Parietal Lobe Damage: Balint's Syndrome and Unilateral Spatial Neglect

Parietal lobe damage can result in a wide range of neurological deficits, often associated with spatial perception and attention. Lesions or atrophy in this landmark can compromise the processing of spatial relations, resulting in attentional deficits. Left hemispheric injuries typically cause language impairments, whereas right hemispheric damages often lead to attentional and spatial disorders. Two of which are visual hemineglect and Balint’s syndrome. Though both disorders impair an individual’s ability to process visual information and are caused by brain damage, they influence different aspects. This essay will compare and contrast the two conditions in the following characteristics: (1) clinical symptoms, (2) neuropsychological assessments; (3) neuroimaging and pathophysiology. 

Clinical symptoms  

Visual hemineglect (or unilateral spatial neglect) can occur due to acute stroke causing the patient to ignore input from the contralesional side of the visual fields. The neglected hemifield is commonly the left side, found in 82% of right hemisphere patients (Stone et al., 1993). The severity, size and location of the brain damage can vary symptoms. However, the common deficits include (1) failure to attend to the contralesional side of space in visual exploration; (2) failure to acknowledge intrapersonal space of the contralesional side, leading to dressing, grooming half of the body or eating half of the dinner; (3) difficulty in reaching objects on the contralesional side of space; (4) difficulty in performing tasks that require attention to both sides of space such as reading or copying a picture; (5) difficulty in judging position or size of objects appear on the contralesional side. Their neglect can lead to omitting large objects or people in the extrapersonal space. In addition, some patients fail to acknowledge and use their contralesional body parts (Parton, Mahotra & Husain, 2004). Failure to effectively use limbs is called “motor neglect” (Karnath, Ferber & Himmelbach, 2001). 

Balint’s syndrome is a rare condition that affects saccadic eye movements, attending to visual stimuli and maintaining visual memory. This syndrome is well-known for its three subtypes of symptoms (1) Simultanagnosia; (2) Oculomotor apraxia, also known as gaze apraxia, a deficit of visual scanning; (3) Optic ataxia - the inability to reach objects accurately. 

Hemineglect, usually seen in patients with brain lesions in the temporoparietal junction, can often be confused with Balint’s syndrome, given their slight similarities in the subtype disorders. For example, eye movement deficits in hemineglect patients mimic those of oculomotor apraxia, and weak hand movements may appear like optic ataxia. Therefore, it is essential to use multiple neuropsychological tests as part of the evaluation to differentiate the symptoms of these two conditions. 

Neuropsychological Tests 

The evaluation of neurological disorders typically involves a range of assessments. Besides neuroimaging scans, behavioural-related assessments can be carried out to pinpoint the patients’ conditions. 

For hemineglect, the most accessible test is the line bisection test (see Figure 1), in which patients are asked to define the midline on a sheet of paper aligned with the body midline. The second standard test is the star cancellation test. Often, the stimuli include 52 large stars, 13 letters and 10 short words with 56 smaller stars on an 8.5’’ x 11’’ piece of paper (Zelter & Menon, 2008). The paper is positioned at the patient’s midline, and the patient must cross out all the small stars (Zelter & Menon, 2008). . The third most popular test is the Albert Task. A piece of paper with randomly-oriented lines is positioned at the patient’s midline. The patient is requested to cross out all the lines. Hemineglect is indicated when the lines on the contralesional side are left uncrossed. Notably, this task can also be used as part of the evaluation for patients with hemianopia. 

The copying and drawing tests, though widely used and accessible, it is subjective and have limited sensitivity in detecting patients with hemineglect (Friedman, 1991) (Bailey, Riddoch & Crome, 2000). Moreover, impaired copying may indicate other conditions, such as constructional apraxia (Agrell, Dehlin & Dahlgren, 1997). Line bisection and star cancellation tests have a sensitivity of 76.4% compared to 57.5% in copying tests (Bailey, Riddoch & Crome, 2000). 

