From the visualisation and construction of narratives in our minds to the recall of familiar objects, imagination is a fundamental aspect of the human experience. By bridging historical theories with contemporary neuroscience, we can understand the phenomenon of imagination, identifying the brain regions and networks involved and their intricate interactions. This exploration promises a deeper insight into the nature of imagination and its significance.
Historical Perspectives on Imagination
In ancient Greece, Plato conceptualised the world in two realms—'being' and 'becoming.' Within this framework, imagination manifests in two forms: 'being' imagination, involving perfect and unchanging ideas, and 'becoming' imagination, linked to personal experiences and beliefs. Plato's ideas lay the foundation for understanding the various facets of imagination. His theories introduce the notion of mental visual imagery formed through past experiences and knowledge, but also recognise the influence of our personal beliefs and “inner world.” Philosopher Immanuel Kant expanded on these ideas, proposing that imagination is not just limited to the representation of objects but also aesthetics, morality, and cognition.
Examining these historical theories reveals the complex and abstract nature of imagination, with ideas of mental visual imagery, and the impact it has on our experiences in life. The recognition of imagination taking place in our brains then sets the stage for exploring the concept from the perspective of cognitive neuroscience.
Neural networks and brain regions
In 1980, Kosslyn introduced the 'quasi-pictorial' theory, suggesting that mental imagery involves imperfect representations, or 'quasi' pictures, constructed in a specific brain locus known as the "visual buffer." This theory highlights the overlap between the visual buffer and the brain's visual system, emphasising key brain structures like retinotopic maps and the occipital cortex. While these early investigations shed light on mental visual imagery, recent research also suggests alternative systems involved in imagination.
Imagery neural system
For instance, Agnati and colleagues (2013) distinguish between imagery and imagination, with the former using neural structures already engaged in established functions (e.g., the motor system) and the latter creating entirely new mental images from the "inner world." Their theory suggests the tinkering of existing perceptual information to form imaginative ideas, utilising existing functional modules within the brain. These functional modules are suggested to reorganise and reassemble themselves in a variety of ways to result in the creation of new mental ideas, which are also being shaped by our inner world. The default mode network (DMN), a network active during passive rest, may also play a role in imagining future events.
They also dive into the possible involvement of mirror neurons in mental imagery and, therefore, imagination. When an animal observes another animal acting, mirror neurons activate to replicate that action in the brain as a form of mental visual imagery. Their involvement in imagination, however, is suggested by the fact that some are active even without sensory input. The authors suggest that the perceived motor activity is a new image created from the “inner world” of an animal, rendering the process more creative than just representing an image physically seen in the brain. Overall, imagination is proposed to be a more creative process of developing new ideas, while mental imagery is just a clear representation following perception.
The Hippocampus, Episodic Memory, and the 'Imagination Network'
In an fMRI study, Addis et al. (2007) discovered right hippocampal engagement in tasks related to "future event construction," indicating an overlap with systems engaged in episodic memory. Hassabis et al. (2007) further identified such brain regions using an fMRI paradigm when investigating the neural basis of episodic memory. Participants were asked to imagine made-up experiences, and the researchers determined which brain regions may be involved in the process of generating the scene and visualising the spatial context. They found activation across brain regions like the hippocampus, parahippocampal gyrus, and retrosplenial cortex. From these findings, they suggest that scene construction makes use of processes seen in both episodic memory and imagination. They also suggest that more brain regions may also be recruited into this network to support processes like episodic memory.
Imagination as Dreaming
Imagination extends into different states of consciousness, particularly during sleep. When we are asleep, we often experience mental imagery and creativity in the form of dreams. Our dreams can include a mixture of past experiences and influences from our inner world to produce a unique story that we do not experience when we are awake. Vyshedskiy (2019) investigated the mechanism of imagination when dreaming, contrasting it to the mechanism of imagination when we are awake. He found that, when awake, the internal imagery in our minds is controlled by the lateral prefrontal cortex. He theorised that because this area is in charge of our executive control, the functions of reasoning and strategising can be used to pull together different memories into new combinations, forming our imagined stories.
