On 8 Jun 2006 09:20:51 -0700, "chadmaester" <chad.d.johnson at gmail.com>
>r norman wrot
>> More seriously, the working out of brain function involves far more
>> than neurons 'firing' action potentials. There is an enormous amount
>> of analog (continuously variable) signal processing going on in the
>> microcircuitry of the dendrites and anaxonal or short axonal neurons,
>> not to mention all the biochemical and molecular biological of the
>> second messenger metabotropic synapses to account for. All these
>> factors probably play a larger role in establishing the phenomenon we
>> call 'thought' than simple action potentials.
>>Do you think neurotransmitters and secondary messengers are critical to
>>> Short term memory has many guises and is important for all aspects of
>> neural function including sensory and motor processing. There is no
>> one single short-term memory store.
>>When neurons are done firing, how is it that we can remember something
>we recently thought of for at least a few moments afterwards? Are there
>temporary connections formed somewhere?
Clearly the notion of neuromodulation and secondary messengers and the
ancillary effects of second messengers (beyond simply causing ion
channels to open to cause an electrical potential) are critical to
emotions. The nervous system really is not a simple computer whose
operation depends on which cells are "active" (firing action
potentials) and which are not. The background of cellular and
biochemical activity is an integral part of the system.
These events I am talking about are a critical part of the "memory"
you are interested in. Electrical events can perpetuate themselves
for a short time in "reverberant circuits". However the metabotropic
transmitters and modulators produce changes in cellular activity that
can last for a very long time. Google "synaptic plasticity" or
"synaptic modulation" or, especially "long term potentiation" for
examples. In particular, a metabotropic transmitter/modulator can
trigger a second messenger event that activates a system that can
change gene activity. The activation or inhibition of specific
proteins can then lead to permanent changes in cell structure and
The electrical activity of neurons is intimately connected to this
cellular activity. Electrical activity mediated by those metabotropic
chemicals (or by Calcium channels) can produce long-lasting changes in
cellular metabolism and gene regulation. These, on the other hand,
can result in changes in membrane proteins, receptors and ion
channels, and hence in the production of electrical activity. The
electrical events and the cell physiology are all part of the story.
That is why I originally said that looking only at action potentials
is a small part of the picture of the nervous system.
That being said, it is also true that many aspects of neural
"computation" are produced purely or mainly by the electrical side of
things (as in rscan's comments citing the early Hubel and Wiesel
studies of vision as electrical responses to patterns of light.
However, developmental and plastic changes are not included in this
paradigm and, especially, Hubel and Wiesel's studies on the influence
of experience on development in the visual system involve these
cellular changes as mechanisms.