Hummingbirds, or ‘hummers’ as their biggest fans like to call them, are the only birds in the world that can fly backwards. Quite a trick. But what is also fascinating about the hummingbird is its ability to judge the passage of time. Just as humans can guess when 20 minutes have passed, so can hummingbirds.
They visit a plant, hover there, wings ablur, while they dip their stick-thin bills and elongated tongues into the long flower tubes and suck out the nectar. Having had their fill, they move on. The rufous-tailed hummingbird protects its source of food by aggressively seeing off any other birds that enter its territory, but it has a second technique of ensuring it gets to the nectar before anything else does. This is known as trap-lining and allows the hummingbird to calculate exactly when 20 minutes have passed – the time it takes for the flower to replenish its nectar. By returning with such precise timing the hummingbird beats other birds to this life-giving substance.
So we know that hummingbirds can judge the passage of 20 minutes, but have they evolved to measure only this interval or could they somehow learn to judge shorter time intervals too? To find out, researchers at Edinburgh University created fake flowers with a nectar replenishment cycle of 10 minutes instead of 20. Could the hummingbirds in the lab learn to judge when 10 minutes had passed? It turns out they could.20 And it isn’t just exotic birds that possess this remarkable skill. The everyday feral pigeon can be trained to judge time intervals with a fair degree of accuracy too.
As we saw in the last chapter, humans have this ability too. We can detect the millionths of seconds necessary to locate the direction of a noise, but we can also make a stab at guessing the year of every individual memory we hold. In this chapter, I will consider the competing explanations for how the brain copes with this range of time frames. It feels as though there must be a clock in the brain that ticks away the milliseconds, seconds, minutes and hours, allowing us to make judgements about time, but so far neither through dissection or ever-improving brain scanning techniques has a single clock structure been found. Just as Einstein’s theory of relativity tells us that there is no such thing as absolute time, neither is there an absolute mechanism for measuring time in the brain.
We do have a body clock, but this only controls our 24-hour circadian rhythms. It has no role in the judgement of seconds, minutes or hours. What neuroscientists in this field are all trying to establish is how the brain counts time when there is no organ to do so.
Just as Chuck Berry’s experience of time was dilated by terror during his long fall through the sky, and Mrs Hoagland’s by her fever, it is clear that however the brain counts time, it has a system that is very flexible. It takes account of all the factors I discussed in the last chapter – emotions, absorption, expectations, the demands of a task and even the temperature. The precise sense we are using also makes a difference; an auditory event appears longer than a visual one. Yet somehow the experience of time created by the mind feels very real, so real that we feel we know what to expect from it, and are perpetually surprised whenever it confuses us by warping.
You can easily test your own skills at time estimation by starting the stopwatch on your phone, looking away and then trying to guess when a minute has passed without counting in any way. Most of us are fairly good at it, but there is individual variation and our skills decrease with age. We are also easily distracted; people can estimate the length of a song fairly accurately if that’s all they are concentrating on, but if you ask them to focus on the pitch of the song as well, they will overestimate its duration. Not surprisingly, people who are particularly prone to boredom tend to give an underestimate of that minute passing. Time has dragged so slowly that they might think the minute is over in just 30 or 40 seconds.
Discussion of any of these studies can be confusing because there are two ways of measuring time estimation: prospectively – where you ask sometime to estimate a minute starting from now – or retrospectively, where you give them a task and then afterwards you ask them to guess how much time has elapsed. If time is moving slowly a person will underestimate the passing of a minute at the time, but if they’re asked afterwards they will overestimate the duration. Both signify time passing slowly. Imagine you’re at a play that is particularly dull. If while you sat impatiently hoping for the interval, you were asked to say when an hour had passed, time would be dragging so much that you might guess an hour had passed after only 40 minutes. When the interval finally does arrive you look back and insist the first half felt like two hours rather than an hour. So, glancing at the figures, one looks like an underestimate and one an overestimate, but they both indicate the perception that time is slow-moving.
Although no single clock of the brain has been discovered, several areas have been found to be implicated in time perception, each of which also reveal something about our experience of time. Let’s begin with the cerebellum. This area at the back of the brain, down towards the nape of the neck, accounts for just 10 per cent of the brain’s volume yet contains half of all our brain cells. The cerebellum, which means ‘little brain’, helps us to co-ordinate movement by processing huge quantities of information from the rest of the nervous system. It is thanks to this part of the brain that when we wake up in the morning we can immediately detect the position in which we are lying (a sense known as proprioception) because the cerebellum is constantly monitoring the position of each limb. Though this might sound inconsequential, having met Ian Waterman, who contracted a rare neurological illness at the age of 19 which severed the pathways sending messages from his body to his cerebellum, it is clear that this sense is vital. He has now learnt to learn to walk again and can drive a car, but in order to do so he must watch his own arms and legs continuously, consciously observing and thinking about every movement he makes. If he loses his focus for just a second, an action as simple as holding an egg results in the egg either smashed on the floor or crushed in his hand.
