The Pineal Gland

Usually I don’t dedicate much of my time to watching television series, however during lockdown my go to when I need to switch my brain off for a while has been ‘The Good Karma Hospital’ on ITV. A medical drama set in Goa, India it follows a group of doctors convoluted love lives and their interactions with enigmatic patients. One episode we are introduced to a patient who is convinced she is the Hindu Goddess Lakshmi. It is later revealed that she suffers from a benign tumor on her pineal gland which results in her lack of need for sleep, hallucinatory visions and psychic powers.

*enters research rabbit hole*

There was a two pronged interest in the pineal gland for me: the physiological and the cultural significance of it.

Physiological

The pineal gland is found in the brain. It is very small, about the size of a grain of rice, and shaped like a pine cone ( pineis= pinecone in Latin)(Figure 1) .

Figure 1: Location of the Pineal Gland

It is differs from other parts of the brain as it doesn’t have a twin structure and it isn’t separated by the blood brain barrier. It’s formed of cells called pineocytes which synthesize seratonin and its derivative melatonin. The pineal gland is indirectly linked to the retina, and the synthesis of melatonin is controlled by the detection of light (Figure 2).

Figure 2: How the pineal gland is linked to the retina. Light is detected at the retina, enervating ganglion cells which initiate the following pathway
Abbreviations:
PVN- Paraventricular Nucleus
SCG- Superior Cervical Ganglion
NE- Norepinephrine (hormone secreted by the Superior Cervical Ganglion which is detected by receptors on the Pineal Gland)


The exact mechanism of how the pineal gland works is still not entirely understood. However is is widely accepted that one of its main functions is to synthesize melatonin (Figure 3).

Figure 3: Biochemical pathway which produces Melatonin


Melatonin is a hormone which is associated with circadian rhythm ( biological clock). High melatonin production occurs at night and low melatonin production during the daytime. Individuals with circadian sleep rhythm disorders the production of melatonin is not regulated in the usual manner :an example being Non-24-hour sleep-wake disorder, which often affects blind individuals because the circadian clock is set by the light dark cycle, can cause lack of sleep time and quality.

Abundant melatonin levels in children are believed to inhibit sexual development and pineal tumor have been linked to disruptions or changes in the onset of puberty. Furthermore pinealectomy on rodents ( the way most research is conducted on the pineal gland) highlights the influence of the pineal gland on the secretion of hormone involved in menstruation FSH and LH. Melatonin is also thought to influence bone deposition.

Cultural


Due to its deep seated location in the brain the pineal gland has long been associated with myticism and ideas regarding the soul. Pre Galen ideas about the function of the pineal gland was that it was a motile structure which regulated the flow of ‘psychic pneuma’ between middle and the posterior (rear) section of the brain. Galen, correctly so, identified it as a non motile extra-cerebral structure.Then building of the ventricular localisation doctrine of Nemesisus and Posidonious, Ibn Sina projected the psychological distinctions found in Aristotles ‘On The Soul’ onto the ventricular system of the brain. All these ideas were assimilated, in typical Islamic Golden Age fashion, by Qusta Ibn Luqa’s theory of the memory valve, which greatly influenced medieval and renaissance psychology (Figure 4).


Figure 4:Qusta ibn Luqa’s Theory. Thinking is associated with the animal spirit in the middle ventricle (II), memories are stored in the posterior ventricle (III). Left: people who want to remember look up because this raises the worm-like obstacle and enables the passage of memories from the posterior to the middle ventricle. Right: people who want to think look down because this depresses the worm-like obstacle and isolates the middle ventricle from the contents of the posterior ventricle.


This flow of spirits thing continued for a while until the Renaissance period where Niccolo Massa noted that that ventricles aren’t filled with vaporous spirit rather with cerebro-spinal fluid. Vesalius rejected ventricular localisation theories and the regulation of the flow of spirits idea.


This leads us to Descartes who cites the pineal gland as ‘the principal seat of the soul’.Descarte got a lot wrong in the light of modern scientific understanding, include the anatomical position of the pineal gland. He was interested in the relationship between spirit (res cogitans) and body-machine (res extensa), where the pineal gland was the organ which linked mind and body- the seat of the soul. This Cartesian hypothesis had its critics and declined very quickly. Anatomical criticisms such as Willis’ who posited that since animals had pineal glands ( in some cases more developed than humans), but lacked superior properties such as imagination or memory, meant that it couldn’t be the seat of the soul and center of reasoning. Philosophical criticism came from Hume and Kant the former posing that personality was simply a a sum of sensory experiences therefore attempting to locate or substantiate the mind as a mere illusion, the later attributing a spiritual nature to the soul which couldn’t be anatomically limited.

Though I’ve outlined a western academic cultural history of the pineal gland, depictions of the pineal gland as a ‘third eye’ pervade many traditions. In pharonic Eygpt it takes the form of the ‘Eye of Horus’, in Hinduism the ‘Eye of Shive’ the organ of spiritual vision. More recently (1900s), Georges Bataille describes the ‘pineal eye’ as a blind spot of western rationality as an organ of excess and delirium.

The pineal gland continues to take hold interest scientifically and mystically. Have a youtube dive, and you’ll find Allopaths abound delineating it’s role in our health. It is rather marvellous that such a small structure informs our perception of the world, and has held academics and mystics in raptures for centuries!

Bibliography


https://www.elsevier.es/en-revista-neurologia-english-edition–495-articulo-the-pineal-gland-as-physical-S2173580812000429

2-Minute Neuroscience: Pineal Gland

Endocrinology | Pineal gland

https://plato.stanford.edu/entries/pineal-gland/

https://en.wikipedia.org/wiki/Pineal_gland

N.Marieb, E., 2004. Human Anatomy & Physiology. 6th ed.

https://books.google.co.uk/books?id=ip1hCQAAQBAJ&pg=PT104&lpg=PT104&dq=niccolo+massa+pineal+gland&source=bl&ots=46u0aEP5jb&sig=ACfU3U1mDTvsKKD958xv_45wh45NUnKaEw&hl=en&sa=X&ved=2ahUKEwjJgYiK4qvpAhUtQhUIHfFZCjYQ6AEwCXoECAsQAQ#v=onepage&q=niccolo%20massa%20pineal%20gland&f=false

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