That is energetically very expensive to maintain. Herculano-Houzel says our brains are rather standard primate models, except for the fact that we have a massive number of brain cells compared to other species. This leads to the bigger question of what makes human brains special. So that's a pretty large difference actually.' Even though it may sound like a small difference the 14bn neurons amount to pretty much the number of neurons that a baboon brain has or almost half the number of neurons in the gorilla brain.

And not one that we looked at so far has the 100bn.

'We found that on average the human brain has 86bn neurons. The great advantage of this method is that unlike counting the number of neurons in one part of the brain and then extrapolating from that, it gets over the problem that different brain regions may have more or less densely packed neurons. You then take a sample of the soup, count the number of cell nuclei belonging to neurons (as opposed to other cells in the brain such as glia) and then scale up to get the overall number. The method involves dissolving the cell membranes of cells within the brain and creating a homogeneous mixture of the whole lot. She told me that so far, she has only looked at four brains, all of them from men. 'But the thing is we have been learning so much by this method we've been getting numbers that people had not been able to get … It's really just one more method that's not any worse than just chopping your brain into little pieces.' 'It took me a couple of months to make peace with this idea that I was going to take somebody's brain or an animal's brain and turn it into soup,' she told Nature. All of the men had died of non-neurological diseases and had donated their brains for research. Her team took the brains of four adult men, aged 50, 51, 54 and 71, and turned them into what she describes as 'brain soup'. This involved a remarkable – and to some I suspect unsettling – piece of research.

How many neurons in a human brain