Skip to Content
Uncategorized

A Thermodynamic Limit on Brain Size

If our brains have to be cooled like computer chips, is there a limit on how big they can be?

In recent years, chip makers have conlcuded that the race to produce ever faster circuits is a fool’s game. As the clock speed increases, the amount of energy lost as heat becomes too large to dissipate efficiently and in any case, the waste is unjustifiable.

That raises some interesting questions about the human brain, says Jan Karbowski at the Sloan-Swartz Center for Theoretical Neurobiology at the California Institute of Technology. Karbowski points out that the problem of heat transfer could be a serious factor shaping brain evolution and so has embarked on a program to determine the relationship between brain temperature, its size, cerebral power generated and neural activity.

The question on Karbowski’s mind is whether there is any thermodynamic limit on brain size. And if so, does 5 kg, which Karbowski says is the mass of the largest mammalian brain, approach that limit?

Karbowski points out that brain cooling is not a classic problem of surface-area to volume. Instead, brain cooling is more closely comparable to that in a combustion heat engine where a liquid coolant removes heat.

“In the brain, the role of the coolant is played by the cerebral blood, but only in the deep region because there blood has a slightly lower temperature than the brain tissue,” says Karbowski.

But in the regions closer to the surface, it is the oter way round: brain tissue is colder than the cerebral blood which warms the brain.

This implies that the thermodynamics of heat balance does not restrict the brain size. And this in turn suggests that brains could be heavier than 5 kg, says Karbowski.

(And of course they do get bigger than this. The sperm whale’s brain can be 9 kilograms).

That leaves plenty of growing room for humans which have brains of only 1.5 kilograms on average.

Ref: http://arxiv.org/abs/0905.3690: Thermodynamic Constraints on Neural Dimensions, Firing Rates, Brain Temperature and Size

Keep Reading

Most Popular

DeepMind’s cofounder: Generative AI is just a phase. What’s next is interactive AI.

“This is a profound moment in the history of technology,” says Mustafa Suleyman.

What to know about this autumn’s covid vaccines

New variants will pose a challenge, but early signs suggest the shots will still boost antibody responses.

Human-plus-AI solutions mitigate security threats

With the right human oversight, emerging technologies like artificial intelligence can help keep business and customer data secure

Next slide, please: A brief history of the corporate presentation

From million-dollar slide shows to Steve Jobs’s introduction of the iPhone, a bit of show business never hurt plain old business.

Stay connected

Illustration by Rose Wong

Get the latest updates from
MIT Technology Review

Discover special offers, top stories, upcoming events, and more.

Thank you for submitting your email!

Explore more newsletters

It looks like something went wrong.

We’re having trouble saving your preferences. Try refreshing this page and updating them one more time. If you continue to get this message, reach out to us at customer-service@technologyreview.com with a list of newsletters you’d like to receive.