User:RiaIsarina/sandbox

= Dyschiria = Dyschiria, also known as Dyschiric syndrome, is a neurological disorder in which a patient is unable to recognize or correspond to sensations on one half of their body or space. The term dyschiria is rarely used in modern scientific research and literature. Dyschiria is most often referred to as unilateral neglect, visuo-spatial neglect, or hemispatial neglect from the 20th century onwards.

Psychologists formerly characterized dyschiric patients to be unable to discriminate and report external stimuli leaving them incapable of orienting sensory responses in their extrapersonal and personal space. Patients suffering from 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.

Dyschiric patients suffer deficiencies in sensory, motor, visual, and introspective zones of consciousness. These symptoms are associated with somatoparaphrenia, hysteria, and brain lesions that 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 that is both unilateral and bilateral.

History
The findings of dyschiria are complex in nature, aligning with cases studying syndromes of spatial neglect and related disorders that have been published in medical literature in the early 19th century. Ernest Jones, a Welsh psychiatrist, proposed the three stages of dyschiria as a mental syndrome in 1909. He studied the first case of achiria discovered by French psychologist Pierre Janet in 1899, alongside the phenomena of allochiria by Austrian neurologist Heinrich Obersteiner from 1882 , to define the dyschiric syndrome and its redefinition of allochiria.

From the 20th century onwards, the term dyschiria had been replaced by unilateral neglect or hemispatial neglect, and such related neurological disorders. The term unilateral neglect replaced dyschiria in 1970 when Marcel Kinsbourne, an Austrian neurologist, published his study on the model mechanisms of unilateral spatial neglect which had a greater theoretical influence than previous experiments on dyschiria.

Neglect disorders have become one of the major concerns in the study of neuropsychology. Neglect was chosen as the umbrella term for classification of neurological disorders of distinct subtypes such as the visual, somatosensory, 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, modality and chronology of neglect disorders also enhance the understanding of the neural networks in the brain of patients.

Types
There are three forms of dyschiria in the corresponding stages: achiria, allochiria, and synchiria, that manifests the neurological disorder in distinct capacities of sensory, motor and introspective recognition.

Achiria
Achiria refers to when a patient has no significant knowledge and awareness at all to the side of the stimulus. It is considered to be the primary stage of dyschiria. The patient can effectively locate the point, nature, and intensity of the stimulus, with the exception of the side where the stimulus is applied.

Sensations that are tactile cannot be carried out by patients suffering from motor deficits, unless the limb is specified in the absence of “left” or “right” descriptions. Involuntary and habitual movements of the same limb can be performed as regular such as reflex mechanisms. Despite this, the functioning of this limb becomes more imprecise when more conscious and directed effort is required.

Patients experiencing achiria have lost the memory for feeling the affected body part, regardless of having the ability to recognize its existence. This experience is closely associated with the attitude of “depersonalization” felt by patients who suffer from severe forms of hysterical anesthesia.

Allochiria
Allochiria refers to when a patient is able to recognize the exact location of the stimulus on the corresponding position on the opposite side of the body. The locations to which the stimulus is pointed at on the corresponding opposite half of the body is done with exact symmetry.

If patients are asked to carry out motor responses on the affected limb, they will instantly direct 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 in both sides of the body, only when it is asymmetrically commanded.

Synchiria
Synchiria refers to when a patient is capable of recognizing the stimulus in both corresponding sides of the body as two concurrent sensations, though the sensory stimulus is only applied to one affected part. 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 Ernest Jones, a Welsh psychiatrist, patients could feel the affected side being displaced and shifting between the two halves of the median plane of their body.

Achiria
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 disorders, however the time taken for recovery and reacquiring the senses can differ among the two groups.

As one recovers from the disorder, their aesthesic senses can recover quicker than their memory focused ones. Ernest Jones described this variation as a “paradoxical cleavage” and theorized it to be the cause of achiria. Achiric patients' symptoms could be explained by them recovering their ability to recognize touch before being able to distinguish between their left and right side.

Allochiria
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 lesions or other forms of brain damage (often caused by strokes) can lead to neglect of one’s contralesional space. Information from the left and right egocentric spaces is principally understood by the neurons of the right parietal cortex. 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 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
The presence of synchria is also attributed to brain lesions. A study focused on a patient suffering from a brain lesion on their left hemisphere. The individual was able to detect touch, however could not correctly identify the point of contact. Specifically, he claimed to have experienced tactile sensation on both his left (ipsilesional) and right (contralesional) hands, when in reality only his left hand was stimulated.

Research has suggested there to be two pathways for somatosensory activity. The first pathway is the contralateral pathway, where each hemisphere receives sensory information from and transmits motor information to their opposite egocentric spaces  (i.e, left side of the body to right hemisphere). The second pathway, the ipsilateral pathway, allows for transmission of information along the same side of the body (i.e, left side of the body to left hemisphere).

In a healthy individual, when a hand is stimulated by touch, there is increased brain activity in the contralateral hemisphere, and decreased activity in the ipsilateral hemisphere. This suggests the presence of mechanisms to inhibit the hemispheres from processing ipsilateral 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.

Future Developments and Treatments
The phenomena of dyschiria on body representation needs further investigation for the development of theories and mechanisms around neuropsychological dissociations in concepts of the body schema and body image. These various concepts coincide with the nature of neglect syndromes akin to dyschiria to better understand the functioning of the brain.

Recovery and Therapies
No treatment is established to be entirely effective on patients suffering from 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.

Treatments for rehabilitation included virtual reality (VR), prismatic adaptation (PA), non-invasive brain stimulation (NIBS), alertness-training, visual scanning and exploration training, neck muscle vibration, neglected-field eye patching, and repetitive optokinetic stimulation.

Some recovery protocols were used in conjunction creating amplified positive results. Neck muscle vibration technique alongside simultaneous visual exploration training resulted in sound enhancements of patients with spatial neglect.