The learning matrix

The old dog now has an excuse for failing to learn new tricks. Research from Karen Christopherson, Erik Ullian, Ben Barres (Stanford University, Stanford, CA), and colleagues may help to explain why the young make better learners. The work identifies a youth-related factor that is needed for synapse formation.

Learning depends in part on new synapse formation. But neurons make few synapses in the absence of astrocytes, which seem to secrete a synaptogenic factor. Christopherson et al. now show that this synaptogenic activity is thrombospondin (TSP)-1 and –2.

To find the synaptic helpers, the authors fractionated astrocyte-conditioned medium. From this soup, TSPs were both necessary and sufficient for neurons to form synapses in vitro. TSPs are extracellular matrix proteins that alter cell adhesions by binding to other matrix proteins or to membrane receptors....