What’s a few billion neurons between friends?
March 14, 2012 §
Reading through various articles linked by Anil Seth’s piece in the Guardian that I reviewed yesterday one in particular caught my attention. The article, ‘How many neurons make a human brain? Billions fewer than we thought‘, reports on the research of Dr Suzana Herculano-Houzel that indicates that the healthy human brain contains about 86 billion neurons; this is 14 billion less than widely quoted figure of 100 billion.
Dr Herculano-Houzel’s methodology has attracted attention. She took the brains of four adult males and reduced them to a “brain soup” then counted the number of cell nuclei belonging to neurons from a sample of the “soup”. From this she was able to estimate that the total number of neurons in the brain. The advantage of this method over taking a count of neurons from a sample of a specific brain region is that it is not affected by the differing density of neurons found in different areas of the brain.
However, it was not the methodology that I was most interested in. What surprised me is that the previous estimate of 100 billion neurons has been widely quoted despite no one seeming to know where the figure came from. It seems strange that science, a field of inquiry that should be rigorous and reliable, should accept a figure that cannot be verified. Which reminds me of a figure often repeated in relation to dieting and weight loss – but that’s for another day.
That aside how important is this research? 14 billion neurons are we are told roughly that of a baboon brain or half that of a gorilla brain. This gives some idea of the large number of neurons that the human brain contains in comparison to other primates. The human brain is typical for a primate except for the number of neurons; it would seem that for brains at least it is size that matters.