The Pineal Gland is, as the show presents, a mass located at the center of the Brain. It's real function is to produce melatonin which regulates sleep patterns in humans and mammals. The additional information provided by Chris Argent is also true but considered pseudoscience in the real world.
This is the first time Alisha Boe and Ross Butler worked together. They would go on to be co-stars again in 13 Reasons Why (2017).