Hemispatial neglect is a neurological syndrome defined by a failure of attention and awareness directed toward one side of space. This condition is not caused by a primary problem with vision, sensation, or motor function. Individuals with neglect behave as if an entire half of their world, body, or environment simply does not exist. This lack of awareness impedes the ability to perform daily activities, often leading to a challenging recovery and greater dependence on caregivers.
The Underlying Cause in the Brain
The neurological origin of hemispatial neglect typically involves physical damage to one side of the cerebral hemisphere. The condition is most commonly observed following a stroke that affects the right side of the brain. This damage disrupts the brain’s attentional network, a system responsible for directing focus and processing sensory information from the environment. The posterior parietal cortex, located in the parietal lobe, is the area most frequently implicated in this disruption.
The right hemisphere of the brain plays a unique role in controlling attention for both the left and right sides of space. Conversely, the left hemisphere primarily manages attention only for the right side of space. When the right hemisphere is damaged, its ability to process the left side of the world is lost, and the remaining left hemisphere cannot compensate for this deficit. This imbalance causes attention to be strongly pulled toward the side of the brain lesion, resulting in a failure to acknowledge stimuli on the opposite, or contralesional, side.
How Hemispatial Neglect Presents
The manifestations of hemispatial neglect consistently reflect an inability to orient to the neglected side of space, typically the left side following a right hemisphere lesion. For example, a person might eat only the food on the right half of the plate, failing to notice the untouched portions on the left side. When reading, they may only read the right half of each sentence. This deficit extends beyond the visual field and can affect auditory, tactile, and even olfactory perception.
The condition is often categorized into two types: personal and spatial neglect. Personal neglect involves ignoring one side of the body, such as shaving only half of the face or failing to dress the neglected limb. Spatial neglect, on the other hand, involves the space around the body, causing the individual to bump into objects or doorways on the neglected side while walking. Some individuals with the syndrome may also exhibit anosognosia, which is a lack of awareness that they even have a deficit, making rehabilitation efforts more challenging.
Clinical Tools for Diagnosis
Diagnosis of hemispatial neglect relies on standardized behavioral and paper-and-pencil tasks that compel the patient to interact with the neglected space. The Line Bisection Test is a common assessment where the individual is asked to mark the exact center of several horizontal lines. Individuals with neglect consistently mark a point significantly shifted toward the non-neglected side, revealing their spatial bias.
Cancellation tasks require the patient to cross out target symbols, such as stars or letters, scattered across a page. A person with the syndrome will only cancel the targets on the non-neglected side, leaving the targets on the opposite side untouched. Drawing or copying tasks are also highly informative; patients asked to draw a clock or a house often omit or compress all the features onto the non-neglected side. These tests provide a quantifiable measure of the severity and type of spatial inattention.
Rehabilitation and Management
Therapeutic strategies for hemispatial neglect aim to re-engage the patient’s attention toward the neglected side of space. Visual Scanning Training is a widely used method that trains individuals to actively and systematically move their head and eyes toward the neglected side. This technique encourages the patient to use a “lighthouse” strategy, consciously scanning the full environment to compensate for the automatic attentional bias.
Another approach is Prism Adaptation, which involves wearing special glasses that horizontally shift the entire visual field toward the non-neglected side. Initially, this causes the patient to miss targets, but the brain quickly adapts to the shift. When the glasses are removed, a temporary after-effect biases attention back toward the formerly neglected space. Sensory stimulation techniques, such as Limb Activation Training, ask the patient to actively move the neglected arm or leg into the neglected space. These interventions work to recalibrate the brain’s spatial map, improving the patient’s ability to attend to the full environment.