Neurons need ion channels to be able to convert incoming signals into electrical impulses. Pores in the membrane allow charged particles such as sodium or potassium ions to flow in and out of the cell in a controlled manner. A scientist from the Massachusetts Institute of Technology (MIT) in Cambridge, USA, Discover now the amazing peculiarity of the human brainOur neurons have a much smaller number of microchannels than do other mammals. The working group around Mark Harnett believes that this fact could make the high computing power of the human thinking organ possible in the first place.
The researchers examined neurons in the brain slices of 10 different mammals — from Etruscan shrews, the world’s smallest mammal, to rats, rabbits and macaques, right up to humans. Human preparations were tissue surgically removed from epilepsy patients during a surgical procedure. With the help of ultra-thin pipettes, the team measured the electrical properties of pyramidal cells in the cerebral cortex. This enabled her to infer the amount of ion channels.
Only humans get out of line
A consistent principle was found in all types of animals examined: the density of ion channels in neurons increases with the size of the neuron. In the brain of a small Etruscan shrew, which is full of very small neurons, there are more neurons in a given brain size than in a rabbit, which has much larger neurons. However, since the latter contains more ion channels, the channel density per tissue volume is the same for both types.
“It appears as if the cerebral cortex is trying to maintain the number of ion channels per brain volume, so energy costs are constant across all species,” Harnett says. Only humans are out of line here. Scientists have found far fewer ion channels in our species than would be expected based on this principle. They suspect that this allows the human brain to invest more energy in more complex connections or higher rates of fire. “If the brain saves energy by decreasing the density of ion channels, it can spend more energy on other neural processes,” says the neuroscientist.
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