Unilateral Neglect

Original Editor - Emily Wood

Lead Editors   - Kathy Bueckert, Alexandra Dansereau

Definition

Unilateral neglect is an attention disorder that arises as a result of injury to the cerebral cortex  (Hills, 2006). Unilateral neglect is also commonly known as contralateral neglect, hemispatial neglect, visuospatial neglect, spatial neglect, or hemi-neglect (Menon, Plummer). In unilateral neglect, patients fail to report, respond or orient to meaningful stimuli presented on the affected side (Menon). In most cases, the right parietal cortex is injured and the left side of the body and/or space is/are ignored . Unilateral neglect is a heterogeneous condition; different individuals may present with different symptoms. Unilateral neglect may involve various modalities, including visual, auditory, somatosensory or kinetic . Unilateral neglect is generally classified in one of two ways: by the modality that is affected or by the space that is affected (i.e. personal or extrapersonal space). It is important to remember that these classifications may overlap and intersect (Plummer).

Mechanism of Injury / Pathological Process

Unilateral neglect usually results from damage to the right parietal area, often the posterior parietal cortex (Hillis, 2006). Normally, neurons in the right parietal cortex strongly attend to both the left and the right side of the space, while neurons in the left parietal cortex weakly attend to the right side of the space only (Heilman & Van Den Abell, 1980). Therefore, in right parietal lesions, attention to the right side of the space is maintained by the left parietal cortex, but attention to the left side of the space ceases. In left parietal lesions, attention is typically maintained on both sides of the space by the right parietal cortex (Heilman & Van Den Abell, 1980).

However, lesions in different cortical and subcortical areas may also lead to neglect by causing dysfunction in brain networks (Vuilleumier, 2013). Usually, unilateral neglect results from stroke; however, it may also result from traumatic brain injuries or a neoplastic disease. Neglect is most likely in cases of large right hemisphere stroke (Yang, Zhou, Chung, Li-Tsang, & Fong, 2013).
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Clinical Presentation

Unilateral neglect is a heterogeneous syndrome; the clinical presentation varies largely between individuals. Typically, the syndrome occurs following a lesion of the right parietal cortex of the brain, and the left side of the body or space is neglected. Right-sided neglect may also occur, but usually to a much lesser extent than left-sided neglect (Heilman & Valenstein, 2012, p297). In unilateral neglect, individuals behave as if the space opposite to the lesion does not exist anymore (Danckert & Ferber, 2006). Individuals may fail to report, respond, or orient to stimuli presented on the contralesional side (Yang, Zhou, Chung, Li-Tsang, & Fong, 2013). Visual, somatosensory, kinesthetic, and auditory modalities may be disregarded, despite intact primary visual/somatosensory/auditory/vestibular areas (Yang et al., 2013). Active exploration of the environment is also biased toward the ipsilesional side (Fruhmann Berger, Karnath, 2005).

The disorder may have a different distribution in different individuals: the neglect may differentially affect the personal space and the extrapersonal space (Danckert & Ferber, 2006). In neglect of the personal space, individuals fail to be aware of one side of their own body (HeilmanK. M.; Valenstein, E., 2012, p299). They may fail to dress, shave, or groom the affected side (Danckert & Ferber, 2006). In severe cases, individuals may deny ownership of the limbs on affected side, a phenomenon called somatoparaphrenia (Vallar G; Ronchi R. (2009). In neglect of the extrapersonal space, the individuals fail to acknowledge and respond to stimuli located in their extrapersonal space (Danckert & Ferber, 2006). Typical behaviours include eating food only on one side of a plate and bumping into objects on the affected side as they navigate in a space. Furthermore, individuals may either ignore visual stimuli on the affected hemifield, or they may ignore one half of all objects (object-centered neglect), regardless of the location of the objects (HeilmanK. M.; Valenstein, E., 2012, p299). Individuals with neglect also may shift their gaze toward the ipsilesional side when at rest (Fruhmann-Berger & Karnath,2005). They may also shift their posture toward the ipsilesional side (Danckert, 2006). Neglect may also affect internal maps of spatial representations (HeilmanK. M.; Valenstein, E., 2012, p.306-307). Representational neglect may be anterograde or retrograde. In anterograde representational neglect, individuals perceive stimuli in the contralesional hemispace, but are unable to recall them. One example is failure to recall auditory information presented on the affected side after distraction (HeilmanK. M.; Valenstein, E., 2012, p.306-307). In retrograde representational neglect, individuals are unable to recall the contralesional half of a previously known scene. However, they are able to recall those details when imagining themselves facing the opposite direction (HeilmanK. M.; Valenstein, E., 2012, p.306-307).
In motor, or intentional unilateral neglect, the initiation of motor behaviour may be affected (HeilmanK. M.; Valenstein, E., 2012;Hills 2006). In motor neglect, the individual may be aware of the stimuli, but fail to move the contralesional side of the body to respond to them despite normal strength (HeilmanK. M.; Valenstein, E., 2012, p299). In addition, patients may not realize that they are missing half of the space, a symptom called anosognosia (Vocat et al. 2010).

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