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Hallucination – Are we the only ones “seeing” things or animals hallucinate, too?

Hallucination is defined as perceiving something that seems real but in fact it is not. Some references take it as a synonym for delusion. Both hallucination and delusion are a perception or belief that something seems real. However, the individual that experiences hallucination senses a vision, sound, or other perceptions later on denies it to be real based on evidence or logic. People with delusion, in contrast, believe something as real in spite of refuting evidence.  

hallucination
Hallucinations – a brain glitch – apparently could occur in animals, too. At least, according to a recent experiment on lab mice using optogenetics technique. [Img credit: Rick Harris (Flickr), by CC BY-SA 2.0]

Common causes of hallucination

Hallucination does not occur frequently. Nonetheless, it could be a common experience in individuals suffering from mental disorders like schizophrenia. Accordingly, >70% of those suffering from schizophrenia experience visual hallucinations whereas 60-90% believe they heard voices.[1] Additionally, other conditions that result in hallucinations include certain cases of Parkinson’s disease, Alzheimer’s disease, migraines, brain tumor, and epilepsy. Apart from these conditions certain medications – called “hallucinogens”  — have also caused hallucinations. For example, “Lysergic acid diethylamide” drug causes hallucination, in particular, by acting on serotonin (5-hydroxytryptamine [5-HT])-receptors.

High caffeine intake was also implicated to hallucinations. Accordingly, people who drink more than seven cups of instant coffee in a day turned out to be three times more likely to “hear voices” than those who drink less.[2] In this case, scientists explicated that high caffeine intake led to an increased cortisol (a stress hormone), which, in turn increased proneness to hallucinate.

People experiencing hallucinations may feel afraid from the perceptual experience. Seeing a vision like a seemingly floating light, hearing sounds like footsteps, or a crawling feeling on the skin that later on are construed as not real could really be scary.  

Neurobiological factors

Why does hallucination occur? In essence, hallucinations involve defects in the structure and function of the primary and secondary sensory cortices of the brain. In the case of Alzheimer’s disease, visual hallucinations are associated with grey and white matter abnormalities. “Seeing”, “hearing”, or “feeling” things is by chance spontaneous and also a transitory personal experience. Thus, understanding the biological phenomenon of hallucination remains a challenge to neurobiologists and scientists alike to this day.

Do animals hallucinate?

Do animals hallucinate, too? Scientists can hardly tell but studies implicate animal models such as lab mice making a head-twitch response (a hallucinatory behavior) when administered with hallucinogen.[3] However, some scientists argue it was not a compelling proof of such animals hallucinating.

Recently, though, a team of researchers from Stanford Medicine claim that they made lab mice hallucinate without injecting hallucinogen. Instead, they made use of optogenetics technique. In this case, they inserted light-sensitive genes into their brain. As a result, certain neurons tend to fire with particular light wavelengths. The genes would produce two types of proteins: one, causing neurons to fire when exposed to infared laser light and another, causing neurons to glow green when activated.[4]

The scientists, then, trained the mice to lick a water spout when exposed to a pattern of moving parallel lines (i.e. perfectly vertical or horizontal lines). Based on the green glow response of the visual cortex, the scientists knew which neurons were firing, thus responding. These neurons supposedly were the ones responsible for “seeing” the pattern of lines. [4,5]

Gradually, researchers dimmed the projections while triggering the target neurons with their special laser. Eventually, they stopped showing the line patterns and yet the mice would still lick the water spout when scientists hit the same target neurons with laser. The result therefore implies that the mice might have experienced “true hallucination”, seeing “ghost” line patterns.[5]

— written by Maria Victoria Gonzaga

References:

1  Fowler, P. (2015, August 27). Hallucinations. Retrieved from WebMD website: Link

2  Durham University. (2009, January 14). High Caffeine Intake Linked To Hallucination Proneness. ScienceDaily. Retrieved from Link

3  Can animals have hallucinations? – Quora. (2018). Retrieved from Quora.com website: Link

4  Stanford Medicine. (2019, July 18). Scientists stimulate neurons to induce particular perceptions in mice’s minds. ScienceDaily. Retrieved from Link

5  Specktor, B. (2019, July 19). It’s a Mystery Why We Are Not Constantly Hallucinating, Trippy New Study Suggests. Retrieved from Live Science website: Link