Considered the center of their spirit, the Trii is is vital to their functioning, closely connected to the brain and is primarily used for telepathic and empathic links between two individuals, due to the sensitivity and speed of exchange between the Trii and the cerebral cortex. Placing their Triis against each other, two people can feel each other's emotions; gifted people called Tri-Nadh can read thoughts.
In the first two weeks of an Iskai youngs life, the Trii has an ability to receive and replace the baby's brain with one of an existing Iskai. This kills the baby's mind, as it is overwritten by the mind of the sender. This is known as the Sebai ritual. It is highly illegal and considered morally wrong to do this without express permission of the Council of Jarinaar; however, most Iskai believe that a newborn has no personality of its own, and the ritual is seen as normal and acceptable when performed by a Chosen one, deemed worthy of the honor.
Those finely attuned to the way that Triis work can also use this as an exchange of emotion and sense, for example the deaf and mute Mellthas was able to hear just by touching Sira's forehead. However, those who are unfamiliar with Triis and those who are not attuned to the way Triis work will receive minor head and spine injury from the shock delivered from touching one.
The Trii is, in effect, an extension and communication port to the brain. If the Trii is damaged or destroyed, the effects on the individual is devastating. Even minor injuries can result in amnesia, personality changes or a form of Alzheimer's Disease. Major injuries can cause paralysis, brain death, or actual death. There is no known cure among Iskai for major damage to the Trii, but minor damages usually heal by themselves, with an impact to the effectiveness of it during telepathic exchanges. This is usually very distressing for the afflicted.