Already in numerous studies done thus far the effectiveness of confrontation therapy in the treatment of anxiety disorders has been demonstrated. Here the patient is exposed to a fear-encompassing situation under the guidance of his or her therapist, until the anxiety has dissipated. It is taken as certain that sleep is an important process in the consolidation of human memory. Both aspects have now been able to be employed by scientists at Northwestern University in Chicago, USA, in the successful resolution of previously behaviourally-conditioned fear in their subjects.
Anxiety associated with odours
In their study, which they recently had published in the prestigious journal Nature Neuroscience, the scientists generated fear reactions in each of the 15 participants by showing them two images of human faces; while they were looking at the pictures they were exposed to mild electric shocks. At the same time they linked each image to a specific smell, such as lemon, peppermint, new sneakers, clove or wood. The degree of anxiety and fear was measured by the scientists through electrical conductivity of the skin of their subjects. This is directly related to the production of perspiration from the skin during periods of anxiety and fear. In parallel, the researchers recorded changes in brain regions involved actively in olfactory conditioning.
Confrontation: smell during sleep
Then the subjects laid themselves down for a short nap of about an hour. While the study participants drifted into deep sleep, the scientists confronted each subject again with the smell he or she had perceived while looking at one of the two images.
At first the electrical conductivity of the skin increased – a sign that the odours activated memories associated with fear. Over time, the sweat production of the skin did however subside. In the waking state, the subjects when viewing the corresponding image showed less anxiety than when they looked at the picture whose associated smell was the one to which they had not been exposed during their sleep. High-resolution functional magnetic resonance imaging showed altered activity of the amygdala after the anxiety of the subjects had dissipated. The amygdala is part of the limbic system and instrumental in the development of anxiety. Sleep seemed to be significantly involved in getting rid of the learned fear again, since the same experimental set-up demonstrated no fear diminishing effect when subjects watched a nature documentary rather than having a short sleep.
Sleep duration obviously crucial
Prof. Dr. Jan Born is a neurobiologist at the University of Tübingen and was not involved in the study. The study results of the researchers from Chicago were referred to by the Leibniz prizewinner in his communication with DocCheck as being a complete surprise. “This study is so exciting because it presents something totally unexpected”, he said. Prof. Born and his colleagues in July this year published the results of their study, in which they had examined how well subjects were able to recall a conditioning-induced anxiety-provoking situation after a dormant or sleepless night. Volunteers without sleep deprivation suffered significantly more from their fears than their fellow students who had been denied sleep – at first glance a contrary result with respect to the current study. Professor Born’s explanation: “This effect is likely associated with the period of time in which the subjects were retained in the REM-sleeping phase”. Short sleep episodes, as examined in the study by his colleagues from Chicago, have little or no REM phases, which it is believed consolidate emotional memories. The length of sleep could be decisive in whether anxiety-carrying memories are deleted or amplified. “I suspect that REM sleep is especially important in permanently stamping fear into the memory”, says Prof. Born. The sleep researchers would especially find interesting repeating the fellow researchers’ study using a night sleep phase instead of just a one hour nap.
Potential therapeutic approach for phobics
Study leader Dr. Katherina Hauner of the Feinberg School of Medicine at Northwestern University sees in its study results potential for future therapeutic strategies in combination with confrontational approaches to phobias. She hypothesises that exposure therapy can possibly be reinforced through specific actions in the sleep of patients. However the researchers have not gotten so far yet, for in this study fearful memories were generated within a short time and wiped out again, the authors point out. This does not necessarily match the reality faced by patients with phobic disorders. Such disorders often develop over many years before they are identified and then possibly treated. Whether long-term memories can be disabled in the same way as was done in this study will thus be the subject of future research.