Are you someone that has experienced voices in your head? Or maybe even visions of things that aren’t really there? You don’t have to have schizophrenia or take LSD to have a hallucination, and they don’t always have to be scary either. In fact, hallucinations are actually fairly common, and an everyday occurrence for many people around the world. But, what exactly is a hallucination? Technically, a hallucination is a “false perception” of reality and it can occur with a whole range of senses, but the most common ones are visual and auditory hallucinations.
While hallucinations are fairly common, we as a whole are still trying to understand whether there are different forms of hallucinations or whether there is only one type that takes different shapes, depending on the individual person. Normally our brain is good at distinguishing between a sound or image that is occurring in the outside world, and one that is just a product of our mind. But occasionally something can go awry, and that could be the case when it comes to hallucinating.
One major theory is that hallucinations are caused when something goes wrong in the relationship between the brain’s frontal lobe and the sensory cortex, said neuropsychologist Professor Flavie Waters from the University of Western Australia.
Interestingly, recently, a team of researchers from the University of Oregon in Eugene has strived to uncover more information about how hallucinations affect brain activity. Their new study which was conducted in mouse models has since revealed some surprises, which the investigators present in a paper that appears in the journal Cell Reports.
The researchers worked with mice that they injected with a substance called 4-iodo-2,5-dimethoxyphenylisopropylamine (DOI), a hallucinogenic drug that investigators often use in animal research. Like other hallucinogenics, including LSD, DOI interacts with serotonin 2A receptors, which are involved in the serotonin re-uptake process, though they may also play other, less well understood, roles in the brain. Once they gave the mice this drug, the researchers showed them several on-screen images and used various specialised methods to record neural (brain cell) activity in these particular rodents.
The team also discovered that contrary to what they had expected, the mice did experience reduced signalling between neurons in the visual cortex, which is the brain region largely responsible for interpreting visual information. The timing of the neurons’ firing patterns also changed throughout the study.
“You might expect visual hallucinations would result from neurons in the brain firing like crazy, or by mismatched signals,” notes senior author Cris Niell, who is an associate professor at the University of Oregon. He then continued, “We were surprised to find that a hallucinogenic drug instead led to a reduction of activity in the visual cortex.”
During the study, the in-house researchers also discovered that the visual signals that were sent to the visual cortex were similar to signals sent in the absence of the drug, meaning that the brain still received the same visual information, however it was unable to process it correctly.
“Understanding what’s happening in the world is a balance of taking in information and your interpretation of that information. If you’re putting less weight on what’s going on around you but then over-interpreting it, that could lead to hallucinations.”
According to the researchers, this suggests that the same drugs alter brain activity in both animals and people. However, future studies should pay closer attention to the animals’ reactions to visual stimuli in the presence versus the absence of drugs.
“I don’t feel like we’ve necessarily found the smoking gun for the entire underlying cause of hallucinations, but this is likely to be a piece of it,” Niell says.
“The data we’ve collected will provide a foundation for additional studies going forward. In particular, we plan to use genetic manipulation to study particular parts of this circuit in more detail,” the senior researcher added.