Hemispatial neglect

Hemispatial neglect results most commonly from strokes and brain unilateral injury to the right cerebral hemisphere, with rates in the critical stage of up to 80% causing visual neglect of the left-hand side of space. Neglect is often produced by massive strokes in the middle cerebral artery region and is variegated, so that most sufferers do not exhibit all of the syndrome's traits. Right-sided spatial neglect is rare because there is redundant processing of the right space by both the left and right cerebral hemispheres, whereas in most left-dominant brains the left space is only processed by the right cerebral hemisphere. Although it most strikingly affects visual perception ('visual neglect'), neglect in other forms of perception can also be found, either alone or in combination with visual neglect. For example, a stroke affecting the right parietal lobe of the brain can lead to neglect for the left side of the visual field, causing a patient with neglect to behave as if the left side of sensory space is nonexistent (although they can still turn left). In an extreme case, a patient with neglect might fail to eat the food on the left half of their plate, even though they complain of being hungry. If someone with neglect is asked to draw a clock, their drawing might show only the numbers 12 to 6, or all 12 numbers might be on one half of the clock face with the other half distorted or blank. Neglect patients may also ignore the contralesional side of their body; for instance, they might only shave, or apply make-up to, the non-neglected side. These patients may frequently collide with objects or structures such as door frames on the side being neglected. ==Language and communication impairments==

Although hemispatial neglect is most commonly described as a visuospatial disorder, research shows that it also produces systematic impairments in language comprehension, reading, writing, inference, and discourse-level processing. These deficits arise because neglect reduces attention to information presented on the left side of space, the left side of visual words and sentences, and the left side of communicative scenes or narratives. Neglect dyslexia improves when text is shifted toward the right visual field. This further demonstrates its dependence on spatial attention rather than linguistic ability. Patients may also show difficulty placing words or maintaining spatial layout on a page, consistent with disruption of visuospatial attention. Narrative performance commonly shows reduced coherence and difficulty integrating themes or connecting events, proving right-hemisphere functions in managing discourse. Effects Though it is frequently underappreciated, unilateral neglect can have dramatic consequences. It has more negative effect on functional ability, as measured by the Barthel ADL index, than age, sex, power, side of stroke, balance, proprioception, cognition, and premorbid ADL status. Its presence within the first 10 days of a stroke is a stronger predictor of poor functional recovery after one year than several other variables, including hemiparesis, hemianopsia, age, visual memory, verbal memory, and visuoconstructional ability. Neglect is probably among the reasons patients with right hemisphere damage are twice as likely to fall as those with left-side brain damage. Patients with neglect take longer to rehabilitate and make less daily progress than other patients with similar functional status. Patients with neglect are also less likely to live independently than patients who have both severe aphasia and right hemiparesis. ==Causes==

Brain areas in the parietal and frontal lobes are associated with the deployment of attention (internally, or through eye movements, head turns or limb reaches) into contralateral space. Neglect is most closely related to damage to the temporo-parietal junction and posterior parietal cortex. The lack of attention to the left side of space can manifest in the visual, auditory, proprioceptive, and olfactory domains. Although hemispatial neglect often manifests as a sensory deficit (and is frequently co-morbid with sensory deficit), it is essentially a failure to pay sufficient attention to sensory input. Although hemispatial neglect has been identified following left hemisphere damage (resulting in the neglect of the right side of space), it is most common after damage to the right hemisphere. This disparity is thought to reflect the fact that the right hemisphere of the brain is specialized for spatial perception and memory, whereas the left hemisphere is specialized for language - there is redundant processing of the right visual fields by both hemispheres. Hence the right hemisphere is able to compensate for the loss of left hemisphere function, but not vice versa. Neglect is not to be confused with hemianopsia. Hemianopsia arises from damage to the primary visual pathways cutting off the input to the cerebral hemispheres from the retinas. Neglect is damage to the processing areas. The cerebral hemispheres receive the input, but there is an error in the processing that is not yet well understood. ==Theories of mechanism==

