OK… let’s dwell on a question that I find infinitely fascinating, for so many reasons. Time, how do we do time? Yes, I said do. I have no reflections, at least none I’m confident enough to offer here, about the concrete physical nature of time. I’ll leave that conundrum up to far more qualified individuals (big ups Albert E!, don’t let the news about super fast neutrinos get you down). I’ll accept as a point of fact that time is relative and part of the fabric of space itself. But still, do? Yes, do. I’m not really interested in how we experience time either…not directly at least. Yes, we experience time linearly. Let’s move on. What I’m interested in, is that third great question about time. I want to know how your brain keeps time. How, in essence, your brain computes time, and how we hold any sequence of events together, in time. Is this a valid question to even ask? I think so, but I think we need to be careful where we tread with this one.
Where do we even start with a question of this magnitude? I guess there are several places you could, but I prefer to start with the one that seems the most basic, if time is relative, is our computation of time also relative- that is to say, do I compute time different than you? Does the now me compute time differently than the me of two years ago. What would it mean if we computed time differently? Would my neurons be firing faster? Faster firing neurons would allow me to encode more information from each fleeting moment. It would also theoretically allow me to think about that information faster, would this make those instants seem slower? Do the overall rhythms of firing in our brain speed up and slow down based on mental states or experiences? Neuroscientist David Eagleman (I do not intend to attack him here, see elsewhere on this blog) seems to think this idea has some merit. He first became interested in the idea of how the brain computes time during an extended fall from the roof of his house, during which he experienced the ubiquitous human experience of time slowing to a standstill. Eagleman’s hypothesis posits that what was happening in his brain at that time was that his nervous system had sped up, in effect causing his experience of each instant of time to elongate exponentially. It is an interesting thought, intriguing even, but it doesn’t really seem to jibe with what we know about the nervous system and his results didn’t bolster his initial hypothesis. For one thing, the firing rates of neurons possess a physical limit, a speed at which they can not exceed without violating basic principles of physics, and individual neurons already fire quite close to this theoretical maximum. Rates of firing in populations of neurons do change with different rhythms, we’ve all seen those squiggly lines from sleep studies. But let’s think about what this hypothesis would mean for the function of the brain as a whole. As far as we know now (admittedly not much), there exists no one place in the brain that “experiences” life. That is to say despite certain popular theories, there is no solid evidence that one part of the brain is the “CEO” of the brain, overseeing, understanding and coordinating the rest of the brain’s activity. Eagleman’s hypothesis would then have to suggest that the entire brain somehow speeds up in these situations. But we know this isn’t how the brain works. Yes, the brain operates at different firing rates, different cortical rhythms that propagate throughout systems in the brain. These rhythms aren’t exclusive though, the brain doesn’t fire as a whole at one rhythm. These rhythms seem to be a mechanism that the brain uses to link information related to certain objects or ideas being processed in disparate areas of the brain, the so called “binding problem”. It is unlikely that the brain processes time as a function of the rate of firing.
The prevailing theory for understanding this experience is based on an idea of filtering and encoding. This theory suggests that your brain spends most of its energy every waking moment filtering out extraneous information that bombards you from all angles. This is an absolutely necessary process, it is what allows you to simply make sense of your world. Basically, you are not a computer; you forget most of the information that comes into your brain. If you didn’t, it would be virtually impossible to encode, recall and decipher anything. Think about what the act of recognizing your best friend would be like if you spent several minutes studying every minute aspect of the skin of their face. You quite simply can’t do this, but you do recognize your friend, because your brain chooses the most salient features from your world and gives weight to those features. In these moments of “near death” experiences, your brain applies more emotional weight to all information. Moments of highly intense emotional reactions are known to increase memory recall. With this extra rate, the mechanisms in your brain that work to encode memories encode more of the information more strongly. So upon reflection on the moment. even moments later, the experience seems more vivid, more full of detail, and your experience of it feels slower as you play back through an incredibly detailed “mental movie” of the moment. Clearly, this isn’t exactly based on the way your brain processes time. Eagleman’s ideas are interesting for several reasons though. First, they posit that there is no central time keeper in the brain, no one area that keeps time consistently, no one “clock” that events in the world are measured against to achieve flow and coherence. He thinks the brain’s experience of time is a function of the way the brain encodes all information. In my next post on Thursday, I will continue this search into how our brain computes time with new information from noted memory researchers at Boston University. Perhaps this will offer an alternative point of view, one that I think makes more intuitive sense, and one that has experimental data to back it up.