SB 4.22.31
bhrasyaty anusmrtis cittam
jñana-bhramsah smrti-ksaye
tad-rodham kavayah prahur
atmapahnavam atmanah
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
When one deviates from his original consciousness, he loses the capacity to remember his previous position or recognize his present one. When remembrance is lost, all knowledge acquired is based on a false foundation. When this occurs, learned scholars consider that the soul is lost.
Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
The living entity, or the soul, is ever existing and eternal. It cannot be lost, but learned scholars say that it is lost when actual knowledge is not working. That is the difference between animals and human beings. According to less intelligent philosophers, animals have no soul. But factually animals have souls. Due to the animals’ gross ignorance, however, it appears that they have lost their souls. Without the soul, a body cannot move. That is the difference between a living body and a dead body. When the soul is out of the body, the body is called dead. The soul is said to be lost when there is no proper knowledge exhibited. Our original consciousness is Krsna consciousness because we are part and parcel of Krsna. When this consciousness is misguided and one is put into the material atmosphere, which pollutes the original consciousness, one thinks that he is a product of the material elements. Thus one loses his real remembrance of his position as part and parcel of the Supreme Personality of Godhead, just as a man who sleeps forgets himself. In this way, when the activities of proper consciousness are checked, all the activities of the lost soul are performed on a false basis. At the present moment, human civilization is acting on a false platform of bodily identification; therefore it can be said that the people of the present age have lost their souls, and in this respect they are no better than animals.