Phobias and traumatic events are like scars in our mind. Recalling these stressful memories or thinking about them can paralyze you with fear, causing the same damaging physiological reaction as the initial event. But it’s all in your mind; you’re not in any real danger, so why doesn’t the fear subside? Why do some of us have trouble stripping these debilitating reactions from memories?

A recent study published in Nature Neuroscience says now we can – with a little chemical help.

Unwinding the web of fear

Surprisingly the drug is a common one that’s already in use for managing blood pressure in people with heart conditions: Propranolol. It was previously observed in 2007 that people who had traumatic events like car accidents or assaults, had a reduced stress levels when remembering these memories if they had taken propranolol before recalling the event.

But very emotional and fearful memories are notoriously hard to vanquish, and often return even after extensive traditional therapy. From an evolutionary viewpoint it makes sense that very important events are vividly recorded and recalled – Saber tooth tigers mean danger, thunder means lighting is around and seeing our children makes us remember how important they are.

But anyone with a phobia is aware that these emotionally charged memories can be debilitating, causing more harm than benefit. If the emotional-physiological response could be removed or erased from these memories then it could be a treatment for difficult to manage symptoms like post traumatic stress disorder.

To examine if propranolol can eliminate the fear associated with specific memories, the researchers in the recent study showed people images of spiders while simultaneously shocking them with small electric charges. As expected, when these people were shown pictures of spiders in the future without a shock, they still exhibited signs of stress, showing they had become fear-conditioned to the sight of spiders.

After these people were fear-conditioned these people were given propranolol before being shown the spiders again. Intriguingly they weren’t startled or stressed. But even more amazingly, on future occasions when they were again shown spider images and shocked, they didn’t develop a fear association like they did previously. Even without any further doses of propranolol, it seems the fear response to spiders had been permanently broken.

I’ve touched briefly before on how your memories are not actually fixed and can change slightly every time you recall them in the context of nostalgia, but this holds true for all kinds of memories. Though it’s an over simplification, you can think of a memory not as a discrete chunk of data, but as a series of instructions on how to rebuild a memory when asked to recall it.  Altering the process of recalling it can therefore change the memory, and that’s where propranolol comes in.

Before we venture down the road of fanciful science fiction like “Eternal Sunshine of the Spotless Mind” let’s take a moment to avoid falling into the stupidly sloppy journalism floating around that thinks scientists are now able to erase specific memories. To illustrate why propranolol or any other drug can’t erase specific memories, lets take a quick look at how our brain actually forms and stores memories.

How memories work

When we learn or experience something new and we lay down a brand spanking new memory it’s because of the plasticity of individual neurons in our brain.

What this means is that each one of our billions of neurons is connected to tens of thousands of other neurons. That’s a lot of connections to consider, but it’s even more complicated than just a numbers game. Not all these connections are equal – some are strong and some are weak.
In a simplistic overview we can say when you form a memory you are tracing a path through this vast network. The more emotional the impact of the experience, the stronger or more permanent the connections become. In the case of a non-traumatic experience like learning a new skill, the increase in connection strength comes from repeated practice that refines the path and slowly solidifies the neuronal connections.

So at a molecular level our memories lie in the strength of the connections between neurons; everything from phobias to knowing how to ride a bike.

These connections are called synapses – the small gap between cells where one neuron releases a chemical signal called a neurotransmitter to pass an electrical signal along to the next neuron in the pathway. The strength of the connections can be directly modified by changing the number of proteins that help release neurotransmitters, and the number or receptors that sense them on the receiving neuron. Change the balance of these two systems and you can make any individual connection weaker or stronger. Wikipedia has a surprisingly good write up about synapses if you’re interested in getting into a more detailed view.

Of course each single neuron can be connected to many thousands of others and only some of these connections are made strong or weak depending on what you’re learning. Move onto the next neuron and repeat the process, and you can see pretty quickly why we can’t “see” into anyone’s head and say “ahh here’s his memory of how to ride a bike”, and why it’s impossible for anyone to erase a specific memory.

To make things even more complicated, these neurons and connections don’t seem to be localized to any defined region of the brain, but may instead be distributed across many regions.

Reinforcement of bad things

Our painful memories and phobias are probably encoded so strongly because of association with emotion during the traumatic event and the associated stresses that run throughout our body. When you recall that memory, the same systems kick in and cause stress hormones to cascade through your body once more. Apart from being unpleasant, this recall with stress helps to further reinforce the fear response and the phobia is formed.

While we don’t know for certain yet, propranolol may interfere with this reinforcement step by interfering with adrenaline receptors in the amygdala; the key hormone and key region that moderates the brain’s response to stress and emotion.

Cure?

Unfortunately this is only the early days of this line of research and many elements still remain to be tested. Pictures of spiders are not car accidents. It’s also unknown how long this removal of fear association will last as the study only tested people up to 3 days after the initial treatments.

Clearly though this is a line of investigation worth pursuing. Many millions of people suffer from debilitating emotional disorders and post traumatic stress so any advance, no matter how small, is a reason for optimism.

Perhaps this is a ray of sunshine for our spotless minds.

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original image by shawncampbell remixed by Patrick

February 23rd, 2009