Hallucinatory Palinopsia

Submitted by palmergrabner on Tue, 11/22/2022 - 17:32

In a previous blog post, we discussed palinopsia of the illusory type (read more here). Hallucinatory palinopsia consists of the palinopsia types of formed image preservation, patterned visual spread, categorical incorporation, and scene preservation. This formed image preservation differs from the illusory version in that it lasts much longer. While illusory palinopsia momentary image preservation normally lasts for a few seconds to a few minutes at most, the hallucinatory version can last for days. Patterned visual spread is where the pattern of one object in the visual field is transferred to other parts or the whole visual field. For example, the lines on a ruled piece of paper might be transferred to a wall, shoes, or across one's entire field of vision. 

Image 1: This is an example of formed image preservation. The hand is fixed at that position in the visual field even in the absence of the stimuli. 

Categorical incorporation is similar to patterned visual spread, but it involves a singular characteristic of an object being transferred to other similar objects. For example, if one saw a person with pink hair, that trait would be incorporated into everyone else that they see, even if it's not there. Finally, scene preservation is when one observes a scene or action, such as itching their arm, and then sees the same action superimposed onto their visual field a few minutes later. Unlike psychosis or schizophrenia, people that have hallucinatory palinopsia, for the most part, do not believe that their hallucinations are real. This distinction separates hallucinatory palinopsia from being something psychiatric. 

Image 2: This is an example of categorical incorporation. The spire of the building is transferred to other buildings in the scene. 

Unlike illusory palinopsia, hallucinatory palinopsia is caused by brain damage or the sporadic activation of neurons in the visual memory system. This stimulation causes the lingering objects, images, or effects to reappear in the visual field. The main cause of spontaneous activation is epilepsy, while the main cause of damage is brain lesions. Epileptic seizures cause epileptic discharges in the neurons in the visual pathway. This leads to their excitation which can manifest as all types of hallucinatory palinopsia. On the other hand, brain damage caused by lesions (these can arise from cancer, brain surgery, etc.) leads to cortical deafferentation or focal cortical irritation. Cortical deafferentation results in a neuron, normally in the visual memory system, becoming hyperexcitable. The hyper-excited neuron can then have an easier time getting activated. This results in the memories contained in the brain network getting incorporated into the visual field. 

Image 3: This is an example of a tumor in the occipital lobe that can lead to hallucinatory palinopsia. 

There are no treatments that target hallucinatory palinopsia directly; instead, similarly to illusory palinopsia, the underlying issue must be treated. If the underlying cause is due to seizures, this could include managing someone's blood glucose levels, carnitine levels, or looking for tuberculomas. If the underlying issue is due to a lesion or brain damage to the posterior part of the brain, then the treatment would vary drastically depending on the nature of the lesion. For example, a provider would treat a brain lesion from surgery much differently than they would treat a tumor. 

 

Overall, hallucinatory palinopsia types last longer than illusory palinopsia and have pronounced differences in the ways that affect one’s perception. Categorical incorporation, scene preservation, patterned visual spread, and image preservation all involve issues with the visual memory system that cause previously experienced stimuli to reappear even when they are not there. These hallucinations differ from those found in psychosis and other psychiatric disorders in that those with hallucinatory palinopsia do not lose touch with reality. They know that their perception is inaccurate. 

 

Sources: 

https://doi.org/10.1016/j.survophthal.2014.06.003

https://tinyurl.com/yc2re3zx

 

 

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