Researchers have debated about whether neglect is a disorder of spatial attention or spatial representation, or even non-spatial deficits of attention combined with a directional bias that results from unilateral brain injury. Spatial attention Spatial attention is the process where objects in one location are chosen for processing over objects in another location. In this theory, neglect is seen as disorder of attention and orientation caused by disruption of the visual cortex. Patients with this disorder will direct attention and movements to the ipsilesional side and neglect stimuli in the contralesional side despite having preserved visual fields. The result of all of this is an increased sensitivity of visual performance in the unaffected side. Spatial representation Spatial representation is the way space is represented in the brain. A neglect patient who was very familiar with the map of France was asked to name French towns on a map of the country, both by a mental image of the map and by a physical image of the map. The image was then rotated 180 degrees, both mentally and physically. With the mental image, the neglect stayed consistent with the image; that is, when the map was in its original orientation, the patient named towns mostly on the East side of France, and when they mentally rotated the map they named towns mostly on the West side of France because the West coast was now on the right side of the represented field. However, with the physical copy of the map, the patient's focus was on the East side of France with either orientation. This leads researchers to believe that neglect for images in memory may be disassociated from the neglect of stimuli in extrapersonal space. The study was run on a neglect patient by tracking his eye movements while he slept, during the REM cycle. Results showed that the majority of the eye movements were aimed to his right side, indicating that the images represented in his dreams were also affected by hemispatial neglect. Another example would be a left neglect patient failing to describe left turns while describing a familiar route. This shows that the failure to describe things in the contralesional side can also affect verbal items. These findings show that space representation is more topological than symbolic. Patients show a contralesional loss of space representation with a deviation of spatial reference to the ipsilesional side. In these cases we see a left-right dissimilarity of representation rather than a decline of representational competence. ==Diagnosis==

Neglect test Some of the neglect tests. File:Letter search neglect test.png|Letter search neglect test File:Letter search neglect test result.png|Letter search neglect test result File:Line cancellation neglect test.png|Line cancellation neglect test File:Line cancellation neglect test result.png|Line cancellation neglect test result File:AllochiriaClock.png|The Allochiria phenomenon might be revealed by the request to draw a clock. File:Neglect LINE BISECTION test.png|The patients has to mark the half of the line. In order to assess not only the type but also the severity of neglect, doctors employ a variety of tests, most of which are carried out at the patient's bedside. Perhaps one of the most-used and quickest is the line bisection. In this test, a line a few inches long is drawn on a piece of paper and the patient is then asked to dissect the line at the midpoint. Patients exhibiting, for example, left-sided neglect will exhibit a rightward deviation of the line's true midpoint. A patient may also be asked to read a page out of a book. The patient will be unable to orient their eyes to the left margin and will begin reading the page from the center. Presenting a single word to a patient will result in the patient either reading only the ipsilesional part of the word or replacing the part they cannot see with a logical substitute. For example, if they are presented with the word "peanut", they may read "nut" or say "walnut". A vast array of impaired mechanisms are found in neglect. These mechanisms alone would not cause neglect. These patients tend to neglect the opposite side of their lesion, based on the midline of the body, head, or retina. For example, in a gap detection test, subjects with egocentric hemispatial neglect on the right side often make errors on the far right side of the page, as they are neglecting the space in their right visual field. The next range of neglect is "allocentric" neglect, where individuals neglect either their peri-personal or extrapersonal space. Peri-personal space refers to the space within the patient's normal reach, whereas extrapersonal space refers to the objects/environment beyond the body's current contact or reaching ability. These two broad categories may be further subdivided. Patients with egocentric neglect may ignore the stimuli leftward of their trunks, their heads, or their retinae. So, for example, if patients are presented with an upside-down photograph of a face, they may mentally flip the object right side up and then neglect the left side of the adjusted image. In another example, if patients are presented with a barbell, patients will more significantly neglect the left side of the barbell, as expected with right temporal lobe lesion. If the barbell is rotated such that the left side is now on the right side, patients will more significantly neglect the left side of the object, even though it is now on the right side of space. During the study, the patients were presented with two arrays of seven triangles. The first array ran from southwest to northeast (SW-NE) and the second array ran from southeast to northwest (SE-NW). In a portion of the experimental trials, the middle triangle in the array contained a gap along one side. Participants were tested on their ability to perceive the presence of this gap, and were instructed to press one response button if the gap was present and a second response button if the gap was absent. A double simultaneous stimulation procedure was utilized, during which the patients were touched lightly and simultaneously on the left and right side of the wrist of one hand. The patients were tested both with their palms facing down and with their palms facing up. This experimental condition allowed the scientists to determine whether neglect in the somatosensory system occurs with respect to the sensory receptor surface (egocentric) or with respect to a higher-order spatial frame of reference (allocentric). The results of this experiment showed the hemispatial neglect patients neglected somatosensory stimuli on the contralesional side of space, regardless of hand orientation. These findings suggest that, within the somatosensory system, stimuli are neglected with respect to the allocentric, spatial frame of reference, in addition to an egocentric, sensory frame of reference. Ultimately, the discoveries made by these experiments indicate that hemispatial neglect occurs with respect to multiple, simultaneously derived frames of reference, which dictate the nature and extent of neglect within the visual, auditory, and tactile fields. ==Treatment==

