What if you couldn't forget?

A woman came up to me at the end of one of my presentations recently and told me she was cursed with her memory. Intrigued, I asked her what she meant.

She explained that she had always had a photographic memory, and I'm still thinking that wouldn't be so bad! In addition, she was able to recall all the telephone numbers and contact details of her family and friends. Wow, I thought, how useful. Except, she advised that this included all of their information going years back. She was frustrated that all this "useless" information, as she called it, was hampering her ability to remember other items. Her brain was so full of out of date contact details, she believed her ability to remember other information was consequently impaired.

At the time I was a bit bemused, but I could see her point. What is the use of remembering all that stuff, if it's not helpful anymore? And especially if it then meant you couldn't remember those things you wanted to. How do we forget?

A lot of attention has been focussed on how the brain learns and encodes memory for future use. Neuroscience has shown us that our plastic brains are constantly looking for new opportunities for our neurons to form new synaptic connections - continuing our lifelong process of taking in new information and then remembering it.

Simultaneously our brain has the ability to break connections that are no longer required. This process is called synaptic pruning, which suggests the brain acts like a giant pair of garden shears, cutting off those connections no longer required. In reality it is thought that the connections simply get resorbed back into the dendrites of the corresponding neuron.

But is this process active or passive?

Until now it has been thought to be a more passive occurrence, taking place when neural circuits weren't being stimulated any more. But new research using fruit flies suggests that our forgetting is a very active process as much as the formation of new synaptic connections is.

Moreover the researchers suggest that the act of forgetting is also regulated.

Ron Davis from the Scripps Institute led the team, which has discovered that it is the neurotransmitter called dopamine, which is highly involved in the process of remembering and forgetting.

When we first form a memory, a dopamine forgetting mechanism is also activated which starts to erase some memories, unless there is some importance attached to them. Memories become more resistant to being lost if they have been consolidated, by having some extra meaning or relevance attached to them.

We have two different receptors for dopamine. When dopamine neurons begin signalling, the first receptor becomes activated leading to memories being formed. Once a memory has been acquired, the same dopamine neurons keep firing, except this time the signals go to the second receptor, which triggers the loss of recently acquired and not yet consolidated memories.

So it's an active and self-regulating mechanism - forming new memories takes up more synaptic space, so the ones not being terribly useful are thrown out.

Davis states this could explain something about the Savant syndrome, where certain individuals have a very highly developed memory in a specialised area. It has been believed that savants possess an unusual ability to form memory - but perhaps the explanation could be that they actually have a bad forgetting system.

While this may be cold comfort to the individual who shared her "curse" of her memory with me, it may be of potential interest to those looking to develop drug therapies. Therapies that could enhance memory and cognition, through inhibiting our ability to forget.

Ref:Jacob A. Berry, Isaac Cervantes-Sandoval, Eric P. Nicholas, Ronald L. Davis. Dopamine Is Required for Learning and Forgetting in Drosophila. Neuron, 2012; 74 (3): 530 DOI: 10.1016/j.neuron.2012.04.007