What is the essence of thought? How dependent upon the brain is it? In Raymond Moody's revolutionary book "Life After Life," People who had witnessed NDE's (Near Death Experiences) insisted that these experiences yielded lucid awareness of surroundings and sharper vision. In fact, those whose senses were dulled by illness or medication reveled in this sudden improvement in perception. The reports were consistent.

Is a single mind dependent upon the brain to think, or merely using the organ as a tool to remain cohesive and prevent thoughts from dispersing?

My personal theory lies somewhere in between. When one dies, their bioelectricity is released from the body, and dissipates into the air to join that frequency of consciousness. Some stray bits mingle with others to form a new consciousness, thus imbuing the new being with slivers of recall from several former lives.

In rare cases, one may come across a set of collected thoughts from a previous life. These may dominate a new persona, either from birth or by invasion (the latter is much less likely to happen as the movies would have you think, and not quite with the same effect or purpose. Perhaps "introducing these elements into the consciousness" is more accurate terminology), or perhaps in extremely rare cases, where the bioelectricity can actually manipulate molecules to the point of moving items noticeably...

Once the fetal brain has developed sufficiently, it starts to draw from the viscous soup passing through everyone and everything. These become the first electrical impulses to kickstart the new brain. As it develops, it gathers more "soul soup." Development of both thought and body commence. I believe "life" begins at different stages of fetal development for different babies. One cannot pinpoint before or after which stage consciousness actually begins.