Why hallucinate when tired

It was as if I was on Fear Factor, trapped in a glass case full of spiders and centipedes and all sorts of creepy-crawlies.

Partway through the hour-and-a-half class, the itchiness became all I could concentrate on. The itchiness became unbearable as I scratched at my thighs under my desk. I started jiggling my legs and stamping my feet to make the itchiness go away, but nothing was working. I felt as if there were millions of needles stabbing me in the legs and I was afraid I was going to start crying in the middle of the lecture. I got up and went into the hallway to get my legs moving.

Out in the hallway, the itchiness quickly dissipated, much to my relief. I went back inside, took my seat, and assumed everything was fine. I tried to concentrate on what my professor was saying, but when I looked at her, something strange happened. Her short pixie cut began to grow. Her brown hair lengthened out to her shoulders, then her chest, then down towards her waist, all in a matter of seconds. My eyelids no longer felt heavy as I stared at her, wide-eyed with shock.

This is impossible, I told myself. But it looked so real. I had just witnessed something magical. I looked left and right to my classmates, but they were all staring straight ahead, completely unfazed. I looked back at my professor. Her hair was short again. What just happened? I wondered. Then, a man entered the room. He walked past all of us students and headed straight for our professor. Something bad was about to happen. Results from the fMRI indicated that this was due to defective top-down visual processing.

In another study at Brookhaven National Laboratory, fourteen healthy adult men were asked to perform a similar visual attention task while undergoing fMRI in the well rested state and again in the sleep deprived state. In the well rested state, the harder the task was, the more the top-down network was activated and the bottom-up network was deactivated. But in the sleep deprived state, this pattern fell apart: top-down biasing was no longer strengthened in comparison with bottom-up visual processing.

A healthy brain is complex; a hallucinating brain is mysterious, perplexing. No two hallucinating brains are exactly alike. In mental states that are characteristically prone hallucinations, however the brain consistently has trouble making predictions about visual input. In the absence of sensory input, your brain's own world making machinations keep on truckin' nevertheless. So that pirouetting polar bear that appears at your bench in the middle of an all-nighter in the lab?

Read the original post and comments. Learn more about giving opportunities for the neurosciences at Stanford. Skip to content Skip to navigation. Wu Tsai Neurosciences Institute. Search form Search. Why do humans hallucinate on little sleep? Hollow Mask Illusion. Feb 19 NeuWrite West. By Whitney Heavner What do psychosis, psychedelics and sleep deprivation have in common? Vivid dreamlike experiences—called hypnagogic or hypnopompic hallucinations—can seem real and are often frightening.

They may be mistaken for nightmares, and they can occur while falling asleep hypnagogic or waking up hypnopompic. During these hallucinations, you may feel someone touching you, hear sounds or words, or see people or creatures near you or even lying in your bed. Relapse in schizophrenia.

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