MOLECULAR DEVICES IN NEURONAL LEARNING MACHINES (OR, THE SYNTACTIC APPROACH TO BIOLOGICAL LEARNING)

Learning alters information encoded in the brain about the world, and hence constitutes a change in neuronal semantics. Yet current neurobiological research on learning is very limited in its ability to address problems of neuronal semantics, due to lack of appropriate methodologies that can deal with the coding of discrete items of information in neuronal systems. In contrast, molecular and cellular approaches disclose ample information on elementary and general mechanisms operating in neuronal systems that subserve learning and memory. Current advances in the neurobiology of learning are thus in the domain of general cellular syntactic rules rather than in the domain of molar semantics of neuronal systems. The syntactic approach has revealed the nature of elementary molecular and cellular devices that operate in learning, including cellular acquisition devices, conjuncture devices, and information storage devices. Cellular acquisition devices identified so far in neuronal systems that subserve learning are membrane-bound receptors for neurotransmitters and cellular receptors for Ca²⁺. Cellular conjuncture devices are exemplified by the NMDA receptor and the Ca²⁺ /calmodulin-sensitive adenylate cyclase. Cellular information storage devices are protein kinase systems and molecular cascades that alter gene expression and/or synaptic morphology. The identification of these elementary devices enables heuristic translation of behavioral phenomena, such as contiguity detection or consolidation, into molecular language.