There’s no confusion about why LSD was made illegal in 1966. But if a trippy new study is right, the mystery is why more of us don’t spend the day hallucinating. Mice, at least, don’t need classic psychedelic drugs to trip out, according to a study published in Science in July of 2019. For them, lasers will do just fine. And only a teeny tiny minority of a mouse’s neurons are able to trigger a perception of something that’s just not there. Here’s how the example of weird science went down, and what it might mean for humans:

When lasers make mice trip

How does one make a mouse hallucinate? This cross-departmental research team from Stanford University researchers cut a window into a mouse’s skull. That hole exposed part of the visual cortex, the area of the brain that processes signals from the retina in the eye. The researchers used the opening to shine a light onto the mouse’s brain with a laser. As they expected, this made the mouse hallucinate. What the neuroscientists didn’t anticipate is that only a minuscule amount of neurons had to receive the laser signals for a mouse to “see” a non-existent pattern on the wall. This reaction was prompted when light from the laser hit just 20 or so of a mouse’s many million neurons.

The research on mice may have far-reaching implications in the study of human hallucinations, according to the team. “It’s quite remarkable how few neurons you need to specifically stimulate in an animal to generate a perception,” the study’s senior author, bioengineering professor Dr. Karl Deisseroth said in a statement. “A mouse brain has millions of neurons; a human brain has many billions. If just 20 or so can create a perception, then why are we not hallucinating all the time, due to spurious random activity?”

An optogenetic advance

This work is just the latest chapter for Deisseroth, who is known as the pioneer of optogenetics. His technology innovation lets researchers stimulate specific neurons in animals who are still moving around.  For this study, Deisseroth and his colleagues made the mice brains able to respond to a pulse of laser light by inserting a two-gene combo into their visual cortexes. The first gene caused neurons to fire if they detected a pulse of laser light that was a very specific color. The second encoded a protein that would glow when the mouse’s visual cortex neuron was active.

“Back in 2012, we had described the ability to control the activity of individually selected neurons in an awake, alert animal,” Deisseroth added. “Now, for the first time, we’ve been able to advance this capability to control multiple individually specified cells at once, and make an animal perceive something specific that in fact is not really there — and behave accordingly.”

How many people hallucinate?

A 2015 study led by The University of Queensland and Harvard Medical School didn’t claim people were in a constant state of hallucination. But it did conclude that one in 20 respondents had seen things no one else could at least once. The study included interviews with more than 31,000 people in 18 countries as part of a mental health survey  It’s important to note that these hallucinations happened to people who weren’t schizophrenic, didn’t have bipolar disorder, and weren’t drinking alcohol, taking drugs or dreaming at the time.

The prevalence of wide-awake hallucinations with no chemicals involved merely proves that this kind of brain activity is way more common than anyone previously suspected. According to a statement from co-author Dr. John McGrath, a professor at the Queensland Brain Institute in Australia, “We used to think that only people with psychosis heard voices or had delusions, but now we know that otherwise healthy, high-functioning people also report these experiences.”