No angel or spirit is allowed to talk with one of us from the angel’s or spirit’s own memory, only from that of the individual in question. Angels and spirits actually have memory just as we do. If a spirit were to talk with us from his or her own memory, then it would seem to us entirely as though the thoughts were our own, when they would really belong to the spirit. It is like remembering something that we have never seen or heard. I have been granted knowledge of the truth of this by experience.
This is why some of the ancients were of the opinion that after some thousands of years they would return to their former life and all its deeds, and that they had in fact returned. They gathered this from the fact that sometimes a kind of memory would come up of things that they had never seen or heard. This happened because spirits had flowed from their own memory into the images of these people’s thoughts.
There are also spirits called natural and physical spirits who do not unite with our thoughts when they come to us the way other spirits do but rather enter our bodies and take over all its senses, talking through our mouths and acting through our limbs. It seems to them entirely as though everything of ours were theirs. These are the spirits that possess people; but they have been cast into hell by the Lord and moved decisively away; so possession like this no longer occurs nowadays.
from Heaven and Hell, Sections 256, 257