The pineal gland is an endocrine gland between the thamalic bodies. The habenula is anterior to the pineal gland. The pineal gland receives input from the suprachiasmatic nuclei which receives its input from the retina. The pineal gland converts the inputs to hormone signals. The pineal gland also has serotonin containing cells.Function

The pineal gland produces melatonin, which regulates circadian rhythm (sets internal biological clock). The retina provides the regulator input for the pineal gland through the suprachiasmatic nucleus.  The gland shrinks in puberty, suggesting a role in sexual development. It may also function in addictive behavior.

Disease

Dysfunction of the pineal gland would result in abnormal sleep cycles and/or sexual development.

Diagnosis

It is often calcified, making it visible in neuro-imaging. Melatonin levels would also be measured to determine hyper or hypo activity in the pineal gland.

Treatment 

Treatment would be pharmacological.