Behavioral activation (BA) has emerged as an effective intervention for major depressive disorder, ever since the unique role of BA in Beck' s cognitive therapy (CT) was recognized, in which BA is found to be as effective as the whole CT package (including interventions targeting autonomic dysfunctional thoughts and core beliefs, as well as BA) (1), with the latter subsequently evolving into cognitive behavioral therapy (CBT). In the subsequent literature, BA was described as a standalone therapy for depression (2). Behavioral activation is proposed as a common mechanism of change across different therapeutic approaches and disorders (3), which encourages the depressed patients to engage in anti-depressant activities which is reinforced and sustained. These behavior change may explain the enduring effects of BA in the prevention of relapse for depressed patients (4). For patients with moderate to severe depression, BA is more effective than CT (5). Contemporary BA also include many variations which were regarded as a “third wave” CBT, and focused on contextual factors and functional analysis of behaviors in assessment and intervention of depression (6). This review aims to present a conceptual overview of the BA followed by reviewing empirical evidences supporting its efficacy for treatment of depression.

The model of behavioral activation (BA) is derived from the groundbreaking theoretical and empirical work of behaviorist in explanation and treatment of depression, typically Ferster (functional analysis of behavior) (7), Lewinsohn and Libet (8) (pleasant events scheduling), Rehm et al. (9) (self-control model of depression) and Beck et al. (10) (cognitive therapy and its BA component). These models can be classified as response- and action-based models. (1) The response model offers a mechanistic explanation for the causes of behavior, which regards behavior as a type of response, including physiological reflexes, ecological fixed behavior patterns, and conditional and non-conditional psychological responses. (2) The action model offers a teleological explanation that behaviors are not triggered by stimuli but are controlled by animals' perceptions of the consequences of actions. Therefore, changes in motivation or a new understanding of goals and values can lead to changes in goals and values (11).

The manualized behavioral activation for depression was developed based on response- and action-based model to achieve the following primary goals: (1) discern the living environment that induces depression; (2) clarify and reduce the maladaptive coping patterns that sustain and exacerbate depression; and (3) improve the adaptive coping patterns which increase exposure positive reinforcement in the environments bringing pleasure or the sense of control (25).

As the earliest study dismantling BA component from CT as the standalone treatment for depression, Jacobson's regimen includes 20 sessions that involve: (1) monitoring daily activities; (2) assessing the pleasure and sense of control associated with various activities; (3) assigning increasingly difficult tasks that may reduce pleasure or the sense of control; (4) conducting cognitive rehearsals, during which patients imagine themselves participating in various activities to identify factors that may prevent patients from gaining pleasure or the sense of control from the activities; (5) discussing specific issues such as sleeping difficulty, and behavioral techniques to deal with these issues; and (6) taking measures to improve social skills such as self-confidence and communication skills (1). On the basis of Jacobson's regimen, Martell et al. (2) developed a more comprehensive manual and included other intervention strategies for behavioral activation, such as repeated freedom from issues or unpleasant events (distraction technique), mindfulness training, and self-reinforcement (2). This manual originally developed for adult depression was modified into the Adolescent Behavioral Activation Program (A-BAP) to treating depressed adolescents (age 12–18) which typically consists of 12–14 sessions (26).

Alternatively, Lejuez et al. (27) developed a brief, 12-session behavioral activation treatment for depression (BATD) that includes daily monitoring, social support contracting, activity selection and scheduling, and post-activity rewards. In contrast to BA manuals of Jacobson and Martell et al. which aim to explicitly increase approach behavior as an alternative to depressant (e.g., avoidant/ruminative) behaviors, BATD predicted that increase in reinforcement for healthy (e.g., approach) behaviors could lead to decrease in depressant behaviors and thus increase healthy behaviors, based on the matching law. BATD is more suitable for depressed patients indicated for brief and well-defined treatment (28).

