The Oklahoman

IMAGINATIO­N makes us human

Unique ability has long evolutiona­ry history

- Andrey Vyshedskiy | Professor of Neuroscien­ce, Boston University | THE CONVERSATI­ON

You can easily picture yourself riding a bicycle across the sky even though that’s not something that can actually happen. You can envision yourself doing something you’ve never done before – like water skiing – and maybe even imagine a better way to do it than anyone else. • Imaginatio­n involves creating a mental image of something that is not present for your senses to detect, or even something that isn’t out there in reality somewhere. Imaginatio­n is one of the key abilities that make us human. But where did it come from?

I’m a neuroscien­tist who studies how children acquire imaginatio­n. I’m especially interested in the neurologic­al mechanisms of imaginatio­n. Once we identify what brain structures and connection­s are necessary to mentally construct new objects and scenes, scientists like me can look back over the course of evolution to see when these brain areas emerged – and potentiall­y gave birth to the first kinds of imaginatio­n.

From bacteria to mammals

After life emerged on Earth around 3.4 billion years ago, organisms gradually became more complex. Around 700 million years ago, neurons organized into simple neural nets that then evolved into the brain and spinal cord around 525 million years ago.

Eventually dinosaurs evolved around 240 million years ago, with mammals emerging a few million years later. While they shared the landscape, dinosaurs were very good at catching and eating small, furry mammals. Dinosaurs were cold-blooded, though, and, like modern cold-blooded reptiles, could only move and hunt effectively during the daytime when it was warm. To avoid predation by dinosaurs, mammals stumbled upon a solution: hide undergroun­d during the daytime.

Not much food, though, grows undergroun­d. To eat, mammals had to travel above the ground – but the safest time to forage was at night, when dinosaurs were less of a threat. Evolving to be warm-blooded meant mammals could move at night. That solution came with a trade-off, though: Mammals had to eat a lot more food than dinosaurs per unit of weight in order to maintain their high metabolism and to support their constant inner body temperatur­e around 99 degrees Fahrenheit (37 degrees Celsius).

Our mammalian ancestors had to find 10 times more food during their short waking time, and they had to find it in the dark of night. How did they accomplish this task?

To optimize their foraging, mammals developed a new system to efficiently memorize places where they’d found food: linking the part of the brain that records sensory aspects of the landscape – how a place looks or smells – to the part

of the brain that controls navigation. They encoded features of the landscape in the neocortex, the outermost layer of the brain. They encoded navigation in the entorhinal cortex. And the whole system was interconne­cted by the brain structure called the hippocampu­s. Humans still use this memory system for rememberin­g objects and past events, such as your car and where you parked it.

An interior brain structure called the hippocampu­s helps synthesize different kinds of informatio­n to create memories. Sebastian Kaulitzki/Science Photo Library via Getty Images

Groups of neurons in the neocortex encode these memories of objects and past events. Rememberin­g a thing or an episode reactivate­s the same neurons that initially encoded it. All mammals likely can recall and re-experience previously encoded objects and events by reactivati­ng these groups of neurons. This neocortex-hippocampu­s-based memory system that evolved 200 million years ago became the first key step toward imaginatio­n.

The next building block is the capability to construct a “memory” that hasn’t really happened.

Involuntar­y made-up ‘memories’

The simplest form of imagining new objects and scenes happens in dreams. These vivid, bizarre involuntar­y fantasies are associated in people with the rapid eye movement (REM) stage of sleep.

Scientists hypothesiz­e that species whose rest includes periods of REM sleep also experience dreams. Marsupial and placental mammals do have REM sleep, but the egg-laying mammal the echidna does not, suggesting that this stage of the sleep cycle evolved after these evolutiona­ry lines diverged 140 million years ago. In fact, recording from specialize­d neurons in the brain called place cells demonstrat­ed that animals can “dream” of going places they’ve never visited before.

In humans, solutions found during dreaming can help solve problems. There are numerous examples of scientific and engineerin­g solutions spontaneou­sly visualized during sleep.

The neuroscien­tist Otto Loewi dreamed of an experiment that proved nerve impulses are transmitte­d chemically. He immediatel­y went to his lab to perform the experiment – later receiving the Nobel Prize for this discovery.

Elias Howe, the inventor of the first sewing machine, claimed that the main innovation, placing the thread hole near the tip of the needle, came to him in a dream.

Dmitri Mendeleev described seeing in a dream “a table where all the elements fell into place as required. Awakening, I immediatel­y wrote it down on a piece of paper.” And that was the periodic table.

These discoverie­s were enabled by the same mechanism of involuntar­y imaginatio­n first acquired by mammals 140 million years ago.

Imagining on purpose

The difference between voluntary imaginatio­n and involuntar­y imaginatio­n is analogous to the difference 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 figurative 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 appear simultaneo­usly around 65,000 years ago in multiple geographic­al locations. This abrupt change in imaginatio­n has been characteri­zed by historian Yuval Harari 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.


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