The Arzy Experiment: The Ghosts Are in Our Head

Have you ever felt like someone else was there, even when there wasn't? In this article, we're going to tell you about the common, imaginary perceptions we've all experienced. They tell a fascinating story about how delicate our brain is.
The Arzy Experiment: The Ghosts Are in Our Head

Last update: 08 June, 2020

The Arzy experiment has tried to prove something few have dared to before. For a long time, anything related to alterations in our perception, such as seeing shadows or feeling a presence, had been treated as paranormal things. But thanks to new brain exploration techniques, we can now study most of those things through a scientific lens.

Everyone has felt at least once that someone was watching them. Although you’ve probably found yourself doubting your own senses, that doesn’t make you “crazy”. This is because the brain is such a complex sense organizer that any alterations can lead to errors of perception. 

The Arzy experiment

Shahar Arzy is a professor at the Swiss Federal Institute of Technology Lausanne, Switzerland. In his research, he has proven that there’s a physiological aspect to hallucinatory states and brain areas involved in multi-sensory assimilation.

Feeling that someone else is near you when there’s no one there is something that has been described by both psychiatric patients and mentally stable people.

A woman with her hand on her face, feeling extremely distressed.

How did he carry out the experiment?

In his experiment, Arzy managed to induce a sensation in a subject that there was another shadow in the room. He did that through focal electrical stimulation.

Arzy conducted the experiment on a subject who had no history of mental problems. He stimulated the subject’s temporoparietal junction (TPJ). Each time Arzy stimulated that area, the subject began to feel that there was a shadow behind him.


Arzu repeated the experiment with the subject in other positions, but the shadow would always be in the same place with respect to the subject. That would suggest that the shadow is simply a projection of our own body. 

That would likely happen due to a multi-sensorial or sensory-motor processing alteration as a result of TPJ stimulation. What makes that even more interesting is that we used to associate TPJ with self-processing and the distinction between the self and others.

The role of the TPJ

As its name suggests, the temporoparietal junction is the part of the brain where the parietal and temporal lobes meet. The parietal lobe has a strong relationship with your body’s somatosensory and motor mapping.

The temporal lobe deals with language processing and creates connections with subcortical areas for emotional processing. But the meeting point between these two lobes, the TPJ, isn’t just a place for multi-sensory assimilation. It’s also related to self-processing cognitive aspects.

The TPJ and out-of-body experiences

The Arzy experiment focused on an intense activation of this part of the brain because it processes things such as:

In this experiment, when Arzy stimulated the TPJ, the subject didn’t experience the shadow as a projection of themselves. They experienced it as an outside presence. That phenomenon is due to the temporal lobe’s role in our linguistic sense of self.

The feeling that someone else is there

The first question you might be asking yourself after reading about the Arzy experiment is: how could we not be aware of that level of dissociation? Should we be? The experiment suggests that those sensations feel external to the subjects. The theory is that our brain’s “sense of self” is extremely fragile.

Any structural, electrical, or functional alteration can, therefore, lead to errors of perception. In other words, our sense of self, or our ability to differentiate between our perception of our own body and everything else, isn’t as stable as we used to think.

The role of the amygdala

The amygdala is a subcortical structure that’s part of the brain’s limbic system. This nervous system structure is a fundamental part of processing the emotional side of your experiences.

Any alterations caused by TPJ stimulation feel foreign to your brain, which is why your immediate reaction is fear. You’re not used to the feeling of experiencing your body as outside of yourself. That’s why the amygdala gives a negative emotional response, but that can often end up worsening the hallucinations.

According to the Arzy experiment, the amygdala plays a role in feeling like someone's there when they're not.

What kind of experiences can this sensory blurring lead to?

The experiences can be really varied. From a clinical point of view, the overarching experience would be “out-of-body experiences”. The most common ones are:

  • Feeling like you’re floating.
  • Looking at your body from outside yourself.
  • Feeling an external presence.
  • Extremely lucid thoughts and dreams. 

Are these experiences signs of mental illness?

As Arzy shows in his experiment, these dissociation experiences can happen just as much in subjects without any history of mental health issues.

But there are some conditions where people experience unusual things due to their brain alterations. For example:

  • Sleep paralysis. These are linked to hypnagogic and hypnopompic hallucinations. Sleep paralysis is when a person wakes up before they have control over their body. They’ll try to move, but can’t due to their muscle paralysis. As a consequence, their brain’s perception of movement is altered.
  • Epilepsy and intense migraines. Electrical brain alterations can cause similar effects to what Arzy described in his experiment.
  • Neurodegenerative diseases. Hallucinations are very common with these. The deterioration of nervous tissue leads to sensory assimilation problems. In most cases, elderly people experiencing this will associate the outside presence with a beloved friend or family member.

But there are also some cases where your sensory processing can be thrown out of whack, due to other reasons:

  • Excess stress.
  • Sleep deprivation.
  • Sensory deprivation.

Our brain is fascinating!

The Arzy experiment will surprise even the most skeptical readers. Our ability to recognize our own bodies is so much more complex and fragile than you’d think.

But that’s not all. Part of the problem is also that we’ve just considered these things “paranormal” for a long time. But now science is proving that it’s not always the case.

Seeing a shadow while you walk or thinking a mannequin is a person are similar to small hallucinations. They’re tiny errors of perception that don’t say anything about your mental health. But understanding more about why they happen can help us better understand ourselves.

This text is provided for informational purposes only and does not replace consultation with a professional. If in doubt, consult your specialist.