Occupational Therapy Anchoring During Reading for Unilateral Neglect

Effigy 1: Drawing of a clock by a patient with left-sided neglect.

Hemineglect, also known as unilateral fail, hemispatial neglect or spatial fail, is a common and disabling condition post-obit brain damage in which patients fail to be enlightened of items to one side of space. Neglect is well-nigh prominent and long-lasting later on damage to the right hemisphere of the human brain, specially following a stroke. Such individuals with right-sided brain impairment often fail to be aware of objects to their left, demonstrating fail of leftward items.

The deficit may exist then profound that patients are unaware of large objects, even people, towards their neglected or contralesional side - the side of space opposite brain damage. They may eat from only 1 side of a plate, write on one side of a page, shave or make-up just the non-neglected or ipsilesional side of their face (same side as brain damage). Their drawings may fail to include items towards the neglected side, for case when placing the numbers in a cartoon of a clock (Fig.1). Many patients are often also unaware they have a arrears (anosognosia).

Classically, the fail syndrome has been associated with damage to the right posterior parietal cortex. More recent studies take begun to challenge this view, suggesting instead that a more widespread network of areas may be involved, including those that have been implicated in studies of neuroimaging of attention (discussed farther in the Neuroanatomy of neglect below; see also Corbetta & Shulman, 2002 and Husain & Rorden, 2003). Differences in the location and extent of lesions (brain damage) beyond patients may contribute to the heterogeneity of the condition.

1 Primary sensory and motor representations may be intact in neglect
2 A gradient of neglect
3 Unconscious or implicit processing of neglected information
4 Measuring neglect: neuropsychological tests
5 Neuroanatomy of fail
6 Mechanisms underlying neglect
- 6.one Spatial or directional attention deficits
- 6.2 Deficits in spatial frames of reference
- vi.three Spatial or directional motor deficits
- 6.4 Spatial working retentivity deficits
- 6.v Non-spatial attending deficits
7 Attempts to modulate or care for fail
- 7.one Behavioural or device-mediated therapies
- vii.ii Neuropharmacological modulation
eight References
9 Recommended reading
10 External links
xi Encounter as well

Chief sensory and motor representations may be intact in neglect

Figure ii: Heart movements during visual search in an individual with left-sided neglect attempting to discover letter Ts amidst Ls. Red dots show fixations and yellow lines depict saccadic eye movements from 1 fixation to another.

Individuals with neglect exercise non necessarily suffer from any principal disorder of sensation or movement. For instance, their visual fields may be completely intact. And so they may be able to detect a salient, vivid item on their neglected side if it is flashed on a night background. Only even though they may not be blind, patients may fail to report the same stimulus if it is presented in a chaotic background. People with fail may as well accept no weakness of their eye or limb muscles, yet fail to straight their gaze or hands to explore contralesional space (due east.g., Behrmann et al., 1997; Husain et al., 2001). Their visual search may, instead, exist directed only towards items to their ipsilesional side (Fig.2).

Neglect may be multimodal, extending to involve visual, auditory and somatosensory systems. Information technology may also affect memories of scenes - then-chosen representational fail. In their famous experiment, Bisiach and Luzzatti (1978) asked patients with left-sided visual fail from Milan to imagine viewing the primal square, the Piazza del Duomo, from the cathedral in the eye of the square. They reported that these patients often omitted to mention places or streets off to the left side of the foursquare from that viewpoint. However, when asked to imagine looking directly at the cathedral, i.e., shifting their viewpoint past 180 degrees, the same individuals at present neglected to mention places on the side of the square they had just reported - ones which now fell to their left from the new imagined point of view. Instead, they now recalled places to the right of the new imagined vantage indicate.

A gradient of fail

Importantly, the border between neglected space and non-neglected space is:

non sharp and accented as in a primary visual field arrears such as hemianopia
and does non necessarily respect (align with) the vertical midline or meridian (Fig. 3).

Figure 3: Number of target items found (circled As) on a visual search or counterfoil task may vary with the number of distractor items in the array (adapted from Kaplan et al., 1991).

The probability of reporting items varies in many patients (eastward.yard., Kaplan et al., 1991; Smania et al., 1998; Chatterjee et al., 1999):

with the highest probability being on the ipsilesional side (right side for right brain-damaged patients) and the lowest on the contralesional / neglected side (left side for right-hemisphere patients)
with the degree of clutter in the visual environment - the greater the number of distractor or not-target items on the ipsilesional side, the greater the neglect of items on the contralesional side (Fig. 3).

