Neuroplasticity: The Key to Why We Dream
Written by Deekshita Sundararaman
Illustrated by Emily Nguyen
For thousands of years, humans have spent the better part of their days dreaming. For approximately 2 hours every night, we see bizarre images, ranging from whales to our dead grandfathers. The question is, how do we visualize these scenarios with our eyes closed? And why do we do it? We can find the answer to these questions by understanding the fundamentals of neuroplasticity.
Neuroplasticity, or neural plasticity, is the brain’s ability to structurally and functionally change according to new experiences and our responses to them. The constant formation of new synaptic connections between neurons is a pillar of human evolution. Our neurons can be rewired to such an extent that the visual cortex, which typically only receives inputs from our eyes, can begin to receive inputs from our ears after being blindfolded for just an hour. This frequently happens in individuals who become blind after an accident, for whom rewiring of auditory inputs into the visual cortex makes their hearing stronger and helps them survive without sight. These findings have revealed that contrary to popular belief, certain parts of the brain can adapt to perform different functions as needed.
The same phenomenon may be the reason why we dream. Human beings spend about one-third of their lives sleeping. This means that for a good part of each day, the visual cortex doesn’t receive any information from our eyes. Since our brain is constantly molding to new experiences, it only makes sense that our visual cortex would begin rerouting to receive inputs from somewhere else to avoid deteriorating its function. Clearly, though, it would be extremely taxing to repeat this process every time we go to sleep. Dreaming offers an alternative. Even though our eyes are closed, our visual cortex remains active while we’re dreaming. We see vivid scenarios of anything from the stranger at the grocery store to our repressed subconscious desires. This keeps the neurons in the visual cortex active and preserves their function.
This is exactly what Dr. David Eagleman, a neuroscientist who specializes in neuroplasticity, has been studying. He calls it the “defense activation theory,” which proposes that the brain defends its territory in the absence of input from the eyes. Most of our dreams happen during REM sleep, which is triggered by a special set of neurons that directly activate our visual cortex, enabling us to see things with our eyes closed.
But why did this mechanism evolve? To answer this question, Dr. Eagleman and his colleagues investigated primates with “pre-programmed” brains versus more flexible brains. Animals that develop more rapidly have less flexible brains at birth, hence referred to as “pre-programmed.” By contrast, animals that take longer to mature have more flexible brains, allowing them to adapt as they grow. After recording their sleep activity, the team found that species with brains that have higher degrees of neuroplasticity had higher levels of REM sleep compared to their “pre-programmed” counterparts. This makes sense, as brains that are more susceptible to plastic changes need to dream more in order to preserve the visual cortex.
To help humans practically apply this research in their daily lives, researchers could create products that accurately track sleep cycles, along with methods to increase it. Similar to the electrocardiogram feature on the Apple watch, a robust tracker for REM sleep can help individuals improve their eye health. Consistently recording the amount of REM sleep we get and working to improve it can do wonders to keep our visual cortices intact, allowing us to have the best vision possible.
While the results of the study may be limited to the specific species being examined, it’s certainly an interesting advance on a long-pondered-on subject. Philosophers, shamans, and scientists all around the world wonder why we dream. Do they predict the future? Are they messages from our ancestors? Or do they uncover our subconscious desires? As intriguing as these questions are, the answer may simply concern the brain’s preferred evolutionary method to preserve peak function.