Exercise, Hedgehogs and AI: Brain health, ultrasonic hedgehog hearing, and autocomplete bias in Guardian Science Weekly

Three science stories anchor this episode: a University College London study probes how physical activity might influence the brain by measuring brain-derived neurotrophic factor, or BDNF, and finds fitness-related spikes after brief, intense exercise even when resting cognition doesn't improve; hedgehog researchers reveal these critters can hear ultrasound and discuss potential, designer deterrents to reduce road deaths while weighing ecological tradeoffs; and Cornell researchers show that AI autocomplete suggestions can subtly shift people’s attitudes on hot-button issues, even when participants are warned about bias. Madeline Findlay talks through the findings with Ian Sample and considers what these results mean for brain health, wildlife conservation, and the ethics and governance of AI-assisted writing.

Overview

Three science stories anchor this episode: a University College London study probes how physical activity might influence the brain by measuring brain-derived neurotrophic factor, or BDNF, and finds fitness-related spikes after brief, intense exercise even when resting cognition doesn't improve; hedgehog researchers reveal these critters can hear ultrasound and discuss potential, designer deterrents to reduce road deaths while weighing ecological tradeoffs; and Cornell researchers show that AI autocomplete suggestions can subtly shift people’s attitudes on hot-button issues, even when participants are warned about bias. Madeline Findlay talks through the findings with Ian Sample and considers what these results mean for brain health, wildlife conservation, and the ethics and governance of AI-assisted writing.

Exercise, BDNF and the brain

Ian Sample explains that the UCL study recruited sedentary, high-BMI participants, put them on a 12-week cycling program with gradually increasing intensity, and tracked blood BDNF levels along with attention and memory tests and brain activity scans. They found no improvement on cognitive tasks or resting BDNF, but fitness improvements correlated with a spike in BDNF during short, intense exercise bouts, and some prefrontal cortex activity suggested potential benefits.

"if you're fitter, then you seem to produce more of this BDNF when you have a sharp, short bout of exercise" - Ian Sample

Ultrasound hearing in hedgehogs and deterrents

Researchers led by Dr. Sophie Lund Rasmussen describe how hedgehogs hear ultrasonic sounds and discuss how this could inform new deterrents. CT scans from injured hedgehogs helped build a model of their middle and inner ears, showing structures analogous to other ultrasonic-hearing animals. Live testing with 20 rehabilitated hedgehogs measured brain responses to ultrasound, revealing hedgehogs' hearing from about 4 kHz to at least 85 kHz, with peak sensitivity near 40 kHz. The goal is to design sound-based deterrents that minimize roadkill without driving hedgehogs away from gardens altogether.

"hedgehogs hear sounds from around 4 kilohertz up to at least 85 kilohertz" - Dr. Sophie Lund Rasmussen

AI autocomplete bias and attitude shifts

Cornell University researchers ran large-scale experiments where participants wrote essays on topics like standardized testing, death penalty, fracking, GMOs and voting rights, while some saw AI autocomplete suggestions biased toward a particular stance. A pre/post questionnaire assessed attitude change. The results showed that attitudes shifted in the same direction as the AI bias, and participants were largely unaware of the influence. Even when told the AI could be biased or when bias was shown in alternative text, the shift persisted. The researchers speculate about the mechanism—typing with live AI suggestions may feel like the author’s own reasoning—and discuss implications for journalism, education, and policy.

"not only did their actual attitudes to issues change in the same direction that the AI was biased, they were unaware of this" - Madeline Findlay