Researchers at the Max Planck Institute of Neurobiology, Munich/Germany have discovered that long-term potentiation (a strengthening of synaptic connections that is thought to be the cellular basis for learning and memory) in a hippocampal neuron goes along with morphological changes in specialized microscopic structures, the so-called dendritic spines (Nature, May-6th, 1999). Most neurobiologists believe that memories are encoded in the changing strength of synaptic connections in the brain, that is, in the effectiveness with which one neuron in the brain communicates with another. As the human cerebral cortex contains about 1014 (100 trillion) synapses, a lot of information could be stored.
Understanding how memory works is one of the fundamental problems in neurobiology. Naturally, then, many neurobiologists are concerned with how synaptic strengths are regulated to store information. One problem in particular has been to answer the question whether the functional changes in the strength of synaptic transmission are also correlated with structural changes in neurons as this could "engrave" the information in the brain in a more durable and permanent way than a mere physiological change. An especially attractive candidate for such structural changes is the postsynaptic spine, a tiny protrusion of the dendritic tree that is distinguished by several features: it is the almost exclusive carrier of the postsynaptic sites of excitatory synapses, it covers a neuron in numbers far greater than a thousand and it has so far managed to dodge the efforts of neuroscience to elucidate its function quite effectively.
Florian Engert and Tobias Bonhoeffer at the Max Planck Institute of Neurobiology in Munich have now shown that indeed -- as has long been speculated -- spines do change their morphology when synapses are functionally strengthened.
This advance has been possible through the combination of two new techniques,
two-photon laser scanning microscopy
Contact: Tobias Bonhoeffer