Anhedonia: The case for studying transdiagnostic symptoms

Have you ever found yourself not enjoying something you used to enjoy? Whether that may look like not feeling that it’s worth it to finish reading the science fiction book that you bought yourself ages ago, or feeling as though leaving your house to spend time with a dear friend is far too much effort, many people have had the feeling that something that used to be fun just doesn’t feel like much fun anymore. When this feeling becomes persistent or gets in the way of actually engaging in activities that bring joy, it may be better described as anhedonia.

Anhedonia is typically defined as a loss in the experience of pleasure from previously enjoyed activities (Der-Avakian & Markou 2012). It is generally thought of as a core feature of depressive disorders (Keedwell et al. 2005) as well as an important negative symptom characteristic of psychosis spectrum disorders such as schizophrenia (Marder & Galderisi 2017). For all that it has a significant impact on functional outcomes in these disorders, individuals with a psychosis or depressive disorder are not the only ones who might experience symptoms of anhedonia. Research has found that individuals with myriad diagnoses experience this symptom, from substance use disorders (Garfield et al. 2014; Stull et al. 2021) to attention-deficit/hyperactivity disorder (ADHD; Becker et al. 2015). Anhedonia is even found at varying levels of severity in the general population; that is, individuals who do not fully meet criteria for any psychiatric diagnosis (Barkus & Badcock 2019). The widespread nature of anhedonia highlights its importance as a transdiagnostic symptom: a symptom that is not unique to one psychiatric diagnosis, but experienced by a wide spectrum of individuals.

Why should we care about transdiagnostic symptoms? For many years (and to some extent even today), research in clinical psychology has focused on fitting individuals into specific boxes: people with mood disorders as distinct from people with substance use disorders as distinct from people with trauma-related disorders. Even in the manual that clinicians and researchers use to provide diagnoses, shared features like cognitive deficits and anhedonia are not discussed beyond the importance of engaging in differential diagnosis, or the process of determining which box an individual best fits. This method is hugely useful in terms of providing specific labels to describe what a person struggling with their mental health is experiencing, and comes in handy when researchers want to be specific and deliberate in what populations they are studying. Over the past decade or so, much more attention has been paid to the idea of symptoms of psychological distress being transdiagnostic entities. Initiatives such as the National Institute of Mental Health Research Domain Criteria (RDoC) have paved the way to investigating individual variability in symptoms without the constraints of tethering those symptoms to a particular diagnosis (Cuthbert & Insel 2013). While researchers still often rely on categories of diagnoses to investigate mental health, transdiagnostic research is becoming more common (e.g., Krueger & Eaton 2015). This has afforded scientists and the general public the opportunity to expand our typical categorical view of defining mental wellness and illness, and broadened our understanding of how different diagnoses share commonalities despite historically being considered entirely separate entities. This has even led to speculation into whether there might be a general unifying factor to help us describe the experience of psychopathology as a whole, transcending individual diagnoses entirely (Shields et al. 2021).

Anhedonia is a prime example of how we can use symptoms rather than diagnoses to explore different perspectives of mental health. We know from a large body of literature that adolescence is a vulnerable stage during which individuals experience a number of external (e.g., different school environments, taking on new responsibilities, evolving relationships with peers) and internal (e.g., puberty onset, continued neural development) changes, some of which provide adolescents with additional supports and resources, and others that directly challenge mental wellbeing (Patel et al. 2021). As hinted earlier, anhedonia is not something that only affects individuals who have received a psychiatric diagnosis from a professional. In fact, anhedonia appears to be a relatively stable trait in adolescence that impacts upwards of 10% of the population (Bennik et al. 2014). Not only is it important to consider anhedonia as a transdiagnostic symptom because of the variety of people it impacts, but also because of the degree of influence the experience of anhedonia has on other aspects of life. Anhedonia has been linked with differences in treatment outcomes for clinical populations (McMakin et al. 2012), changes in social functioning (Barkus & Badcock 2019), and alterations in reward processing (Barch et al. 2014; Geaney et al. 2015). In adolescents, those with higher levels of anhedonia have been shown to be more vulnerable to the later development of clinical disorders like depression (Wilcox et al. 2004). 

These wide varieties of populations affected by anhedonia and outcomes stemming from its presence make a strong case for the importance of investigating this symptom regardless of an individual’s current diagnostic status. By focusing less on the boxes we fit people into and more on the transdiagnostic symptoms that go beyond these labels, we encounter opportunities to truly broaden our understanding of the human experience.

References

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