A decade later, Lejuez published the revised BATD treatment manual (BATD-R) (29), which shortens the number of sessions from 12 to 10. Detailed revisions include: (1) more emphasis on the basic principles of treatment, including client-therapist relations; (2) clearer descriptions of life, values, and activities; (3) simplified and fewer treatment sessions; (4) more details about the program, including a concept review of obstacle elimination and late-stage treatment; and (5) a new revised daily monitoring schedule for patients with low education levels (30). Lejuez et al. state that the number of sessions may be adjusted according to the patient and clinical context.

Single session BA treatment was also developed for college students who significantly reduced depressive symptoms after they received the single BA session (31). During a 90-min session, the following issues will be covered: psychoeducation about depression which depend on behavioral activation model, and life areas consistent with individualized values/goals, activity scheduling according to life areas which will be monitored to be completed within 2 weeks after the session. Computerized single-session BA was developed for high school students, which was appraised as acceptable and feasible by students and educators (32).

Future research should take into account the following considerations:

(1) Clarification of the Neurobiological Mechanism of Change Underlying BA Intervention. BA model postulates that insufficient or loss of positive reinforcement (reward) leads to and sustains depressive behaviors and emotions. Past studies have shown that the reward circuit was modulated by BA (21, 22). Future research needs to clarify the neurobiological mechanism of BA, such as the regulated neurotransmitters and electrophysiological activities of dopaminergic neurons in the reward neural network.

(2) Individualization of Treatment Needs. Activity scheduling is one of the key elements of BA therapy which showed robust effect size (18). The types of activities and how these activities are connected to the client' s values and life goals are important considerations when developing a treatment plan suitable to a patient's cultural background and specific needs. Artificial intelligence techniques such as machine learning can be used to detect treatment needs and meet individualized treatment requirements.

(3) Active Ingredients and Variants of BA. Behavioral activation has become a more comprehensive treatment approach with the rise of the third wave of CBT, which emphasize targeted value-based BA. Traditional oriental practices and fitness routines such as Yoga, Tai chi, Qigong, and mindfulness are being incorporated into BA to improve happiness experience (71). Therefore, more empirical research dealing with the active ingredients and variants of BA under the third wave of CBT needs to be conducted.

(4) Translation and Validation of BA in China. Overall, mental health literacy in China is increasing and there is still a gap with other countries, among domestic regions and groups (e.g., higher education and younger age) (72–74), mental health literacy could be improved through education and training in order to better understand depression and implement prevention and treatment measures. To date, empirical evidence for effectiveness and mechanism of BA is increasing rapidly in China (18 clinical trials published in Chinese, 2011~2022), and yet still limited compared with traditional and third wave CBT evidence. As the low-intensity and easily trained BA is gaining more attention, the development and translation of the manual and computerized/smartphone-based software BA is gaining more attention, for example, the introduction of internet cognitive-behavioral therapy (ICBT) for depression (MoodGYM) by Beijing Suicide Research and Prevention Center (BSRPC) (64), our translation of BA manual by Martell et al. (33) into Chinese (published in 2017, ISSN 978-7-5621-8052-4), and clinical trial of guided self-help BATD treatment for geriatric depression following the manual by Lejuez et al. (29, 75).

Based on BA treatment manual following Martell et al. (33) and Lejuez et al. (29), there has been increasing evidence of BA' s effectiveness for both sub-threshold and clinically diagnosed depression, as well as depressed patients comorbid with mental illness or physical diseases. Limitations pertaining to the e-mental health modalities and the underlying mechanism of change of BA should be addressed in the future research.

XW and ZF conceived of the presented design of the study. XW collected literatures, reviewed relevant researches, and drafted the manuscript in consultation with ZF. All authors contributed to the article and approved the submitted version.

This research was financially supported by the Youth Cultivation Foundation of Medical Science in Army Medical University (2016XPY08), the National Youth Cultivation Foundation of Military Medical Science (17QNP002), and the Chongqing Social Science Planning Project (2017QNSH21).

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

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