Why our Nervous System follows the Rhythms of the year

How Light, Circadian Rhythms, and Bodily Processes Carry Us Through the Seasonal Cycle — and What That Means for Your Well-Being

IIn our culture-shaping narrative, the year begins on January 1st. Yet for our nervous system, the seasonal cycle has already started long before we write down our first resolution — and it doesn’t end with the first birdsong in spring.The reality is this: our nervous system is seasonally attuned. It responds to light, temperature, and environmental cycles long before we consciously notice that “something feels different.”

Why Light Is So Central

The central control centre of our biological clock is located in the brain. A tiny region known as the suprachiasmatic nucleus acts like an inner conductor. It receives light signals via the eyes and uses them to coordinate sleep, wakefulness, and the release of certain hormones.

Through this mechanism, our circadian rhythms emerge: internal timing systems that operate on an approximately 24-hour cycle and signal to the body when it is time for activity, rest, or sleep. Put simply, circadian rhythms are the inner “schedules” by which our nervous system operates.

As light conditions change over the course of the year, these internal schedules adjust accordingly. When days grow longer, nighttime melatonin levels decrease (melatonin is often referred to as the “sleep hormone”), while serotonin levels rise. Serotonin plays an important role in mood regulation, motivation, and emotional balance. These hormonal shifts have immediate effects on energy levels, alertness, and overall well-being.

In winter, however, reduced daylight dampens these processes. The nervous system remains in energy-saving mode for longer periods of time. This helps explain why many people experience increased fatigue, a greater need for sleep, or a so-called “winter blues” during the darker months — even without meeting the criteria for a clinical condition such as Seasonal Affective Disorder (SAD).

Our Nervous System Knows Seasons, Not Just Days

Research also shows that brain functions vary not only from day to day, but across the year. Depending on the season, attention and memory processes fluctuate, and even the functional connectivity between different brain networks changes over time.

This means that our nervous system does not only respond to sunrise and sunset — it adapts over weeks and months to seasonal light and environmental conditions.

This is no biological coincidence. It is an evolutionary legacy. In nature, continuous daylight in summer signals the availability of food, warmth, and social interaction. In contrast, winter darkness and cold prioritise energy conservation. Even though we now live with artificial lighting and heating, our internal timekeeper remains deeply connected to these ancient rhythms.

Hormones as Seasonal Messengers

Hormonal adjustments are another key mechanism through which our nervous system follows the seasons:

• Melatonin is produced in greater quantities as darkness increases, signalling to the body: “It’s night.”

• Cortisol, an important stress and energy hormone, shows seasonal patterns in its release — generally higher in winter and lower in summer — aligning with changes in activity and alertness.

These seasonal differences influence not only sleep-wake cycles, but also metabolism, immune function, and mood.

Why We Feel Different in Spring Than in January

Many people notice a rise in energy, mood, and motivation during spring — and this shift has a clear biological basis:

• Daylight hours increase, naturally boosting our circadian rhythms.

• Light directly affects neurochemical systems involved in serotonin and dopamine regulation.

• The nervous system undergoes adjustments that “release” us into more active behaviour and social engagement.

You may recognise how your internal clock changes as the sun rises earlier and sets later. This isn’t a feeling we simply miss on the calendar — it’s a physical rhythm shaped by light.

What This Means for Your Well-Being

If you try to “go all in” in January and find it difficult, this isn’t necessarily a sign of weakness. More often, it’s a sign that you’re working against your own biology. Your body is essentially asking:“Are you in sync with this season — or are you rushing ahead?”

A winter-adapted nervous system is biologically programmed to conserve energy and respond to reduced light. Expectations that belong to other seasons can therefore lead to frustration and stress.

3 Practical Ways to Support Your Seasonal Rhythm

🟡 Use Light Intentionally

Just 20–30 minutes of natural morning light can help reset your internal clock.💡 During darker months, a daylight lamp can intentionally simulate light as a timing cue.

🧠 Respect Your Rhythm

If your body asks for more sleep in winter, this isn’t a lack of discipline — it’s a reflection of seasonal biological needs.

🌿 Adapt Your Well-Being Seasonally

Movement, social interaction, nutrition, and sleep routines can all be adjusted to support your nervous system’s seasonal rhythm.

In Closing: The Nervous Sense Within the Seasonal Cycle

Our nervous system is not an isolated timekeeper responding only to the 24-hour day. It is a finely tuned biological rhythm shaped by seasons, light, hormones, and evolutionary history.

We are not clockwork mechanisms functioning independently of nature.We are beings with biological rhythms — carrying an internal seasonal cycle long before we ever consult a calendar.And the more we learn to respect this rhythm rather than override it, the more at home we feel within ourselves — in every month, in every season.

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Sources & Further Reading

1. Foster, R. G., & Kreitzman, L. (2014).The rhythms of life: what your body clock means to you. Experimental Physiology, 99(4), 599–606.→ Überblick zu circadianen Rhythmen und biologischer Zeitsteuerunghttps://pubmed.ncbi.nlm.nih.gov/24558138/

2. Czeisler, C. A. et al. (1999).Stability, precision, and near-24-hour period of the human circadian pacemaker.Science, 284(5423), 2177–2181.→ Grundlagenforschung zur inneren Uhr (SCN)https://pubmed.ncbi.nlm.nih.gov/10381883/

3. Wehr, T. A. (2001).Photoperiodism in humans and other primates: evidence and implications.Journal of Biological Rhythms, 16(4), 348–364.→ Saisonale Veränderungen von Schlaf, Hormonen & Stimmunghttps://pubmed.ncbi.nlm.nih.gov/11506378/

4. Meyer, C. et al. (2016).Seasonal variation in human brain activity.Proceedings of the National Academy of Sciences (PNAS), 113(11), 3066–3071.→ Nachweis saisonaler Veränderungen in Hirnnetzwerkenhttps://www.pnas.org/doi/10.1073/pnas.1518129113

5. Lambert, G. et al. (2002).Effect of sunlight and season on serotonin turnover in the brain.The Lancet, 360(9348), 1840–1842.→ Zusammenhang zwischen Tageslicht, Serotonin & Stimmunghttps://pubmed.ncbi.nlm.nih.gov/12480356/

6. Partonen, T., & Lönnqvist, J. (1998).Seasonal affective disorder.The Lancet, 352(9137), 1369–1374.→ Grundlagen zu SAD & subklinischen saisonalen Stimmungsschwankungenhttps://pubmed.ncbi.nlm.nih.gov/9802278/

7. Touitou, Y. et al. (2017).Biological rhythms in human health and disease.Dialogues in Clinical Neuroscience, 19(1), 17–29.→ Jahres- und Tagesrhythmen aus neurobiologischer Sichthttps://pubmed.ncbi.nlm.nih.gov/28533768/

Note: The studies cited reflect average biological tendencies. Individual experiences may vary depending on lifestyle, neurodivergence, health status, and environmental factors.