Woah-oh, what I want to know, where does the time go? -

(Credit: When Time Stood Still- © Victor Bregeda

Keeping track of time in the era of social distancing has become something of a problem for just about everyone. I am sure you have noticed that your daily life is a little looser, somewhat deranged, and certainly not normal. Months lose definition while days fly by haphazardly. Emily VanDerWerff wrote an article for Vox called What day is it today? about the confusion pandemic has managed to bring to our sense of time. It resonated with me and the quote from The Grateful Dead that is the title of this piece sums it up nicely.

There are many internal clocks, the best known is the circadian clock responsible for the daily cycle of sleep and wakefulness plus a myriad of biorhythms having to do with metabolism. But, there are other conspicuous brain rhythms; alpha, gamma, theta, and the rest. Our heartbeat is timed by special pacemaker cells in the SA node. Motor rhythms rely on brain stem pacemakers that govern the elaborate cycles involved in walking. Neural timers are also key to speech production and cognition. The list is long, in fact it is probably true that every cell has its own intrinsic timekeeper based on enzyme and gene expression loops. All of this is subconscious, a great example being the musician who syncs her performance to the beat effortlessly and precisely. The important thing is that none of these biological timers give a hoot about the seconds and minutes on your cell phone.

Some details are known about internal rhythm generators, the circadian clock being one. What we do not know much about is our perception of time. The time warp of self-isolation brings up questions about the brain’s timekeepers, how we perceive time, why experience of time is so fluid, and about the nature of time itself.

Subjective time

The subjective experience of time is steeped in mystery. We interpret and synchronize inputs from multiple sensory streams, auditory and visual for example, that work together but on very different time scales, but how? And by some miracle we stitch together memories of past events as we plan future actions.

At its core, the perception of time has a great deal to do with a dynamic relationship between emotion and attention. The emotion we experience influences the attention we bring into play, and vice versa. Perhaps that explains why time consciousness is so fluid.

When relaxed and doing something positive, we experience what psychologists call flow, a state of relaxed outwardly-directed attention. It is pleasant, either calming or exhilarating, and allows us to briefly step outside of ourselves. A key feature of flow is a distorted sense of time, in the moment it feels that time has expanded, but on reflection it seems to have passed quickly. Children experience flow easily, losing themselves in imagined worlds where time is boundless.

The delightful experience of awe changes time perception. When in awe we feel in-the-moment and view time as abundant. A journey into nature, shinrin-yoku, slows subjective time so that a walk on a forest trail is perceived as longer in duration than a walk in the city even if they were the same in minutes and seconds. Meditation can do this, in fact whatever puts you in the zone changes time consciousness, especially if you ignore your watch. Now that’s an idea, leave the Fitbit behind!

Common temporal illusions give proof to the fact that internal clocks do not care about external time. We often experience a disconnect between our experience of time as it is happening and our judgment of the passage of time in retrospect. There is an example I have wondered about since I was a kid called the return trip effect. When on a road-trip, the journey out seems to take longer than the trip home, even if the actual time by the clock is the same. It is mysterious. Most of us have felt time slow down when frightened or in an emergency. This is often attributed to sharpened attention and focus which would bring added survival value. But that is wrong, research shows that the effect only appears later, on reflection rather than simultaneously with the fearful event as it happens. If that is the case then it has more to do with the time code assigned during memory consolidation which, of course, is not constrained to align with external time. It helps to remember that in an emergency we are moving about half a second ahead of our perception of moving.

Being in quarantine places its own, sharply different, demands on our attention. No matter what your situation, you are probably experiencing some stress or anxiety. Your routine is disrupted and you are not doing what you normally would or would desire to be doing. You are broken out of flow so it is no wonder that your sense of time is broken, too.

Adrian Bardon, philosophy professor at Wake Forest, says the opposite of flow is inwardly-directed attention under a cognitive load, meaning that you have a lot of stuff on your mind. The result is rumination; repetitive, obsessive thoughts about your situation or the world situation. It is associated with feeling that time has slowed to a crawl. Paradoxically, while you feel that time is dragging one moment, it can seem to fly by the next. When out of our routine, events unfold devoid of their normal structure, rhythm, and sequence. Removed from the things that normally make us feel productive, we feel like we are treading water trying to deal with a situation we have no control over. And then, looking back it seems that time went by quickly because we did not accomplish anything. Slipping between flow and rumination can seriously mess with time consciousness.

