A biological neuron is shown in Figure 11.15. In the brain, coded information flows (using electrochemical media, the so-called neurotransmitters) from the synapses toward the axon. The axon of each neuron transmits information to a number of other neurons. The neuron receives information at the synapses from a large number of other neurons. It is estimated that each neuron may receive stimuli from as many as 10,000 other neurons. Groups of neurons are organized into subsystems, and the integration of these subsystems forms the brain. It is estimated that the human brain has around 100 billion interconnected neurons.
Figure 11.16 shows a highly simplified model of an artificial neuron, which may be used to stimulate some important aspects of the real biological neuron. An ANN is a group of interconnected artificial neurons, interacting with one another in a concerted manner. In such a system, excitation is applied to the input of the network. Following some suitable operation, it results in a desired output. At the synapses, there is an accumulation of some potential, which in the case of the artificial neurons, is modeled as a connection weight. These weights are continuously modified, based on suitable learning rules.
FIGURE 11.17 Schematic diagram of a multilayer feed-forward neural network.
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