The difference between voluntary imagination and involuntary imagination is analogous to the difference between voluntary muscle control and muscle spasm. Voluntary muscle control allows people to deliberately combine muscle movements. Spasm occurs spontaneously and cannot be controlled.
Similarly, voluntary imagination allows people to deliberately combine thoughts. When asked to mentally combine two identical right triangles along their long edges, or hypotenuses, you envision a square. When asked to mentally cut a round pizza by two perpendicular lines, you visualize four identical slices.
This deliberate, responsive and reliable capacity to combine and recombine mental objects is called prefrontal synthesis. It relies on the ability of the prefrontal cortex located at the very front of the brain to control the rest of the neocortex.
When did our species acquire the ability of prefrontal synthesis? Every artifact dated before 70,000 years ago could have been made by a creator who lacked this ability. On the other hand, starting about that time there are various archeological artifacts unambiguously indicating its presence: composite figurative objects, such as lion-man, bone needles with an eye, bows and arrows, musical instruments, constructed dwellings, adorned burials suggesting the beliefs in afterlife, and many more.
Multiple types of archaeological artifacts unambiguously associated with prefrontal synthesis appeared simultaneously around 65,000 years ago in multiple geographical locations. Historian Yuval Harari characterized this abrupt change in imagination as the "cognitive revolution." Notably, it approximately coincides with the largest Homo sapiens' migration out of Africa.
Genetic analyses suggest that a few individuals acquired this prefrontal synthesis ability and then spread their genes far and wide by eliminating other contemporaneous males with the use of an imagination-enabeled strategy and newly developed weapons.
So, it's been a journey of many millions of years of evolution for our species to become equipped with imagination. Most nonhuman mammals have potential for imagining what doesn't exist or hasn't happened involuntarily during REM sleep; only humans can voluntarily conjure new objects and events in our minds using prefrontal synthesis.
Andrey Vyshedskiy is a professor of neuroscience at Boston University.
This article is republished from The Conversation under a Creative Commons license. You can find the original article here.