Do Neurons Change Fire Rate Over Time?

[David Carroll]

I have a question for those who are in the know: Do neurons fire at the same rate throughout a person's life or does the average rate change over time? I ask this because - and this, of course, is speculative - it could figure into why time seems to speed up as one ages, i.e. by anecdote I know that a year at the age of 80 seems faster than a year at the age of 5. If fewer neurons fire per unit time, this I imagine would create the subjective experience of time speeding up in the same way that a slow-rated motion picture camera creates a quicker looking film (like films of World War I).

 

[analogdesign]

Actually, if there were fewer neurons firing per unit time I would think that would lead to a subjective slowing of perception, like running a film slower. Your analogy with the WWI films is a consequence of running slow film at a faster rate than which it was captured. That's not the same thing as slowing neural activity.

There isn't a lot of research on firing rates, but a recent paper did find slowing firing rates for a very specific type of neural circuit related to memory.

However, there is no evidence in general that neural firing rates decline with age. In fact, there is evidence they may speed up (if anything). http://www.nature.com/nrn/journal/v7/n1/full/nrn1809.html

My thinking on perceived speedup of time is about how time is structured. I have much less unstructured time now because I spend 50 hours at work and 10 hours a week commuting. I only have a couple of hours of free time a night. When I was a child I could easily have 6 or 7 hours of unstructured time. As you know, no time is slower than unstructured time, such as waiting in a doctor's office!

 

[zoobyshoe]

Actually, if there were fewer neurons firing per unit time I would think that would lead to a subjective slowing of perception, like running a film slower.

If you always perceive the time between "frames" as the same, which assumption I think the OP is making, then fewer "samples" of the external world per unit time would give the impression the world had speeded up. More would have happened between frames, but you would be under the impression the # of frames per unit time was the same, therefore the world around you would appear to be going faster.

If you take 4 frames per second and project them at 24 frames per second, then 6 seconds of events would be packed into every second of viewing time. Alternately, if you take 144 frames per second and project them at 24 frames per second, the events witnessed would seem to have slowed down. You would be stretching each "real" second out to 6 seconds of viewing time. All that, assuming there is some mechanism that causes us to perceive the time between "samples" of the external world as the same amount of time.

 

[Doug Huffman]

I once read a functional description of the perception of time involving awareness of the beat frequencies of a number of neurons (five or seven IIRC) buzzing away at random but personally consistent rates.

 

[analogdesign]

I once read a functional description of the perception of time involving awareness of the beat frequencies of a number of neurons (five or seven IIRC) buzzing away at random but personally consistent rates.

You're thinking of theta waves : http://en.wikipedia.org/wiki/Theta_rhythm

The idea of it corresponding to perception of time is a non-standard theory (who knows, though?). Typically researchers think that waves are related to learning and memory.

 

[David Carroll]

I once read a functional description of the perception of time involving awareness of the beat frequencies of a number of neurons (five or seven IIRC) buzzing away at random but personally consistent rates.

Personally consistent? So the rates vary one person from the next? If that were the case, then two different people would vary in acuteness in perception of time, I imagine. But I suppose if you have billions of neurons each firing at random all at once, any discrepancies would cancel out the more neurons there are that are firing.

 

[analogdesign]

Personally consistent? So the rates vary one person from the next? If that were the case, then two different people would vary in acuteness in perception of time, I imagine..

That would not surprise me at all.

 

[DiracPool]

I have a question for those who are in the know: Do neurons fire at the same rate throughout a person's life or does the average rate change over time? I ask this because - and this, of course, is speculative - it could figure into why time seems to speed up as one ages, i.e. by anecdote I know that a year at the age of 80 seems faster than a year at the age of 5. If fewer neurons fire per unit time, this I imagine would create the subjective experience of time speeding up in the same way that a slow-rated motion picture camera creates a quicker looking film (like films of World War I).

I am unaware of any studies that look at changes in the conduction velocity of neurons over a life span. If anyone comes across one, please post it. The perception of time is much a subjective property and therefore a bit tricky to quantify. However, novelty seems to play a particularly significant role. When you're young, your mind/brain is essentially a tabula rasa, and what happens is that your brain is continually constructing nerve cell assemblies or attractors via the selective strengthening of synapses. These attractors help you to navigate your environment in your home range through a process Piaget refers to as "equilibration."

