Hallucinations are a brain malfunction in which the sufferer experiences false images or sounds that do not exist in the real world. Hallucinations can be caused by a number of different underlying problems, but they are generally very unpleasant and disorienting for people who experience the malfunction. They’re not confined only to seeing a ghost in the dark or hearing a creepy “avenge me” at night; they can come in all tactile sensations that the brain can produce by accident.

For example, a tactile hallucination is when you feel something crawling on your skin, though nothing is there. Sometimes the hallucinations can be simple, such as seeing a pattern of colors obscuring the visual field. Other times they can be immensely complex, such as seeing buildings, people, or even imaginary animals and creatures. The level and type of hallucination depend entirely on what region of the brain is malfunctioning or which signals have been lost to injury or disease.

Hallucinations are not to be confused with an illusion, which is simply the distortion or misinterpretation of real perception. For example, a magician can create the illusion of “levitation” by hiding the wires that lift him off the ground. Without seeing these, the brain wrongly assumes that the magician is levitating through his own power, a common illusion. A hallucination, on the other hand, would be seeing a magician who is not actually there. While some hallucinations can be pleasant, others can often turn dark or scary or generally be disruptive to everyday life.

In general, there are three basic issues that can cause hallucinations. They include (1) diseases of the eye, (2) diseases within the nervous system, and (3) in some cases the use of drugs.
Brain Issues. Whenever the chemistry of the brain is affected in some way, there are changes in patterns of thought and the general way the brain perceives and analyzes the senses. If something disrupts the visual cortex, for example, we can easily misinterpret visual information and our brain will produce a hallucination. We know that there are mechanisms involved that include neurotransmitters and feedback between nerves, but the complexity of the brain makes it hard to pinpoint where a hallucination originates.

There are many brain diseases that include hallucinations as symptoms. Schizophrenia and delirium are both highly associated with hallucinations. Schizophrenics often experience auditory hallucinations, such as a voice that seems to be coming from outside their body. Many other brain diseases also cause hallucinations, likely because the normal audio or visual systems are interrupted and the brain must fill in the gaps somewhere. Delirium is another mental illness that often leads to hallucinations and a variety of other symptoms. Delirium can be caused by everything from high fever to alcohol withdrawal, yet a third of all people with delirium will experience visual hallucinations.

Strokes and other injuries that cause brain damage are also highly associated with hallucinations, in part because they change the very nerves that must process and deal with external signals. When a stroke happens in the occipital lobe, the hallucinations will likely be visual, as this area is usually used to process visual cues. If the damage happens within the temporal lobes, auditory hallucinations are more common because these areas are largely in control of auditory processing.

People with severe migraines often experience “Alice-in-Wonderland” syndrome, a type of visual hallucination in which objects are distorted, gaining or losing size as the patient views them. In fact, part of the masterpiece behind Carroll’s story is Alice’s constantly changing perspectives. Modern doctors would likely diagnose Alice as having severe hallucinations.

Many people experience hypnagogic (sleep- inducing) or hypnopompic (exiting sleep) hallucinations that occur as their minds slip into or out of reality while they sleep. Further, seizures are largely related to hallucinations, in part because they change the chemistry and processing within various regions of the brain. Many seizure patients have reported olfactory hallucinations, such as bad smells, likely indicating that there is some damage within the olfactory lobes of the brain.

Drug-Induced Hallucinations.

While we don’t understand all of the mechanisms behind drug-induced hallucinations, humans have been using a number of plants, fungi, and animal derivatives to induce hallucinations throughout history.

There are many street drugs that cause hallucinations, in part because they stimulate or reduce activity in various regions of the brain. These drugs include LSD and PCP, though there are many legal medicines that have hallucinations as an adverse side effect. Many of these drugs regulate or control various chemicals that nerves use to communicate. Interrupting these signals can lead to many types of hallucination, from visual to olfactory. Interestingly, some of the drugs designed for Parkinson’s disease affect the dopaminergic network, which in effect causes hallucinations in some patients.
Psychedelic drugs typically work by affecting receptors in your brain that alter the way the nerves communicate with each other. When stimulated by drugs, certain regions of your brain start firing more than normal and can lead to the end user experiencing patterns, colors, or even full- blown visual hallucinations like objects, animals, or people. Research has suggested that hallucinations are largely caused by interactions they have within the brain’s cortex, which is the area that processes incoming signals. Many of these drugs activate 5-HT2A receptors, which are normally triggered by natural chemicals within the brain. In fact, some hallucinations are caused because the receptors are not just turned “off” or “on” but are put into a completely different mode of activation that the brain is not used to. This likely causes the hallucinogenic effects of many drugs, as your brain tries to put a reality to its new internal mechanisms.

