The brain is a famously hungry organ, but thinking hard does not make it much hungrier. A new review concludes that solving cognitive tasks is typically accompanied by either a minimal increase in overall energy expenditure or no change at all.
The review, “Brains are expensive, but cognition is often cheap”, was written by Kacper Kondrakiewicz of NeuroElectronics Research Flanders (imec, KU Leuven and VIB) in Leuven, Belgium, and Jagoda Nawrocka of the University of Warsaw. It was published online on October 29, 2025 in Neuroscience & Biobehavioral Reviews.
Rest is not cheap
The authors take aim at a widely held belief: that because energy limits constrain neural computation, every bit of cognitive activity must be metabolically costly. They pull together evidence from brain imaging and from whole-body energy measurements in mammals.
That evidence, they argue, points the other way. Maintaining the resting state can be as costly as engaging in an explicit task, so switching from idling to concentrating changes the total bill very little.
Why curiosity makes sense
One consequence is that holding back from mental effort is often not an efficient way to save energy. The authors use this to explain behaviour that has puzzled researchers, such as curiosity-driven information seeking that brings no immediate reward.
If cutting back on exploration does not meaningfully reduce metabolic costs, then an animal loses little by poking around, and evolution has little reason to suppress it.
The authors propose that the key open question is how the brain’s different homeostatic mechanisms interact to keep its overall energy use relatively steady. Answering it, they write, would help uncover fundamental principles of neural computation.
Study Details:
- Title: Brains are expensive, but cognition is often cheap
- Authors: Kacper Kondrakiewicz, Jagoda Nawrocka
- Journal: Neuroscience & Biobehavioral Reviews
- Publication Date: October 29, 2025
- DOI: 10.1016/j.neubiorev.2025.106450