Preliminary communication
Interacting with nature improves cognition and affect for individuals with depression

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Abstract

Background

This study aimed to explore whether walking in nature may be beneficial for individuals with major depressive disorder (MDD). Healthy adults demonstrate significant cognitive gains after nature walks, but it was unclear whether those same benefits would be achieved in a depressed sample as walking alone in nature might induce rumination, thereby worsening memory and mood.

Methods

Twenty individuals diagnosed with MDD participated in this study. At baseline, mood and short term memory span were assessed using the PANAS and the backwards digit span (BDS) task, respectively. Participants were then asked to think about an unresolved negative autobiographical event to prime rumination, prior to taking a 50-min walk in either a natural or urban setting. After the walk, mood and short-term memory span were reassessed. The following week, participants returned to the lab and repeated the entire procedure, but walked in the location not visited in the first session (i.e., a counterbalanced within-subjects design).

Results

Participants exhibited significant increases in memory span after the nature walk relative to the urban walk, p < .001, ηp2 = .53 (a large effect-size). Participants also showed increases in mood, but the mood effects did not correlate with the memory effects, suggesting separable mechanisms and replicating previous work.

Limitations

Sample size and participants' motivation.

Conclusions

These findings extend earlier work demonstrating the cognitive and affective benefits of interacting with nature to individuals with MDD. Therefore, interacting with nature may be useful clinically as a supplement to existing treatments for MDD.

Introduction

Major depressive disorder (MDD) is characterized by cognitive impairments such as compromised working memory (Lyubomirsky et al., 2003), and by affective impairments such as persistent negative mood (Nolen-Hoeksema et al., 2008). Prior research indicates that interacting with nature enhances cognitive functioning (Berman et al., 2008, Cimprich and Ronis, 2003, Kaplan and Berman, 2010, Taylor and Kuo, 2009) and specifically increases working-memory span and improves mood (Berman et al., 2008).

Kaplan and colleagues (Kaplan, 1995, Kaplan and Berman, 2010) have proposed Attention Restoration Theory (ART) to explain how interacting with nature improves cognitive abilities. ART draws on research demonstrating that attention can be separated into two components: involuntary attention, in which attention is captured by salient stimuli, and voluntary or directed attention, in which attention is directed by cognitive-control processes. This distinction, first proposed by William James (James, 1892), has been validated by behavioral and neuroscience research (Buschman and Miller, 2007, Corbetta and Shulman, 2002, Fan et al., 2002). ART identifies directed attention as the cognitive mechanism that is restored by interacting with nature, and others have implicated a critical role for directed attention in many contexts (Diamond et al., 2007, Posner and Rothbart, 2007), including short-term memory performance (Jonides et al., 2008).

According to ART, interacting with environments that contain inherently fascinating stimuli (e.g., sunsets) modestly invoke involuntary attention, allowing directed-attention mechanisms a chance to replenish (Berman et al., 2008, Kaplan, 1995, Kaplan and Berman, 2010). That is, the requirement for directed attention in such environments is minimized, and attention is captured in a bottom-up fashion by features of the environment itself. Thus, following an interaction with natural environments, individuals perform better on tasks that depend on directed-attention abilities. Unlike natural environments, urban environments contain bottom-up stimulation (e.g., car horns) that capture attention dramatically, requiring directed attention to overcome that stimulation (e.g., avoiding traffic, ignoring advertising, etc.), making urban environments less restorative.

Although interacting with natural environments has been found to be beneficial for healthy individuals, it's not clear whether these benefits would generalize to individuals with MDD. On one hand, to the extent that interacting with natural environments (e.g., parks) replenish cognitive resources (Berman et al., 2008, Kaplan and Berman, 2010), individuals with MDD may show the same or even greater cognitive gains than those demonstrated by healthy individuals. It has been hypothesized that individuals who are more attentionally fatigued may obtain greater benefits from interacting with nature (Kaplan and Berman, 2010), and fatigued participants have been found to gain greater benefits from other types of interventions (Masicampo and Baumeister, 2008). Given that individuals with depression are likely more mentally/attentionally fatigued than are nondepressed individuals due to their depressive symptoms (e.g. ruminations, psychomotor problems, etc.), it is possible that individuals with depression may show increased cognitive and affective gains from a nature interaction.

