Since the decade of the brain, 1990-1999, neuroscience has captured enormous amounts of attention from both the scientific community and the general public. Many books and media reports describe the brain’s basic anatomy and function. There has been a proliferation of neuroscience institutes at universities. In laboratories all over the world, neuroscience has become one of the most exciting and productive branches of inquiry.
Yet not everyone is completely pleased with what neuroscience has to tell us. In particular, some decry neuroscience for trying to delegitimize the “mind.” Going back to the original Cartesian mind-body duality, these critics insist that neuroscience can only go so far by describing the function of neurons and neurotransmitters. What cannot be reached by science, they say, is that ineffable “mind” that constitutes the human spirit. For them, neuroscience is purely an attempt to reduce the complexities and wonders of human experience to brain scan images and electrical recordings from axons and dendrites.
In a new book, Neuroscience at the Intersection of Mind and Brain (Oxford University Press, 2018), one of us (Jack) attempts to allay fears that neuroscience will somehow reduce human experience and creativity to the “mere” workings of the physical brain. There is, in fact, nothing “reductive” about the physical brain. Rather, the brain is a gloriously complex, fascinating, and well-organized structure that constitutes, as neuroscientist Eric Kandel so eloquently put it, “the organ of the mind.”
Biologists versus Psychologists
As a resident in psychiatry in the late 1970s, Jack witnessed the emergence of psychopharmacology as the dominant discipline for academic psychiatry and lived through the often bitter battles between “biologists” and “psychologists.” This may be, in part, where the mistrust of neuroscience began. The biologists believed that their method of treating psychiatric illness—medication—was based on solid science and rejected psychotherapy as unscientific. They also believed that neuroscience explained why the new psychiatric drugs worked and therefore promoted brain science as the basis for their discipline. Every lecture about depression or schizophrenia in those days began with a picture of a pre- and postsynaptic neuron forming a synapse across which neurotransmitters like serotonin, noradrenaline, and dopamine carried information. The new medications interact with receptors for these neurotransmitters and, it was taught at the time, this explains how they work to treat depression, anxiety, and psychosis.
It turns out that the picture of neurons everyone used back then was a vast oversimplification of what a synapse really looks like and that almost nothing we know about neurotransmitters and their receptors actually explains how psychiatric drugs work. But what really bothered the psychologists was the complete dismissal of psychotherapy by the biologists. Years of studying various types of psychotherapy convinced them that indeed they had science on their side. Furthermore, they objected to the biologists’ emphasis on inherited abnormalities as the sole basis for psychiatric illness. Psychologists had always been more interested in the ways that human experience, from birth onwards, shaped personality and behavior.
Over time, many (but thankfully not all) psychologists came to see neuroscience as the branch of science devoted to promoting pharmacology as the only treatment for psychiatric illness and to trying to prove that those illnesses were entirely due to inherited brain abnormalities. Biologists stood with nature; psychologists with nurture.
This fear of neuroscience’s aims is entirely misplaced. Over the last several decades, neuroscience has, in fact, focused a great deal of attention on the biology of experience, elucidating the ways in which what happens to us in life affects the structure and function of the brain. Every time we see, hear, smell, or touch something, learn a new fact, or have a new experience, genes are activated in the brain, new proteins are synthesized, and neural pathways communicate the new information to multiple brain regions.
Neuroscience is not, therefore, synonymous with psychopharmacology, nor does it invalidate the complexities of human experience. It has shown, for example, that early life interactions between a parent and child shape how the brain will function for the rest of a person’s life.
This has tremendous implications for understanding the mechanism of action of psychotherapy if we accept the idea that psychotherapy itself is a form of life experience and therefore capable of changing brain function at molecular, cellular, and structural levels. Here are two examples that illustrate ways in which neuroscience informs psychotherapy.
CBT and the Prefrontal to Amygdala Connection
It is now clear that the expression of conditioned fear is dependent upon an intact, functioning amygdala. Scientists have shown that the amygdala, located in a primitive part of the brain often referred to as the limbic cortex, reciprocally inhibits and is inhibited by a more evolutionarily advanced part of the brain, the medial prefrontal cortex (mPFC). Thus, under circumstances of heightened fear, the amygdala shuts down the ability of the mPFC to exert reason over emotion and initiates a cascade of fearful responses that include increased heart rate and blood pressure and freezing in place. When the mPFC is able to reassert its capacity for logic and reason, it can, in turn, inhibit the amygdala and reduce and extinguish fear.
