Forest or Sea: Your Nervous System Reacts Differently
by Laurent Glatz – for Athletic Carnivore
We often talk about “getting some fresh air” as a casual gesture. A walk in the city, a stroll in the forest, a moment facing the sea. Yet these seemingly simple choices profoundly alter our physiology, nervous system activity, and even immunity.
For about twenty years, research in environmental neuroscience and stress physiology has shown that the place where we walk is not neutral. It modulates our autonomic nervous system, hormonal secretion, and cognitive abilities.
The Forest: A Measurable Physiological Effect
The work of Japanese physician Qing Li on “Shinrin-yoku,” literally “forest bathing,” represents one of the most robust bodies of research on the subject. Studies conducted in Japan compared groups walking in forest environments to others walking in urban settings.
The results are remarkably consistent.
There is a significant decrease in salivary cortisol, a drop in blood pressure, a reduction in sympathetic nervous system activity—the system associated with stress response—and an increase in parasympathetic activity, linked to rest and recovery.
Even more surprisingly, some studies show an increase in natural killer (NK) cell activity, immune cells involved in defending against infections and tumor cells. These effects can persist for several days after exposure.
Why Does the Forest Produce These Effects?
Several mechanisms are proposed.
Phytoncides, volatile compounds emitted by trees, seem to play a role. Inhaling these molecules appears to have a direct impact on immune activity and stress modulation.
Light filtered through the forest canopy reduces direct light intensity and creates a less aggressive visual environment. Natural sounds, characterized by low variability and irregular but gentle frequencies, differ radically from the intermittent and unpredictable noise of urban areas.
The forest also reduces sensory overload. Fewer rapid visual signals, less traffic, fewer social demands. The brain exits a constant state of alert.
Cognitive effects are also documented. Marc Berman’s work shows improved directed attention and working memory after walking in natural environments. The attention restoration theory suggests that nature engages a “soft fascination,” allowing executive attentional circuits to rest.
Thus, the forest appears to deeply restore cognitive capacity.
The Sea: Rapid Emotional Regulation
Marine environments, studied notably by Mathew White and colleagues through the concept of “blue spaces,” present a different profile.
European data indicate an immediate increase in subjective well-being, a reduction in mental rumination, decreased reported anxiety, and a sensation of mental openness.
The effect often seems faster than that observed in forests.
Several hypotheses explain this response.
The open horizon reduces visual load and the feeling of confinement. The human brain, shaped by vast environments, seems to respond favorably to this depth of field.
The sound of waves has characteristics close to “pink noise,” a natural sound spectrum associated with calming effects on brain activity.
The brighter light typical of marine environments stimulates retinal pathways involved in circadian regulation and serotonin secretion. Light exposure directly influences mood via hypothalamic circuits.
Some researchers also mention atmospheric negative ions present by the sea. Their exact effect remains debated, but hypotheses suggest influence on cellular oxidation and mood modulation.
Possible Neurophysiological Differences
Available data suggest a functional distinction.
The forest promotes deep parasympathetic recovery. It improves heart rate variability, an indicator of autonomic nervous system flexibility. It seems more effective at calming an organism subjected to prolonged stress or intense training.
The sea, on the other hand, acts more on immediate emotional regulation. It enhances perceived energy, reduces repetitive negative thoughts, and fosters a sense of psychological expansion.
In other words, the forest supports deep nervous system recovery. The sea more directly stimulates mood and motivation.
And What About the City?
Dense urban environments, characterized by intermittent noise, traffic, abundant visual signage, and social unpredictability, increase sympathetic activity and cognitive load.
Brain imaging studies suggest stronger amygdala activation in urban settings, a region involved in stress response.
This does not mean the city is pathological in itself. But it maintains a higher alert level, often incompatible with optimal physiological recovery.
What Science Does Not Clearly Show
No study demonstrates an absolute superiority of the forest over the sea, or vice versa. Effects vary according to individuals.
Some data suggest that more introverted or cognitively burdened profiles benefit more from forest environments, while marine environments seem particularly effective for people under high emotional load.
The optimal exposure dose remains unclear. Ten minutes already produces measurable effects, but the precise dose-response relationship is not fully established.
Implications for Recovery and Performance
After intense training, an environment that promotes parasympathetic activation and improves heart rate variability can accelerate recovery. The forest seems particularly suited for this phase.
Conversely, during periods of demotivation or emotional fatigue, the sea can act as a rapid trigger for affective regulation.
Choosing a walk is therefore not trivial. It modulates stress chemistry, immune dynamics, attentional activity, and autonomic balance.
Perhaps we should stop considering nature as mere scenery. It is a biological modulator.
And maybe the real question is not just “Are we getting outside enough?” but “In which environment do we choose to regulate our organism?”
To go further, you can [take the free questionnaire](/en/questionnaire-neuroprofil.html) and observe whether your profile recovers better in the calm of the forest, the openness of the sea, or an alternation of both.
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