Hemispatial neglect is a complex neurological condition that affects an individual’s awareness of one side of space. It arises from damage to specific areas of the brain, leading to a profound lack of attention to stimuli on the side opposite the brain injury.
Understanding Hemispatial Neglect
Individuals with hemispatial neglect often behave as if an entire half of their world simply does not exist. This can manifest in various ways, such as eating food from only one side of a plate, shaving or applying makeup to just one side of the face, or bumping into objects on the neglected side. When asked to draw a clock, a patient might place all the numbers on one half of the clock face, or omit numbers entirely from the neglected side. This lack of awareness extends beyond visual input, potentially affecting auditory, tactile, and even motor responses.
The condition differs from blindness or a sensory deficit; the eyes and sensory organs often function properly, but the brain fails to process or pay attention to the information. Patients might not even realize they have this deficit, a symptom called anosognosia, which can pose additional challenges. The impact on daily life can be substantial, affecting activities like dressing, reading, and navigating one’s surroundings, often leading to increased dependency.
Key Brain Regions Affected
Hemispatial neglect is most frequently associated with damage to the right cerebral hemisphere, particularly the right parietal lobe. Within the parietal lobe, the inferior parietal lobule, which includes the angular and supramarginal gyri, and the temporoparietal junction are commonly implicated areas. These regions are involved in spatial attention and awareness, playing a central role in directing attention to various points in space.
Beyond the parietal lobe, other brain regions and pathways also contribute to the manifestation of neglect. The frontal lobe, specifically areas like the superior frontal gyrus and ventrolateral prefrontal cortex, can be involved. These frontal areas are connected to attention networks and contribute to the voluntary control of attention and eye movements.
Subcortical structures, located beneath the cerebral cortex, can also play a role. The thalamus and basal ganglia have been identified in some cases of neglect. White matter pathways, which are bundles of nerve fibers connecting different brain regions, are also significant. Damage to tracts like the superior longitudinal fasciculus and inferior fronto-occipital fasciculus can disrupt the communication between cortical and subcortical areas, contributing to neglect symptoms.
How Brain Damage Leads to Neglect
Damage to these brain regions disrupts the intricate networks responsible for spatial attention. The right parietal lobe, for instance, is uniquely important because it attends to space on both sides of the body, while the left parietal lobe primarily attends to the right side only. When the right parietal lobe is damaged, there is no sufficient “backup” from the left hemisphere to process information from the left side of space.
This imbalance results in a reduced ability to direct attention and awareness toward the side opposite the brain lesion. The disruption affects how the brain integrates sensory information and how it plans and executes actions within spatial contexts. The functional consequences extend to a reduced ability to shift attention, maintain alertness, and form a coherent map of one’s surroundings.
Common Causes of Brain Damage
The most frequent cause of brain damage leading to hemispatial neglect is a stroke, particularly an ischemic stroke affecting the middle cerebral artery territory in the right cerebral hemisphere. Such strokes can be extensive, impacting multiple brain regions involved in spatial processing.
Other causes of brain injury can also result in hemispatial neglect. Traumatic brain injuries (TBI) are recognized causes. Brain tumors or lesions that grow in or near the brain regions can also disrupt normal brain function and lead to neglect. Less commonly, neurodegenerative diseases may also contribute to the development of this condition.