Pulse Halo

In the minutes between an emergency and the hospital, a patient's level of consciousness can slip. The Pulse Halo is a lightweight band for paramedics that sits around the head, reads the brain's activity, and delivers gentle electrical stimulation at gamma frequencies to help keep the patient alert and responsive until they reach care.

The idea

The brain runs on rhythms. Fast gamma rhythms, around 30 to 100 Hz, are closely linked with alertness, attention and conscious awareness, while deep sleep and sedation are dominated by much slower waves. The Pulse Halo is designed to support the fast rhythms of wakefulness when a patient is at risk of drifting into unresponsiveness.

It works in a closed loop, which means it listens before it acts and keeps listening while it acts:

1. Read. Sensors on the halo, with clips on the earlobes, pick up the brain's electrical activity (EEG) and the patient's pulse.
2. Interpret. Onboard software tracks the patient's brain state in real time: alert, drowsy or sliding toward unresponsiveness.
3. Respond. Electrodes resting over the bones of the skull deliver a mild alternating current, at a fixed gamma frequency or a dynamic frequency that keeps adjusting to the brain state it reads.
4. Report. The paramedic sees a simple live readout of the patient's brain state and every stimulation the halo has given, and that record travels with the patient into the hospital.

The science it builds on

Transcranial alternating current stimulation (tACS). tACS passes a weak, rhythmic current through the scalp to nudge brain oscillations toward a chosen frequency. Unlike muscle stimulation (EMS), which makes muscles contract, tACS targets brain rhythms and is typically felt, if at all, as a faint tingle. Gamma-frequency tACS is being studied for attention and in clinical trials with patients in disorders of consciousness.

Closed-loop stimulation. Researchers have built systems that read EEG and adjust stimulation in real time, matching the timing of each pulse to the brain's own rhythm. The Pulse Halo applies that idea to a portable, emergency setting.

Ear clips. Earlobe clips are a standard part of EEG, serving as reference points that make scalp readings cleaner. They are also a common spot for measuring pulse and blood oxygen. On the halo, they do both jobs.

How it is designed

• Halo band. A flexible, adjustable band that positions electrodes at set points over the skull, so a paramedic can fit it in seconds.
• Combined sensing and stimulation. The same band carries the sensors that read the brain and the electrodes that stimulate it.
• Ear clips. EEG reference plus pulse and oxygen monitoring.
• Two stimulation modes. A fixed gamma mode, around 40 Hz, and a responsive mode where the frequency adjusts continuously to the patient's brain state.
• Built for the field. Battery powered, rugged, quick to clean, and simple enough to use in the back of a moving ambulance.

Open questions we are working on

• Not hiding the warning signs. To paramedics, a patient's level of consciousness is a vital sign. A falling level can be the first sign of bleeding in the brain, low oxygen or another emergency. The halo must never mask that signal. This is why every reading and every stimulation is logged and shown to the crew, and why the halo is designed to support assessment, not replace it.
• Reading while stimulating. Stimulation creates electrical noise that can drown out the EEG it is trying to read. Separating the brain's signal from the stimulation is a central engineering challenge for any closed-loop system.
• Noise in the field. An ambulance is full of movement and electrical interference. Clean signals under those conditions take careful electrode and filter design.
• Who it is for, and who it is not. Clear rules on where it should not be used, such as seizures, skull fractures, open head wounds and implanted devices, developed with emergency physicians and neurologists.
• Does it work? Whether stimulation in this setting measurably improves responsiveness, and in which conditions, can only be answered through careful clinical study.

Why it matters to us

Paramedics carry tools to support the heart and the lungs, but very little that lets them see, moment to moment, what is happening in the brain. Even before stimulation is proven, a halo that gives crews a live window into brain state could change how patients are monitored on the way to care. Supporting the people who look after others in their worst moments is stewardship at its most direct.