question- field potential & population spike

Hannah Dvorak hdvorak at
Fri Sep 22 14:10:58 EST 1995

In article <43smo8$hgd at>, mglinws at (MGLinWS) says:
>I want to make sure you do not misunderstand a recent post by
>hdvorak at (Hannah Dvorak), 
>who wrote:
>:The extracellular signal from a single neuron is extremely small 
>:and thus next to impossible to record. 
>This is not true.  Extracellular recording methods allow one to record
>precisely these events.  

To further clarify: it _is_ possible to record single-unit activity,
but only in the form of spikes, i.e. signals seen when the neuron
fires action potentials.  Subthreshold postsynaptic potentials,
which need to be recorded when measuring synaptic strength, cannot
be recorded from individual neurons extracellularly except under
very unusual conditions (e.g. some flat-dish electrode arrays, when
the neuron cultured on the dish makes a very tight seal around the

>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.,

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).

- Hannah

Hannah Dvorak			hdvorak at
Division of Biology 216-76
California Institute of Technology, Pasadena, CA 91125

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