Original article

Sudimac S, Kühn S. Can a nature walk change your brain? Investigating hippocampal brain plasticity after one hour in a forest. Environmental Research. 2024.

Research Question

Can a single 1-hour walk in a forest produce measurable changes in brain structure compared with a walk in an urban environment?

Why This Matters

Previous studies have shown that:

• Nature exposure reduces stress and anxiety.
• Urban living is associated with higher rates of depression and other mental disorders.
• The biological mechanism behind these effects remains unclear.

This study investigated whether nature can induce rapid neuroplastic changes detectable by MRI.

Study Design:Participants

• 60 healthy adults
• Randomly assigned to:
  • Forest walk group
  • Urban street walk group

Intervention

• 1-hour walk
• Same duration and similar physical activity
• Different environmental exposure

Measurements

Before and after the walk:

• High-resolution MRI of the hippocampus
• Psychological questionnaires
• Rumination assessment

Brain Area Studied

Hippocampus

The hippocampus is involved in:

• Memory formation
• Learning
• Emotional regulation
• Stress responses

Subiculum

A major output region of the hippocampus.

Functions:

• Stress inhibition
• Regulation of the HPA axis
• Emotional processing
• Contextual memory

Main Results

Forest Group

• Increase in subiculum volume
• Reduced self-reported rumination

Urban Group

• No significant volume increase
• No comparable improvement

Correlation

Participants with greater subiculum volume increases tended to report:

• Less rumination
• Better emotional state

Statistical Caveat

This is the most important point for clinicians.

The observed increase in subiculum volume:

❌ Did not survive Bonferroni correction for multiple comparisons.

Meaning:

• The finding may represent a real effect.
• But statistical confidence is insufficient to declare definitive proof.

Therefore:

Interpretation should be cautious.

Strengths

1. Randomized Design

Helps reduce selection bias.

2. Objective Outcome

MRI-based measurements rather than self-report alone.

3. Real-World Intervention

Simple one-hour walk.

4. Novelty

One of the first studies examining very short-term structural brain changes after nature exposure.

Limitations

Small Sample Size

• Only 60 participants.

Healthy Volunteers

• Results may not apply to:
  • Depression
  • Anxiety disorders
  • PTSD
  • Dementia

Short Follow-Up

• Effects measured immediately.
• Long-term persistence unknown.

Multiple Comparison Issue

• Weakens certainty of the MRI findings.

Clinical Implications

Current evidence supports:

Nature Exposure

Likely beneficial for:

• Stress reduction
• Mood improvement
• Cognitive restoration

Practical Recommendation

For patients:

• 30–60 minutes in green spaces
• 3–5 times weekly
• Walking preferred over passive exposure

Particularly useful as an adjunct in:

• Mild depression
• Generalized anxiety
• Burnout
• Chronic stress
• Recovery from mental fatigue

Public Health Implications

The study supports:

• Urban green-space development
• Forest preservation
• Therapeutic gardens near hospitals
• School and workplace green environments

Bottom Line

What is well supported?

• Spending time in nature improves mental well-being.
• Forest walks reduce rumination and stress.

What is suggested but not yet proven?

• A single 1-hour forest walk may produce detectable hippocampal (subiculum) structural changes.

Clinical takeaway: Nature walks are a low-cost, low-risk intervention with growing neuroscientific support, but larger studies are needed before claiming that a one-hour forest walk definitively changes brain structure.

Evidence Level

Moderate for mental-health benefits Preliminary for MRI-detected structural brain plasticity.

Full article link

https://pure.mpg.de/view/item_3606667/

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