When looking into the dreaming that occurs during rapid eye movement (REM) sleep, he found that the lateral prefrontal cortex was inactive while the posterior cortex was active. He suggested that if the usual executive control function was inactive during this time, then the novel combinations being formed in the posterior cortex would now be unexpected and ultimately different from the usual, allowing us to imagine in a way that is not possible when awake. He deemed dreaming to be a bottom-up mechanism and the imagination built by the lateral prefrontal cortex to be a top-down mechanism.
Prefrontal synthesis
In line with this, Vyshedskiy proposes top-down mechanisms of imagination involving the spatial combination of objects stored in memory. The Hebbian model of ‘neurons that fire together, wire together', also known as 'binding by synchrony,' is used to explain the creation of novel conscious perceptions. The Hebbian rule describes the perception of objects that we have previous knowledge of, but Vyshedskiy proposes that it can also apply to novel perception.
Neuronal ensembles that code the sensory components of objects exist in the posterior cortex of our brains and are active when we recall an object we have seen. Ensembles that encode each sensory component are activated in synchrony, allowing us to consciously perceive the full object. To produce novel objects in our imagination, he suggests that ensembles that do not relate to each other begin to fire in synchrony, building up a new conscious perception. When the synchronisation is driven by the lateral prefrontal cortex, this is named ‘pre-frontal synthesis.' When this process is driven from the back, however, this is now dreaming or hallucination. There is not much experimental evidence to directly support this theory, however.
Further ideas proposed include the existence of modifiers in our brains. When we recall an object we know, like a book, we can imagine that book in different colours. Vyshedskiy states that by doing this, we are modifying which neuronal ensembles are being activated for the simulation of the object. Furthermore, we can imagine something like a lamp with a missing bulb. In this way, we are now performing desynchronisation - the ensemble that encoded a specific component is no longer firing with the rest to produce the gap in our imagery.
Bottom-Up Mechanisms of Imagination
During REM sleep, communication between the neocortex and hippocampus is disrupted by high levels of acetylcholine. Vyshedskiy suggests that the waves specific to REM sleep lead to neuronal ensembles activating spontaneously, resulting in imagination. Dopaminergic cells in the ventral tegmental area may also be involved in increasing or decreasing the intensity of our dreams at this stage. When the ensembles activate in synchrony, a whole and novel image is formed; if they activate asynchronously, separate objects are perceived. If ensembles that are completely different from each other activate in synchrony and by accident, then they will appear as a “novel hybrid object.” Through these suggested mechanisms, the number of hybrid and novel images that can be perceived during REM sleep is unlimited. Direct evidence, however, is needed to provide support for these theories.
Imagination Beyond Memory and Visualisation
Through these studies, we can begin to see the depth of imagination; however, the topics explored only cover it as a form of creating images in our minds. Is there a role beyond that? For example, it could help us empathise with and act kindly towards others, adding value to these situations. Referencing evidence of memory, imagination, and empathy interacting with each other, Gaesser (2013) aimed to promote research in the direction of looking at how imagination can influence empathy.
As we have previously discussed with future episodic memory, memory can play a role in imagining the future. This involves the use of already-stored memories being reassembled to form new imaginative situations. This ability may help simulate different versions of the future and test them out to help us plan our next actions by seeing how our behaviour might play out. If this is true, then imagination may have a role beyond just visualising objects and spatial memory; it may also have the adaptive function of helping us plan out the future and see the possible value of different behaviours.
Moreover, Gaesser examined work showing that participants whose minds simulated an experience repetitively in their minds were more likely to have these imagined experiences. The neural basis for these effects is not yet well established, but there is a suggested role for the precuneus.
Conclusions and Future Directions
Overall, imagination emerges as a multifaceted phenomenon, weaving through historical perspectives, early neuroscience theories, and contemporary research. From the distinctions between mental imagery and imagination to the exploration of top-down and bottom-up mechanisms, the complexity of the topic becomes apparent. While hypotheses abound, direct research is essential to validate these theories and deepen our understanding of the neural basis of imagination. Understanding this is crucial - not only for unravelling the intricacies of memory but also for comprehending human behaviour and decision-making as we navigate the dynamic interplay between simulation and reality.
This article was written by Kunashe Gonye and edited by Julia Dabrowska. Interested in writing for WiNUK yourself? Contact us through the blog page and the editors will be in touch!
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