Unconscious or implicit processing of neglected information

Several studies have revealed that even though a stimulus to the neglected side of space may fail to exist reported, information technology may nevertheless be candy to a substantial degree - to the level of its identity or pregnant (Berti & Rizzolatti, 1992). The most hit examples come from investigations of semantic priming (eastward.g., McGlinchey-Berroth et al., 1993). In 1 experiment, stimuli to the left which were unreported (neglected) by the patient, nonetheless speeded subsequent responses to a word if information technology was semantically related to the neglected item (e.g., tree and apple) compared to if it was unrelated (e.thou., bed and apple). Another report showed a patient pictures of an undamaged business firm and one called-for with the flames on the left side of the house (Marshall & Halligan, 1988). When asked which firm they would prefer to live in, a patient with left-sided neglect, who did non study seeing the flames of the burning business firm, all the same chose the undamaged house significantly more ofttimes. Note that the level to which stimuli may exist processed implicitly or unconsciously in neglect patients is far more substantial than that reported in individuals with blindsight who have main visual field deficits. Functional imaging studies have demonstrated activation in intact early visual areas even when patients have no conscious awareness for visual stimuli (Rees et al., 2000; Rees 2001; Vuilleumier et al., 2001). See too sections in Attention and Consciousness.

Measuring neglect: neuropsychological tests

Neglect may exist measured in diverse ways. Dissimilar patients may show deficits on different types of test, so there is no unmarried test used to diagnose the condition (Azouvi et al., 2002; Parton et al., 2004). Many patients will show fail behaviour in their everyday life when interacting with others, and then observation of the patient is crucial. In improver, batteries of neuropsychological tests have been devised to capture and quantify the degree of neglect.

Most batteries include:

Counterfoil job. These are visual search tests, consisting of multiple targets, presented on a sheet of paper in front end of the patient who is asked to circle or cancel out all the targets they can find (e.g. Fig. 3)
Line bisection. The patient has to mark the midpoint of a horizontal line presented on a sail of newspaper.
Copying task. The examiner asks the patient to copy one or more than line drawings.

Neuroanatomy of fail

Figure iv: Right hemisphere of man brain showing some cortical areas implicated in neglect including the inferior parietal lobe (IPL) which consists of the angular (Ang) and supramarginal (Smg) gyri; the temporoparietal junction (TPJ); right inferior frontal gyrus (IFG) and middle frontal gyrus (MFG). SPL denotes superior parietal lobe while ips refers to intraparietal sulcus.

Classically, neglect has been associated with lesions of the right posterior parietal cortex, particularly the inferior parietal lobe (IPL) or temporoparietal junction (TPJ) (Vallar & Perani, 1986) (Fig.4).

More recently, some authors take proposed a critical association with harm to the right superior temporal gyrus (Karnath et al., 2001), though this view has been strongly challenged (Mort et al., 2003) and remains a subject of much argue and controversy (Doricchi & Tomaiuolo, 2003; Karnath et al., 2004a, 2004b; Mort et al., 2004). What is clear, even so, is that there is no one single lesion location associated with the syndrome.

In add-on to posterior cortical areas, virtually researchers hold that subcortical lesions (for case, involving the thalamus and basal ganglia) that practice non encroach direct on the cortex can lead to fail, although this may exist via indirect furnishings on overlying cortical regions (Hillis et al., 2002, 2005). Moreover, it has also go evident that isolated lesions of the correct frontal lobe may be associated with neglect, without involvement of posterior parietal or temporal regions (Husain & Kennard, 1996). Contempo studies also implicate white matter pathways, connecting, for example, posterior cortical and frontal regions in individuals with neglect (Thiebaut de Schotten et al., 2005; Bartolomeo et al., 2007).

Different patients have unlike combinations of posterior cortical, frontal, subcortical and white matter harm. This heterogeneity may be a key factor determining the diversity of functional deficits reported in this condition (see Mechanisms underlying fail).

Left hemisphere damage may also lead to neglect of rightward items, though this is usually less profound and less long-lasting than leftward neglect post-obit right brain damage. The development of language and praxis in left posterior and frontal regions may be a reason for this hemispheric difference. Right hemisphere regions in the inferior parietal and frontal lobe may accept a special function in sustained attention and right parietal regions have as well been implicated in spatial working memory. When combined with a rightward directional bias post-obit strokes to these regions (see Directiona Attentional Deficits below), this might pb to more profound neglect subsequently right compared to left hemisphere lesions.

