In terms of order of magnitude, how does a the energy consumption of a typical mammalian neuron (in the brain) compare with the state of the art MOSFET?
Semiconductor Physics – Are Neurons More Energy Efficient than Transistors?
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Best Answer
Not surprisingly, it isn't so easy to get the power consumption of a cell. What is the power consumption of a cell? makes various estimates. One estimate for a human cell is
$$P_{cell} = 3 \cdot 10^{-10} W$$
When you read it note that power is measured either in Watts or ATP/sec. ATP, or Adenosine TriPhosphate is the molecule that stores energy in cells. An ATP is the amount of energy liberated by removing a phosphate group.
As Martin Modrak pointed out, the brain has $2\%$ of the body's mass, but uses $20\%$ of its energy. The neurons use $80\%$ of this $20\%$. I will estimate that the brain is $25\%$ neurons. That means neurons use roughly $32$ times more energy than a typical human cell, or
$$P_{brain \space cell} = 10^{-8} W$$
More surprisingly, the power consumption of a MOSFET isn't as simple as you might expect. And not all MOSFETs are created equal. Some are intended for high voltage switching power supplies. Guide to MOSFET Power Dissipation Calculation in High-Power Supply gave an example power supply where the dissipation is $1.23 W$.
But you are probably thinking of a transistor used in a computer. I found an unsupported rough estimate in If every transistor in a modern CPU was replaced with an old vacuum tube, how much power would that CPU take? that the power of a transistor is
$$P_{transistor} \approx 10^{-7} W$$
As Joao Mendez pointed out, power consumption is directly related to clock speed. This is because most of the power is used while switching between 1 and 0. This is the limiting factor of clock speed. Too much power consumption means raises the temperature of the chip too high, even with good cooling. Also, for mobile devices, it drains the battery more quickly.
Keep in mind that a brain and a computer achieve immense computing power in completely different ways.
A typical computer might use $10^{10}$ MOSFETs in the CPU and GPU, and > $10^{11}$ in a large bank of RAM. A typical clock speed is > $10^9$ Hz. It might run hundreds of threads "in parallel" using $\approx 10$ processors. From Transistor count,
On the other hand, a brain has about $10^{11}$ neurons Are There Really as Many Neurons in the Human Brain as Stars in the Milky Way?. It also has about 3 times that many glial cells, Neuroglial Cells. It has what might loosely be called a "clock speed" of about $ 5 - 80$ Hz, What is the clock speed equivalent of the human brain?, and is massively parallel.
MP 2Ring, Joe, and Stephan Matthiesen point out that a neuron has many dendrites, is much more complex than a transistor, and therefore a more powerful computing element. This is true, but a transistor is much faster and can do many operations in the time a neuron can do one.
I have no good way of defining computing power that would apply to both, and much less hope of comparing them. A brain and a computer each can do things the other can't touch. Anything simple, like comparing clock speeds and dendrite counts, is surely misleading.