Cognitive behavioral therapy (CBT) is an evidence-based intervention that is the first-line treatment for most anxiety disorders and for mild, moderate, and in many cases even severe depression. Because the automatic, irrational fears and avoidance behaviors manifested by patients with anxiety disorders and depression resemble the behavior of rodents in Pavlovian fear conditioning experiments, scientists have wondered if CBT works, at least in part, by strengthening the prefrontal cortex to amygdala pathway, thereby reducing amygdala activity. Indeed, many studies have shown that anxious and depressed patients have reduced activity in this pathway and exaggerated amygdala responses to fearful stimuli. Studies have also shown that successful CBT for social anxiety disorder decreases amygdala activation.
Most recently, a group of scientists from Oxford, Harvard, and Berkeley showed clearly that stimulation of the prefrontal cortex in human volunteers reduced amygdala activation and fear. Maria Ironside and colleagues selected 18 women with high levels of trait anxiety and randomized them to receive either transcranial direct current stimulation (tDCS) to the prefrontal cortex or sham tDCS. The subjects underwent functional magnetic resonance imaging (fMRI) of the brain and performed an attentional load task that tests vigilance to threat. Real, but not sham, tDCS increased activity in the prefrontal cortex, decreased activity in the amygdala, and decreased threat responses.
This study is one example of preclinical and clinical neuroscience coming together to suggest a biological mechanism for the efficacy of a psychosocial intervention. We know that the cognitive portion of CBT strengthens a patient’s ability to assert reason over irrational thoughts and fears and that this decreases amygdala activity in some studies. We know clearly from animal studies that stimulating the prefrontal cortex reduces amygdala activation and potentiates fear extinction. Now we also know that in a group of anxious people, direct stimulation of the prefrontal cortex does the same thing as it does in animal studies and, in addition, reduces threat responses. With a plausible hypothesis for how CBT works, scientists can now push further to see if brain imaging can ultimately help select patients with particularly weak prefrontal to amygdala pathway strength who might be prime candidates for CBT and then to track how they are doing in therapy objectively by repeating the brain imaging studies to see if and when that pathway is strengthened.
Psychoanalysis and Reconsolidation
CBT has been proven effective by many high-quality clinical trials and therefore is a prime candidate for biological studies, but can the same be said for widely used but less empirically validated treatments such as psychoanalysis and psychoanalytic psychotherapy? In 2011, Jack and his colleague, Columbia psychiatrist and psychoanalyst Steven Roose, proposed that another aspect of fear conditioning—reconsolidation of fear memories—may explain one biological mechanism of action for how psychoanalysis works. In rats, when a conditioned fear memory is reactivated, it temporarily becomes labile and can be completely erased by blocking the biological mechanisms that permit reconsolidation of the memory. Could it be that in psychoanalytic therapies, the patient undergoes a process of reactivating distressing early memories that, once made conscious through the psychoanalytic process, can be manipulated by the therapist’s interpretations? According to this hypothesis, those now altered memories can then be reconsolidated into permanent memory in a less disturbing format.
The theory has been considered since then by many scientists and psychoanalytic theorists and a number of experiments show that the phenomena of labile reactivated memories and blockade of reconsolidation do indeed occur in humans. Blocking reconsolidation of reactivated memories has been shown to be effective in experiments attempting to help addicts overcome the powerful tendency to succumb to subtle cues and resume taking drugs even after successful rehabilitation. Here again, information gained from the basic neuroscience laboratory and from clinical neuroscience studies may help us understand how one aspect of psychoanalysis works to change the brain in ways that are helpful to people suffering with mental illness.
It is not necessary to invoke an ineffable “mind” to explain our unique human characteristics. Understanding the complexity of the human brain is sufficient to reveal how we are able to take what we experience and transform it into scientific theories, poetry, and philosophical ideas. Neuroscience is not superficial or reductionistic and it is not at all in the sole service of psychopharmacology and the genetic explanation for mental disorders. This becomes clear as we recognize the tremendous contributions neuroscientists have made to elucidating basic mechanisms that allow experiences to change the physical structure and function of the brain on a second-by-second basis. Everything we experience during life is translated into events that occur in the brain.
Psychotherapy is a form of life experience that changes the way the brain works, often ameliorating abnormalities caused by adverse experiences and stressful life events. So yes, there is a science to psychotherapy, one that can be readily understood by learning about some of the fundamental and fascinating ways our brains work. Neuroscience at the Intersection of Mind and Brain tries to do just that.