How many neurons does a human brain have, and more importantly how many connections?

According to Wikipedia the human brain has between 50 and 100 billion neurons, and 1000 trillion connections. Now those are huge numbers. Now according to other respectable sights (university sites) the  human brain’s estimated number of neurons range quite widely: 10 billion100 billion, 200 billion. So maybe we don’t know the exact number but it is in the billions, and more likely in the 100 to 200 billion range, but what about the number of connections? That is where the real meat is.

New neuroscience results have been widely publicized on the net (for example gizmodo) this week talking about the number of connections in the human brain based on a new paper in Neuron.  Using a new technique called array tomography researchers at Stanford report in the Neuron journal that in mice brains they find a higher level of synaptic connections than they imagined before. The original Standford press release.

From the cnet article which many people used in their reporting:

They found that the brain’s complexity is beyond anything they’d imagined, almost to the point of being beyond belief, says Stephen Smith, a professor of molecular and cellular physiology and senior author of the paper describing the study:

One synapse, by itself, is more like a microprocessor–with both memory-storage and information-processing elements–than a mere on/off switch. In fact, one synapse may contain on the order of 1,000 molecular-scale switches.”

In a related finding there was a new article that suggest the difference between human and other primates is the space between neurons in the prefrontal cortex, with humans having more space, which is speculated to allow more connections.

Now where things become really interesting is when Stephen Smith then extrapolates these results to the human brain:

A single human brain has more switches than all the computers and routers and Internet connections on Earth.”

Now that really makes you scratch your head, not to mention turn you around a few times as you try to get your head around the meaning of that statement, and numbers. There are a lot of switches in the average computer chip that is in almost every device humans make these days. According to the Moore’s Law article on wikipedia in 2008 the highest count of transistors on a chip was around 2 billion, but that was at extreme top end chip. The chips we are more familiar such as the low powered atom has 47 million, and the core  intel i7 (quad) has 731 million according to wikipedia. Now a transistor, far as I understand acts as an electronic switch which is what Mr. Smith is referring to when comparing the number of switches in a human brain compared to all the computers (plus routers and internet connections) switches. I have no idea how many computer chips exist in the world, and couldn’t find an estimate in my short search, but I am pretty sure it is a big number, billions I presume. I will let you do the estimated math of the number of ‘switches’ in all the world’s computers.

Interestingly, this general science news story was also picked up by in this piece, and this is interesting because Ray Kurzweil has made the prediction that computers will achieve the ability to simulate  the human brain by around 2030. However, this was based on the premise that the human cortex has 22 billion neurons 220 trillion synapses. I wonder if these new findings of each synapse having 1,000 or so molecular switches in each of them, and hence resulting in far greater connections of human neurons than we previously thought throws off Kurzweil’s predictions?

1 comment for “How many neurons does a human brain have, and more importantly how many connections?

  1. neuron kabir isiaka
    November 16, 2011 at 8:54 am

    i want to get the detail on me as iwas discoverded as a neuron 2010 and all my documents was chaned to neuron same year,and i started the computer programme dec 1 2010 which lasted for three months till march 2011 after some few months isent my computer programme result to united nation organization but i am yet to get the reply in my email please i need your assistant may almighty god reward you abundantly thank you