Our perception of time changes with age, but it also depends on our emotional state. Research is steadily improving our understanding of the brain circuits that control this sense, opening the way for new forms of treatment, particularly for Parkinson’s disease.

Time is an integral part of our daily life, regardless of whether we are in a hurry, relaxed, gripped by an emotion or bored stiff. We may be walking, driving, listening to music, hearing the phone ring, taking part in a conversation or doing a sport, but time is always there, omnipresent and immaterial. Whereas all our senses – sight, touch, hearing, smell and taste – bring into play specialised sensory receptors, there is no specific receptor for time. Yet it is present in us, our brain being a real timing machine.

Very young children “live in time” before gaining an awareness of its passing. They are only able to estimate time correctly if they are made to pay attention to it, experiencing time in terms of how long it takes to do something.

The awareness of time improves during childhood as children’s attention and short-term memory capacities develop, a process dependent on the slow maturation of the prefrontal cortex. To gauge the time required for a task they must pay attention to it. But they must also memorise a stream of time-data without losing concentration. So children suffering from attention-deficit hyperactivity disorder find it hard to gauge time correctly.

On the basis of our early ability to estimate passing time, researchers suggested in 1963 that time as perceived by our brains (subjective time) was synchronised with the ticking of an internal clock, in much the same way as our daily life is governed by the ticking of our watch (objective time). They modelled a mechanism for measuring time, a sort of internal clock. It consists of a pacemaker, continuously emitting pulses (ticking), which are stored in an accumulator. The subjective duration of time depends on the number of pulses that have accumulated (since the beginning of the stimulus). When the internal clock speeds up, the number of pulses increases, creating the impression that time is passing more slowly.

At the beginning of the century, Professor Warren Meck, at the Duke Institute for Brain Science, North Carolina, developed a more physiologically realistic model. According to the striatal beat-frequency model of interval timing, the representation of time is underpinned by the oscillatory activity of brain cells in the upper cortex. The activity of each oscillator cell is characterised by a specific rhythm. The frequency of oscillations is detected by certain cells in the dorsal striatum, a substructure of the basal ganglia, located at the base of the forebrain.

Alongside this model, in which estimates of time intervals originate in neuronal activity, the brain structures involved in processing time-related data differ depending on whether they are estimating the duration of a stimulus (explicit timing) or gauging the lapse of time, or interval, separating us from an event expected to occur in a few seconds or minutes (implicit timing).

“For durations ranging from a few milliseconds to several minutes, the processing of explicit and implicit timing does not bring into play the same neuroanatomical regions,” says Jennifer Coull, a senior research fellow at the Cognitive Neuroscience Laboratory, at Provence University in Marseille. These differences are due to the fact that “implicit-time processing is almost always used to achieve a motor-task goal – ‘Do I have time for a coffee before my meeting?’ – whereas explicit-time processing aims to estimate a duration as such”, Coull explains. Studies of explicit timing show that two cortical structures, the supplementary motor area, which co-ordinates complex movements, and the right prefrontal cortex, are constantly activated.

Above all, the brain’s perception of time involves processes linked to memory and attention: witness the impression that time is passing more quickly when we are busy, or doing something amusing or exciting. Time flies even when we are in love. In contrast, a watched pot never boils. Minutes drag by when we are bored.

Recent research by neuro-physiologists and chemists working on time processing is beginning to show how emotions may speed up or slow down our perception of time. In 2011 Professor Droit-Volet and Sandrine Gil, a lecturer on cognition and learning at Poitiers University, France, published a study of how changes in the emotional state of subjects caused by watching films affected their sense of time.

“Fear distorted time, the stimulus being perceived as longer than it really was,” says Droit-Volet. Fear prompted a state of arousal that speeded up the rate of the internal clock.

But, “quite unexpectedly, sadness does not affect our perception of time, no doubt because the emotion felt when watching a sad film is not strong enough to slow down physiological functions,” Droit-Volet explains. However, she adds, work is needed on the profound sadness associated with periods of severe depression.

The theory of embodied mind (or cognition) helps explain how the perception of other people’s emotions changes our sense of time. Embodied cognition hinges on an internal process that mimics or simulates another’s emotional state, enabling us to tune in and understand their feeling. Accordingly, when a teenager spends time with a senior who speaks and walks more slowly, the young person’s internal clock slows down. There is also a subjective slowing of time, which enhances social interaction between the two people.

“Our perception of time is very revealing of our emotional state,” says Droit-Volet, pointing out that temporal distortion caused by emotion is not the result of a malfunction in the internal clock, but on the contrary an illustration of its remarkable ability to adapt to events around us. She adds: “There is no single, uniform time, but rather multiple times which we experience. Our temporal distortions are a direct translation of the way in which our brain and body adapt to these multiple times, the times of life.”

In Durée et Simultanéité, A propos de la théorie d’Einstein (Duration and simultaneity, with reference to Einstein’s theory) the French philosopher Henri Bergson explained that “we must put aside the idea of a single time; all that counts are the multiple times that make up experience”. In other words our perception of time is always relative.