Molecular cascades in learning

Learning is behavioural modification resulting from experience. Since all behaviour reflects actions of the nervous system, behavioural modification must result from changes in the behaviour of the nervous system. Hence, lasting plasticity in neuronal function is a prerequisite for learning. Biophysical substrates for neuronal plasticity have been examined in the vertebrate. At the synaptic level, plasticity is expressed by changes in the amount of transmitter released or in the sensitivity of postsynaptic receptors for the transmitter. Although each synaptic function that is modulated during plasticity must be described individually, we can begin to discern some features common to several systems at the molecular level. For example, persistent plastic changes appear to require the activation of intracellular second messengers or the phosphorylation of certain proteins.