Mechanisms underlying neglect

Many unlike cognitive deficits have been identified in patients with fail (Driver & Mattingley, 1998; Heilman & Watson, 2001; Halligan et al., 2003; Husain & Rorden, 2003; Mesulam, 1999). These experimental findings take led to a range of hypotheses about the mechanisms underlying the status. A large number of dissociations have been reported with some patients showing deficit A but not B, and others showing B but not A (Vallar, 1998). Many patients testify combinations of deficits, but the exact combination differs beyond patients (Buxbaum et al., 2004).

1 way to consider the mechanisms underlying the syndrome is to divide them into spatial or directional deficits versus not-spatial or non-directional ones.

Spatial or directional attention deficits

Many researchers have proposed that neglect may be due to a deficit in directing spatial attention, specifically in disengaging attention from ipsilesional objects and shifting information technology contralesionally towards the neglected side of space (for reviews come across Losier & Klein, 2001 and Bartolomeo & Chokron, 2002). Such a mechanism was originally implicated in patients with visual extinction following unilateral brain damage (Posner et al., 1984). Cueing attention towards the neglected side of space tin help to reduce spatial biases, for example in line bisection (Riddoch & Humphreys, 1983).

Other investigators accept emphasized a spatially lateralised bias or gradient of attention in neglect, due to disruption of the normal remainder between the hemispheres in directing attention (Kinsbourne, 1993). Thus, after right hemisphere damage, left hemisphere mechanisms which normally orient attention rightwards may be left relatively unopposed (Corbetta et al., 2005). Hence the ipsilesional bias in attention observed in patients with fail.

Some researchers have considered the spatial attention deficit in terms of the biased competition theory of attending, with ipsilesional stimuli winning in the competition for pick over contralesional ones in neglect (Duncan et al., 1997). According to such accounts, more stimuli on the non-neglected, ipsilesional side would also hinder attention existence directed toward contralesional items (see Fig. iii).

Evidence from a written report in which the eye position of right hemisphere patients was monitored shows that their rightward bias can be completely corrected if the visual salience of stimuli to the left is increased relative to those to the right (Bays et al., 2010). Indeed, if leftward stimuli are made highly salient then these patients' gaze tin be shifted into previously neglected space. These findings would be consistent with an ipsilesional directional bias modulated past competition between leftward and rightward items in neglect patients.

Deficits in spatial frames of reference

Several studies have shown that the degree of fail may be modulated by the position of stimuli relative to the torso, head, eye position and even gravitational field (e.g., Ladavas, 1987; Karnath et al., 1998). Thus dissimilar egocentric spatial reference frames appear to exert an influence on the sector of space that is neglected. Some investigators have also reported neglect for stimuli in nearly space or far space in dissimilar patients. All these reports have fatigued inspiration from computational considerations of the transformations involved in sensorimotor control, as well equally neurophysiological studies of the office of monkey posterior parietal cortex in sensorimotor transformations and motor command (Andersen, 1997). In general, these findings support the hypothesis that there may exist a deficit of spatial representation in neglect (Bisiach & Luzzatti, 1978). However, an impaired spatial representation in neglect might besides be secondary to reduced attention or exploration of contralesional space.

Spatial or directional motor deficits

Testify also exists for a arrears in directing eye or limb movements contralesionally or to targets in contralesional space in some individuals with neglect (Heilman et al., 1985; Mattingley et al., 1992). This may be a disorder of initiating movements (sometimes referred to as directional hypokinesia) or in slowness of movement execution (termed directional bradykinesia). Directional motor deficits may be modulated by locations of visual targets. One study has demonstrated slowness in initiating leftward movements to targets in left hemispace, only not those in right hemispace, in right parietal patients with neglect (Mattingley et al., 1998).

Spatial working memory deficits

Contempo investigations take revealed that some neglect patients too have difficulty in keeping track of spatial locations beyond saccadic eye movements (Husain et al., 2001; Mannan et al., 2005). Such a arrears in spatial working retention appears to exacerbate any lateralised biases in these patients. The findings advise limitations in visual curt term memory, peculiarly for the locations of objects (Pisella et al., 2004; Malhotra et al., 2005; Ferber & Danckert 2006).

Non-spatial attention deficits

A range of techniques has been used to probe not-spatial or non-directional deficits. The attentional blink paradigm has revealed a profound and long-lasting deficit in the temporal dynamics of visual processing for stimuli presented at fixation in right-hemisphere neglect patients (Husain et al., 1997). When attending is engaged on one item, such patients have difficulty in attention to subsequent items for >1 2nd, fifty-fifty when items are presented centrally, a finding reminiscent of non-spatial extinction in parietal patients (Humpreys et al. 1994).

