Dyschiria, also known as dyschiric syndrome, is a

neurological disorder Neurological disorders represent a complex array of medical conditions that fundamentally disrupt the functioning of the nervous system. These disorders affect the brain, spinal cord, and nerve networks, presenting unique diagnosis, treatment, and ...

where one-half of an individual's body or space cannot be recognized or cannot respond to sensations. The term dyschiria is rarely used in modern scientific research and literature. Dyschiria has been often referred to as

unilateral neglect Hemispatial neglect is a neuropsychological condition in which, after damage to one hemisphere of the brain (e.g. after a stroke), a deficit in attention and awareness towards the side of space opposite brain damage (contralesional space) is obse ...

, visuo-spatial neglect, or

hemispatial neglect Hemispatial neglect is a neuropsychological condition in which, after damage to one hemisphere of the brain (e.g. after a stroke), a deficit in attention and awareness towards the side of space opposite brain damage (contralesional space) is obs ...

from the 20th century onwards. Psychologists formerly characterized dyschiric patients to be unable to discriminate or report external stimuli. This left the patients incapable of orienting sensory responses in their extrapersonal and personal space. Patients with dyschiria are unable to distinguish one side of their body in general, or specific segments of the body. There are three stages to dyschiria: achiria, allochiria, and synchiria, in which manifestations of dyschiria evolve in varying degrees. The dyschiric syndrome was defined in the early 20th century by

Ernest Jones Alfred Ernest Jones (1 January 1879 – 11 February 1958) was a Welsh neurologist and psychoanalyst. A lifelong friend and colleague of Sigmund Freud from their first meeting in 1908, he became his official biographer. Jones was the first En ...

, a Welsh psychiatrist, and has encapsulated several explanations of theoretical mechanisms for each stage. Over the course of time, the decreased significance of dyschiria's biopsychological influence led to its replacement by 'neglect' under neurological disorders in

neuropsychology Neuropsychology is a branch of psychology concerned with how a person's cognition and behavior are related to the brain and the rest of the nervous system. Professionals in this branch of psychology focus on how injuries or illnesses of the brai ...

. Dyschiric patients have deficiencies in motor, sensory, visual, and introspective zones of

consciousness Consciousness, at its simplest, is awareness of a state or object, either internal to oneself or in one's external environment. However, its nature has led to millennia of analyses, explanations, and debate among philosophers, scientists, an ...

. These symptoms are associated with

brain lesion Brain injury (BI) is the destruction or degeneration of brain cells. Brain injuries occur due to a wide range of internal and external factors. In general, brain damage refers to significant, undiscriminating trauma-induced damage. A common ...

hysteria Hysteria is a term used to mean ungovernable emotional excess and can refer to a temporary state of mind or emotion. In the nineteenth century, female hysteria was considered a diagnosable physical illness in women. It is assumed that the bas ...

, and

somatoparaphrenia Somatoparaphrenia is a type of monothematic delusion where one denies ownership of a limb or an entire side of one's body. Even if provided with undeniable proof that the limb belongs to and is attached to their own body, the patient produces elab ...

which all affect cognition. In clinical studies, dyschiria is also referred to as the mislocalization of sensations (visual, auditory, and tactile) to the opposite half of the body which can be both unilateral and bilateral. Treatment is limited and unestablished clinically to be proven effective for dyschiric patients, while rehabilitation methods cannot sustain stable effects. Therapeutic options majorly consist of virtual reality (VR), neglected field eye patching, and prismatic adaptation (PA) alongside other rehabilitation therapies.

History

The findings of dyschiria complexly align with cases studying syndromes of spatial neglect and related disorders that have been published in medical literature in the early 20th century. Dr. Ernest Jones proposed the three stages of dyschiria as a mental syndrome in 1909. Jones studied the initial case of achiria alongside the phenomena of allochiria perceived by French psychologist

Pierre Janet Pierre Marie Félix Janet (; ; 30 May 1859 – 24 February 1947) was a pioneering French psychologist, physician, philosopher, and psychotherapist in the field of dissociation and traumatic memory. He is ranked alongside William James ...

(1899) and Austrian neurologist

Heinrich Obersteiner Heinrich Obersteiner (13 November 1847 – 19 November 1922) was an Austrian neurologist born in Vienna. In 1870 earned his doctorate from the University of Vienna, where he worked in the laboratory of Ernst Wilhelm von Brücke (1819–1892). In ...