So, if pandemic is weighing on you, consider what Edvard Moser, Nobel laureate who studies time-keeping in the brain, says “…that by changing the activities you engage in, the content of your experience, you can change the course of the time-signal in the timing networks in your brain and thus the way you perceive time.” Or, to put it more elegantly, do as Bob Marley famously said, “…lively up yourself and don’t be no drag.”

Timekeepers in the Brain

Time stamping systems in the brain record our experiences and produce memories that can be recalled with precise time structure and sequence for a lifetime. That is a miracle I would love to understand. Over the course of evolution multiple biological clocks have appeared. What separates the many timekeepers is the scale of time they measure and the phenomena they are tuned to. Many things that the nervous system does require timing, sometimes very precise timing. For example, exact timing of information from multiple sensory streams is essential for key aspects of perception, motivation, and action. Motor control systems are thoroughly dependent on high speed temporal computations needed to create the rhythm of movements, something that requires a high degree of plasticity and is the job of the basal ganglia and cerebellum, truly massive brain structures.

Time keeping on the scale of seconds, even milliseconds, is an easy task for neural networks and there are many circuit configurations that could do the job, although all are prone to failure. It is much harder to think of timekeepers that operate on the timescale of our experiences and memories. I am going to mention two current ideas and provide links at the end that will take you further.

First, an example of why the brain does not have a mechanism to register time 0n an absolute scale. It would not work. Most people are good at perceiving synchrony between sensory events in the external world, but how? Information reaches us at wildly different speeds. Sound travels in air at about 330 m/s, light travels at 300,000,000 m/s. So, for events involving both sound and light, only those occurring at the “horizon of simultaneity”, a distance of 10-15 m, will result in synchronous arrival of sound and image information at the primary receiving areas of the brain. Sound will arrive before visual if the source is closer than 15 m, visual arrives first if the source is further away. But we perceive intersensory synchrony for many events, not just those at 15 m. That illusion is just a mental construct. Neural processing times differ, too. Visual processing in the brain is about five times slower than auditory processing.

Memory of events in temporal order

Encoding time and then attaching time code to events is central to memory. Current thinking goes something like this. We know we do not perceive the duration of events with a standardized unit like a minute or hour. Neuronal timekeepers do not work that way. Science at this stage is searching for clues.

One idea is that subjective time is event dependent. Edvard Moser and his colleagues at the Kayli Institute in Norway have some insight into a brain timing network. Moser says, “This network provides timestamps for events and keeps track of the order of the events we experience.” It is event dependent. In their view, it is experience and the succession of events within experience that is the kernel around which subjective time is measured by the brain. The idea is based on recordings from populations of cortical neurons that activate in temporal relationship to specific events as an animal performs a repeated sequence of behaviors. And, it is played back in those neurons when the animal only thinks about performing the behaviors. Activity in the population does not encode clock time but a subjective time derived from the flow of experience. This is all very intriguing, but it brings up lots of questions. For example, is the timing network they study robust enough to time stamp a memory for a lifetime and if so what is the nature of the decoder that stitches a remembered temporal sequence back together on recall?

Time cells in the hippocampus

When you recall what you did this morning, you remember events in the order in which they occurred. This is a key feature of long-term memory and we do it so effortlessly that we take it for granted. The mental account of what happened, where it happened and when appears to depend on a region of the brain called the hippocampus. What the hippocampus does is miraculous, and it works along with the network the Moser group studies to pull it off. Current science has found a large population of neurons in the hippocampus that are grouped into ensembles with specific time preference. The activity in each ensemble encodes a sequential moment in the series of events that compose a distinct experience. These are termed time cells. Different groups of time cells fire in well choreographed succession during a temporally structured behavior, the grouping of units allowing elapsed time to be read out from the state of the network rather than from the activity of a single neuron, a feature that makes the code reliable. The important thing is that the groups of cells fire in the same sequence if the animal is merely rehearsing the behavior and not moving. This all occurs in computational time appropriate to neural processing giving an accuracy of 10 msec, give or take, which is roughly 10 to 50 times faster than conscious perception. So, on that score it seems possible that time cells could provide a mechanism for organizing episodic memories in time. There is so much more to learn about time cells and there are a lot of people working on it. I added some links at the end.

The arrow of Time

Eventually brain time has to meet up with physics time. Out of respect for that axiom, I have been reading what cosmologists are saying about time, time’s arrow, and why time forces us to consider multiverses. If that kind of thing interests you, I suggest a TED talk by Sean Carroll at Caltech, Distant time and the hint of a multiverse.

Finally, all this talk about time is great but then again, what if time really is just (quote The Good Place)-