Posted: October 27, 2010 by Wildcat in Uncategorized

Philosophy and Simulation- The emergence of Synthetic Reason- M. DeLanda

mattermedia:

The standard model of neurons places the manipulation of gradients of metallic ions, potassium or sodium ions, for example, at the heart of their functioning. Manipulating these chemical gradients – keeping potassium at high concentrations inside the cell and at low concentrations outside of it – produces yet another gradient, one of electrical potential. The key to the conversion of one gradient into another is the selective permeability of a neuron’s membrane to metallic ions: as membrane permeability changes ions flow in and out of the cell creating variations in the gradient of electrical potential. Neurons use these smooth low-level variations to record the electrical signals acting as their input. Producing an output involves changing the electrical gradients from continuous to discrete, transforming them into a chain or train of practically identical electrical spikes. This spike train is used to produce a chemical signal that, when received by other neurons, increases the permeability of their membranes if the chemical substances are excitatory or decreases it if they are inhibitory. To provide a mechanism for habituation in simple creatures all we need to assume is that the supply of an excitatory substance in a sensory neuron becomes progressively depleted after successive stimulations, so that less and less of this substance crosses the gap to affect the permeability of a motor neuron’s membrane leading to a decrease in its response. A similar mechanism can account for sensitization if we add a secondsensory neuron interacting with the first causing it to increase production of the excitatory substance and therefore the amount of the latter that reaches the motor neuron. 

Manuel DeLanda

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