(1882), respectively. These independent cases defined the dyschiric syndrome and redefined allochiria. From the 20th century onwards, "dyschiria" had been replaced by "unilateral neglect," "

," and other related neurological disorders. "

Unilateral neglect Hemispatial neglect is a neuropsychological condition in which, after damage to one hemisphere of the brain (e.g. after a stroke), a deficit in attention and awareness towards the side of space opposite brain damage (contralesional space) is obse ...

" replaced "dyschiria" following Austrian neurologist

Marcel Kinsbourne Marcel Kinsbourne (3 November 1931 – 21 April 2024) was an Austrian-born pediatric neurologist and cognitive neuroscientist who was an early pioneer in the study of brain lateralization. Background Kinsbourne was born in Vienna, Austria on 3 No ...

's publication on the model mechanisms of unilateral spatial neglect. The study had a greater theoretical influence than previous experiments on dyschiria. Neglect disorders have become one of the major concerns in the study of

. Neglect is the umbrella term for classification of

s of distinct subtypes including the visual,

somatosensory The somatosensory system, or somatic sensory system is a subset of the sensory nervous system. The main functions of the somatosensory system are the perception of external stimuli, the perception of internal stimuli, and the regulation of bod ...

, motor, extrapersonal, personal, and representational subdivisions. Therefore, diverse neurological mechanisms have since then been proposed to investigate and explain higher cognitive functioning in the clinical study of neglect disorders. Symptom severity,

pathophysiology Pathophysiology (or physiopathology) is a branch of study, at the intersection of pathology and physiology, concerning disordered physiological processes that cause, result from, or are otherwise associated with a disease or injury. Pathology is ...

, modality and

chronology Chronology (from Latin , from Ancient Greek , , ; and , ''wikt:-logia, -logia'') is the science of arranging events in their order of occurrence in time. Consider, for example, the use of a timeline or sequence of events. It is also "the deter ...

of neglect disorders also enhance the understanding of the

neural network A neural network is a group of interconnected units called neurons that send signals to one another. Neurons can be either biological cells or signal pathways. While individual neurons are simple, many of them together in a network can perfor ...

s in the brain of patients.

Types

There are three forms of dyschiria in the corresponding stages: achiria, allochiria, and synchiria, that manifest the neurological disorder in distinct capacities of sensory, motor and introspective recognition. Each stage of dyschiria has been theorized to consist of various biological and psychological mechanisms.

Achiria

Unknown awareness and knowledge of the side of the stimulus is the earliest sign of achiria. Effective location of the point, nature, and intensity of stimulation is possible by the patient; with the exclusion of the side where the stimulus is applied. Sensations that are tactile cannot be carried out by patients with motor deficits, unless the limb is specified without "left" or "right" descriptions. Involuntary and habitual movements of the same limb, such as reflex mechanisms, can be performed as regular. Despite this, the functioning of this limb becomes more imprecise when a more conscious and directed effort is required. Patients experiencing achiria have lost the

memory Memory is the faculty of the mind by which data or information is encoded, stored, and retrieved when needed. It is the retention of information over time for the purpose of influencing future action. If past events could not be remembe ...

of feeling the affected body part, regardless of having the ability to recognize its existence. This experience is closely associated with the attitude of "

depersonalization Depersonalization is a dissociative phenomenon characterized by a subjective feeling of detachment from oneself, manifesting as a sense of disconnection from one's thoughts, emotions, sensations, or actions, and often accompanied by a feeling of ...

" felt by patients who have severe forms of hysterical

anesthesia Anesthesia (American English) or anaesthesia (British English) is a state of controlled, temporary loss of sensation or awareness that is induced for medical or veterinary purposes. It may include some or all of analgesia (relief from or prev ...

Theoretical Mechanism: Paradoxical Cleavage

Senses can be categorized into two types: memory-focused and aesthesic. Memory-focused senses are those obtained through previous experiences (e.g. knowing the difference between left and right). Aesthesic senses are obtained through ongoing experiences (e.g. smell and touch). Both senses can be damaged by

functional disorder Functional disorders are a group of recognisable medical conditions which are due to changes to the functioning of the systems of the body rather than due to a disease affecting the structure of the body. Functional disorders are common and compl ...

s, however the time taken for recovery and reacquisition the senses can differ among the two groups. In recovery from functional disorders, aesthesic senses usually recover quicker than memory-focused senses. Dr. Ernest Jones described this variation as a "paradoxical cleavage" and theorized it as the cause of achiria. Earlier recovery of tactile sensations relative to recognition between left and right sides underscores achiric symptoms.

