Hallucinatory palinopsia is a subtype of

palinopsia Palinopsia (Greek: ''palin'' for "again" and ''opsia'' for "seeing") is the persistent recurrence of a visual image after the stimulus has been removed. Palinopsia is not a diagnosis; it is a diverse group of pathological visual symptoms with a wid ...

, a visual disturbance defined as the persistent or recurrence of a visual image after the

stimulus A stimulus is something that causes a physiological response. It may refer to: *Stimulation **Stimulus (physiology), something external that influences an activity **Stimulus (psychology), a concept in behaviorism and perception *Stimulus (economi ...

has been removed. Palinopsia is a broad term describing a group of symptoms which is divided into hallucinatory palinopsia and illusory palinopsia. Hallucinatory palinopsia refers to the projection of an already-encoded visual memory and is similar to a complex visual hallucination: the creation of a formed visual image where none exists. Hallucinatory palinopsia usually arises from posterior cortical lesions or

seizures An epileptic seizure, informally known as a seizure, is a period of symptoms due to abnormally excessive or neural oscillation, synchronous neuronal activity in the brain. Outward effects vary from uncontrolled shaking movements involving much o ...

and can be the presenting symptom of a serious neurological disease. Hallucinatory palinopsia describes afterimages or scenes that are formed, long-lasting, high resolution, and isochromatic. The palinoptic images are not typically reliant on environmental parameters and often present with homonymous visual field deficits. Hallucinatory palinopsia occurs unpredictably and the persistent images can appear anywhere in the

visual field The visual field is the "spatial array of visual sensations available to observation in introspectionist psychological experiments". Or simply, visual field can be defined as the entire area that can be seen when an eye is fixed straight at a point ...

, regardless of the location of the original

. A patient will often have only a few episodes of hallucinatory palinopsia. Visual

perseveration Perseveration, in the fields of psychology, psychiatry, and speech-language pathology, is the repetition of a particular response (such as a word, phrase, or gesture) regardless of the absence or cessation of a stimulus. It is usually caused by a ...

is synonymous with palinopsia. The term is from Greek: ''palin'' for "again" and ''opsia'' for "seeing".

Signs and symptoms

Formed image perseveration

Formed image perseveration refers to a single, stationary object that remains fixed in one's visual field. These pathological afterimages look realistic and have the same color and clarity as the original stimulus. The palinopsia lasts at least 15 seconds, but may persist for hours or days. For example, a patient sees a cat, and an identical copy of the cat remains fixed in the field of view for 30 minutes. A patient commonly complains of the perseverated fingers of an examiner. These afterimages often occur in visual field deficits but may occur anywhere in the visual field, regardless of the location of the original stimulus. The generation of the afterimages is not affected by external conditions such as the length of fixation, brightness of the stimulus, contrast, or motion. The palinoptic image can appear immediately after seeing the original image or may be delayed in time.

Scene perseveration

Scene perseveration refers to seeing a previously-viewed, short stereotyped scene that continuously replays for several minutes. For example, a patient might view a person throwing a ball, and then an hour later, perceives the same action sequence repeated many times. The palinoptic scene usually has the same color and clarity as the original. Our understanding of

visual memory Visual memory describes the relationship between perceptual processing and the encoding, storage and retrieval of the resulting neural representations. Visual memory occurs over a broad time range spanning from eye movements to years in order ...

considers a short scene as a unit of memory, similar to an image, thus scene perseveration is probably mechanistically related to formed image perseveration.

Categorical incorporation

Categorical incorporation refers to seeing an object or feature and superimposing it onto comparable objects or people. For example, after seeing a person wearing a hat, that same hat is seen on each subsequent person seen. Or a person sees the spire of a building and then incorporates it to the top of other structures seen. The palinoptic images have the same characteristics as the original stimulus, and episodes of categorical incorporation usually last a few minutes. Categorical incorporation highlights the brain's use of constructs to process

stimuli A stimulus is something that causes a physiological response. It may refer to: * Stimulation ** Stimulus (physiology), something external that influences an activity ** Stimulus (psychology), a concept in behaviorism and perception * Stimulus (eco ...

Patterned visual spread

Patterned visual spread describes the spread of a pattern in a field of view. For example, a patient sees a checkered pattern on a lamp, which then contiguously spreads to objects such as the floor or a desk. Contextual clues do not influence patterned visual spread, distinguishing it from categorical incorporation.

Cause

Of the published cases of palinopsia from posterior cortical lesions or seizures, 93% described hallucinatory palinopsia. Hallucinatory palinopsia may be caused by many types of posterior cortical lesions such as

neoplasms A neoplasm () is a type of abnormal and excessive growth of tissue. The process that occurs to form or produce a neoplasm is called neoplasia. The growth of a neoplasm is uncoordinated with that of the normal surrounding tissue, and persists ...

