Unilateral Neglect – Disorders of Movement
Neglect is most temporarily found mostly in the right side of the brain (left neglect). The right partial lobe appears to play a dominant role in spatial cognition in man. The function of the partial lobe involves the viso-motor control of behavior. There are four types of unilateral neglect – horizontal axis (left and right space), altitudinal coordination (upper and lower spaces), and radial co-ordinates (near and far space). Radial co-ordinates occur in a parapersonal and extra personal way. Parapersonal involves attention deficits to the area reaching the space tested. Extra personal includes deficits that are beyond the reaching space.
Many wonder whether neglect is related to hemianopia, which is the loss of vision in half of both eyes. According to The Royal Society For The Blind, this is a condition that sometimes is found after a stroke or another injury to the brain. The
condition does not directly affect the eye. This relates to the brain’s impaired ability to receive the information it transmits through both eyes. The person with the disease experiences difficult in seeing one side of their visual environment.
Hemianopia can be complete or partial. If complete, the affected person can see only one side while looking ahead. With partial hemianopia, objects seem different in brightness or clarity. Other symptoms include double vision and difficulty interpreting visual information. Sometimes these images may disappear or seem distorted.
In some cases, the condition resolves naturally over time. However, the majority is permanent. SEETEC (a service provided by Guide Dogs Association) uses portable machines to assess damage and provide training exercises for those affected. This helps to gain confidence in the affected and allows for safety while walking, household tasks, leisure and other daily living activities.
One can be tested for unilateral neglect by drawing in which one is to copy a series of images by memory. Readings are also used to detect the disorder by single word detection (dyslexia sometimes apparent as well) or whole word omissions in whole text readings. Dissociations found in neglect include neglect dyslexia in which people will ultimately see words in different orders. Most of the time, the results included a word that was the same number of letters of the word that the tested one should have responded with. However, words rotated 90 degrees were read normally. Neglect is initially effective in the early stages of visual processing and an early representation of letter string.
Some patients will also omit large numbers of words from one side of the page, but later read single words without errors. In other cases, one can read all of a passage of text, but will make mistakes in specific locations of the words. Most of these whole word omissions occurred on the left side of the page (spatial neglect). Another dissociation included neglect of a mental image. Two patients were asked to describe a familiar scene using imagery. However, the landmarks on the right, were described in an imaginary sense.
There are three models to describe this disorder. First Bisiach’s model, which believes that neglect reflects failure to construct neural representation of the external environment. Damage to one’s hemisphere is assumed to destroy the representation of the opposite side of the space. A weakness to this model is its lack of clarity of how well it accommodates object-centered neglect According to Brain in 1941, some patients demonstrate “visual” but not representational neglect.
Another model to describe neglect is Kinsbourne’s attentional model, which concludes that each hemisphere that controls orientation in the contra version direction. (Right side of brain – leftward view and vice versa). The left hemisphere has a stronger orientating tendency than the right. In a 2000 thesis by Kay Peterson, the model was developed in 1970 as a “so-called efferent attention model of hemispheric asymmetry.” It is described as efferent because it is at a level of hemispheric activation that works top-down and determines how this information will be processed.
He describes the techniques of the model in which there is a possible specialization of one hemisphere for a particular function where there is no significance. However, it is at this level of activity in the hemispheres with a stimulus present that is important. If one of these sections has a higher level of activity, the sensory input will be processed better because of the crossing over of these pathways on their way from the periphery to the brain. This however can lead to the preference of a certain visual field.
Rizzolatti’s premotor model views neglect as the combination of attentional and representational accounts. The attention involved in the selection of an object is action. Spatial attention involves multiple circuits which sub-serve different regions
of space. These neurons in these spaces are used to control movements. Neglect patients are impaired at making eye and pointing movements to left-sided stimuli.
In an University of Waterloo presentation, treatment of unilateral neglect is described as using two approaches. The first targets visual attention deficiency, which uses scanning, and training. The other targets spatial representation deficiency through mental imagery training, by using eye patches, prism treatment, and/or stimulation therapy.
The conclusions made through these models are that neglect is not an unitary syndrome. The range of deficits involved reflect the amount of damage to various functional networks. Rehab can occur spontaneously. However, scanning training, caloric stimulation, limb activation and increased arousal can help with this disorder as well.
