statistically speaking, there
is no "proof" of causation.)


Mark Laubach
Wake Forest University


P.S. My intent was simply to ensure that the original poster of this 
series was not confused in thinking that action potentials can not 
be recorded extracellularly.  

P.P.S. I know that there are no direct data that suggest a role for LTP in

mediating learning.  I leave it to those who study LTP to tell us all when

they have finally resolved the issue of LTP and its role in brain
processes.

P.P.P.S. I hope that the result IS due to network properties.  This is
what 
I study!



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