Brain Science Podcast discussion

Apparently the number of 100 billion neurons that is quoted in almost every popular talk about neuroscience is wrong ...

http://www.guardian.co.uk/science/blo...

The more interesting is actually the original research that talks about the human brain being a scaled up version of a primate brain and implications for evolution

http://www.ncbi.nlm.nih.gov/sites/ent...

Iva, I too found the guardian report interesting. Of course, the degree of connectivity between cells and regions is as important or even more so, but fundamentally, the excess population of neurons beyond those necessary for sensation and movement is what sets us apart from other species. When considering intelligence, it's even more interesting to consider the impact that the resolution and bandwidth of the senses have on how the brain scales and how it impacts resources. Anyway, you are making a good and important point for anyone interested in how resources are allocated, the amount of fixed vs dynamic resources, and what it takes to link them all together associatively.

The quote "100 billion neurons" has been proved to be wrong by a group in (I believe) Austrailia who completely disolved some brains, then counted nuclei/ml. It turns out that the actual number of neurons is closer to 80 billion.

Dalton wrote: "The quote "100 billion neurons" has been proved to be wrong by a group in (I believe) Austrailia who completely disolved some brains, then counted nuclei/ml. It turns out that the actual number of ..."

I heard this report also. It is not yet clear what the significance of this finding will be.

The significance, as I see it, between 100 billion and 80 billion neurons goes right to the heart of intelligence and the difference between ourselves and lower species. It is the excess of neurons over, over and above what it takes to manage the body and successfully survive in our environment that appears to endow us with superior intelligence and abilities.

Dalton wrote: "The significance, as I see it, between 100 billion and 80 billion neurons goes right to the heart of intelligence and the difference between ourselves and lower species. It is the excess of neurons..."

But it might turn out that the difference is more than just in neuron numbers. There seems to be some preliminary data that some human neurons are unique and that the human synapse might also be more complex.

What you say is true, but that does not negate the validity of my statement concerning the excess population of cells being fundamental to intelligence. Without adequate resources, variation in phenotypes would be fruitless. I realize that some resources are dynamically allocatable to accommodate the needs of the moment, but experience tells me that the resources that can be dynamically allocated are limited due to competing demands. Without the excess, we would be limited to hard wired reflexes.

The variation in synapses you mention (type and structure) seem to me to have a lot more to do with who gets to mate with who during development and plastic adaptations. The role that variation in size plays may have more to do with meeting the demands made on their duty cycle than any potential influence or domination of one over another.

I just saw this conversation topic... I believe that this "controversy" has been somewhat hyped. This is what I commented in a recent post of Carl Zimmer's blog:

"I am cautiously skeptical about knowing “everything” about the brain by just mapping its connections. Whatever the human brain does, it is much more than that. There are multiple factors that not accounted for in this concept, namely, the influence of glia, neurotransmitter spillover, autoreceptors, etc.
Also, with all due respect, I am seeing a trend about the “86 billion neurons” figure in several popular science websites. I believe that this number comes from Azevedo et al., (2009) J Comp Neurol. 513(5):532-41. If so, if I remember correctly the actual figure for the calculated number of brain cells in the paper above is 86 ± 8 billion. Based on this, the upper limit seems to be about 94 billion neurons, not so different from usual 100 billion that most of us think about. Moreover, based on the same data, this number can go as low to about 78 billion, but no one points this out. As interesting and important as this paper is, it had a rather small sample and I believe it is yet to be replicated. That said, these are indeed exciting times for brain research!
My two cents… (:-)"