Science Weekly (Guardian) · The Guardian

Exercise and brain function, hedgehog hearing, and can AI change our minds? – podcast

March 12, 2026·20 min·1 clip

One in three hedgehogs killed on roads could be saved by ultrasonic deterrents tuned to 40 kilohertz.

This episode of Science Weekly from The Guardian, hosted by Madeleine Finlay with co-host Ian Sample, covers three recent research stories. The first is a UCL study on the links between exercise and brain function. The team recruited unfit, sedentary volunteers with high BMIs and put them through a 12-week progressive exercise-bike regime while a control group carried on as usual. They measured blood levels of brain-derived neurotrophic factor (BDNF), a protein produced in the brain and often called fertilizer for the brain because it protects neurons, drives growth of new neurons, and supports new connections. Cognitive tasks did not improve after the programme, and resting BDNF did not rise. However, fitness improved and fifteen-minute bouts of intense exercise produced a bigger BDNF spike than before. Brain imaging hinted at changes in prefrontal cortex activity. The second story, led by Dr Sophie Lund-Rasmussen at the University of Oxford, shows that hedgehogs can hear well into the ultrasonic range. Madeleine sets out the conservation stakes: hedgehogs face drastic declines in Europe, with roughly one in three killed by vehicles and estimates of 335,000 road deaths a year in the UK, plus losses from pesticides, habitat fragmentation, strimmers, and robotic lawnmowers. The researchers used CT scans of a euthanised injured hedgehog to build a 3D middle and inner ear model, finding structures like those in echolocating bats. They then tested 20 anesthetised rescue hedgehogs using scalp electrodes to measure auditory brainstem responses, finding hearing from about 4 kilohertz up to at least 50 kilohertz, with peak sensitivity near 40 kilohertz. Lund-Rasmussen hopes this could lead to ultrasonic deterrents for cars and mowers, while warning that bats and mice share the same range. She also plans to study how hedgehogs themselves communicate at these frequencies. The third story covers Cornell University research on biased AI autocomplete. Two large experiments with more than 2,500 participants had people write essays on standardized testing and then on the death penalty, fracking, GMOs, and voting rights, with some receiving biased autocomplete suggestions. Participants' expressed attitudes shifted in the direction of the AI's bias, they did not notice the shift, and warnings did not mitigate it. A condition with biased static text produced a much smaller effect, suggesting that mid-sentence completions are unusually persuasive. Ian wonders whether the attitude shifts would persist weeks later. The hosts close with plugs for The Guardian Long Read and production credits naming producer Ellie Sands, sound designer Joel Cox, and executive producer Ellie Beery.

As heard by us

Three science threads, handled with calm curiosity and a light touch.

This episode keeps three ideas in play: exercise, hedgehog hearing, and AI autocomplete. The order is a little odd, but it never feels random. Each segment stays close to evidence, which helps the show avoid the usual puffed-up science tone.

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Why you'd press play

Exercise, hedgehogs, and AI, tied together by unusually steady science.

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