Depression – a biological response to threat?

Published in Counselling Matters, (the magazine of the National Counselling Society) August 2022.

What do we know about depression?  We can list its symptoms such as low mood, low energy, a slowing of thought and movement, loss of concentration, and loss of pleasure and interest in activities.  There is also a disruption of our patterns of appetite and sleep, negative, hopeless, and sometimes suicidal thoughts, and a loss of both the ability and desire to socialise with others. 1     But what exactly is depression?   I am going to argue that it is a normal biological response to threat which has become “stuck”. 

Our human nervous system can respond to danger and life-threat in two key ways.  The first is by going into fight-flight, a state of heightened metabolic arousal. The second is by means of a bodily shut-down brought about by a sudden metabolic collapse. 2     This two-fold “threat response system” can be best understood by looking at the context in which it evolved – one animal’s need to catch and devour another, and the prey animal’s need to stay alive.   

When a predator attacks its prey, the prey goes into a state of highly aroused running or fighting to help it escape.   However, if this fight-flight response fails, an older threat response shuts down the body and the prey collapses, as we can see when a cat catches a mouse.   This collapse, which is the same biological mechanism as a faint3, stops the predator’s attack and can lead to a window of opportunity for escape if, for example, the predator has to fight off competition.  If such an escape route opens up, there is a sudden metabolic switch from collapse back into fight-flight4.   Then, if a place of safety is reached, the prey animal can rest and relax, and the threat response system switches off.

This threat response, which I refer to as our “Fear System”, evolved in the context of relatively brief attacks and chases5, but where the danger lasts too long or there is no place of safety that can be reached afterwards, the fear system becomes dysfunctional and is unable to switch off, and, as a result, fight-flight or shutdown reactions to any level of threat, whether real or imagined, become habitual6.   As humans evolved as intensely social animals, for whom expulsion from the group was a life-threatening danger, this fear system was wired-up to react to social threats, such as rejection, bullying or loss of status, with metabolic arousal or collapse, in the same way as if they were physical attacks7.   

I am proposing that this threat-induced collapse is the biological mechanism underlying depression.   Such a theory could clearly explain the experience of depression.  The metabolic collapse is brought about by a drop in heart rate and blood pressure8 that disables energy production by starving cells in every part of the body of the glucose and oxygen they need to function9.  This means muscle cells stop working, and our limbs feel heavy as lead.  Lack of understanding has stigmatised depression sufferers by treating energy loss as if it was just imagined.  This theory points to the physical (biological) reality of energy loss in depression.   

It would also explain many of the other symptoms of depression, as this shutdown de-energises brain cells, so we can no longer concentrate, or think clearly, and what thinking capacity remains is negative and hopeless.    The same de-energising of brain cells in the cortex deactivates our social engagement system10, so we lose both the desire and the ability to relate socially to others.  Unsurprisingly, we therefore lose all sense of pleasure in life. 

This theory raises the question as to why depression does not normally present as the full physical collapse seen in prey animals when they are caught by the predator.  I think the answer to this lies in our social engagement system which has developed to powerfully control our fear system responses (thus making social life possible).  However, where the fear system has become chronically stuck, and can’t deactivate, the ability of the social engagement system to control fear responses becomes impaired.  I think this impairment is the underlying cause of depression which can be seen as a metabolic collapse that has been partially but ineffectively controlled by the social engagement system11.  Thus, there may be “gradations in reactions to life threat” 12 so that the threat-based shutdown can be experienced not only as a full physical collapse, but also at lower levels of intensity, in the same way as we can experience a full faint, and also various levels of “feeling faint”.

Seeing depression as a stuck form of bodily shutdown would explain why it is so often experienced alongside anxiety, which can be viewed as a stuck form of the fight-flight response.  Where the overall threat system cannot switch off, these are the two most common states in which we are trapped.  Some people are affected predominantly by anxiety, others by depression, but many oscillate between both.

We see from the context of prey and predator that one way out of bodily shutdown is back through fight-flight.   When psychological therapists help people to get in touch with anger that has previously been inaccessible, they are helping them to reconnect with the physical sensations of fight-flight which can trigger a raising of mood. 13

However, the key factor in switching off the overall threat response system is safety14.  This system can only switch off if we can find safe places in which we can relax.  In a world of increasing poverty, zero-hours contracts, over-monitored employees, government-created “hostile environments”, over-tested schoolchildren, collapsing care services and fear-driven and polarised politics, safe places where we can truly relax are disappearing, and unsurprisingly, levels of anxiety and depression are rising.   

As a sense of safety depends on the contexts in which we live and work, this theory suggests that depression is not some sort of “defect” in the individual sufferer but arises from a normal biological response to threat. However, if there is insufficient support to enable us to return to a sense of safety in the aftermath of a threat, or we live in contexts where threats are unrelenting, the threat response cannot deactivate, and will manifest as anxiety and depression.

Michael Guilding                                                                                        

Notes

  1. American Psychiatric Association. (2000) Diagnostic and Statistical Manual of Mental Disorders. Fourth Edition, Text Revision. Washington, DC, American Psychiatric Association. p.356
  2. Porges, S. W. (2017) The Pocket Guide to the Polyvagal Theory; The Transformative Power of Feeling Safe, New York, WW Norton & Co Inc., pp. 53-56
  3. Porges, S. W. (2017)  pp.10-11.
  4. Levine, P. (2010).   In an Unspoken Voice: How the Body Releases Trauma and Restores Goodness, Berkeley, North Atlantic Books.  pp. 47-50
  5. Sapolsky, R.M. (2004). Why Zebras don’t get Ulcers (3rd Ed.), New York, Holt Paperbacks.  pp.154-5. (When flight-fight is activated, the immune system increases activity for about 30 minutes then drops back to normal levels by about one hour.  If stress continues beyond this point, the immune system is impaired, compromising the ongoing defence of the body.) 
  6. Levine, P. (2010) p. 19-30, 54
  7. Sapolsky, R.M. (2004).  pp. 355-383
  8. Van der Kolk, B. (2014). The Body Keeps the Score. London, Allen Lane. p. 82
  9. This process is very clearly explained in Myhill, S. (2014).  Diagnosis and Treatment of Chronic Fatigue Syndrome. London, Hammersmith Health Books. pp. 20-24
  10. The biological system involved in sending and receiving signals of safety which enable us to engage with each other without activating defensive responses.  Porges, S. W. (2017)  p.26.
  11. Guilding, M. (2020). What is Complex Trauma?  Perspectives on Trauma. The Journal of the Complex Trauma Institute,Volume 1, Issue 1, pp. 3-18. 
  12. Porges, S. W. (2017)  p.12.
  13. Agazarian, Y.M. (2004). Systems Centered Therapy for Groups, London, Karnac.  p. 203. See also Levine, P. (2010) pp. 73-95. and Ogden, P., Minton, K., Pain, C. (2006)  Trauma and the Body:  A Sensorimotor Approach to Psychotherapy,  New York, WW Norton & Co Inc. pp.186-187
  14. Porges, S. W. (2017) pp.xv-xvi.

For a fuller account of the thinking behind this theory, see the article “Rethinking Depression“