Thr flow of information in thr CNS is dependent on the type of informa
tional operations. Two modes of the neuronal electrochemical transmiss
ion coexist there. Wire transmission is mediated by the classical neur
otransmitters using synapses for communication. Volume transmission re
presents a humoral type of transmission, mediated by peptide molecules
. Second messengers play a significant role in the regulation of neuro
nal plasticity involved in learning and memory. The artificial neural
nets (the Association and the Perceptron) are based on the associative
memory. Cognitive behavior arises in circuits resemblant to some biol
ogical systems.