Those split second decisions, made almost without thinking. When to put your foot on the pedal when you’re at the red light. When to check how those sausages are doing. Remembering to grab your lunch from the fridge seconds before you leave the house. Or – too often – 20 minutes after. And those carefully considered ones. Do I just finish this paragraph before I make a cup of tea? Or do I wait until the boss is clear of the kitchen?
Timing, that is our perception and estimation of time, is key in determining how we behave and in the decisions we make. New findings suggest that time in the brain is relative, not absolute. This means that your brain ‘encodes’ your sense of time depending on what happens to you, and not by the second, minute or hour. And this in turn determines how you behave.
Alas, you could be forgiven for feeling that the units of time common to everyone worldwide, except perhaps the odd Amazonian tribe, are pretty well ingrained. My partner and I will often make a quick bet on what time it is before we check our phone (all sigh!/rejoice! [delete as appropriate], the dwindling watch-less generation). And we’re both pretty good at getting to within 5 or 10 minutes, even if we haven’t known the exact time all day. He’s normally better at it, perhaps because he’s male? Perhaps it tends to fly/drag for me because I’m having more/less fun? Perhaps that’s another story.
In the 2004 reality TV show Shattered, contestants who had been sleep-deprived for over 140 hours went head-to-head to predict when an arbitrary amount of time had passed – in this case, one minute and seven seconds. With the pressure of £100,000 prize money at stake, Dermot O’Leary grimacing nearby, a studio audience rustling in the darkness, and no cues except their ‘inner clock’, contestants were almost unbelievably close. The loser, Jonathan, was 0.4 seconds out, while Jimmy, the winner, was just one tenth of a second out.
As an aside, contestants lost the game if they fell asleep while enduring one of the following hour-long challenges:
- A relaxing facial massage
- Cuddling a giant teddy bear
- A bedtime story, repeated again and again
- Watching paint dry in a warm, comfy chair
- Counting sheep on a television
- A lecture on triangles they had already seen earlier in the week
But how do you go about trying to work out what exactly it is that determines our sense of time?
“We know that for actions to have successful outcomes, the brain has to keep track of time,” says Dr Joe Paton, head of the Learning Lab at the Champalimaud Neuroscience Programme, Lisbon, Portugal. “Time is implicit in nature, difficult to tease apart from the on-going behavioural and sensory context, which makes studying it quite challenging.”
Timing is influenced by signalling of the neurotransmitter dopamine in the striatum, which lives near the front of the brain and is involved in movement, planning, and other cognitive functions. Damage to or deterioration of the dopamine-producing cells or to the striatum itself causes conditions such as Parkinson’s disease, which causes a person’s perception of time to dysfunction.
Just last week, headlines announced that in the relatively near future, scientists may be able to create a vaccine to prevent a protein from destroying dopamine-producing cells, and therefore block the progress of Parkinson’s disease. The striatum influences all aspects of perceptual timing, from clock functions, to decisions and memory mechanisms, and so it was the obvious choice for Paton’s research team to investigate. And so they looked at activity in the striatum of some rats.
The rats performed a timing task where they had to press a lever to receive a reward, which was available periodically,” says Gustav Mello, a graduate student in the lab. “For example, during a sequence of 15 trials, the reward would only become available after 30 seconds had passed since the last reward. To see whether the rat would be able to estimate different durations, after those 15 trials, the waiting time would change randomly to be either shorter or longer,” he explains.
The team found that the rats changed their behaviour according to the different waiting time schedules. “Similarly to how we would behave when waiting at a red light, the rats also seemed to prefer not to waste their energy, and pressed the lever only when enough time has passed,” Mello says.
To find out what underlies this behaviour in the striatum, the researchers recorded the activity of individual neurons while the rats were performing the timing task. They found that the representation of time was coded across the population of neurons.
“We found that each time a trial started, the neurons responded in a slow but reliable wave of sequential activity,” says Sofia Soares, a graduate student in the lab. “When the waiting time was longer, the sequence was slower and vice versa. Hence, the sequence was shrinking and expanding in a way that corresponded to the interval between rewards and the behaviour of the animal. You could essentially just look at the location of the wave within the population to read out how much time had passed,” she says.
What does this all mean about the way the brain keeps track of time? According to Mello, “the implication is that time in the brain is relative, not absolute, as it is measured as a position within an interval and not as a unit, such as a second, or an hour.”
“[We found that] populations of neurons encode time in a manner that is consistent with timing behaviour” says Dr Paton. “In addition, we found that the neurons combined motor and timing information.” In other words, our surroundings determine our sense of time, which in turn determines how we learn to time when to complete a task. How we ‘encode’ time and how we behave, are inextricably linked.
Perhaps the observation that we have a pretty good inner sense of seconds, minutes and hours passing supports these findings. Perhaps we all build up an inner 24-hour clock through events around us, and determine when we need to make our efforts to help us survive. After all, our lives have been scheduled against this time system since we were born, so our ‘inner metric clock’ has been getting more and more accurate since then.
I like to think that this study, albeit done in rats, suggests that we all really do walk to the beat of our own drum. We each live in our own personal timezone, depending on the world each of us experience. That said, next time you’re late for work, perhaps best not explain with “But I was on time! It was just in my own timezone.”
Amy Coats can be found, when she has the time, at @amycoats
G Mello, S Soares, J Paton. A Scalable Population Code for Time in the Striatum. Current Biology http://dx.doi.org/10.1016/j.cub.2015.02.036
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