I have investigated a few hauntings and ghostly phenomenon. In reality I was investigating the ghost-hunters who were investigating alleged hauntings. A few patterns quickly emerged. One is that actual sightings and reported events tended to cluster around a few individuals, or even one individual. Another is that such events never occurred when there was a skeptical investigator present.

Also very interesting, however, was that the real interesting stuff did not start happening until the early morning hours, such as 2 or 3 in the morning. Ghost hunters invent lore to explain this phenomenon (the haunting hours), but my hypothesis is that this is the perfect time for sleep deprivation to be taking its toll.

When the evidence for a phenomenon is reported subjective experience, we need to ask if those experiences are being generated by something happening outside the person, or just inside their brain. When the brain is sleep-deprived, it can become glitchy. We can fall asleep briefly without realizing it. We can start to slide into a dream state, and might even experience a fusion of the waking and dream state, even to the point of hallucinations.

One common report is the feeling of presence (FoP) – the sense that there is another entity in the room with us, although we can’t quite see it as it is lurking just at the edge of our vision. I have experienced this myself, during hypnagogic episodes when I am very sleep deprived.

Neuroscientists have recently published a paper exploring the possible neurological causes of the FoP. First they studied patients who report FoP following a neurological injury, such as stroke. Lesion analysis is one method used to explore the correlation between neuroanatomy and mental phenomena.

They found consistent correlations with injury to the temporoparietal, insular, and especially frontoparietal cortex. From this they hypothesize that the FoP is the result of glitchy processing of sensory information as it relates to our sense of our own body. These are called own-body illusions.

This fits well with our current understanding of how our brains construct our sense that we exist, occupy our bodies, and own and control our bodies. While we take these sensations for granted, they do not simply emerge from the fact that we are our bodies. The sense of self, physical location, and ownership are all actively constructed by the brain. The primary method used by the brain to construct these sensations is to compare in real time different sensory streams, vestibular sensation (sensing acceleration and position relative to gravity), proprioception (the sense of where our body is in three-dimensional space), tactile sensation, motor sensation (sensing the contraction of our own muscles) and vision. I want to move my arm, I see my arm move, feel it move, and receive feedback from the muscle indicating they are contracting – all is good, and this constructs the subjective experience that I own and control my arm.

When these various sensory streams get out of sync, even by a little bit, that can create various self-illusions, such as out-of-body experiences. Researchers in the lab can generate OOB sensations, or the sensation that we occupy a dummy or a virtual avatar.

The researchers in the current study therefore tried to induce a FoP in the lab by exploiting the same principles. They studied 12 healthy subjects with a robot-slave device. The subjects had a control in front of them that controlled a robot arm behind them. When they moved the control the robot arm behind them would touch their own back. When the control and robot arm were in sync, this produced the illusion that the subjects were massaging their own back.

The experimenters then delayed the robot arm by about 500 milliseconds. This setup disrupted the illusion of control over the robot arm and generated a FoP – the subjects felt one or more presences in the lab with them, or that they were being watched. Some also sensed that they were moving backwards, toward the source of the sensation. Two of the 12 subjects found the sensation disturbing enough that they asked for the experiment to immediately end.

Conclusion

While this is one small study, it is a compelling demonstration and it is in line with a larger body of prior research. The consistent pattern emerging from this research is that the brain uses the synchronization of various sensory streams to construct the various aspects of our sense of self. This process can be disrupted by injury, disease, stress (such as sleep deprivation) or experimental setups.

When these various circuits are disrupted or confused by any of the above, they can produce illusions of self, including out of body experiences, occupying other locations or bodies, phantom limbs, alien-hands, or a feeling of presence.

The deeper lesson from these lines of evidence is that we cannot trust our own experiences. When someone tells me of an unusual experience they had, they are relating a constructed and reconstructed memory of flawed and filtered perceptions that were themselves constructed into an internal model of events. Given what we currently know about neuroscience, it would be naive to interpret the experience as solid evidence for a real phenomenon, especially a real and highly unusual or even supernatural phenomenon.

We should be especially cautious with experiences that are typical of those we can now reliably reproduce in the lab.

External objective corroborating evidence would be required to even take the hypothesis seriously that such experiences are the product of an external phenomenon rather than just a glitchy brain. While ghost hunters often claim they have such evidence, so far they have only produced very uncompelling anomaly hunting.

With the current state of the evidence, the neuroscientific explanation for ghostly experiences seems far more likely.