In neuro-anatomy, a nucleus is a CNS structure that is composed mainly of gray matter, and which acts as a hub or transit point for electrical signals in a simple neural subsystem. The term Hebenula originally denoted the stalk of the pineal gland, but gradually has come to refer to a neighbouring group of nerve cells in the brain with which pineal gland is believed to be associated.

"The hebenula is interestingly involved in receiving input from the brain via stria medullaris thalami and output to many midbrain areas involved in releasing personality related neuro-modulators such as dopamine,norepinephrine, and serotonin (from the ventral tegmental area. locus coeruleus, and raphe-cells, respectively)."

What may be of particular interest to the spiritual practictioners and yogi-scientists is the unique role of two pairs of colliculi (hills) just beneath the pineal body. Called Inferrior and Superrior Colliculi, these two pairs of hills have sometimes been referred to as South and North routes to carry Auditory and Visual stimulus, respectively, to the pineal body and may also be playing a key role in controlling thirst and hunger.

"Inferrior Collicuculi (lower hill) together with the superior colliculi form the eminences of the corpora quadrigemina, and also part of the tectal region of the midbrain. The inferrior colliculi has caudal (tailend) to its counterpart- the superior colliculus- above the trochlear nerve, and at the base of the projection of the medial geniculate nucleus (MGN) and the lateral geniculate nucleus (LGN)".

"The inferior colliculus is the principal midbrain nucleus of the auditory pathway and receives input from several more peripheral brainstem nuclei in the auditory pathway, as well as inputs from the auditory cortex. The inferrior colliculus has many subnucei. The pair of inferior colliculi of the midbrain , are located just below the visual processing centres known as the superior colliculi. The inferrior colliculiculus is the first place where vertically orienting data from the fusiform cells in the dorsal cochlear nucleus can finally synapse with horizontally orienting data. This homecoming of the aural dimensions puts these dual mesencephalic bumps in the position to fully integrate all the sound location data."

The inferior colliculus has a relatively high metabolism in the brain. It is metabolically more active than other parts of the brain. "The inferior colliculus, which receives almost all ascending and descending auditory signals, plays a crucial role in the processing of auditory information. While the majority of the recorded activities in the inferior colliculus are attributed to GABAergic and glutamatergic signalling, other neurotransmitter systems are expressed in this brain area including opiate peptides and their receptors which may play a modulatory role in neuronal communication."

"The superior colliculus (higher hill) is a pineal structure that is part of the brain's tectal area. The two superior colliculi sit below the thelamus and surround the pinal gland in the mesencephalon of vertebrate brains. It comprises the rostral aspect of the mid brain, posterior to the peri-acqueductal gray and adjacent superior and the inferior colliculus. The inferior and superior colliculi are known collectively as the Corpora-quadrigemina. "

In humans, superior colliculus is involved in the generation of saccadic eye movements and hand-eye coordination. Superior colliculus can also mediate some oculomotor movements without cortical involvement.

It is quite likely that yogic spiritual practices like dry-fasting , kiirtan and dhya'na contribute towards the process of activating the pineal gland through these structures and thereby bring ecstatic experiences (bliss, ananda) and samadhiis of different types to the yogiis and spiritual practitioners.