top of page

Sleep and Sand: Mysteries of the Tiny Pineal Gland

Have you got sand on the brain? Although it’s the right time of year for it here in the US, I’m not talking about your plans to go to the beach this weekend. The brain is a source of truly infinite fascination, in large part because there’s so much about it that we don’t fully understand. One of the more mysterious and lesser appreciated structures in the brain is the pineal gland – a pea-sized and pine cone-shaped organ that lies deep in the brain’s interior.

The pineal gland has been a source of mystical speculation for millennia and is associated with the concept of “the third eye.” This refers to the pineal gland as being a source of connection between the physical and spiritual worlds and a window into realms beyond ordinary perception.


The ancient Egyptians employed spiritual imagery related to the third eye and may not have been the earliest civilization to do so. The well-known Eye of Horus symbol is now believed to be a sort of early anatomical drawing, with the pineal gland representing the iris of the eye. Hindu deities are often portrayed with a third eye on their foreheads, and it’s widely believed that this is a reference to the pineal gland.

Connections between a spiritual realm and the pineal gland were suggested by one of the fathers of modern anatomy, the Greek Galen, and more recently the French philosopher René Descartes suggested that the pineal gland is the location at which the soul is joined to the body.


As it turns out, the pineal gland actually is a sort of third eye. Or was. The pineal gland is the last stop on a journey consisting of many stages which begins with the light sensing cells of the retina. The pineal gland is an endocrine organ which releases a hormone called melatonin – the same compound you may give to your dog to calm it down or help it sleep.

Melatonin, and by extension the pineal gland, helps to regulate circadian rhythms. The production of melatonin is modulated by darkness and light and helps prepare the body for sleep. A properly functioning circadian rhythm is essential to optimal health, and a variety of conditions can occur if this rhythm is disrupted. Additionally, melatonin serves as an anti-inflammatory and antioxidant which helps protect cells in the brain from harmful free radicals.

While the pineal gland is still responsive to changes in light, it used to respond to these stimuli more directly. The cells of the pineal glands of several existing species like birds, amphibians, and fish share many similarities with retinal cells. The human pineal gland may actually be a vestigial eye meaning that it served as an actual light perceiving organ in the distant evolutionary past but no longer serves that purpose.


So what does sand have to do with the pineal gland? A distinguishing feature of the pineal gland and one that makes it of special interest to radiologists because of its function as a landmark in radiological images is the presence of corpora arenacea which translates directly as “sandy body.” But of course this anatomical curiosity isn’t actually sand like you see on the beach, which is primarily made of molecules consisting of silicon. Brain sand is made of calcium and magnesium salts, some of which are found in normal bone tissue, and is produced in several parts of the brain including the meninges (see this video for more information on the meninges).

Depending on your age there’s a pretty good chance you have some of this sand in your brain right now, as some studies have shown it to be present in 70% of subjects. Should you be worried? Probably not. The question of whether brain sand leads to any pathological conditions is unresolved, with some arguing that increases in this substance are a normal part of aging.

On the other hand, some studies have shown that higher levels of brain sand are correlated with disorders such as Alzheimer’s disease and schizophrenia although the mechanism by which it would lead to these disorders is unclear. It’s also unclear if calcification of the pineal gland interferes with its ability to synthesize melatonin.

While calcification is common in several tissues in the body, it happens in the pineal gland at a higher rate than anywhere else. Calcification, along with shrinking of the gland, appears to be a normal part of the development of the pineal gland in the life cycle. While it’s more prevalent in older adults, it has also been observed in infants and toddlers.


The pineal gland, like dendritic cells , receives minimal attention in standard undergraduate level anatomy and physiology textbooks. However it’s an important anatomical structure involved in several aspects of healthy body function which depend in large part on maintenance of regular daily cycles.

The pineal gland is conserved in a wide variety of animal species and calcification is observed in many other animals such as birds and fish. This organ has been the subject of anatomical and even spiritual inquiry for millennia, and its evolutionary history gives us a glimpse into the sensory world of animal ancestors from the distant past.

The pineal gland is a small but fascinating structure which exemplifies the mysteries associated with the study of the human brain. While most of us would rather have warm sand under our feet than inside our skulls, we have the proper functioning of our pineal gland to thank for keeping us on a regular sleep schedule, so we can be grateful for its presence even if it does deposit a bit of sand in the brain along the way.

31 views0 comments


bottom of page