Chapter 6: Our Premortal Life, A: Intelligence, or the light of truth, is eternal and has always existed.

We know from the scriptures that we have always existed. Our spirit bodies and physical bodies always existed in the elemental form before they were our bodies, in one sense. But, also our "intelligence" has always existed. We, individually, have always existed.

Man was also in the beginning with God. Intelligence, or the light of truth, was not created or made, neither indeed can be.
D&C 93:29

The Lord made it know to Moses (See Book of Moses Chap. 3) and also to Abraham (Abraham Ch. 3) and it is expressed in several revaltions, that man was in the beginning with God. In that day, however, man was a spirit unembodied. The beginning was when the councils met and the decision was made to create this earth that the spirits who were intended for this earth, should come here and partake of the mortal conditions and receive bodies of flesh and bones. The docrtine has prevailed that matter was created out of nothing, but the Lord declares that the elements are eternal. Matter always did and, therefore, always will exist, and the spirits of men as well as their bodies were created out of matter. We discover in this revelation that the intelligent part of man was not created, but always existed. There has been some speculation and articles have been written attemptint to explain just what these "intelligences" are, or this "intelligence " is, but it is futile for us to speculate upon it. We do know that intelligence was not created or made and cannot be because the Lord has said it. There are some truths it is well to leave until the Lord sees fit to reveal the fulness.
Joseph Fielding Smith, Church History and Modern Revelation, 1:401