Eye Issues. Humans are very visual creatures, and our brains have developed complex pathways for interpreting the signals we receive from our eyes. In fact, it is thought that hallucinations are only slightly different than visualization, which is the ability to see images within your mind. When your eyes become damaged due to disease or an accident, your brain sometimes overcompensates for the lack of information and starts filling in the gaps with hallucinations. This been documented in many eye diseases such as macular degeneration.

A common disease with hallucinations is Charles Bonnet syndrome, named for a man who suffered hallucinations after being blinded in both eyes by cataracts. Charles Bonnet syndrome is a form of hallucinating that is caused specifically by the loss of visual signals. Typically, these forms of hallucinations will only be visual, as there is still input from the ears. Without the input from the eyes, the brain fills in the missing information with a “best guess” with previous images.

This syndrome has also been found in other eye diseases, such as macular degeneration. In fact, our brains are so good at hallucinating that anyone can try this at home. Simply tape two ping pong ball halves over your eyes so they can still open but you can see no images. After only a few hours in this condition, many people start to hallucinate visual objects, color, or even people.

In fact, psychologists have studied this phenomenon in the lab. By placing healthy volunteers in a sensory-deprivation room, they were able to determine that it only takes around minutes of deprivation for most people to start hallucinating sounds, images, and tactile sensations. Not only this, but most of the volunteers felt a depressed mood or paranoia. This supports the conclusion that our brains rely on sensory information not only to build a picture of reality but also that the sensory information itself is helping us maintain a happy and healthy mind.

This is further evidence that hallucinations are an extension of the brain’s ability to visualize, only the visualization replaces the absent sensory signals, such as eyesight. Researchers call this ability “faulty source monitoring,” as the brain forgets where the signal came from and thus believes that the visualization came from outside of the body.

Psychologist Oliver Mason of the University College London summed up the situation in this way: “Basically, something that actually is initiated within us gets misidentified as [being] from the outside.”
This seems to show that hallucinations in and of themselves are not a disease but simply the symptom of losing access to a sensory signal. The separation between visualization and hallucination is a fine line that is normally separated by the reality of information we are receiving through our eyes. Without that information, visualizations can become stronger and eventually the brain replaces the lost signals with creations of its own. For example, people have also experienced sound hallucinations after losing their hearing, as the brain malfunctions in a similar way and tries to replace the lost signal.

Although we don’t like to admit it, sometimes our memories are flat-out wrong.

For instance, suppose you are in a fight with your significant other about whose turn it is to wash the dishes. You feel that your memory is a steel trap and you did the dishes for the past week, so obviously it is their turn. Yet they swear the same thing. Whose memory is inaccurate, and how can you even begin to determine that?

Obviously one party’s memory is incorrect, or both of them are. And yet there is such confidence that each person’s representation of the past is true and unflawed. What’s happening when a small conflict like this occurs? Is someone trying to maliciously lie or bend reality to suit their own needs? What about when this happens with larger consequences, such as with testimony in a lawsuit? It wouldn’t be inaccurate to say that our existences are the sum of our memories, and yet they can be so fragile, fickle, and outright inaccurate.

In most cases, this is due to a malfunctioning of our memory systems. What else might be affected by these errors besides the dishes? A lot! You would be right to question some of the bigger events of your life and if they happened the way you think they did.
Our memories are an unreliable narrator at best, and even if they remember the concrete, black and white events, they will inevitably be altered by our individual perspectives and biases. For instance, you may feel that you’ve done the dishes for days in a row, but in actuality you only feel that way because there is a long history of squabbling over household chores. Our memory is its own editor and director of photography and will create its own version of reality. It gets us into trouble, causes misunderstandings, and makes us doubt ourselves. It works for us, and this is a distinctly different function than being accurate.

It’s beneficial to first take a quick look at the structure of memory and how it works before discussing the design flaws. Memory is how we store and retrieve information for use, and there are three steps to creating a memory. An error in any of these steps will result in information that is not effectively converted to memory—a weak memory or the feeling of “I can’t remember his name, but he was wearing purple…” The three steps are as follows: 1. Encoding 2. Storage 3. Retrieval

Encoding is the step of experiencing information through your senses. We do this constantly, and you are doing it right now. We encode information both consciously and subconsciously through all of our senses. If you are reading a book, you are using your eyes to encode information. The more attention and focus you devote to an activity, the more conscious and deep your encoding becomes. This gives information the best chance to continue along the path to becoming a memory and consequently whether that information stops at short-term memory or makes it all the way to long-term memory. However, over longer periods of time, we are even able to subconsciously encode information into long-term memory.
Storage is the next step after you’ve experienced information with your senses and encoded it. What happens to the information once it passes through your eyes or ears? The information goes to a processing center that determines what happens to it—its path is determined by how deeply encoded it was through focus, repetition, or practice. There are three choices for where this information can go, and they determine whether it’s a traditional memory—a piece of information that you consciously know—or something you won’t remember the next day or even hour.