, infarctions,

hemorrhages Bleeding, hemorrhage, haemorrhage or blood loss, is blood escaping from the circulatory system from damaged blood vessels. Bleeding can occur internally, or externally either through a natural opening such as the mouth, nose, ear, urethra, ...

arteriovenous malformations Arteriovenous malformation is an abnormal connection between arteries and veins, bypassing the capillary system. This vascular anomaly is widely known because of its occurrence in the central nervous system (usually cerebral AVM), but can app ...

aneurysm An aneurysm is an outward bulging, likened to a bubble or balloon, caused by a localized, abnormal, weak spot on a blood vessel wall. Aneurysms may be a result of a hereditary condition or an acquired disease. Aneurysms can also be a nidus (s ...

abscesses An abscess is a collection of pus that has built up within the tissue of the body. Signs and symptoms of abscesses include redness, pain, warmth, and swelling. The swelling may feel fluid-filled when pressed. The area of redness often extends b ...

, and

tuberculoma A tuberculoma is a clinical manifestation of tuberculosis which conglomerates tubercles into a firm lump, and so can mimic cancer tumors of many types in medical imaging studies. They often arise within individuals in whom a primary tuberculosis ...

s. Hallucinatory palinopsia from seizures may be secondary to a focal cortical lesion or may be secondary to a non-structural disturbance. Causes of seizures that are reported to cause palinopsia include metabolic disturbances (

hyperglycemia Hyperglycemia is a condition in which an excessive amount of glucose circulates in the blood plasma. This is generally a blood sugar level higher than 11.1 mmol/L (200 mg/dL), but symptoms may not start to become noticeable until even ...

carnitine Carnitine is a quaternary ammonium compound involved in metabolism in most mammals, plants, and some bacteria. In support of energy metabolism, carnitine transports long-chain fatty acids into mitochondria to be oxidized for energy production, an ...

deficiency),

ion channel Ion channels are pore-forming membrane proteins that allow ions to pass through the channel pore. Their functions include establishing a resting membrane potential, shaping action potentials and other electrical signals by gating the flow of io ...

disturbances,

Creutzfeldt–Jakob disease Creutzfeldt–Jakob disease (CJD), also known as subacute spongiform encephalopathy or neurocognitive disorder due to prion disease, is an invariably fatal degenerative brain disorder. Early symptoms include memory problems, behavioral changes, ...

, and seizures of unknown cause.

Pathophysiology

Hallucinatory palinopsia is a dysfunction of

, caused by localized cortical hyperexcitability or hyperactivity in the posterior visual pathway. Post- geniculate cortical lesions or seizures may cause cortical deafferentation, focal cortical irritation, and epileptic discharges, the proposed mechanisms of hallucinatory palinopsia.

Cortical deafferentation

Palinopsia can occur from posterior visual pathway (post-geniculate)

deafferentation Peripheral neuropathy, often shortened to neuropathy, is a general term describing disease affecting the peripheral nerves, meaning nerves beyond the brain and spinal cord. Damage to peripheral nerves may impair sensation, movement, gland, or o ...

, which causes homonymous visual field deficits. This mechanism is thought to be similar to the deafferentation hyperexcitability seen in

visual release hallucinations Visual release hallucinations, also known as Charles Bonnet syndrome or CBS, are a type of psychophysical visual disturbance in which a person with partial or severe blindness experiences visual hallucinations. First described by Charles Bonnet in ...

(Charles Bonnet syndrome), which are distinguished from palinopsia by whether the formed image or scene previously occurred. It is hypothesized that deafferentation hyperexcitability is the cause of

neuropathic pain Neuropathic pain is pain caused by damage or disease affecting the somatosensory system. Neuropathic pain may be associated with abnormal sensations called dysesthesia or pain from normally non-painful stimuli (allodynia). It may have continuous ...

. Molecular changes from deafferentation include an increase in pre synaptic neurotransmitter vesicles and heightened post-synaptic

receptor Receptor may refer to: * Sensory receptor, in physiology, any structure which, on receiving environmental stimuli, produces an informative nerve impulse *Receptor (biochemistry), in biochemistry, a protein molecule that receives and responds to a ...

sensitivity.

Epileptic discharges

Palinopsia from epileptic discharges, confirmed by

electroencephalogram Electroencephalography (EEG) is a method to record an electrogram of the spontaneous electrical activity of the brain. The biosignals detected by EEG have been shown to represent the postsynaptic potentials of pyramidal neurons in the neocortex ...

, have been reported during a seizure aura, during the seizure, or post-ictally. The seizures can originate anywhere in the posterior

visual pathway The visual system comprises the sensory organ (the eye) and parts of the central nervous system (the retina containing photoreceptor cells, the optic nerve, the optic tract and the visual cortex) which gives organisms the sense of sight (the a ...