Allochiria

Being able to recognize the precise location of the stimulus on the corresponding position on the contralateral side of the body is referred to as allochiria. The location to which the stimulus is pointed on the corresponding opposite half of the body is done with exact

symmetry Symmetry () in everyday life refers to a sense of harmonious and beautiful proportion and balance. In mathematics, the term has a more precise definition and is usually used to refer to an object that is Invariant (mathematics), invariant und ...

. If patients are asked to carry out motor responses on the affected limb, they will instantly direct the movement of the opposite limb with full conviction. These confusions occur in bilateral allochiria. However, the affected limb can only be directed using its opposite direction (i.e. using the right hand requires the term "left" to be used) or it loses physiological function in unilateral allochiria. Allochiric patients do not have the full ability to feel the affected limb in unilateral senses. The affected limb can only be felt on the opposite side and rarely on the correct half of the body as directed in movement. These patients may feel a "dead" limb and an "active" limb on the unaffected side of the body, while the affected half is seldom felt at all. Often, patients will feel that they only have one limb out of a pair on the unaffected side of the body. Bilateral allochiric patients have the mental capacity to feel both limbs on both sides of the body, only when it is asymmetrically commanded.

Theoretical Mechanism: Central Nervous System Damage

Tactile allochiria is present in individuals with damage to the central nervous system. A study found 20 patients with cerebral hemorrhage unable to correctly localize tactile stimulation. When pinched on their arms, they incorrectly localized it to the corresponding area on the opposite arm. The same result was obtained when participants were exposed to other forms of tactile stimulation (e.g. exposure of the arm to cold/hot objects and vibration).

Brain lesion Brain injury (BI) is the destruction or degeneration of brain cells. Brain injuries occur due to a wide range of internal and external factors. In general, brain damage refers to significant, undiscriminating trauma-induced damage. A common ...

s or other forms of

brain damage Brain injury (BI) is the destruction or degeneration of brain cells. Brain injuries occur due to a wide range of internal and external factors. In general, brain damage refers to significant, undiscriminating trauma-induced damage. A common ...

(often caused by strokes) can lead to neglect of one's contralesional space. Information from the left and right

egocentric Egocentrism refers to difficulty differentiating between self and other. More specifically, it is difficulty in accurately perceiving and understanding perspectives other than one's own. Egocentrism is found across the life span: in infancy, ear ...

spaces is principally understood by the

neuron A neuron (American English), neurone (British English), or nerve cell, is an membrane potential#Cell excitability, excitable cell (biology), cell that fires electric signals called action potentials across a neural network (biology), neural net ...

s of the right

parietal cortex The parietal lobe is one of the four major lobes of the cerebral cortex in the brain of mammals. The parietal lobe is positioned above the temporal lobe and behind the frontal lobe and central sulcus. The parietal lobe integrates sensory informa ...

. The right region is also weakly managed by the neurons of the left parietal cortex. Damage to the right parietal cortex is thus more severe as it solely maintains the attention towards the left space. This makes neglect of the left space more prevalent as there is no mitigating component. The neglect caused by the lesion does not undermine the detection of tactile sensations, however hinders tactile localization. When stimulated by touch on the contralesional arm, the touch is detected, however the location of contact is transposed by the patient to the ipsilesional arm as the contralesional space cannot be acknowledged.

Synchiria

Recognition of stimulus in both corresponding sides of the body as two concurrent sensations, when only applied to one affected part, is known as synchiria. In terms of motor response, the patient carries out movement on both sides of the body simultaneously even when asked to conduct motion on the affected side. This movement is only felt by the affected side of the patient's body. Introspectively, the patient is under the impression that they are moving their affected limb and is unable to differentiate between the two halves of their body. According to Dr. Ernest Jones, patients could feel the affected side being displaced and shifting between the two halves of the

median plane Whether in reference to the anatomy of the human or other members of the Bilateria, the median plane, also called the midsagittal plane and related terms, is used to describe the sagittal plane as it bisects the body vertically through the midline ...

of their body.

