New clues to memory formation may help better treat dementia

Do fruit flies hold the key to treating dementia? Researchers at the University of Houston (UH) have taken a significant step forward in unraveling the mechanisms of Pavlovian conditioning. Their work will help them understand how memories form and, ultimately, provide better treatments to improve memory in all ages.

Gregg Roman, an associate professor of biology and biochemistry at UH, and Shixing Zhang, his postdoctoral associate, describe their findings in a paper titled "Presynaptic Inhibition of Gamma Lobe Neurons Is Required for Olfactory Learning in Drosophila," appearing Nov. 27 in Current Biology, a scientific bimonthly journal published by Cell Press.

"Memory is essential to our daily function and is also central to our sense of self," Roman said. "To a large degree, we are the sum of our experiences. When memories can no longer be retrieved or we have difficulty in forming new memories, the effects are frequently tragic. In the future, our work will enable us to have a better understanding of how human memories form."

Roman and Zhang set about to unravel some of these mysteries by studying the brains of fruit flies (Drosophila). Within the fly brain, Roman says, there are nerve cells that play a role in olfactory learning and memory. Olfactory learning, he says, is an example of classical conditioning first described by Pavlov in his experiment with dogs. In their study, the flies were trained to associate a weak electric shock with an odor. After training, the flies avoided that odor.

"We found that these particular nerve cells - the gamma lobe neurons of the mushroom bodies in the insect brain – are activated by odors. Training the flies to associate an odor with an electric shock changed how these cells responded to odors by developing a modification in gamma lobe neuron activity, known as a memory trace," he said. "Interestingly, we found that training caused the gamma lobe neurons to be more weakly activated by odors that were not paired with an electric shock, while the odors paired with electric shock maintained a strong activation of these neurons. Thus, the gamma lobe neurons responded more strongly to the trained odor than to the untrained odor."

The team also showed that a specific protein - the heterotrimeric G(o) protein – is naturally involved in inhibiting gamma lobe neurons. Roman says removing the activity of this protein only within the gamma lobe neurons resulted in a loss of the memory trace and, thus, poor learning. Therefore, inhibiting the release of neurotransmitters from these neurons through the actions of the G(o) protein is key to forming the memory trace and associative memories.

Function

Memory is based on several processes, which account for short term, long term and sensory memories. The processes used encode information as it is received, store the information and make it available for retrieval at any later point. The ability to retrieve information depends on where it is stored in your memory, however. The short term memory stores information that is immediately recalled for only half a minute, while memories that are stored in the long term memory bank are stored indefinitely.