There are three places the information can end up, and thus we can say there are three memory systems: sensory memory, short- term memory, and long-term memory. Sensory memory is the first level of memory, and it stores information for only an instant and as long as it is important. This is how a piece of sand feels to sit on. Short-term memory is what we’re most familiar with, and it can retain “seven plus or minus two” pieces of information for roughly seconds on average. This is the phone number of a restaurant you are researching for dinner. Long-term memory is where memories become a real, physical manifestation as a result of neurons making connections. This is your home address or social security number.

The last step of the memory process is retrieval, which is the act of recalling information or remembering it. This is when a piece of information is actually useful—when it can be recalled at a later point either consciously or unconsciously. Again, how easily you can retrieve it depends on how deeply the information was encoded in the first place and which memory system it ended up in.
If the information was deeply encoded, you might be able to recall it from nothing. If it was something you should have rehearsed a bit more, you might need a cue or reminder to call up the information. Most memory isn’t necessarily focused on retrieval—it’s focused on the storage aspect and what you can do to shoehorn memories from sensory and short-term areas into long-term areas or at least retain information long enough so we can pass a test or secure a promotion.

Memory may seem relatively simple, but there are many moving parts and at least three steps where the process can go wrong—and that’s with me skipping most of the minutiae. All of this adds up to tell us exactly how inaccurate and faulty our recollections can be. You may have what you think is your true view of the world, and it can be disconcerting to realize that what you think you know is completely inaccurate.

Even a relatively minor phenomena you’ve probably dealt with known as tip of the tongue (TOT) is an insight into the complexity of memory. This occurs when you know what you wanted to say but your mind suddenly runs blank or when you walk into a room and realize you have no idea why you did so. We might confidently feel that we know something but come up empty when we seek to recall specific details. It probably occurs to me on a daily basis.

Psychologist William James first coined the term TOT in 1890: “A sort of wraith of the name is in it, beckoning us in a given direction, making us at moments tingle with the sense of our closeness and then letting us sink back without the longed-for term.”

For the next few decades, it was noted as a peculiar trait of memory. It wasn’t until 1966 that researchers from Harvard University studied why knowledge appears to be at our fingertips and yet so far away. In the 1966 study, researchers read aloud word definitions to participants and then asked them to recall the defined words. They found that there was a very specific set of behaviors they engaged in if they were in a TOT state—they could remember what the word was and perhaps even what it meant. They could also provide synonyms for it and words that rhymed with it. However, they were still not always able to recall the exact defined word.

If this feeling feels like torture to you, it’s because the researchers accurately characterize it as the feeling of imminent recall. If we keep hunting around for it, we might find it. We might also never come up with the trigger for it, despite ruminating for hours or days. The sensation of knowing that you know something yet don’t know it at the moment is supremely frustrating. It’s like being on the verge of a satisfying sneeze for hours.

100 A study from McMaster University has posited that the TOT phenomenon occurs because specific words get lost in translation from the brain to the mouth. The brain translates a thought or memory from an abstract, intangible concept into a word, and then the word is sent to our sensory systems to make the proper sound. This is the process of expressing anything via speaking, and it’s far more complex than we give it credit for. This means information stored as a memory is now also subject to the moving parts of the language expression system.

The McMaster researchers put participants into TOT states by asking, “What do you call the sport of exploring caves?” This is something the participants vaguely knew but were typically unable to correctly recall. They were given time to think, and if they didn’t produce the word, the researchers provided them with the answer. Days or weeks later, the participants were asked the same question and were shown to exhibit the same TOT states. They pointed to this as proof that TOT behavior is something that 101 can be reinforced, just like a memory. In other words, if you make the same error and fall into a TOT state, you are likely to do it again with that same word. Other hypotheses about the TOT effect are that the brain has limited capacity, and anything that isn’t immediately rehearsed or introduced into long-term memory exists in a hazy, cloudy region where TOT is just a byproduct. You might know that you know the information, but you may have neglected to rehearse sufficiently to actually be able to recall it without a strong clue, such as “The color rhymes with blorange.” Essentially, this is a failure in memory encoding or memory retrieval. With memory encoding, the information simply may not be there, while with memory retrieval, the information is there, but there may be too many distractions or barriers for you to effectively recall it.