Sources of Anxiety

I recently read an article in Nature that explores the nature of anxiety, found here.  The paper notes previous studies on conditioned anxiety.  That is, anxiety that isn't inborn, but rather learned.  However, the paper instead explores anxiety that is hard-wired into the brains of mice, which are assumed to have similar anxiety pathways as humans.  They looked at the amygdala, which is known to mediate emotional learning, or the attaching of certain emotions to memories.  Given that many anxieties have a root at some traumatic, memorable experience, it makes sense that this region is explored.  But again, they were not looking for evidence of anxiety due to such memories, but rather anxiety without a root memory.

In mice, there are some documented memory-less anxieties.  Specifically, the authors looked at a specific mouse behavior that is reminiscent of agoraphobia.  Mice naturally tend to avoid wide open areas, and show anxiety when in such open areas.  Given that mice are small prey animals, one can see the selective advantaged conferred by such a behavior.  With anxiety of open areas, mice avoid such exposed positions, limiting their chances of becoming the next meal for a predator.  Of course, usually one can be a meal only once, so this would not really work as a learned behavior.

The authors constructed experimental mazes which would make it apparent when mice showed anxiety or not.  In addition, they conducted cell physiology work, in which it is possible to measure the activity of a single protein pump on a single neuron.  Using these techniques, it is possible to very accurately quantify neuronal activity.  Using the constructed apparatus, they were able to trigger the anxious agoraphobic behavior in mice.  Watching videos of the mice moving in the experiments (included in the paper's supplemental material) makes it very clear that the authors are, in fact, able to control the anxiety.  The mice show the anxiety within a second or two of activation of the apparatus, and they return to normal just as quickly when the procedure is stopped.

I would like to go into more detail than this, but I honestly do not understand the methods in their entirety.  I do not think the methods are the important take-home point anyway.  The authors were able to prove that there is such a thing as totally inborn anxiety, and they were able to map out a significant part of the neuronal circuitry involved with it.  This could lead to a dramatic improvement in anti-anxiety medications.  The authors point out that we currently do not understand anxiety in its entirety, and that current anti-anxiety medications do not directly target the pathways that trigger anxiety.  Given that we do not know the pathways, it is no wonder that the medications cannot be that specific, eliciting broad, undesirable side effects.

For that matter, there is another subtle point of the paper: there are certain anxieties that are beyond our direct control.  Directly controlling this region of the brain is like directly controlling heart rate.  Yes, it is possible to both reduce and increase heart rate temporarily depending on the actions one performs, but it is not as simple as saying one wants a change in heart rate.  Who knows what inborn fears are lurking in the deep recesses of our amygdala?