Learning requires constant reconfiguration of the connections between nerve cells. Two new studies now yield new insights into the molecular mechanisms that underlie the learning process.
Learning and memory are made possible by the incessant reorganization of nerve connections in the brain. Both processes are based on targeted modifications of the functional interfaces between nerve cells the so-called synapses which alter their form, molecular composition and functional properties. In effect, connections between cells that are frequently co-activated together are progressively altered so that they respond to subsequent signals more rapidly and more strongly. This way, information can be encoded in patterns of synaptic activity and promptly recalled when needed. The converse is also true: learned behaviors can be lost by disuse, because inactive synapses are themselves less likely to transmit an incoming impulse, leading to the decay of such connections.
How exactly an individual synapse is altered without simultaneously affecting nearby nerve cells or other synapses on the same cell is a question that is central to Michael Kiebler's research. Kiebler, a biochemist, holds the Chair of Cell Biology in the Faculty of Medicine at LMU. "It is now clear that the changes take place in the cell that is stimulated by synaptic input the post-synaptic cell and in particular in its so-called dendritic spines," he says, "and particles that are known as "neuronal RNA granules" deliver mRNA molecules to these sites". These mRNAs represent the blueprints for the synthesis of the proteins responsible for reconfiguring the synapses. Kiebler's team has developed a model, which postulates that these granules migrate from dendrite to dendrite, and release their mRNAs specifically at sites that are repeatedly activated. This would ensure that the relevant proteins are synthesized only where they are needed within the cell.
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