Almost one-third of all Americans will experience some form of anxiety disorder at some point in their lives. Behavioral scientists are trying to improve their understanding of anxiety disorders and find the most effective treatments. In one recent experimental paradigm, fear was defined as a response to a specific threat, while anxiety was defined as a response to the unpredictable possibility of encountering a threat. Within this paradigm, people with anxiety disorders show higher levels of anxiety compared to healthy controls, but not higher levels of fear. 

Hoge et al. [Biological Psychiatry] used this paradigm to compare the effects of Mindfulness-Based Stress Reduction (MBSR) and antidepressant medication on objective and subjective measures of fear and anxiety in individuals with anxiety disorders.

The researchers recruited a sample of 93 adults with anxiety disorders and 66 healthy controls (average age=33 years; 72% female; 63% Caucasian). Participants attended baseline lab sessions to measure their startle responses to fear- and anxiety-provoking stimuli. Participants with anxiety disorders were then randomly assigned to either participate in a standard 8-week MBSR program or receive a daily dose of escitalopram (the generic form of Lexapro) for eight weeks. The healthy controls received no intervention. At the end of the eight weeks, participants repeated the lab measure again to assess anxiety and fear responses. Participants also completed self-report measures of anxiety during both the baseline and post-intervention evaluations.

During the lab sessions, participants sat at a computer that displayed a series of images consisting of green circles, blue triangles, and red squares. Participants were administered annoying (but not painful) electrical shocks in conjunction with these visual stimuli. Prior to the presentation of each image series, the computer screen provided information about the nature of the trial. Some trials involved no electrical shocks (neutral trials), while in others, shocks were administered only when a red triangle was present (predictable shock trials). There were also trials where shocks could occur during any stimulus (unpredictable shock trials).

An electromyogram (EMG) was used to measure the magnitude of each participants’ eye blinks—an objective measure of startle response—after exposure to each image. Eye blinks during predictable shock trials were classified as fear startle responses, whereas those during unpredictable shock trials were classified as anxiety startle responses.

Results showed that the group with anxiety disorders had significantly higher anxiety startle responses at baseline compared to the healthy control group. However, their response magnitudes significantly decreased after the intervention, leading to no significant difference between the two groups post-intervention. The reduction in anxiety startle responses was significantly greater for the escitalopram group than the MBSR group.

Subjective anxiety ratings decreased significantly for both intervention groups, a change that was significantly correlated with decreases in the anxiety startle response (r=.27) but not the fear startle response (r=.07). Intervention and control groups did not differ in the magnitude of their fear startle responses at baseline or post-intervention. While the MBSR group significantly reduced fear startle responses and fear subjective ratings from pre- to post-intervention, the escitalopram group did not.

The study shows that both MBSR and escitalopram reduce objective and subjective levels of anxiety so that participants with anxiety-disorders in both interventions no longer differed from healthy controls after intervention. Escitalopram reduced the magnitude of anxiety startle responses more than MBSR, whereas MBSR reduced the magnitude of fear startle responses more than escitalopram. This discrepancy suggests the involvement of distinct mechanisms of action for each intervention.

The study is limited by the absence of a non-intervention control condition for participants with anxiety disorders. 

Reference:

Hoge, E. A., Armstrong, C. H., Mete, M., Oliva, I., Lazar, S. W., Lago, T. R., & Grillon, C. (2023). Attenuation of Anxiety-Potentiated Startle After Treatment with Escitalopram or Mindfulness Meditation in Anxiety Disorders. Biological Psychiatry. 

Link to study