Furthermore there are a lot of really good articles on whether or not therapy works. See for instance Jonathan Shedler's article from the University of Colorado Denver School of Medicine entitled "The Efficacy of Psychodynamic Psychotherapy" published in the American Psychologist (2010, 65(2), 98–109). Schedler makes an impressive case for the fact that psychodynamic psychotherapies are very effective and that their effects persist for years after finishing treatment. However, his article, and many others that I have read do not explain HOW psychotherapy works.
While I am prone to want to explain as much as possible through the physical sciences there are a number of theories that are worth exploring as well. So I will put off the neuroanatomy and biochemistry piece until the end of the blog. We'll get there but let's first look at some of the theories that make a lot of sense even without the functional MRI's to back them up.
If you start with Freud you would find that surprisingly some of his ideas still make sense in terms of how therapy works. Freud believed that we repressed things that were too painful or triggering to manage on a conscious level. These could be aggressive feelings, love feelings, sexual feelings or any manner of things. He felt that urges were going to seek expression one way or another and that it was up to the person to try to find a socially and morally acceptable way to express these baser "drives". So for example a person with a high aggressive drive could become a professional football player (an acceptable "sublimation" of the drive) or could become a thug who goes around beating up people. Some people, for various reasons usually stemming from their early childhood experiences, may have trouble finding acceptable expressions for their not-so-nice drives. Those people might, in Freud's opinion, develop symptoms like panic attacks, bouts of depression, or even more bizarre neurological problems like sudden blindness. He felt that by helping the patient to reconnect to those baser drives and accept their existence, and then find a more appropriate form of expression, patients could be freed from their neurotic suffering. While a lot of what Freud believed now feels outdated and archaic, I agree with his central idea that when we cannot accept parts of ourselves and instead shove those into the unconscious realm we may develop painful symptoms that then lead us to therapy. Many of the different styles of therapy that came after Freud actually took pieces of his theory and modified them, indicating that at least some of what he postulated continues to be useful.
One group of clinicians that I think do a good job of explaining how therapy works is the "(intensive) short-term dynamic psychotherapy" group, also called STDP or ISTDP. Authors in this area include Habib Davenloo (it's originator), David Malan, Robert Neborsky and Marian Solomon. This camp of therapists believe that therapy works in a very predictable (and thankfully replicable) way. First, they conceptualize emotional problems as stemming from fear of experiencing certain painful emotions. These tend to be anxiety, shame, guilt, pain, contempt and disgust. Due to our inability to tolerate these intensely negative feelings we respond in maladaptive ways. For example due to intense shame a person may hide aspects of themselves which leads to feelings of loneliness, disconnection and an intensifying of the shame. From the ISTDP perspective therapy works by helping the client to 1) recognize that they have defensive habits (such as attacking the self), 2) be motivated to change this defensive habit, 3) identify the feelings that are being avoided, 4) allow themselves to experience the avoided feelings within the therapy session (where it can be supported), 5) learn to express those feelings in more adaptive ways outside of the therapy sessions and 6) recognizing that by acting differently with others you have created a new identify for yourself that has replaced the defensive pattern with a more adaptive one. According to research in the Harvard Review of Psychiatry in 2012, is a highly effective type of therapy. For those of us who use psychodynamic theory in our practices ISTDP has many elements that are common to psychodynamic therapy in general. Indeed other studies have shown that psychodynamic psychotherapy is also a very effective form of treatment.
Another theory about how psychotherapy works was highlighted in an article on time.com recently. The article discussed the idea of "narrative". Each of us has a story that we tell ourselves (and others) about our lives. When this story is incomplete or flawed in major ways it can interfere with our happiness. For example if our "narrative" is that we were lazy and never tried hard and that's why we quit college and have never achieved much that story could easily lead us to feel depressed and self-loathing. What if the real narrative was more like we had an undiagnosed learning disability, making it hard for us to learn in a traditional environment, causing us to fall behind due to lack of educational success? That narrative leaves much more room for healthy self-esteem and hope for the future. Some therapists believe that helping patients "rewrite" their narrative or life story in a way that is more balanced can lead to letting go of old pains, shame, guilt and negativity. I do think that this is often a component of successful psychotherapy and have seen this alone change people's lives in dramatic ways.
OK now that we have considered some theories and research on technique we can move on to my beloved psychoneurobiology explanation. In an article published in 2011 in Psychiatric Times numerous brain changes were identified as related to psychotherapy. Some of those were similar to the effects of antidepressants but some were distinctly different. Some of the effects reported included changes in activity/metabolism in various areas of the brain (such as the medial frontal cortex or the hippocampus) while others showed changes in the chemical serotonin and it's transport within the brain. Finally more recent studies have looked at structural changes in individual neurons that are thought to be produced by learning. So while the results of various studies differ in terms of how or where the brain changes are taking place, the overall conclusion is that psychotherapy DOES change the brain chemically and anatomically, and that those changes are related to a reduction of symptoms in the therapy graduates.
While there are other explanations of how therapy works I hope that these at least give you an overview of some of the more well-researched ones. As new research emerges I am sure I will be making updates to this particular blog for those of you who are interested in the underlying curative factors of this strange and powerful endeavor we call psychotherapy.