Researchers discover how space and time interact in the brain

The human brain is remarkable for its ability to synthesize sensory inputs into a coherent perception of the external world. A central aspect of this is its capacity to process spatial and temporal information, such as perceiving the position and duration of a visual event like the flickering glow of fireflies.

Despite the apparent integration of space and time in our sensory experience, the underlying neural mechanisms that enable this synergy remain elusive.

Recent research has explored how the human brain links spatial and temporal dimensions within the visual system. Studies have suggested a dual-stage process for encoding duration. The first stage is spatially specific, potentially tied to early visual cortical areas, while the second is spatially invariant, emerging later in the cortical hierarchy.

However, conflicting evidence complicates this view. For instance, some studies show that adaptation to a moving visual stimulus causes spatially specific biases in duration perception, while others report that these effects transfer across visual fields, suggesting spatial independence.

Functional magnetic resonance imaging (fMRI) studies have provided additional insight. Research indicates that duration processing might involve compressive summation of sensory inputs or unimodal tuning mechanisms organized topographically.

Duration maps—or chronomaps—have been identified in various brain regions, including the occipital, parietal, and frontal cortices. These maps appear to overlap with retinotopic maps in some areas, hinting at a relationship between spatial and temporal processing.

Despite these advances, many studies have not fully explored how spatial and temporal dimensions interact within the brain, leaving key questions unanswered.

To address this knowledge gap, a team of researchers from SISSA’s Cognitive Neuroscience group designed a high-resolution fMRI study. Participants were asked to judge the duration of visual stimuli presented at varying positions within their visual field.

The experiment aimed to uncover how the brain processes these two dimensions simultaneously and identify the neural populations selective for both spatial position and duration.

The researchers found that the brain's ability to process space and time varies across its regions. In the occipital cortex—one of the first areas to process visual information—space and time are tightly linked.

Neural populations here respond to both stimulus position and duration, with longer durations eliciting greater activity. This region integrates spatial and temporal information, reflecting its role as the brain's primary receiver of visual inputs.

As visual information moves through the brain's processing hierarchy, the link between space and time begins to diverge. In anterior regions, such as the frontal premotor cortex, space and time are processed independently.

Neurons in these areas are specialized, with distinct populations dedicated to either spatial or temporal dimensions. Moreover, these populations exhibit a unique organization: neurons that prefer similar durations cluster together, forming what researchers describe as "time maps."

The parietal cortex, located between the occipital and frontal areas, displays a more complex relationship. Some neuronal populations in this region respond to both space and time, while others are selective for one dimension. Temporal responses here show a mix of monotonic and selective patterns, reflecting a blend of mechanisms seen in the occipital and frontal regions.

The study highlights the brain's functional hierarchy in processing spatial and temporal information. In posterior regions, space and time are integrated within the same neural populations.

This integration diminishes in intermediate areas and disappears entirely in anterior regions, where distinct neural populations process these dimensions independently. The findings suggest that different brain areas contribute uniquely to the perception of time, depending on their position within the cortical hierarchy.

“This study advances our understanding of how space and time, two fundamental aspects of our experience, are processed and integrated in the human brain,” the authors conclude. “Moreover, it sheds light on the presence of a functional hierarchy in time processing.

The existence of multiple response profiles to stimulus duration, along with their specific relationship to spatial processing, suggests that different brain areas contribute distinctly to the processing and perception of time.”

By revealing how the brain integrates spatial and temporal information, this research provides a foundation for understanding more complex cognitive processes. It opens the door to exploring how these mechanisms function in naturalistic settings and in individuals with sensory or neurological impairments.

The study's use of high-resolution fMRI also underscores the importance of advanced imaging techniques in uncovering the brain's intricate workings.

As our understanding of space-time processing deepens, it may lead to applications in fields ranging from virtual reality to clinical neurology. For now, this research offers a glimpse into the brain's remarkable ability to weave space and time into the fabric of human perception.

Note: Materials provided above by The Brighter Side of News. Content may be edited for style and length.

Like these kind of feel good stories? Get The Brighter Side of News' newsletter.