A very large-scale study funded by the US NIH is involving human-brain-mapping research groups worldwide. Several are examining the recent discovery that there are many different kinds of neurons in the 80 billion or so that make up the human brain (it was previously thought that there was just one type).

So far (as at 2023) more than 3,300 distinctly different types of neurons have been discovered. Like every other cell in the body, the cells all have the same DNA, but develop differently. It's estimated that the full total of different neuron types could be well over 5,000. To put this into perspective, only a few decades ago it was widely assumed that there were only a few hundred cell types in the entire human body.

It's now assumed that the brain neuron differences may enable them to function in subtly (or perhaps radically) different ways. If this is found to be the case, it would mean the possible levels-of-complexity for widely interconnected neural 'circuits' would be at previously unimagined scales.

At present there is virtually no understanding of what these neuronal differences might mean for the overall functioning of the entire brain.

Volume 382, issue 6667 of the journal Science has a suite of papers covering the current research efforts.

Also see : Thoughtplugin-autotooltip__plain plugin-autotooltip_bigThought

inexplicable

It seems clear that thoughts involve brain-neurones, because damage to (or a reduction in the number of) neurones makes rational thought more difficult. But, like memory, the exact physical and/or biological micro-mechanisms which lead to the formation of ‘thoughts’ are completely unknown. and Memoryplugin-autotooltip__plain plugin-autotooltip_bigMemory

inexplicable

"Although it is commonly accepted that learning and memory occur via enduring changes in neuronal properties such as synaptic strength within a network of neurons, many details of these processes remain unknown, including the mechanisms responsible for the persistence and maintenance of memory over long periods of time.