A sweat-sensing wristband can tell the difference between a relatively safe seizure and one that could kill you. The device works as accurately as an electroencephalogram (EEG), the current standard for gauging seizure severity, and it may even be able to predict seizures – without the patient ever needing to come into hospital.
The wristbands measure skin conductance, or how easily an electrical current can travel across the skin, which is related to how much you sweat. It's a useful way to measure how emotionally aroused a person is – although it can't tell which specific emotion is being felt – because sweat glands are activated only by the sympathetic nervous system, which controls the fight-or-flight response. When something fires you up or sends chills down your spine, your skin conductance goes up.
"The sensors are wireless and comfortable, so we can do experiments in the field," says Javier Hernandez Rivera of the MIT Media Lab in Cambridge, Massachusetts.
Rosalind Picard and colleagues at the Media Lab initially developed the wristbands to study the emotional states of children with autism, who can't always communicate what they're feeling. One of her undergraduate students brought the sensors home over winter break to test them out on his autistic brother.
One day shortly after Christmas, Picard noticed an enormous spike in activity in one wristband, but not the other. The student checked his records and realised that the peak came 20 minutes before his brother had a seizure.
"This was a total accidental finding," she says.
A lot of children on the autism spectrum have seizures, Picard says, and seizure-related consequences kill more people every year than breast cancer. But no one is sure how to tell from the outside which seizures should be allowed to run their course, and which will be life-threatening.
"Other than hitting your head or drowning, why do people die after a seizure?" Picard says. At least one study, led by neurologist Samden Lhatoo of Case Western Reserve University in Cleveland, Ohio, suggests lethal seizures are associated with suppressed brainwave activity after the seizure is over. "That's something that could end your life, if your brain doesn't bounce back," Picard says.
Doctors usually measure the severity of a seizure by how long it lasts, but that turned out not to be related to brainwave suppression. EEGs can measure brainwave activity, but require lots of sensors to be attached to the scalp. Those sensors can get ripped off during a violent seizure, and are impossible to wear all the time.
Picard, her student Ming-Zher Poh, MIT neurologist Tobias Loddenkemper and colleagues fitted wristbands on 11 children who were being evaluated as candidates for brain surgery. They recorded a total of 34 seizures.
They found that the higher a patient's skin conductance during a seizure, the longer it took their brainwaves to return to normal afterwards.
The wristbands also picked up on seizure signals earlier than EEGs in some cases. EEG can only pick up activity in the cortex, the outer layer of the brain.
"If the seizure starts in the amygdala, the EEG won't see it, but the skin sensors will," Picard says. That doesn't necessarily mean the wristbands can predict seizures before they happen. "We think we can predict, but we can't claim that yet," she says. "We need more data."
At the moment, the wristbands are only available for research purposes. But in 2009, Picard co-founded a company called Affectiva to commercialise her lab's work. She thinks the devices could help collect data on epilepsy patients in their daily lives, and help them sleep better at night.
"Let's say I have epilepsy, and I'm afraid to go to sleep at night because I don't know if I'll wake up," she says. If her wristbands record a severe seizure, "I could have it call for help for me."
Lhatoo thinks the wristband "seems a neat little gadget to use", although he hasn't had a chance to try it out yet.
Picard's work also supports his best idea for why patients with suppressed brain waves die: something is wrong with their autonomic nervous system, which regulates heartbeat and breathing. Bugs in that system should show up in skin conductance, he says.
"It strengthens a relationship between autonomic dysfunction and brain suppression," Lhatoo says. "It suggests that, yes indeed, we should focus on [EEG suppression] as being something that could potentially help us identify patients that are most at risk, and thereby give them and their caretakers or relatives reason to heighten awareness."
Journal reference: Neurology, DOI: 10.1212/WNL.0b013e318258f7f1
If you would like to reuse any content from New Scientist, either in print or online, please contact the syndication department first for permission. New Scientist does not own rights to photos, but there are a variety of licensing options available for use of articles and graphics we own the copyright to.