PSYCHOLOGY

In a hypothetical scenario, imagine how your life would be affected if you have suddenly developed hemi-spatial neglect.

 

Hemi- spatial neglect is a known disabling disorder caused by unilateral brain damage, mainly of the right hemisphere. Although the condition can be caused by several diverse pathological disorders, it is most frequently seen after cerebral infarction or haemorrhage and it affects up to two thirds of right hemisphere especially for stroke patients acutely (Husain et.al, 2011). Patients with this condition often fail to be conscious of or recognize items on their contralesional side (that is, the left side for patients with right brain damage) and instead recognize the items that are towards the same side as their brain damage known as their ipsilesional side (Husain et.al, 2011). Their neglect may be so intense that the patients are heedless of large objects, or even persons, in extra personal space.

Hemi-spatial effect on my life can really create a big obstacle in my life. I use my left hand mostly in my day to day activities. Bearing in mind that patients with neglect usually pay less concern to the space on the opposite side to their injury (that is, the left side in cases of right hemisphere injury), and failing to react or respond to objects and individuals and also forgetting to use their limbs (Wilkinson, 2013). Therefore, a damage on my right hemisphere will characteristically mean that I will be unable to attend to my duties.

On the other hand, I am a community social worker, most of the times I am required to address the community and also read many materials. So, a loss due to hemi- spatial neglect three months down the line after the brain damage I will not be in a position to effectively use my limbs since I will be unable to remember. Notably, a patient with an enormous infarct right in the middle of his or her cerebral artery territory normally have their head and eyes twisted to the extreme right and they never look to the left (Cherney, 2001). When a person is given food or a newspaper to read, they only show particular interest in items on their right, disregarding those on their left. Equally, when approached by someone from their left they might fail to recognize them or, if they are spoken to, they may orient themselves to the right and respond with their stare directed away from the individual they are addressing (Cherney, 2001). A year after my brain damage I will not be in a position to even read.

Analytical section

Brain area(s) involved in the impairment (attentional loss)

Typically, the neglect syndrome has largely been connected with the damage of the right posterior parietal cortex (Husain, 2008). More and more research studies have recently started to defy this opinion, proposing in its place that a more extensive network of areas may be involved, comprising those that have been mentioned in studies of neuroimaging of attention (Husain, 2008). However, differences in both the location and degree of the lesions or brain damage among patients may greatly contribute to the heterogeneity of the disorder.

Spatial or directional attention deficits

Many researchers have highlighted a spatially lateralized bias of attention in neglect, owing to the interruption of the standard balance between the hemispheres in trying to direct attention (Kinsbourne, 1993). Therefore, after right hemisphere impairs, the left hemisphere mechanisms which usually orient attention rightwards are normally left quite unopposed (Corbetta et al., 2005). Hence the ipsilesional bias in attention seen in patients suffering from neglect.

Spatial or directional motor deficits

Substantial evidence exists for a deficit or a shortfall in directing eye or limb movements to targets in contralesional space among some persons suffering from neglect (Heilman et al., 1985; Mattingley et al., 1992). This may be due to a condition of starting movements (sometimes denoted to as directional hypokinesia) or rather slowness of movement execution (branded directional bradykinesia). Directional motor deficits may be controlled by positions of visual targets. Some research studies have demonstrated slowness in initiating the leftward movements to targets in the left hemispace, but not targets in the right hemispace, particularly in right parietal patients with neglect (Mattingley et al., 1998). This condition leads to attention loss.

Spatial working memory deficits

Latest studies have shown that some neglect patients also have a challenge in keeping a record of spatial locations particularly across saccadic eye movements (Husain et al., 2001; Mannan et al., 2005). Such a shortage in spatial operational memory seems to worsen any lateralized biases in these particular patients. The discoveries propose restrictions especially in visual short term memory, mainly for the locations of objects (Pisella et al., 2004; Malhotra et al., 2005; Ferber and Danckert 2006). Characteristically, this leads to loss of attention.