On the other hand, individuals with depression are characterized by high levels of rumination (Nolen-Hoeksema et al., 2008). Rumination maintains and exacerbates negative mood, has been linked to impairments in short-term/working memory (Berman et al., 2011, Joormann and Gotlib, 2008, Landro et al., 2001), and may be particularly pronounced during time spent alone. Thus, asking a person with MDD to go for a solitary walk in a park may actually worsen, rather than improve, memory and mood by potentially taxing top-down/directed attention resources.

There are a variety of effective interventions for MDD, including psychotherapy (Robinson et al., 1990), medication (DeRubeis et al., 2005), and alternative treatments such as mindfulness meditation (Grossman et al., 2004). However, in a recent review, Kazdin and Blase (2011) called for more research to explore simple, portable and cost-effective interventions for mood and anxiety disorders. This study is a first attempt to discover if interacting with nature may be one such intervention possibility.

This study was designed to examine whether interacting with nature has beneficial effects on memory performance and affect in individuals diagnosed with MDD. Specifically, we examined whether interacting with nature could improve the typically impaired short-term memory/working memory performance in MDD (Berman et al., 2011, Joormann et al., 2010, Landro et al., 2001). We also examined whether mood would change differentially after a walk in nature vs. a walk in an urban environment, as well as the relation between mood and memory effects. Improvements in mood would be of particular interest given that MDD is characterized by low levels of positive affect (Watson and Naragon-Gainey, 2010).

A conservative task was employed to examine whether interacting with nature was beneficial for individuals with MDD by asking participants to reflect on an intense negative experience prior to going on their walks. In this way, we set the stage for an exposure to nature to maximize its impact on individuals with depression who were primed with negative thoughts and feelings.

Section snippets

Participants

Twenty individuals diagnosed with MDD (12 female, 8 male, mean age = 26) participated in this study. A diagnosis of MDD was made by clinicians who administered the Structured Clinical Interview (SCID) for DSM-IV (First and Gibbon, 1996). Participants were recruited from the University of Michigan and the greater Ann Arbor area through ads on Craigslist and Facebook, as well as fliers that were distributed around the University of Michigan campus and stores/shops in the greater Ann Arbor area.

Working memory capacity

The two-way ANOVA on BDS scores yielded no main effects of location or time (Fs < 3.39, ps > .08), but did yield a significant time × location interaction, F(1, 18) = 20.5, p < .001, ηp2 = .53, indicating that participants' memory capacity increased more after the nature walk than after the urban walk. Indeed, the size of this effect was nearly 5 times larger than that found in our previous work (ηp2 = .14) with a non-clinical sample (Berman et al., 2008). This interaction was driven by reliable increases in

Discussion

This study examined whether interacting with nature has beneficial effects on cognitive and affective functioning in MDD. We found that individuals diagnosed with MDD exhibited cognitive and affective improvements after walking in a nature setting. These effects were observed even though participants were instructed prior to their walks to think about a painful negative experience, which has been shown to prime rumination (Kross and Ayduk, 2008), which in turn has been shown to disrupt working

Conclusion

Researchers have recently called for the development and exploration of brief, simple and portable interventions to treat mood disorders that can be widely disseminated at low-costs (Kazdin and Blase, 2011). The current research fits these aims well. Interacting with nature is, for the most part, widely accessible, simple and affordable. Yet we know virtually nothing about how this process affects mood and cognition in MDD. Although the current findings begin to address this issue, they also

Role of funding source

This work was supported by in part by NIMH grant MH60655 to John Jonides and a TKF Foundation Planning Grant to Marc Berman. The grants helped to pay for the post-doctoral fellow's stipend (Marc G. Berman), research assistants' hourly wages, participant payments, color figure publishing costs and experimental equipment.

Conflict of interest statement

The authors' have no conflicts of interest to report.

Acknowledgements

This work was supported in part by NIMH grant MH60655 to JJ and by a TKF Foundation planning grant to MGB. We thank Alexa Erickson and Catherine Cherny for data collection; Phil Cheng and Hyang Sook Kim for diagnostic interviewing.

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