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The Winter Solstice has recently been upon us, and at this time of year it is easy to feel Seasonal Affective Disorder (SAD).  But what happens in the brain when someone feels depressed, and what steps can be taken to feel better when sunlight-deprived?

By Dr Samantha J. Brooks Ph.D. 


The absence of sunlight to the brain actually has a quantum mechanical explanation, in that sunlight can stimulate our brain cells at a molecular, micro level!  During the summer months, photons (light particles) from the sun’s high frequency ultra-violet rays (but also the lower frequency infrared and visible rays) enter our brains and stimulate the activity of clusters of neurons. This can have a powerful effect on the way our brains create our emotions and the way we think.  Just imagine the powerful chemical reaction to the sun’s rays that occurs within plants to produce growth-stimulating food. Within a plant’s chlorophyll cells, sunlight converts carbon dioxide and water into glucose and oxygen by way of photosynthesis.

In a similar way, our neurons – like the chlorophylls of plants – react to photons arriving at the brain via the retina of the eye.  And during the summer months when there are more hours of constant sunlight, our neurons are kept at a higher frequency of stimulation. Not only can the lower frequency of sunlight (photons) in the winter months lower our mood, but it can also reduce our rate of learning and lessen our memory.  This could be one reason why it is so difficult to get out of a bad mood and to learn a new strategy to cope with life in the winter months!

With all this said, what exactly is going on inside the brain when the sun’s photons stimulate  our brains?  Not only does the sun’s high frequency ultra-violet rays during the summer lead to the synthesis of vitamin D, which is good for our bone strength and general health, but ultra-violet rays also increase the levels of ‘feel-good’ beta-endorphins.  In addition, scientists publishing in the esteemed science journal Cell have recently reported that ultra-violet rays in particular can increase the production of the neuron-excitatory brain molecule glutamate.  Glutamate brain cells work in conjunction with other types of neurons to maintain a good balance in brain function that promotes clarity of thought, memory and – in broad terms – an open mind.  However, when the frequency of photons passing through the retina to the brain slow down (changing from predominantly ultra-violet to visible and infra-red rays) particularly in winter months – like lowering the shutters on your house to keep in energy – the brain closes down a bit too.

The specific brain areas that are most susceptible to high frequency (ultra-violet) sunlight during the summer months are the hippocampus – responsible for forming new long-term memories – and the nucleus accumbens – a brain region in the reward centre of the brain, responsible for learning new, pleasurable memories. Glutamate effects on these brain areas also help to increase activity, which could also be why we feel sluggish in winter when ultra-violet rays are less frequent.  Neuroscience research also suggests that sunlight, particularly ultra-violet light, alters the way serotonin works in the brain.  Serotonin is created from essential amino acids found in some foods, such as bananas, spinach and eggs, meaning that it cannot be produced in the body. And as many of us know, serotonin levels are linked to mood, with low levels linked to depression. Scientists now think that once inside the brain, serotonin binding and transportation potential is influenced by the frequency of photons present.

This means that even when eating the right foods, the potency of serotonin in the brain is naturally lower during winter months with less sunlight.  This could be why we might be drawn to eating foods with high levels of carbohydrates and sugar, to gain a rapid , quick-fix comforting feeling that sugar (glucose) in the brain provides us.  In contrast, stable levels of serotonin enable us to feel naturally well with a good mood – which might not be possible in winter.

So what can be done about this natural state of affairs during the winter months, to prevent the reduced ultraviolet frequency of sunlight, low levels of glutamate and serotonin from reducing our mood, activity and ability to think clearly?

Besides sitting in ultraviolet rooms for hours on end – a popular past-time in Sweden during the long, dark winter months – there are simple things one can do.  For a start, increasing eating foods that contain tryptophan (it gets broken down into serotonin in the body) can saturate the brain with serotonin when it’s effects are less potent than normal.

Exercise too is also known to be an alternative brain stimulator in the winter months.  And if these things don’t work for you during the winter months, a regular meeting with your local friendly psychotherapist can help to remind you of all the great things in life, even when the storms set in, and Table Mountain is cloaked in darkness!  For more information on excellent psychotherapists in the Cape Town area, check out this website.

Click to read all previous articles by Dr Samantha J. Brooks Ph.D.

Samantha Brooks6

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