Treatment consists of finding ways to bring the patient's attention toward the left, usually done incrementally, by going just a few degrees past midline, and progressing from there. Rehabilitation of neglect is often carried out by neuropsychologists, occupational therapists, speech-language pathologists, neurologic music therapists, physical therapists, optometrists, and orthoptists. Forms of treatment that have been tested with variable reports of success include prismatic adaptation, where a prism lens is worn to pull the vision of the patient towards the left, constrained movement therapy where the "good" limb is constrained in a sling to encourage use of the contralesional limb. Eye-patching has similarly been used, placing a patch over the "good" eye. Pharmaceutical treatments have mostly focused on dopaminergic therapies such as bromocriptine, levodopa, and amphetamines, though these tests have had mixed results, helping in some cases and accentuating hemispatial neglect in others. Caloric vestibular stimulation (CVS) has been shown to bring about a brief remission in some cases. however this technique has been known to elicit unpleasant side-effects such as nystagmus, vertigo and vomiting. A study done by Schindler and colleagues examined the use of neck muscle vibration on the contralesional posterior neck muscles to induce diversion of gaze from the subjective straight ahead. Subjects received 15 consecutive treatment sessions and were evaluated on different aspects of the neglect disorder including perception of midline, and scanning deficits. The study found that there is evidence that neck muscle stimulation may work, especially if combined with visual scanning techniques. The improvement was evident 2 months after the completion of treatment. Other areas of emerging treatment options include the use of prisms, visual scanning training, mental imagery training, video feedback training, trunk rotation, galvanic vestibular stimulation (GVS), transcranial magnetic stimulation (TMS) and transcranial direct-current stimulation (tDCS). Of these emerging treatment options, the most studied intervention is prism adaptation and there is evidence of relatively long-term functional gains from comparatively short-term usage. However, all of these treatment interventions (particularly the stimulation techniques) are relatively new and randomised, controlled trial evidence is still limited. Further research is mandatory in this field of research in order to provide more support in evidence-based practice. In a review article by Pierce & Buxbaum (2002), they concluded that the evidence for Hemispheric Activation Approaches, which focuses on moving the limb on the side of the neglect, has conflicting evidence in the literature. The authors note that a possible limitation in this approach is the requirement for the patients to actively move the neglected limb, which may not be possible for many patients. Constraint-Induced Therapy (CIT), appears to be an effective, long-term treatment for improving neglect in various studies. However, the use of CIT is limited to patients who have active control of wrist and hand extension. Prism Glasses, Hemispatial Glasses, and Eye-Patching have all appeared to be effective in improving performance on neglect tests. Caloric Stimulation treatment appears to be effective in improving neglect; however, the effects are generally short-term. The review also suggests that Optokinetic Stimulation is effective in improving position sense, motor skills, body orientation, and perceptual neglect on a short-term basis. As with Caloric Stimulation treatment, long-term studies will be necessary to show its effectiveness. A few Trunk Rotation Therapy studies suggest its effectiveness in improving performance on neglect tests as well as the Functional Independence Measure (FIM). Some less studied treatment possibilities include treatments that target Dorsal Stream of visual processing, Mental Imagery Training, and Neck Vibration Therapy. ==See also==