For Balint’s syndrome, the test battery typically includes (1) the oculomotor apraxia test; (2) the simultanagnosia test; (3) the visual object agnosia test; (4) the attentional set-shifting test; (5) the visual memory test. The oculomotor test includes asking the patients to follow an object in motion with their eyes & to respond to visual cues by making saccadic eye movements such as rapid or jerky. The simultagnosia test assesses the patient’s ability to perceive more than one object simultaneously. The test involves showing images of multiple objects in a context, such as a crowded street, then asking the individual to identify objects and overall understanding of the scene context. The visual object agnosia test assesses the ability to identify and describe the functions of everyday objects. Objects can be shown separately or in groups. 

Pathophysiology and Neuroimaging

Lesions can vary significantly in size. The associated brain regions with hemineglect and Balint’s syndrome are anatomically related and often parts of the visual cortex. However, both conditions have no consensus on anatomical correlates. Balint’s syndrome is rarer and commonly associated with patients with bilateral lesions in the parietal lobes and occipitoparietal regions. On the other hand, unilateral damage of the temporoparietal junction happens in most hemineglect cases (often on the right hemisphere).

Figure 2 shows the right hemisphere's inferior parietal lobule (IPL) of the right hemisphere (in purple). The temporoparietal junction (TPJ) is a part of IPL linked to various cognitive functions such as attention, perception and social cognition. Hemineglect is often associated with this region.

Figure 3 shows a hand-drawn MRI scan of a 70-year-old patient with Balint’s syndrome. The patient had severe headaches and transient left-side weakness and was diagnosed with inflammatory vasculitis of the central nervous system (Short & Graff-Radford, 2003). Examination indicated that the patient had normal visual acuity & visual field, optic ataxia, ocular apraxia, and mild simultagnosia (Short & Graff-Radford, 2003). Bilateral lesions at the occipitoparietal junction were found. 

Imaging techniques such as CT or structural MRI can reveal damages in the regions associated with these dysfunctional modalities. However, other areas that appeared to be intact could be involved in these conditions due to disconnection or imbalanced signals between the injured and spared regions (Corbetta et al., 2005) (He et al., 2007) (Carter et al., 2010). 

In conclusion, understanding these conditions can enhance our insights into the functions of healthy brains and how our proprioception and attention are processed. Additionally, neuropsychological studies of these syndromes raise important research questions regarding prognosis and therapies that can improve stroke patients’ lives. 

References

Carter, A., Astafiev, S., Lang, C., Connor, L., Rengachary, J., Strube, M., Pope, D., Shulman, G., & Corbetta, M. (2010, March). Resting Inter-hemispheric fMRI Connectivity Predicts Performance after Stroke. Annual Neurology, 67(3), 365-375. doi: 10.1002/ana.21905

Corbetta, M., Kincade, M. J., Lewis, C., Snyder, A. Z., & Sapir, A. (2005). Neural basis and recovery of spatial attention deficits in spatial neglect. Nature Neuroscience, 8, 1603-1610. https://www.nature.com/articles/nn1574

Gorea, A., & Sagi, D. (2002). Natural Extinction: A Criterion Shift Phenomenon. Visual Cognition, 9, 913-936.

He, B. J., Snyder, A. Z., Vincent, J. L., Epstein, A., Shulman, G. L., & Corbetta, M. (2007, March 15). Breakdown of Functional Connectivity in Frontoparietal Networks Underlies Behavioral Deficits in Spatial Neglect. Neuron, 53(6), 905-918. DOI:https://doi.org/10.1016/j.neuron.2007.02.013

Short, R. A., & Graff-Radford, N. R. (2003). Balint's Syndrome. In Encyclopedia of the Neurological Sciences (pp. 340-342). Academic Press. https://www.sciencedirect.com/referencework/9780122268700/encyclopedia-of-the-neurological-sciences

Stone, S. P., Halligan, P. W., & Greenwood, R. J. (1993). The Incidence of Neglect Phenomena and Related Disorders in Patients with an Acute Right or Left Hemisphere Stroke. Age and Ageing, 22(1), 46–52. https://doi.org/10.1093/ageing/22.1.46

Published on 15/02/2023