The Brain’s Secret to Memory Formation: Plasticity

by Tanya Thomas on Nov 1 2008 11:16 AM

We so often are taken up with reminiscences of past events and unforgettable flash-backs. Ever wondered how our brains form these memories? Researchers from Duke University Medical Centre claim to have found the answer- unique machinery that enables memory formation.

Plasticity, the ability of the brain to precisely rearrange the connections between its nerve cells, is the framework for learning and forming memories.

The researchers have identified a missing - link molecule that helps to explain the process of plasticity. They hope that the new find might lead to targeted therapies.

Dr Michael Ehlers, a Duke professor of neurobiology and senior author of the study said that the discovery of a molecule called myosin Vb (five b) molecule that moves new receptors to the synapse so that the neuron (nerve cell) can respond more strongly helps to explain several observations about plasticity.

"This may be a general delivery system in the brain and in other types of cells, and could have significance for all cell signaling," he added.

Ehlers said that the movement of neurotransmitter (chemical) receptors occurs through little packages that deliver molecules to the synapse when new memories form. What we have discovered is the molecular motor that moves these packages when synapses are active.

When neurons fire at the same time, their connections strengthen and a person can associate certain features.

"Once you have heard someone's name, seen his face, where he was standing, all these features can be bound into a unified packet of information - a percept - and at a very cellular level this occurs by strengthening synaptic connections between coactive neurons," he said.

"One of earliest changes in Alzheimer's disease is synapse dysfunction, so this molecule might be a new target for that disease," he said.

"Abnormal movement of receptors may be implicated in brain development, in autism," he added.

He said the molecule potentially is involved "in the abnormal electrical activity of epilepsy and the overactive brain pathways of addiction."

During the study, myosin Vb (five - b) molecule in hippocampal neurons responded to a flow of calcium ions from the synaptic space by popping up and into action. One end of the myosin is attached the meshlike actin filaments so it can "walk" to the end of the nerve cells where receptors are. On its other end, it tows an endosome, a packet that contains new receptors.

"These endosomes are like little memories waiting to happen," Ehlers said. "They are reservoirs of neurotransmitter receptors that brain cells deploy to add more receptors to a particular synapse. More receptors equal stronger synapses," he added.

The study is published in the Oct. 31 issue of Cell.