Science Questions

How does my body know to wake up at my train stop?

Sun, 6th Jul 2008

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Ben P. asked:

I commute to work and travel 40 minutes either way. I tend to sleep as the train motion makes me drowsy. In all this time Iíve only once slept through his stop. Most of the time I wake up just before my stop. Is this in some way linked to my body clock or am I just good at it?


We put this question to Professor Russell Foster:

What heís talking about and what I think many of us experience is that you wake up a few minutes before the alarm goes off.  The mechanisms behind this have been much discussed.  If we jump from our species and talk about honey bees.  Honey bees will use their body clock almost like a daily events calendar.  They will consult this internal clock to determine when they will visit a specific type of flower at different times of the day.  For example they will visit one species at 12 noon and then another species 12 hours later.  Theyíre using their body clock to time specific daily events.  Itís thought that we may be able to do the same.  Itís not absolutely clear and there may be other mechanisms but the evidence is pretty good that we can act like little bees.


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Ben P asked the Naked Scientists:
Hi guys,

Just got into the show and have been binging on the podcasts like crazy.
Very enjoyable.

I have been in the work force for the last 12 years. I travel 40 mins to
work either way and tend to sleep to and from work as the travelling motion
tends to make me drowsy.

In all this time I have only once slept through my stop, and that time I
was admittedly quite drunk ont he way home from afterwork drinks.  Most of
the time I wake upless then a minute from my stop. This is consistent in
all weather conditions.

How does my body do this?


Ben Ben P, Fri, 2nd May 2008

  well im not too good with that stuff but your body doesnt do it kind of thing i mean you arent awake so your body cant possibly know well some people may argrue that the lady on the train says we have stopped at watever and you would hear it so ur brain would wake you up but thats not too likely i think benep, Fri, 2nd May 2008

Ofcourse you have to be aware of your surroundings while you are asleep, otherwise you'd never wake up to the alarm clock in the morning.  Hearing particularly, being one of the more primitive senses, is still even when you are asleep.

As you have found out, when you are under the influence of drugs (such as alcohol), it can knock out your senses to the point that you don't wake up when you are supposed to; but when it is not a drug induced sleep, usually some sensory information gets through.

It is not just a case of hearing tannoy announcements, but hearing the train enter tunnels, or changes in the reflection of sound from nearby buildings, or changes in the sound of the wheels over the tracks.

For some people, even their sense time remains pretty good while they are asleep.  For some people, they will wake quite precisely without any need for an alarm clock (for some, they simply don't have an alarm clock; while for others, they seem to wake about 10 minutes before the alarm was due to go off). another_someone, Fri, 2nd May 2008

Everyone has a "body clock" comprising a collection of genes which cyclically turn each other on and off in a form of molecular domino effect which takes about 24 hours to complete one cycle. This process is happening in every tissue in the body, so every cell in the body can keep time.

The "master clock" that sets all of these "cellular slaves" is located in the brain's hypothalamus. It's called the suprachiasmatic nucleus (SCN) and consists of a cluster of a few thousand interconnected nerve cells which use the same genetic programmes to also keep time. But the SCN is also connected to the retina and is reset by daylight, which is how we adjust the clock to compensate for a change in time zone or working a night shift. This master clock is linked to the cellular clocks in the rest of the body through blood-borne hormones such as cortisol.

Consequently, your body has a relatively accurate neurological time-keeping system. When you ask yourself "what time is it, I wonder?" and then ponder, and then check the time, invariably you are pretty close. In other words your brain can read the output from the clock and use it to time events and also as a frame of reference: you know, for example, the sequence of events that happened to you today.

This ability can be further extended by training to modify physiology. You know you need to get up at 7am each working day, so you learn to do that. Similarly, you know you have a certain amount of time before you reach your station, so you subconsciously time yourself.

But, ingenious as it sounds, there may also be non-time cues that are responsible for helping you to achieve your impressive somnolent feat! It might be that you have subconsciously learned how the sound of the train on the rails changes close to your home station, or the sound of a level crossing near your home for instance. All of these subtle cues act as reminders and you have learned to use them to wake you up just before you get home.

I hope this helps

Chris chris, Sat, 3rd May 2008

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