How the human brain creates time in the absence of a clock

According to a recent study, the brain develops our sense of time through a series of unique processing processes across several brain regions rather than relying on a single internal clock. This discovery reinterprets time perception as something that is created gradually rather than being quantified.

Sight-based signals

Thirteen healthy participants assessed short visual flashes as activity moved from the back of the brain to its frontal areas inside a high-field brain scanner. Valeria Centanino of the International School for Advanced Studies (SISSA) traced that development and showed that the physical length of each stimulus was originally encoded by early visual areas.

Then, as they progressed, the initial signals changed from measuring length in a raw manner to more selective patterns that facilitated comparison and understanding. This transition demonstrates how a single moment becomes a useful perception, necessitating an explanation of how each stage modifies the signal.

The brain's starting point for timing

The occipital visual cortex, where visual information initially enters the brain's timing process, was initially more active with lengthier flashes. In certain areas, the signal appeared monotonic, which means that rather than peaking for a single preferred length, the reaction continued to rise over time.

The same lab had previously discovered duration maps in one motor region, but not in this broader sequence. Because greater raw time signals still needed to be converted into useful judgements, early visual coding was unable to fully explain perception.

Deeper brain region activity

Timing became more selective in areas of the brain that connect our actions to what we observe as signals travelled farther into the brain. The brain was able to differentiate between intervals because activity in certain regions peaked for predetermined periods of time rather than increasing gradually.

These regions disperse their preferences over the entire tested range rather than favouring primarily lengthy flashes. The brain most likely acquired a useful code for comparing one time to another during that intermediate stage.

Where signals started to take on more structure

Rather than dispersing randomly across the cortical surface, neurones with similar preferred durations congregated close to one another across several locations. Because neighbouring tissue tends to represent neighbouring values, researchers refer to those ordered arrangements as topographic maps.

In contrast to regions further forward, where timing signals grew more structured, early visual areas at the back of the brain displayed less ordered patterns. That pattern suggested that when the brain was ready to use timing, it grew more structured.

Three processing phases

Three phases were identified by the scientists based on that evidence: the first encoding in visual regions, the middle stage that converts the timing into signals that can be used, and the final stage that transforms it into a choice.

The authors of the study concluded, "Our results show that time perception is not a unitary process, but the outcome of multiple processing stages distributed across the cerebral cortex."

Because each stage altered the signal's representation before the subsequent region took over, that succinct synopsis is appropriate for the paper.

Signals split forward

Links between far-off areas demonstrated that information was not transmitted by the system via a single linear path. Early visual timing was handled by one set of regions, interpretation and awareness were supported by another, and timing-based action preparation was aided by a third.

These connections imply that the brain may process timing via two different pathways, one supporting perception and the other supporting action. This distinction explains why acting on timing and judging duration can seem closely related but not the same.

Where emotion manifests

Instead of covering all durations evenly, preferences congregated around the middle of the tested range near the front of the network. These patterns matched how each participant determined whether a moment felt longer or shorter in one area associated with consciousness.

The supplemental motor area (SMA), another region involved in action planning, contained a portion of the same link. "From encoding physical duration to constructing the subjective experience of time, each stage contributes differently," the scientists continued.

Developing our perception of time

The majority of movement-related regions reacted to the shortest intervals, however there was a significant warning associated with this pattern. The side of the brain where the reaction buttons are pressed is where all of those hotspots were located.

This alignment implies that some of the activity involved not just perceiving time but also getting ready to react. Nevertheless, those movement-related areas continued to be a part of the larger system that creates our perception of time.

Prospects for future research

Researchers could investigate why brief events seem longer or shorter when under stress, ambiguity, or concentrated concentration by using a tiered model of timing. Future tests can examine which cortical step changes when duration judgements bend because distinct cortical steps perform different tasks.

Although patients were not tested in this experiment, such a question is important for diseases characterised by skewed timing.

Nothing has yet been diagnosed by the framework.

However, it provides future research with more precise goals to pursue. When viewed in this light, the brain transforms sensory data until a flash becomes an option rather than just detecting duration. Future research on movement, sounds, and clinical circumstances will demonstrate the true generality of this brain pattern.