Using a flashlight to make someone’s heart race might not be the most effective method, but replace the flashlight with a laser and the subject with a zebrafish, and the scenario becomes unexpectedly intriguing.
Physicist Xiaoshuai Liu from Guangzhou University in China explains that the journey of a light signal from the ear to affecting the heartbeat is more complex than it seems.
Liu and his team have achieved this remarkable feat, and it’s as fascinating as it sounds.
“People often associate light with vision and sound with hearing, which seems natural. However, fundamentally, sound is a form of vibration,” Liu shared with ScienceAlert.
“Inspired by traditional music therapy, which uses rhythmic sound to influence heart rate, we wondered if we could create ‘light music’ with precisely programmed light beams to regulate heart rates,” he said.
The ear, a delicate organ, can detect tiny vibrations due to structures like otoliths—small, stone-like calcium carbonate crystals. These move in response to sound or motion, stimulating sensory cells in the ear.
Optical tweezers have been used by scientists to manipulate tiny objects for years, using radiation pressure to apply force to small items.
The otoliths in zebrafish larvae are particularly small, integral to the fish’s ability to detect sound and motion.
This made them an ideal target for tools that manipulate microscopic objects. If an optical trap could move an otolith without sound, researchers could bypass the initial hearing step.
“We aimed to challenge the typical light and sound associations, exploring if organisms could ‘hear’ light,” Liu explained.
“Once we abandon conventional thinking, any oscillating method can generate sound equivalents.”
So, the researchers experimented. They used optical tweezers to move individual otoliths in live zebrafish larvae while monitoring brain activity. The auditory regions became active, indicating mechanical movement was interpreted by the fish’s hearing system.
Is the fish ‘hearing’ light? That’s more complex to determine.
“The ancient Chinese philosopher Zhuangzi once said, ‘You are not the fish, how do you know the fish’s joy?'” Liu said. “Similarly, we cannot directly communicate with zebrafish to confirm whether they are consciously ‘hearing’ the light.”
Liu noted, “We can’t directly converse with zebrafish to confirm if they consciously ‘hear’ light.”
However, researchers observed a significant increase in activity in auditory neural centers during optical stimulation.
Additionally, when researchers moved a fish’s otolith, its heart rate increased.
During one test, a resting heart rate of about 2 beats per second rose to approximately 2.7 beats per second during stimulation, gradually returning to baseline afterward.
Targeted otolith oscillation could increase the heart rate by about 50 percent, researchers found.
Using optical tweezers for precise control of otolith movement, researchers could recreate music patterns. By altering oscillation amplitude, frequency, and timing, they mimicked loudness, pitch, and rhythm.
This discovery led the research in a new direction.
“Realizing we could use light to mimic musical stimuli and affect heart rate, it was natural to explore correcting abnormal cardiac rhythms,” Liu told ScienceAlert.
“This led to experiments on rescuing drug-induced arrhythmias.”
Researchers used drugs to induce three different types of abnormal heart rhythms in zebrafish larvae, then applied their optical musical stimulation.
In fish with slow heartbeats, the stimulation nearly normalized heart rates.
For fish with uncoordinated heart chambers, normal coordination was restored in six of seven cases.
And in fish experiencing abnormal heart pauses, normal rhythms resumed in five of seven cases.
Remarkably, some improvements persisted even after stimulation ceased.
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Liu remarked, “The most surprising result was that this method could modulate heart rate and rescue drug-induced arrhythmias.”
“The ability of an optical stimulus, through the auditory pathway, to restore normal cardiac rhythm in a disease model surpassed our expectations and may lead to future therapeutic applications.”
These possibilities, however, are distant. Liu describes the study as an early proof-of-concept, with neural signal mechanisms and potential application in larger animals still unclear.
“We view this work not as a definitive answer, but as an invitation to explore a new frontier at the intersection of optics, auditory neuroscience, and cardiac physiology,” he told ScienceAlert.
The findings have been published in Nature Communications.
This article was fact-checked by Fiona MacDonald and edited by Fiona MacDonald. While we pride ourselves on our process, we are only human. If you spot a mistake, please let us know.
