The speed at which an animal’s central nervous system can send and receive signals depends on four main factors: (1) interneuronal distance, (2) transsynaptic transmission time, (3) axon diameter, and (4) axon myelination (Roth & Dicke 2017: 142).
To be clear, this doesn’t tell us how often signals are sent, just how long it takes a signal to get from one point to another, and an upper bound on how often signals can be sent and received?
Another metric that might be investigated is neuronal firing rates. However, this is probably not a good proxy for the subjective experience of time.[50] Different parts of the brain fire at different rates and with different regularity. Among mammals, homologous brain regions appear to exhibit similar firing regimes despite differences in brain size (Mochizuki et al. 2016).
I’m surprised you don’t think it’s a good proxy (if looked at in the right parts of the brain), or at least better than speed at which signals can be sent and received, since the latter doesn’t tell us how often they’re actually sent and received.
Thanks Michael, good question. I think the key issue is that, as far as we can tell, there is no single brain region responsible for temporal experience. And because neuronal firing regimes differ so dramatically across brain regions, we can’t assign overall neuronal firing rates and compare them across species.
Admittedly, this is also somewhat of an issue for some of the other neurological proxies I’ve identified. (For instance, as I mention in the post, axonal conduction velocity varies pretty significantly throughout the central nervous system.)
To be clear, this doesn’t tell us how often signals are sent, just how long it takes a signal to get from one point to another, and an upper bound on how often signals can be sent and received?
Correct. But at least for mammals, we know that homologous brain regions in different animals all fire at roughly the same rate. On the other hand, interneuronal distance does vary across mammals (and even more so across vertebrates). If there are differences in temporal experience across species, I wouldn’t expect mammals to have a uniform rate of subjective experience. So it seems to me that interneuronal distance is likely to be a more informative (though still very imperfect) metric than neuronal firing rate.
To be clear, this doesn’t tell us how often signals are sent, just how long it takes a signal to get from one point to another, and an upper bound on how often signals can be sent and received?
I’m surprised you don’t think it’s a good proxy (if looked at in the right parts of the brain), or at least better than speed at which signals can be sent and received, since the latter doesn’t tell us how often they’re actually sent and received.
Thanks Michael, good question. I think the key issue is that, as far as we can tell, there is no single brain region responsible for temporal experience. And because neuronal firing regimes differ so dramatically across brain regions, we can’t assign overall neuronal firing rates and compare them across species.
Admittedly, this is also somewhat of an issue for some of the other neurological proxies I’ve identified. (For instance, as I mention in the post, axonal conduction velocity varies pretty significantly throughout the central nervous system.)
Correct. But at least for mammals, we know that homologous brain regions in different animals all fire at roughly the same rate. On the other hand, interneuronal distance does vary across mammals (and even more so across vertebrates). If there are differences in temporal experience across species, I wouldn’t expect mammals to have a uniform rate of subjective experience. So it seems to me that interneuronal distance is likely to be a more informative (though still very imperfect) metric than neuronal firing rate.