The neurobiological interpretation of the mental functions in the work of Santiago Ramón y Cajal.

Cajal (1852-1934) first had contact with the fields of psychiatry and psychology through the experimental study of hypnotism. He interpreted this phenomenon as an aberrant failure of the machinery of the brain. It may be that Cajal's initial interest in the theory of hypnotic suggestion eventually led him to study the biological phenomena related to sleep and dreams, in the neurophysiological explanation of which he disagreed openly with Freud's postulates. Finally, Cajal studied the histophysiological mechanisms of the higher mentalfunctions (thought, intelligence, memory, perception, etc.). He proposed that the pyramidal cells of the cerebral cortex, which he called 'psychic cells', formed the substrate of these functions; he proposed the law of 'avalanche conduction', and he speculated on the possibility of a phenomenon of neuronal plasticity in relation to learning processes. After being awarded the Nobel Prize in 1906, Cajal's interests in psychological aspects began to decline.