How can we differentiate between what we perceive as real and what we imagine? Recent findings have uncovered brain pathways that may assist in this distinction, potentially enhancing treatments for hallucinations associated with conditions like Parkinson’s disease.

It’s already established that the brain regions activated during imagination closely resemble those engaged when perceiving real visual stimuli; however, the mechanism distinguishing them remains elusive. “What allows our brains to discern between these signals of imagination and reality?” asks Nadine Dijkstra from University College London.

To explore this, Dijkstra and her team observed 26 participants engaged in visual tasks while their brain activity was monitored via MRI scans. The tasks included displaying static grey blocks on the screen for 2 seconds, repeated over 100 times. Participants were prompted to imagine diagonal lines within each block, with half of the blocks containing actual diagonal lines.

Subsequently, participants rated the vividness of the lines they perceived on a scale of 1-4 and indicated whether the lines were real or imagined.

Through the analysis of brain activity, researchers found that when participants viewed the lines more vividly, the fusiform gyrus, a specific brain area, was more active, irrespective of the line’s actual presence.

“Prior research indicated that this area is engaged in both perception and imagination, but this study reveals its role in tracking the vividness of visual experiences,” notes Dijkstra.

Crucially, a spike in activity in the fusiform gyrus above a certain threshold led to increased activity in an associated area known as the previous island, causing participants to perceive the lines as real. “This additional area connects to the spindle-like moment, possibly aiding decision-making by processing and re-evaluating signals,” she adds.

While it’s likely that these brain regions are not the sole players in discerning reality from imagination, further investigation into these pathways could refine our understanding of treating visual hallucinations linked to disorders such as schizophrenia and Parkinson’s disease.

“Individuals experiencing visual hallucinations might exhibit heightened activity when visualizing their imagined scenarios, or the monitoring of their signals could be inadequate,” Dijkstra suggests.

“I believe this research could be pivotal for clinical cases,” says Adam Zeman, from the University of Exeter, UK. “However, distinguishing whether minor shifts in sensory experiences are driven by real-world events, discerning fully formed hallucinations, and determining the duration of beliefs remains a significant challenge,” he explains.

To address this knowledge gap, Dijkstra’s team is currently studying the brain pathways of individuals with Parkinson’s disease.