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how many neurons?

Nicolas Le Novère lenov at pasteur.fr
Fri Nov 28 05:39:37 EST 1997

Jiri Barton wrote:
> Hannah Dvorak-Carbone wrote:
> If you don't mind answering my next question; what can C. elegans do
> with regard to intelligence? Are those 300 neurons just enough for a
> random movement, or can the organism do something more, such as simple
> decisions?

First of all, movement do not necessitate neurons. In the universe
of monocellular organisms (which is by some side far more diverse than 
the animal kingdom), there are simple behaviors such as food seeking or
reactions to environment information (temperature, pression, acidity and
so on). All this without any neurons (of course).
Different part of the cell play the roles of sensor, transmitter and
responding actors.

Apart from that, we can get simple reflexes with very few neurons. The 
simplest systems are found in cnidarians (medusa, hydra ...). 

One neuron is enought to get a all or none reaction:

sensor >> neuron (transmission of the information) >> reaction

With three neurons, you can introduce the integration concept:

sensor >> neuron1 \\
                     neuron3 >> reaction
sensor >> neuron2 // 

Or even the modulatory concept:

modulator >> neuron3 \\
     sensor >> neuron1 >> neuron2 >> reaction

See the famous aplysia gill reflex.

Nicolas Le Novère
Neurobiologie Moléculaire
25, rue du DR ROUX
75724 Paris cedex
Ph: 33-(0)1-45-68-88-44
Fax: 33-(0)1-45-68-88-44
email: lenov at pasteur.fr

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