Written by Mira White '26
Edited by Yuliya Velhan '25
It’s been previously believed that dreaming is a uniquely human experience. The ability to recall long sequences of events when in a subconscious state involves long-term memory encoding during REM that’s been predominantly explored in humans. This complex ability has led to a multidisciplinary approach to exploring the neural circuitry of learning and memory that is associated with dreaming across many animals. Similar to humans, other animals experience the same subconscious dreamlike state that with further research could provide insight into restorative methods for memory disorders.
The differences in how animals dream can be largely attributed to evolutionary disparities. As visual animals, naturally, we dream visually. Because of the differences in brain evolution across millions of species, it is difficult to claim that all organisms, if they dream, experience dreams under the same circumstances as humans.
To explore this possibility of similar experiences when dreaming, a study at Harvard University focused on the REM-like state in spiders. Speaking primarily with Paul Shamble, a (former) John Harvard Distinguished Science Fellow, he mentions how some spiders are visual whereas others are not, proposing the idea that despite similar brain structures evolutionary differences can result in significant dreaming capabilities [1]. The study performed by Shamble and a former postdoctoral researcher in the University’s lab is believed to be the first of its kind - monitoring the REM behavior of an invertebrate.
The study observed spiders that suspended themselves when sleeping and the bursts of activity that they experienced. Similar to the twitches that humans, dogs, and cats may undergo during sleep, spiders also exhibited these, and more importantly, concurrent eye movement. Classified as muscle atonia [1], decreased limb movement is described as one of the major components of identifying REM sleep. In correspondence with slight twitching, spiders were also observed to be curling their legs from a decrease in pressure [1]. Between these two, it’s clear that spiders do experience muscle atonia and that they are not awake but innately attempting to suppress motion. The synonymous rapid eye movements that occurred during both types of muscle twitches encourage the probable likelihood that spiders do dream.
It is difficult to say what spiders necessarily dream about, but based on their REM cycles it’s reasonable to conclude that they can. A spider's ability to dream raises further questions about which animals dream and the extent to which they can. Explored further in an MIT study by Matthew Wilson, a neuroscientist at MIT’s Center for Learning and Memory (2001), it was ultimately concluded that animals experience complex dreams.
Wilson conducted his experiment for the first time in 2001 alongside a graduate student in his lab. Observing rats, instead of spiders, he engineered a test that had the rats running along a track for a food reward [2]. The brain activity of the rats was monitored during this time and later compared to the activity recorded while the rats were asleep. It was found that roughly half of the original patterned firing was repeated during REM [2]. The correlation between the two instances shows that the rats were able to imagine themselves in the track and replay these memories while they slept - an equivalent of dreaming.
In continuing with his research, Wilson performed another experiment in 2006. This experiment investigated the possibility of visual dreams in the rats and in building off of his 2001 study, Wilson and his associate recorded the synonymous activity between the hippocampus and the visual cortex. Similar to the previous neuronal patterns that were the same while the rats slept and were awake, those patterns in the hippocampus and cortex were also the same [3]. Using this information to evaluate the possibility of visual dreaming, researchers compared the firing activity of the hippocampus to the part of the cortex that receives input from the senses [3]. It was ultimately found that the brain was replaying the same memory events in both places, suggesting the presence of visual imagery.
“These results imply simultaneous reactivation of coherent memory traces in the cortex and hippocampus during sleep that may contribute to or reflect the result of the memory consolidation process,” [3] Wilson wrote in an MIT Tech Talk article.
In his studies, Wilson has not only proved that animals dream, but that they dream about their experiences. In a third experiment, Wilson explored the concept of dream engineering that could provide insight into the approaches of the learning and behavioral therapy of memory through manipulating the brain. Taking place in 2012, this study trained the rats to run in the maze using audio cues - one sound directing the animal to the reward on the right and another sound to the left [4]. Similar to the previous experiments, the rats exhibited the same dream of running through the maze, however, this time an audio stimulus was introduced. When a certain stimulus from when they were awake was played their dream would change to associate their location in the maze with the sound [4].
Through playing a certain audio, Wilson and his colleague were able to reactivate the memory associated with the content. This outcome shows the possibility of more control in the mind and memory during sleep which could lead to biased dream engineering. With this, extensive research in learning and memory therapeutic approaches can be established by using the resting brain as a site for manipulation.
Wilson’s work raises questions about being able to process the dreams of more complex animals. In previous work with just rats (MIT) and spiders (Harvard), we’ve been able to observe the extent to which the subconscious mind and memory interact in the brain. With more research still needed to decipher underlying memory components of the brain, we may be able to bridge the gap between recalling the past when it is intentional versus inadvertent. Dreams present us with the opportunity to problem-solve in an ‘off-line’ way that has been shown to improve solution discovery and re-evaluation of our experiences. The reactivation of memory during sleep has the potential to contribute significantly to memory consolidation. There are speculations of therapeutic methods that could improve memory loss or disorders, however, researchers have not yet discovered a viable approach. This research is likely to take years, although, perhaps, should the researchers sleep on it, the idea may come to them.
References
[1] Siliezar, J. (2022, August 9). Harvard researchers find REM sleep in jumping spiders. Harvard Gazette. Retrieved December 4, 2022, from https://news.harvard.edu/gazette/story/2022/08/harvard-researchers-find-rem-sleep-in-jumping-spiders/
[2] Office, N. (n.d.). Animals have complex dreams, MIT researcher proves. MIT News | Massachusetts Institute of Technology. Retrieved December 4, 2022, from https://news.mit.edu/2001/dreaming
[3] Halber, D. (n.d.). Memory experts show sleeping rats may have visual dreams. MIT News | Massachusetts Institute of Technology. Retrieved December 4, 2022, from https://news.mit.edu/2006/visual-cortex
[4] Picower Institute for Learning and Memory. (n.d.). MIT neuroscientists achieve 'Dream Engineering' in rats. MIT News | Massachusetts Institute of Technology. Retrieved December 4, 2022, from https://news.mit.edu/2012/mit-neuroscientists-achieve-dream-engineering-rats