Ian’s difficulties are caused by the loss of all sensation below the neck, which means that his peripheral nerves are unable to provide feedback to the cerebellum. With its sheltered position at the back of the brain it is rare for the cerebellum itself to become injured, but if it does it’s not only the smooth co-ordination of movement that is disrupted, but the perception of the tiniest fractions of time.
If you puff a tiny amount of air onto someone’s eyeball they will blink in discomfort, but if a signal is given beforehand, then, just as Pavlov’s dogs began salivating at the sound of a bell, a person will blink at exactly the right moment in anticipation of the puff of air. Unlike Pavlov’s classically conditioned reflex to salivate, this blinking demands precision-timing and it is the cerebellum which makes the calculation. The finding that a person with a damaged cerebellum loses this ability is so robust that in 2009 a team working with patients in Cambridge and Buenos Aires found that this air-puff test could be used to predict which patients in a persistent vegetative state might one day recover consciousness. But the strongest evidence of all for the involvement of the cerebellum in time perception comes from a more dramatic technique.
ELECTRIFYING THE BRAIN
When I was shown into the consulting room, an old lady was sitting on a chair in the middle of the room. She looked anxious. The doctor approached her head holding what looked like a giant version of those bubble blowers which children play with at birthday parties. It was attached by a long curly wire to a trolley packed with electrical equipment. I’m afraid when the doctor insisted, in a mittel-European accent, that ‘zis is perfectly armless’ I couldn’t help but think I was in a sci-fi film, with the mad professor intent, despite his assurances, on electrocuting his elderly patient.
‘Look at zis!’ he said, placing the coil against his own head and flicking a switch. Suddenly one side of his top lip was twitching up and down in a sneer. ‘And I can do zis.’ He moved the coil to a different part of his head, switched the machine on again and one of his arms shot up in the air, in a slightly limp version of a Nazi salute. ‘
Do you want a go?’ he said, lunging towards me with the big coil. I was sure I didn’t.
The doctor was demonstrating equipment that induces convulsions through a gentler version of electro-convulsive therapy. The elderly lady was about to try an even milder variant. This weaker coil would simply stimulate a specific area of the brain through a process called Transcranial Magnetic Stimulation, or TMS. She was putting herself through the process because she was so depressed that she felt suicidal. Nothing else had so far made her feel better.
The doctor spent a long time examining her skull. When he was certain he had found exactly the right place he picked up the second coil, counted down from 10 and then applied a series of pulses to her brain. She moaned quietly, more in fear than in pain. But even so, she was hoping for some relief. In trials many people have found this treatment reduces their depression. She would now wait to see whether it would work for her.
The ability of this equipment to target precise areas of the brain makes it useful not only therapeutically, but also for identifying the parts of the brain involved in time perception. The electric pulses can temporarily disable a specific brain region without lasting side-effects and this has provided the strongest evidence to date regarding the involvement of the cerebellum in time perception. When this part of the brain was dampened down using TMS, people found it harder to estimate time. More specifically, it reduces people’s ability to perform in tests where they have to judge milliseconds, but makes no difference when the time intervals are many seconds long. To assess those we need to use another area of the brain.
THE MAN WHO THOUGHT THE WORKING DAY HAD FINISHED
A man sat in the consulting room at the Santa Lucia Foundation on the outskirts of Rome waiting to see Dr Giacomo Koch. Back in the sixties the hospital looked after war veterans, now it specialised in neurological damage and the man was hoping the specialists would be able to help him. He was only 49 years old, yet was finding it hard to concentrate and for a few days he had felt a bit weak down one side of his body.
The case was an intriguing one. The man was convinced something quite serious was wrong, but the doctors could not diagnose a recognisable condition. They ran test after test. To check his memory there was the Digit Span, the Corsi Span, the Rey-Osterrieth Complex Figure test (immediate and delayed recall), the Verbal Supraspan and the Forward and Backward test. To test his visuospatial skills there were the Raven Progressive Matrices. For concentration there was the Trial Making test, for language the Verbal Fluency and Phrase Construction tests. For decision-making there were the Tower of London and Wisconsin Card Sorting tests. The doctors calculated his scores. They were all normal. They had him copy drawings, learn lists of words and complete well-known phrases. Still his scores were normal.21
But the man had also reported another strange sensation; his mind clock and the actual clock seemed to be radically out of synch. He would go into the office, do what felt like a day’s work, get ready to leave and find it wasn’t even lunchtime. On other occasions, events seemed to last for a much shorter time than was the actual case – a minute to him seemed like just 30 seconds.
In the light of this, the doctors performed some time-estimation tasks. In order to get a fair baseline measure, they arranged for eight volunteers, also in their forties, to take the same tests. Each sat alone in front of a computer screen while a series of random numbers appeared one at time. Their task was simply to read the numbers out loud. This would prevent them from counting time in their heads. Afterwards all they had to do was to guess how long the tests had taken. The results of one trial could be down to chance, so they repeated the task with different numbers until they had done it 20 times. In each instance, the man performed worse than the eight volunteers. His ability to judge the passage of time was somehow impaired.
