FWIW I agree that bit also rang hollow to me—my sense was also that neurons are basically as energy-efficient as you can get—but by “computational efficiency” one means something like “amount of energy expended to achieve a computational result.”
For example, imagine multiplying two four-digit numbers in your head vs. in a calculator. Each transistor operation in the calculator will be much more expensive than each neuron spike, however the calculator needs many fewer transistor operations than the brain needs neuron spikes, because the calculator is optimized to efficiently compute those sorts of multiplications whereas the brain needs to expensively emulate the calculator. Overall the calculator will spend fewer joules than the brain will.
FWIW I agree that bit also rang hollow to me—my sense was also that neurons are basically as energy-efficient as you can get—but by “computational efficiency” one means something like “amount of energy expended to achieve a computational result.”
For example, imagine multiplying two four-digit numbers in your head vs. in a calculator. Each transistor operation in the calculator will be much more expensive than each neuron spike, however the calculator needs many fewer transistor operations than the brain needs neuron spikes, because the calculator is optimized to efficiently compute those sorts of multiplications whereas the brain needs to expensively emulate the calculator. Overall the calculator will spend fewer joules than the brain will.