Memory depends on subtle brain signals

The fragrance of hot pumpkin pie can bring back pleasant memories of holidays past, while the scent of an antiseptic hospital room may cause a shudder. The power of odors to activate memories both pleasing and aversive exists in many animals. The intricate biochemical mechanism for storing scent-associated memories differs slightly from a less-understood mechanism for erasing unnecessary memories.

Understanding how brains actively erase memories may open new understanding of memory loss and aging, and open the possibility of new treatments for neurodegenerative disease. In multiple ways, the processes of forgetting and remembering are alike. In fruit fly models of odor-associated learning, both the saving and erasure of memories involves
dopamine activation of the brain cells. This clue in flies is important for understanding the human brain.

The olfactory systems of flies and humans are actually quite similar in terms of neuron types and their connections.activation of the neurons causes them to make an identical messenger molecule,  Tcyclic AMP, leading to a cascade of activity within the cell, either building or breaking down memory storage.

The research team discovered one G protein, called G alpha S, that latched on to a neural dopamine receptor called dDA1, associated with memory formation. They found a different G protein, called G alpha Q, linked up with a nearby dopamine receptor called Damb, associated with the machinery of forgetting. The next question was whether those two different G proteins could be controllers of the fly brain's memory machinery.

To find out, the researchers silenced genes involved in the production of the G alpha Q protein in the flies. The flies with the protein silenced were exposed to odors in aversive situations and sent through mazes to see how well they remembered to turn away in the presence of the scent. It appears in flies that some level of forgetting is a constant, healthy process.

There is a slow process that whittles away memories, and it continues whittling them away unless another part of the brain signals the memory is important and overrides it.It may be that the process of acquiring and forgetting memories ebbs and flows in a state of balance. Important memories like the taste of mom's pumpkin pie might be forever retained, but trivialities like what you wore ten years ago can fade into oblivion without consequence.
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