Unexpected hypotheses arising from brain circuit simulation

[Richard Granger]

jbower wrote that a set of results of ours, published in Science (1990), ...

> "... Was not, in fact, unexpected, as the model was specifically designed
>to do
> just this."

Thanks for giving us the credit for this design.  Since nothing like this
had ever been suggested as a hypothesis of olfactory function (indeed, it's
still studied, and still controversial), if we designed it, it would be a
testament to our inventiveness.

Nonetheless, we admit that the findings actually were quite surprising to
us.  The result emerged only after considerable observation and analysis of
a series of brain network simulations of the anatomical circuits of the
olfactory bulb and cortex (as characterized by Price, Haberly, Shepherd,
and others), operating under normal physiological conditions (as identified
by both in vivo and in vitro work from many labs, including Macrides,
Kauer, Freeman, Haberly,  Eichenbaum, Otto, Komisaruk, Staubli, et al.) and
in response to the physiological induction and expression rules for
synaptic long-term potentiation (LTP; Kanter & Haberly, '90; Jung et al.,
'90).  Extensive references can be found in the many published papers on
the topic; a glance at Medline will readily find most of our papers,
containing these references.  Anyone interested in more detail is welcome
to contact us:  granger at uci.edu

Back to the science of the thing: the hypothesis in question is that the
operation of the bulb-cortex system not only acts to 'remember' odors but
operates (via feedback inhibition over iterative samples of an odor) to
produce first recognition of the general 'category' (or cluster) of an
odor, followed by successively finer-grained recognition over sequential
(theta) cycles of operation, thereby re-using cortical cells over
successive samples to effectively read out a hierarchical description of
the odor.  It's interesting to note that this remains an intriguing
candidate hypothesis that continues to be cited and studied both
behaviorally and physiologically, since its initial publication
(Ambros-Ingerson et al., Science, 247: 1344-1348, 1990).

Many relevant articles from our lab and others' have appeared over the
years; we can send (or post) a list to any interested parties.

-Rick Granger