Last week I reported on a strange illusion I had in the middle of the night. Upon waking early in the morning I experienced a sensation where I felt as though I had been asleep for 5 or 6 hours, but had actually only been asleep for an hour and a half. The experience disappeared for about a week, and returned for a single night 8 or 9 days later. I'm pretty sure no-one was sneaking LSD into my milo, so I wanted to figure out what was going on.

I asked people what they thought in my last post. Commenter Beauness said that our timekeeping was regulated by our circadian rhythms. Commenter Kate pointed me in the direction of an article about the Suprachiasmatic Nucleus (wiki link). The SCN plays a role in regulating the circadian rhythms.

Now every school kid knows we have Circadian Rhythms, and that they are basically our 'body clock'. But knowing that isn't very useful. What is a Circadian Rhythm? How does it work? and is it grounded in something beyond our biology?

In my last post I posed three questions that I thought would help illuminate my strange sensation. I'm addressing them here, briefly, as best I can. There's a lot of information I'm trying to synthesize, so please take what I write with a pinch of salt.

How do we keep time?

Circadian Rhythms (as nebulous as that term currently is) regulate our time perception. Biologically, we have a number of 'clock genes' in our bodies that feed information back to, and receive information from, the SCN (Suprachiasmatic Nucleus). These 'clock genes' operate throughout the body, and appear to be somewhat independent of other 'clock genes'.

Not only is the body full of circadian clocks, but recent imaging studies also

show that the molecular clockwork acts autonomously within individual cells

- Hastings, Maywood & Reddy (2008)

The SCN is responsible for taking all this information and co-ordinating it with external stimuli - chiefly, Solar Time. The SCN resides just above the Optic Chiasm, which isn't at all surprising, given that it needs fairly direct access to visual information regarding light / dark cycles.

Now that we know this we can pin down the Circadian Rhythms concept. So far as I can tell, Circadian Rhythms refer to the expression of various bodily hormones that regulate the wake / sleep cycle. The four primary hormones are growth hormone, melatonin, cortisol and insulin (Hastings et al, 2008).The SCN, in co-ordination with the various timing inputs, co-ordinate the expression of these hormones which regulate our sleep/wake cycle.

While my description thus far is (probably) overly simplified, the interesting thing is that we have a dispersed system of 'body clocks' which seem to be regulated by a fairly central entity, the SCN. The bit which escapes me is how do interpret this biological information as the thing TIME. To my mind one need not know what [the] time is in order to feel sleepy or alert; and I partly fail to understand how being sleepy or alert can inform my perception of time (though on a broad scale it seems somewhat intuitive). 

Given this is way outside anything I've read into before, it doesn't necessary equate in my mind that 'big rhythms' (my term) like the Circadian sleep/wake and hormone cycles necessarily inform our perception of smaller values of time. For instance, you can know that you began reading this paragraph ~10 seconds ago, but is it likely that these 'big rhythms' have change sufficiently to inform you accurately about this passage of time. It seems that there is another system that measures these smaller values - the interval timing clock (Kuriyama et al, 2003). As its name suggests, it 'counts' rhythmic signals and allows one to measure smaller amounts of time. However, the paper I found is light on the actual mechanism. However, it has been shown that working memory loads, time of day, body temperature, and mood are modifiers of (this form of) time perception (Kuriyama et al, 2003).

In a study by Kuriyama et al (2003) they found that, in short, diurnal fluctuations (i.e. the time of the testing session) influenced our ability to assess short lengths of time (10-second periods); and our ability was negatively correlated with core body temperature. The paper concludes by suggesting that circadian rhythms seem to play a larger role in short term time assessment than does cognitive load or mood. I find that surprising, but then, we're pretty remarkable organisms. 

Does it differ when we're asleep?

No evidence I have found suggests that these processes vary between sleep and wakefulness. One would expect a difference in what hormones are released, but the process - it seems - remains constant. It's all about the Circadian Rhythms and an endless feedback loop of information.

There are a group of people, who, it's hypothesized, have a warped sense of time regarding sleep. These people are Insomniacs. Insomniacs have trouble sleeping, and it is thought that a major mechanism in the disorder is their time perception. It has been proposed that stress from not sleeping leads to more stress, further preventing sleep. This hypothesis (reasonably untested as it is) postulates that insomniacs:

a) Overestimate time elapsed before falling asleep, and

b) Underestimate the period of sleep they have experienced

It is argued that these misperceptions maintain the insomnia. Tang and Harvey (2005) asked, if these hypotheses are true, then do insomniacs have a general malfunction in time perception, and, if so, is it context specific (i.e. in the bed, in the bed room).

So Insomniacs and a non-insomnia control group were asked to estimate periods of time elapsed between two electronic beeps. The periods were 5 sec, 15 sec, 35 sec, 1min, and 15min. They did this in the lab at different times, and at home about an hour before going to sleep while lying in bed.

Results show no difference between the groups. Which, considering how prevalent the behavioural theory of Insomnia is, I found surprising.

What the hell happened to me?

In short - No idea. I am different to the insomniacs, however - I don't have trouble falling asleep. In fact, I'm a pro. And I wasn't underestimating the period asleep, I was overestimating it. That was the strangest part. I'm pretty sure we've all woken up at some point and felt as though we hardly slept at all. Well, this was the opposite. It was like I was cramming more hours sleep into my time than nature would permit.

I guess I'll have to be satisfied to not know what went on. It was certainly strange, but more certainly, stranger things have (and will) happen. As a general rule of thumb I've learned that unless a psychological phenomenon causes disruption to one's life then it's not a problem. Self-awarness problems aside, I find that particular insight to be fairly elegent. Strange as the event was it was nothing more than a curio. I slept well again afterwards, and it caused me no particular anxiety.

The lesson I've learned (if you can call it that) from my experience and my readings, is that time is not objective. We all know this intuitively, but I think it's interesting to note that our perception of time, on a biological level, is certainly not beyond being tricked and warped - even without obvious cause. Certainly it seems as susceptible to illusion and error as is our perception of optical illusions and our perception of phantom noises.

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Image ref: http://www.iskcon.net.au/kurma/2011/07/04

Hastings, M., Maywood, E., & Reddy, A. (2008). Two Decades of Circadian Time Journal of Neuroendocrinology, 20 (6), 812-819 DOI: 10.1111/j.1365-2826.2008.01715.x Tang, N., & Harvey, A. (2005). Time Estimation Ability and Distorted Perception of Sleep in Insomnia Behavioral Sleep Medicine, 3 (3), 134-150 DOI: 10.1207/s15402010bsm0303_2Kuriyama, K. (2003). Circadian fluctuation of time perception in healthy human subjects Neuroscience Research, 46 (1), 23-31 DOI: 10.1016/S0168-0102(03)00025-7