Artificial Growth and Developmental Plasticity: Part V

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Morphogenesis and neurogenesis: Figure a shows the interior of a morphological unit. Chemical transcription factors (TFs) diffuse out from the centre of the unit (black circle). TFs are released by expressed genes lying along the genome (black squares are expressed genes; gray squares are non-expressed genes). Unit growth is initiated if the growth TF reaches a threshold concentration, the unit attempts to bud off a daughter cell. The placement of the daughter unit is determined by two additional TFs. The concentration of these two TFs at the centre of the mother unit determine the value of two angles, omege (Θ) and theta (Φ), which determine where on the mother unitís surface the daughter unit is placed. The same procedure is used in neurogeneis: one TF triggers the creation of a neuron, and two additional TFs determine its placement just below the surface of the morphological unit. Aside from threshold events such as unit creation, neuron creation and deletion, and synapse creation and deletion, there are several continuous events, such as neuron and synapse movement. Figure b shows how this is accomplished for neuron movement. For each neuron in a unit, its change in position is given by a vector, m, which is a summation of vectors, as shown in the above equation. u is the number of daughter units attached to the mother unit containing the neuron, plus the mother unit itself (in this example, u=4). vi is the vector originating either at the centre of the mother unit, or from the point on the mother unitís surface where the ith daughter unit attaches. ci is the concentration (ranging between 0.0 and 1.0) of the TF associated with neuron movement at centre of the ith unit.

 

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