Human minds evolved to accomplish incredible feats of cognition and computation — but they also evolved to wander. The imagination is often held up as a totem of our species’ uniqueness, a thing that makes us truly separate from other creatures on Earth. Whether it is a daydream on the commute, a fantasy that helps you get through your workday, or “what if...” style planning we use to guide our life choices, our brains it seems are hardwired to lead our thoughts astray.
Yet the neurobiology of human imagination is a notoriously difficult thing to study, in part because the experience is so subjective. A new study offers some clues as to two biological processes that underlie different aspects of our imagination — specifically, our ability to imagine our own futures.
What’s new — Using a combination of brain imaging and a detailed scale system that allowed study participants to evaluate different aspects of imagined scenarios, a team of researchers was able to monitor which areas of the brain were active during different kinds of imagined scenarios — specifically, of the future.
The study, published Monday in The Journal of Neuroscience, reveals that two distinct processes occur in the brain’s default mode network when someone imagines the future. Previous research indicated that this network activates when we imagine something, and it is involved in daydreaming, planning, and imagining the future. This study moves the needle forward by drilling down into the functions of two subnetworks within this imagination highway: the ventral and dorsal default mode network.
How they did it — The researchers asked a group of 24 participants to imagine 16 different scenarios while awake in a brain scanner called an fMRI machine. Some scenarios were good, others were bad — for example, “imagine you win the lottery.” The point of these positive and negative prompts, according to the paper, is to evaluate “valence” — the brain’s way of judging whether a scenario is negative or positive. The participants were fed separate prompts to test the vividness of their imagination.
Joseph Kable is Baird Term Professor at the University of Pennsylvania and one of the co-authors on the study. He tells Inverse that the reason for separating these two measures out through the tests meant that vividness and emotion could be cleanly distinguished in the brain.
“We wanted to be able to cleanly manipulate two aspects of the scenarios,” he says.
In the study, the participants imagined each event occurring, and then rated them on a seven-point Likert Scale as to whether they imagined each as positive or negative, and as to whether they imagined the possible future event vividly. So a question about vividness would be rated on a 7 point scale rating from “Vague with no details” to “Vividly clear.” To assess valence, participants were asked, “How would you rate the valence of emotions in this event” with anchors of “Very Negative” to “Very Positive.”
What they discovered — The researchers found that the dorsal default mode network, which spans the brain’s ventromedial prefrontal cortex and the posterior cingular cortex, activates only during imagined scenarios that participants rate as positive or negative. This result suggests there is a strong connection between the dorsal default mode network and how you feel about an imagined future.
“The dorsal DMN responded to valence, so it was more active for the positive events than for the negative events,” Kable says.
“But it didn't care about vividness — it was equally active for the events that were imagined very vividly and the ones that were imagined less vividly,” he says.
Conversely, the ventral default mode network, which spans the brain regions known as the hippocampus and the precuneus, appears to respond only to vividness. The network showed greater activity when participants imagined events very vividly, and less activity during less vivid fantasies about the events.
Much like the dorsal subnetwork, the ventral subnetwork shows a kind of specialization in terms of which process of the imagination it may govern.
“[The ventral subnetwork] didn’t care about valence, it was equally active for the positive and the negative scenarios,” Kable says.
Why it matters — Kable says his team had hypothesized that each part of the default mode network may be involved in imagination in some way, but they were surprised that the processes would be so clear-cut.
“Usually with neuroimaging, it can be tricky because lots of parts of the brain are activated by lots of things,” Kable says. “It isn't often that you find these kinds of clean divisions.”
Kable believes those clear distinctions arise when the brain is trying to tell us something important.
“Parts of the brain that care about faces, and there are parts of the brain that care about places,” he says. “Those are clearly defined in neuroimaging. Nature is telling us that those are important.”
He thinks the same is true for the two processes that occur in the default mode network when humans imagine potential future events.
What’s next —Kable says his team hopes to build off these results to tease out how our imagination plays into decision making.
“Now that we know something about this division and the brain networks involved in different aspects of imagination, we can start to use it to investigate questions about what's going on in people's heads when they imagine futures in order to make decisions,” he says.
For example, we already know that the future holds less weight in our decision-making than the present. Kabler suggests that perhaps the vividness of the present compared to an imagined future may be why this is the case. This human capacity for imagining the future based on present events perhaps best described by the poet Robert Burns, in his 1786 poem “To A Mouse.”
Still, thou art blest, compar’d wi’ me!
The present only toucheth thee:
But Och! I backward cast my e’e,
On prospects drear!
An’ forward tho’ I canna see,
I guess an’ fear!
Abstract: Recent work has shown that the brain’s default mode network (DMN) is active when people imagine the future. Here we test in human participants (both sexes) whether future imagination can be decomposed into two dissociable psychological processes linked to different subcomponents of the DMN. While measuring brain activity with fMRI as subjects imagine future events, we manipulate the vividness of these events to modulate the demands for event construction, and we manipulate the valence of these events to modulate the demands for event evaluation. We found that one subcomponent of the DMN, the ventral DMN or medial temporal lobe subsystem, responds to the vividness but not the valence of imagined events. In contrast, another subcomponent, the dorsal or core DMN, responds to the valence but not the vividness of imagined events. This separate modifiability of different subcomponents of the DMN by vividness and valence provides strong evidence for a neurocognitive dissociation between (1) the construction of novel, imagined events from individual components from memory and (2) the evaluation of these constructed events as desirable or undesirable.