Influence of Light and the Pineal Gland on Biological Rhythms

Abstract

More than 300 years ago, the French philosopher René Descartes (1596–1650 AD) was well aware of the existence of the pineal gland and in his treatise “The Passions of the Soul” he described it as playing a crucial role in the interaction between the soul and the body. This 17th century Cartesian concept of the pineal gland as the “seat of the human soul” was probably developed from the much earlier postmortem studies of Herophilus (325–280 BC), an Alexandrian anatomist, who according to the chronicles of Galen (130–200 AD) referred to the pineal gland as a valve regulating the flow of “spirits” between the 3rd ventricle and 4th ventricle of the brain. Looking back at these ancient ideas, it is all too easy to dismiss them as being erroneous, too simplistic, or even superstitious. With the surge of scientific knowledge in recent decades, especially in the fields of biochemistry, neuroanatomy, and molecular biology, we now know that the pineal gland plays an important role as a circadian photoneuroendocrine transducer. And yet, even today many questions remain unanswered about this mysterious “little gland” and speculations regarding the physiological role of melatonin, its principal hormone, are likely to persist well into the 21st century.

“Let us then conceive here that the soul has its principal seat in the little gland which exists in the middle of the brain, from whence it radiates forth through all the remainder of the body by means of the animal spirits, nerves, and even the blood, which, participating in the impressions of the spirits, can carry them by the arteries into all the members.... ”