Non-spatial attention deficits

Numerous groups have reported impaired capability to sustain attention and vigilance over extended periods of time in patients suffering from neglect, even for the central auditory stimuli. Others groups have revealed that there may be a joint constriction of the efficient field of vision the part of space that can be attended to which might also lead to ‘local bias’ and failure to attend ‘generally’ to the periphery (Rafal, 1994; Russell et al., 2004).

A pivotal or a focal damage to the right hemisphere, leads to unilateral spatial neglect (USN). This condition USN is amongst the most outstanding behavioral deformities initiated by a focal brain damage (Hillis, 2006). A vital fact to note here is that, it is not simply a loss of some function but a failure to identify or react to stimuli precisely on the side of space contralateral to brain damage, while perfectly identifying and reacting to stimuli on the ipsilesional side. After right hemisphere stroke, USN will characteristically manifest itself by causing failure to react to pain on the left side of the body, brush one’s hair on the left, read the left side of a page or the first letters of words, or react to a voice emanating from the left side, or even by refutation that the left arm belongs to oneself.

Although this marvel has really captivated neurologists, psychologists, and other neuroscientists for many years, many key questions remain as to the basic neural mechanisms responsible for unilateral spatial neglect. However, it is now extensively accepted that unilateral spatial neglect is a heterogeneous condition. It is also widely agreed that patients suffering from unilateral spatial neglect may abandon or neglect the left side of near space but they do not neglect the left side of far space, or they may also neglect tangible information but not visual info on the left.

References:

Cherney LR et.al (2001), Recovery of functional status after right hemisphere stroke: relationship with unilateral neglect. Arch Phys Med Rehabil 2001; 82:322–8.

Corbetta, M. et.al, (2005). Neural basis and recovery of spatial attentional deficits in spatial neglect. Nat Neurosci 8, 1424-1425.

Ferber, S., and Danckert, J. (2006). Lost in space – the fate of memory representations for non-neglected stimuli. Neuropsychologia 44, 320-325.

Heilman, K.M. et.al (1985), Directional hypokinesia: prolonged reaction times for leftward movements in patients with right hemisphere lesions and neglect. Neurology 35, 855-859.

Hillis, A.E. (2006), Neurobiology of Unilateral Spatial Neglect. Departments of Neurology and Physical Medicine and Rehabilitation, Johns Hopkins University School of Medicine, and Department of Cognitive Science, Johns Hopkins University, Baltimore, MD

Husain M. et.al, (2011), Hemispatial neglect. J Neurol Neurosurg Psychiatry 2004; 75:13–21.

Husain, M. et.al (2001), impaired spatial working memory across saccades contributes to abnormal search in parietal neglect. Brain 124, 941-952.

Kinsbourne, M. (1993), Orientational bias model of unilateral neglect: Evidence from attentional gradients within hemispace. In Unilateral neglect: Clinical and Experimental Studies. I.H. Robertson and J.C. Marshall, eds. (Hove: Lawrence Erlbaum), pp. 63-86.

Malhotra, P. et.al (2005), spatial working memory capacity in unilateral neglect. Brain 128, 424-435.

Mannan, S. et.al (2005), Revisiting previously searched locations in visual neglect: Role of right parietal and frontal lesions in misjudging old locations as new. Journal of Cognitive Neuroscience 17, 340-354.

Mattingley, J.B. et.al (1992). Impairments of movement initiation and execution in unilateral neglect. Directional hypokinesia and bradykinesia.115 ( Pt 6), 1849-1874.

Mattingley, J.B. et.al (1998), Motor role of human inferior parietal lobe revealed in unilateral neglect patients. Nature 392, 179-182.

Pisella, L. et.al (2004), impaired working memory for location but not for color or shape in visual neglect: a comparison of parietal and non-parietal lesions. Cortex 40, 379-390.

Rafal, R.D. (1994). Neglect. Current Opinion in Neurobiology 4, 231-236.

Russell, C. et.al (2004), Attention modulates the visual field in healthy observers and parietal patients. Neuroreport 15, 2189-2193.

Wilkinson D. et.al, (2013), Hemispatial Neglect: Clinical Features, Assessment and Treatment. School of Psychology, University of Kent, Canterbury, Kent

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