Researchers from MIT studying brain plasticity, the reorganization of brain cells and their connections over time, have recently discovered a “backtalk” or retrograde signal from post-synaptic to pre-synaptic neurons that plays a crucial role in synapse development. It has long been known that synaptic strength, the strength of the connections between neurons, plays a central role in learning and memory in neural networks. The scientists hope their work will lead to breakthroughs in understanding and fighting neurological disorders like Alzheimer’s disease.
The research team was led by J. Troy Littleton, an associate professor of biology at the Picower Institute for Learning and Memory and consisted of research scientist Motojiro Yoshihara, graduate student Bill Adolfsen, and MIT affiliate Kathleen T. Galle.
During learning and memory formation in the brain, synapses between active neurons are physically strengthened. In contrast, the synapses in less frequently used neural pathways weaken and sometimes break off completely. This “use it or lose it” reorganization is constantly going on in the brain and is influenced by age, genetics and external stimuli.
In addition to the main electrochemical signals traveling from the pre-synaptic neurons to the post-synaptic neurons, the researchers from MIT have found a signal traveling in the opposite direction that seems to be the key to synaptic strengthening. The scientists knew from previous research that the synapses affected during memory formation stayed electrochemically active during strengthening, but have discovered that calcium plays an important part in signaling the structures to be strengthened, weakened, or broken. This calcium-dependent retrograde signal from the post-synaptic to pre-synaptic neuron lasts for up to 20 minutes after the original pre- to post-synaptic electrochemical “burst” takes place.
“This work suggests a previously unknown role for miniature release in neuronal function,” Littleton said. “This mechanism can mediate which synapses get reinforced and which do not.”
The research was published in the November 4th issue of Science.