Theoretical Mechanism: Brain Lesions

The presence of synchiria is attributed to

s. A study on a patient with a brain lesion on their left hemisphere showed detection of touch to be possible, lacking accurate identification of the point of contact. Specifically, he claimed to have experienced tactile sensation on both his left (ipsilesional) and right (contralesional) hands, when only his left hand was stimulated. It is suggested that there are two pathways for

activity. The first is the contralateral pathway, where each hemisphere receives sensory information from and transmits motor information to their opposite

spaces (i.e., the left side of the body to the right hemisphere). The second, the ipsilateral pathway, allows for the transmission of information along the same side of the body (i.e., the left side of the body to the left hemisphere). In a healthy individual, when a hand is stimulated by touch, there is increased brain activity in the

contralateral Standard anatomical terms of location are used to describe unambiguously the anatomy of humans and other animals. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position prov ...

hemisphere, and decreased activity in the

ipsilateral Standard anatomical terms of location are used to describe unambiguously the anatomy of humans and other animals. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position prov ...

hemisphere. This suggests the presence of mechanisms to inhibit the hemispheres from processing

sensations. This inhibition is necessary to discriminate between the points of contact. The absence or damage of this inhibition is theorized to result in the exhibition of synchiria. Despite there being one tactile stimulation, the sensory information is processed by both hemispheres. This hinders one's ability to localize the touch to one hand and instead results in them feeling the sensation on both hands.

Recovery and Therapies

No treatment is established to be entirely effective on patients with dyschiria and related neglect disorders as the functioning mechanisms of the syndromes are varied. Therapeutic options are unable to maintain stable positive effects and are difficult to transfer for daily-life usage with certainty. Major treatments for dyschiria include virtual reality (VR), neglected field eye patching, and prismatic adaptation (PA).

Virtual Reality (VR)

Virtual reality allows for the simulation of daily life circumstances to rehabilitate control of limbs, eyes, and head movement. This virtual simulation encourages transformations of postural shifts for patients. Improvements in body coordination and sensations in daily-life activities can be practiced as patients achieve targets for movement with varying difficulties through the virtual simulation. VR increases body awareness in neglect disorders like dyschiria with results persisting over five months.

Neglected Field Eye Patching

Neglected field eye patching covers the eye on the affected side of the body through an obstructing spectacle lens or glasses. The eye patch can be placed on either hemifield of the affected eye depending on the patient's weakness in spatial neglect. The covered eye results in hemifield occlusion of vision which enables the individual to focus their awareness on the

space using the deficient side of the body.

Prismatic Adaptation (PA)

Prismatic adaptation therapy involves the production of an optical displacement in patients through

prismatic An optical prism is a transparent optics, optical element with flat, polished surfaces that are designed to refraction, refract light. At least one surface must be angled—elements with two parallel surfaces are ''not'' prisms. The most fami ...

goggles. Patients with prismatic goggles are required to perform visual target tasks such as pointing and throwing. This therapy can lead to the correction of biased body representation, however prismatic adaptation therapy may only focus on motor-intention responses of neglect and dyschiria than space perceptions. Other rehabilitation therapies include * Alertness-training * Neck muscle vibration * Non-invasive brain stimulation (NIBS) * Repetitive optokinetic stimulation * Visual scanning with exploration training Some recovery protocols are used in conjunction to create amplified positive results. Neck muscle vibration technique alongside simultaneous visual exploration training resulted in sound enhancements for patients with spatial neglect.

Future Development

The phenomena of dyschiria on body representation require further investigation for the development of theories and mechanisms around

neuropsychological Neuropsychology is a branch of psychology concerned with how a person's cognition and behavior are related to the brain and the rest of the nervous system. Professionals in this branch of psychology focus on how injuries or illnesses of the brai ...

dissociations in concepts of the

body schema Body schema is an organism's internal model of its own body, including the position of its limbs. The neurologist Henry Head, Sir Henry Head originally defined it as a postural model of the body that actively organizes and modifies 'the impressions ...

and

body image Body image is a person's thoughts, feelings and perception of the aesthetics or sexual attractiveness of their own body. The concept of body image is used in several disciplines, including neuroscience, psychology, medicine, psychiatry, psycho ...

.{{Cite journal , last=de Vignemont , first=Frederique , date=2010-02-01 , title=Body schema and body image—Pros and cons , url=https://www.sciencedirect.com/science/article/pii/S0028393209003789 , journal=Neuropsychologia , series=The Sense of Body , language=en , volume=48 , issue=3 , pages=669–680 , doi=10.1016/j.neuropsychologia.2009.09.022 , pmid=19786038 , issn=0028-3932 These various concepts coincide with the nature of neglect syndromes akin to dyschiria to better understand the functioning of the brain.

References

Syndromes affecting the nervous system