, depending on the location of the pathology. Palinoptic seizures rarely generalize, and there are case reports of palinopsia as the only symptom of a visual seizure. If seizures are persistent, then continual palinoptic episodes often occur.

Focal cortical irritation

Palinopsia, which occurs after

neurosurgical procedures Neurosurgery or neurological surgery, known in common parlance as brain surgery, is the medical specialty concerned with the surgical treatment of disorders which affect any portion of the nervous system including the brain, spinal cord and peri ...

cerebrovascular accident A stroke is a medical condition in which poor blood flow to the brain causes cell death. There are two main types of stroke: ischemic, due to lack of blood flow, and hemorrhagic, due to bleeding. Both cause parts of the brain to stop functionin ...

s, has been partly attributed to focal cortical irritation. Symptoms are associated with perilesional hyperperfusion, which may reflect focal cortical instability and subsequent hyperactivity. While there are reports of palinopsia from each individual mechanism, there is usually a combination of the aforementioned mechanisms. For example, hallucinatory palinopsia may present in a patient with seizure symptoms and visual field deficits, after a neurosurgical procedure. This suggests that the cortical hyperactivity from each mechanism is additive. "Hallucinatory palinopsia, once considered a disorder of the nondominant parieto-occipital lobe, has since been shown to occur from lesions in the dominant or non-dominant temporal, parietal, or occipital lobes. … The predominance of lesions in certain cortical areas is more likely due to the uneven distribution or functional variation of visual cortex-hippocampal neurons. ... All of the hallucinatory palinopsia symptoms occur

concomitantly Concomitant drugs are two or more drugs used or given at or almost at the same time (one after the other, on the same day, etc.). The term has two contextual uses: as used in medicine Medicine is the science and practice of caring for a patien ...

in a patient with one lesion, which supports current evidence that objects, features, and scenes are all units of

, perhaps at different levels of processing. This alludes to neuroanatomical integration in visual memory creation and storage."

Diagnosis

Palinopsia necessitates a full

ophthalmologic Ophthalmology ( ) is a surgical subspecialty within medicine that deals with the diagnosis and treatment of eye disorders. An ophthalmologist is a physician who undergoes subspecialty training in medical and surgical eye care. Following a medic ...

and

neurologic Neurology (from el, νεῦρον (neûron), "string, nerve" and the suffix -logia, "study of") is the branch of medicine dealing with the diagnosis and treatment of all categories of conditions and disease involving the brain, the spinal c ...

history and physical exam. Hallucinatory palinopsia warrants automated visual field testing and

neuroimaging Neuroimaging is the use of quantitative (computational) techniques to study the structure and function of the central nervous system, developed as an objective way of scientifically studying the healthy human brain in a non-invasive manner. Incre ...

since the majority of hallucinatory palinopsia is caused by posterior cortical lesions and seizures. It is generally easy to diagnose the underlying cause of hallucinatory palinopsia. The

medical history The medical history, case history, or anamnesis (from Greek: ἀνά, ''aná'', "open", and μνήσις, ''mnesis'', "memory") of a patient is information gained by a physician by asking specific questions, either to the patient or to other peo ...

typically includes concerning symptoms, and neuroimaging usually reveals cortical lesions. In patients with hallucinatory palinopsia and unremarkable neuroimaging, blood tests or clinical history often hints at the cause. The practitioner should be considering visual seizures in these cases.

Treatment

Palinopsia from

cerebrovascular accidents A stroke is a medical condition in which poor blood flow to the brain causes cell death. There are two main types of stroke: ischemic, due to lack of blood flow, and hemorrhagic, due to bleeding. Both cause parts of the brain to stop functionin ...

generally resolves spontaneously, and treatment should be focused on the vasculopathic risk factors. Palinopsia from

, AVMs, or

require treatment of the underlying condition, which usually also resolves the palinopsia. Palinopsia due to seizures generally resolves after correcting the primary disturbance and/or treating the seizures. In persistent hallucinatory palinopsia, a trial of an anti-epileptic drug can be attempted. Anti-epileptics reduce cortical excitability and could potentially treat palinopsia caused by cortical deafferentation or cortical irritation. Patients with

idiopathic An idiopathic disease is any disease with an unknown cause or mechanism of apparent wikt:spontaneous, spontaneous origin. From Ancient Greek, Greek ἴδιος ''idios'' "one's own" and πάθος ''pathos'' "suffering", ''idiopathy'' means approxi ...

hallucinatory palinopsia should have close follow-up.

References

{{Reflist Memory Disorders of optic nerve and visual pathways Visual disturbances and blindness