As you get older, the brain constructs these attractors at a slower rate because the environment becomes more an more familiar. This is my guess as to why time seems to fly as you get older. I'd also guess that you could take a sedentary old man and put him on a world tour vacation for one year, and time would appear to slow way down for this person during that year. That's just a hunch, though, any relevant anecdotal evidence would be interesting to hear.

 

[zoobyshoe]

Wiki article:

http://en.wikipedia.org/wiki/Time_perception

A take on time perception with age:

http://www.huffingtonpost.com/2013/08/20/slow-down-time_n_3567218.html

I agree with this article. The 'eternity' of an hour in childhood compared to the rapidity of an hour in my fifties seems caused by the fact that, as a young kid I did not have the ability to withdraw into an internal train of thoughts that took my attention off the external world. If you're attention is glued to external events only, they can pass very slowly indeed. Eagleman proposes this is why time seems to slow down during a crisis: you're suddenly paying complete attention to the external world, making note of volumes of minutia you would normally ignore.

 

[David Carroll]

This could also be why, according to personal experience, 20 minutes of zazen seems like such an eternity to an episode of Sponge Bob...even though I enjoy the former more than the latter.

 

[David Carroll]

Another more logical explanation of the subjective experience of the speeding up of time is simply that time be perceived as a ratio of any unit divided by the length of our life so far. Thus 1 month at the age of 20 is 1/240th of the length of one's hitherto life. One month at the age of 80 would be 1/960th of the length of one's hitherto life. If that's the case, we could propose that the subjective perception of some unit of time "u" would be x times faster at age b than at age a, where x is the ratio b/a.

This would also solve a paradox that I used to dwell on when I was a child: "What was it like for me before I was born?" As the subjective length of "u" would approach infinity as one got closer to time zero of birth, this question loses its meaning (assuming it ever had meaning).

 

[zoobyshoe]

Another more logical explanation of the subjective experience of the speeding up of time is simply that time be perceived as a ratio of any unit divided by the length of our life so far. Thus 1 month at the age of 20 is 1/240th of the length of one's hitherto life. One month at the age of 80 would be 1/960th of the length of one's hitherto life. If that's the case, we could propose that the subjective perception of some unit of time "u" would be x times faster at age b than at age a, where x is the ratio b/a.

This would also solve a paradox that I used to dwell on when I was a child: "What was it like for me before I was born?" As the subjective length of "u" would approach infinity as one got closer to time zero of birth, this question loses its meaning (assuming it ever had meaning).

This makes sense. The older you get, a year is a smaller fraction of your life and means less to the totality.

 

[madness]

Not sure that we can make such a clear link between the firing rate of neurons and our perception of time. It is more likely that our sense of time is somehow constructed within the brain, just like space (http://en.wikipedia.org/wiki/Cognitive_map) and motion (http://en.wikipedia.org/wiki/Akinetopsia) are. This is in contrast to being a passive byproduct, for example motion could have been a passive byproduct of the movement of the stimulus across our retina, and space could have been passively received from the location of stimuli on our retina, but both of these are in fact actively constructed representations within our brains, and I believe time is the same. Moreover, I would suggest that our sense of the passage of time is related to the density of memories that occurred over that period and is therefore a retrospective effect.

 

[madness]

Wiki article:

http://en.wikipedia.org/wiki/Time_perception

A take on time perception with age:

http://www.huffingtonpost.com/2013/08/20/slow-down-time_n_3567218.html

I agree with this article. The 'eternity' of an hour in childhood compared to the rapidity of an hour in my fifties seems caused by the fact that, as a young kid I did not have the ability to withdraw into an internal train of thoughts that took my attention off the external world. If you're attention is glued to external events only, they can pass very slowly indeed. Eagleman proposes this is why time seems to slow down during a crisis: you're suddenly paying complete attention to the external world, making note of volumes of minutia you would normally ignore.

There's a few articles linking time perception to working memory.

http://www.ncbi.nlm.nih.gov/pubmed/22124848
http://www.psy-journal.com/article/S0165-1781(12)00319-8/abstract?cc=y
http://www.jneurosci.org/content/18/3/1085.short

I think that sortof goes along with what you're saying.