A brain scan indicated some damage to the right frontal lobe, which as the name implies is near the front of the brain on the right. This gives us a clue as to the next area of the brain implicated in time perception, an area we would normally associate with the ability to hold something in mind known as working memory. It is this skill that allows you to read through a recipe, then remember the list of ingredients while you go to the cupboard to fetch them. The very front of the frontal lobe, the pre-frontal cortex, which is located behind the forehead, seems to be particularly crucial.
The involvement of this area of the brain in time-keeping is backed up by the curious new finding that children with Tourette’s syndrome have recently been found to be better than other children at judging durations of just over a second.22 Suppressing their tics involves activity in the prefrontal cortex and experts have found those children with Tourette’s who were particularly good at suppressing their tics did even better on the timing tasks. This suggests that their need to use this region of the brain to control their tics brings an added advantage in terms of time perception.
So far we have looked at two areas of the brain associated with time perception – the cerebellum, low down at the back of the brain for those millisecond judgements, and the frontal lobe, behind the forehead, for durations of seconds. But what happens when we try to judge much longer durations of hours or even days without access to a clock or any clues as to day and night?
THE PERFECT SLEEP
Do glaciers carve their way through caves underground in the same way as they gouge through mountains above the ground? This was the question that the French speleologist Michel Siffre set out to answer when he planned an underground expedition in 1962. But having made his initial arrangements, he began to ponder a quite different question, one which was to revolutionise another field of study entirely.
He would make the trip as planned, taking all the standard equipment such as tents, ropes, lanterns and food, but would leave one item behind – his wristwatch. Instead of recording glacier measurements, he would systematically record his perceptions of time passing. He wanted to explore the natural rhythms of the body untainted by outside cues. The longest attempts to do this had at that point lasted only seven days, with both American and Soviet astronauts taking part in Cold War isolation studies to assess how people might survive in fall-out shelters after a nuclear attack. Michel had done the same, volunteering to spend a week in silent darkness in an experiment at an air force base in Ohio. Now he wanted to try it out for far longer, in more extreme conditions.
The authorities were not keen on letting a 23-year-old embark on such a risky expedition. But Michel was determined and he had form when it came to persuasion, having convinced a professor at the Academy of Sciences in France to take him on as a geology student when he was only 15. The difference this time was that he was putting his life at risk.
The location Michel had selected for his experiment was the Scarasson Cavern, a cave created from hundreds of horizontal layers of ice, which, unusually for a subterranean glacier, wasn’t linked to a glacier on the surface. To reach the ice cave Michel would need to descend a 130-foot shaft, part of which was S-shaped, meaning that if he were to slip on the ice and break his arm it would be impossible to haul him out; a minor fracture would result in death. Assuming he made it safely down into the cave, he planned to spend two months down there in complete isolation. He offered to sign disclaimers, freeing the authorities from any legal responsibility for his safety, but they insisted they would still be morally responsible. He was too young, they told him, too inexperienced, and above all too optimistic. Even after he made a year of detailed preparations, some still maintained the whole idea was nothing but a stunt. The turning point came when he delivered a lecture on his previous expeditions to his friends at the Club Martel potholing group. They saw that he was serious and agreed to act as a support team. Still he would need funding and written permission. He made numerous visits to the offices of officials where he would sit and wait, only to be told after an hour or more that the person in charge was too busy to see him. Michel started to feel these office visits might require more perseverance than the expeditio
n itself.
While he negotiated all the bureaucratic obstacles, Michel theorised about the experiment he was hoping to carry out on his own mind. He speculated that time existed on three levels: biological time, which stretched across many years; perceived time, created by the brain and conditioned by light and dark; and the objective time as shown on a clock. His interest was in comparing the final two. Specifically he wanted to discover through extreme self-experimentation whether humans have an inner clock that somehow synchs with ‘clock time’ even without any external cues. He also wanted to know how time would feel. On past trips underground he had found that time warped. The subterranean world was so absorbing that whenever he returned to the surface he was astonished to discover how much time had passed.
Eventually Michel raised the necessary funds and persuaded the authorities to let him go ahead. Although he would ultimately be all alone in the cavern, during the preparations he had a team of people helping him. For several weeks beforehand his friends from the potholing club stayed with him in his parents’ house, preparing equipment and supplies during the day and sleeping in the hallways at night. Meanwhile Michel had been instructed to rest. The team loaded the equipment onto trucks and drove as near to the cave as they could. When the trucks got snowed in they even built a primitive telefiric railway with a cable and brakes for moving the heaviest items. They marched through the snow for hours at a time carrying the rest of the supplies to the mouth of the cavern. They negotiated the difficult descent and ensured that Michel would have all the equipment and supplies he needed. Once the underground camp was set up, two of the men spent three nights in the tent as a trial.
Time Warped Page 5