Bilateral deficits (i.eastward. on both sides of space) accept besides been reported in parietal patients, with reduced capacity to encode visual stimuli presented transiently in either visual field (Duncan et al., 1999; Batelli et al., 2001).

Several groups have too reported impaired power to sustain attention or maintain vigilance over protracted periods of time in patients with neglect, even for fundamental auditory stimuli (see Robertson, 2001). Others have shown that at that place may be a bilateral constriction of the constructive field of vision - the sector of space that can exist attended to - which may lead to 'local bias' and failure to nourish 'globally' to the periphery (Rafal, 1994; Russell et al., 2004). Deficits in 'global' visual processing have also been reported in non-neglect patients with correct temporoparietal lesions (Robertson et al., 1988).

In the past, there has been a cracking deal of interest in object-based attention deficits in neglect (Driver et al., 1994; for a review, see Walker, 1995), although a pure-object centred arrears is probably extremely rare (Commuter & Pouget, 2000).

Combinations of spatial/directional and non-spatial deficits appear to exist nowadays in dissimilar patients with fail (Buxbaum et al., 2004). Moreover, some of these deficits can be in isolation of the fail syndrome. For example, deficits in spatial working memory or sustained attention have been documented in right-hemisphere patients without neglect. Yet, when combined with spatially lateralised or directional biases, these deficits tin serve to exacerbate the severity of neglect (run across Husain & Rorden, 2003).

The combination of directional bias plus non-spatial / not-directional deficits may explain why correct hemisphere lesions lead to more severe and longer lasting neglect. Both left and right hemisphere lesions may produce directional biases (e.yard. extinction) but the right hemisphere may have a special role in sustained attention and spatial working memory. When deficits in these domains are comined with a directional bias, neglect may be far more astringent.

Attempts to modulate or treat neglect

Several types of therapy or experimental modulation have been attempted to ameliorate neglect (for reviews run into Robertson & Halligan, 1999; Barrett et al., 2006; Luate et al., 2006; Singh-Back-scratch & Husain, 2008). These take consisted either of behavioural interventions (sometimes including the utilize of specialist devices) or drug treatments. The results of these studies have been variable, nearly likely due to heterogeneity between patients and the pocket-sized numbers of individuals tested. It is unlikely that one treatment will exist suitable for all patients with neglect because, every bit we have seen, unlike patients have different combinations of underlying cognitive deficit.

A related business is that for a particular treatment to exist constructive information technology may exist crucial that certain brain regions or functions are intact. For example, learning a new strategy may depend upon the integrity of prefrontal cortical regions. Patients who take large parts of such critical brain regions destroyed may not be so responsive to certain treatment approaches. Thus mapping the lesions of patients involved in trials may be important to understand variations in response to therapy.

Behavioural or device-mediated therapies

Information technology is now generally acknowledged that interventions which simply attempt to improve exploration of contralesional space, for case by directing gaze in that management on search tasks, are effective in reducing neglect on those tasks but these improvements fail to generalize or 'transfer' to amelioration of fail in everyday life. When placed back into everyday situations, patients do non scan the neglected side of space significantly improve following such training alone. However, when combined with vibration of the contralesional cervix muscles, at that place has been evidence for pregnant improvement in fail and functional outcome measures for up to 2 months follow-up (Schindler et al., 2002). Neck muscle vibration is thought to effect a recentering of the egocentric frame of reference, by an illusory modification of the afferent information regarding the orientation of the caput in space.

In recent years there has also been a great deal of involvement in prism adaptation as a means of improving fail (Rossetti et al., 1998; Frassinetti et al., 2002). The process of adapting to rightward-deviating prisms appears to lead to long-lasting improvements in left-sided neglect. However, the mechanisms underlying this shift in behaviour remain controversial, and it has become evident that not all patients reply to this grade of intervention.

Teaching patients to self-alert or use an alerting device that acts to agitate them has shown benefits in some individuals, as has limb activation therapy which involves directing attention to the contralesional manus (Robertson, 1999).

Some groups have reported improvements in neglect following repetitive transcranial magnetic stimulation administered over the contralesional hemisphere (e.one thousand. Oliveri et al., 2001). The underlying mechanism is considered to be short-lasting inhibition of the intact side of the brain, thereby redressing any imbalance in attentional orienting.

Neuropharmacological modulation

Two unlike classes of pharmacological agent have been used, targeting dopaminergic, noradrenergic, or both systems. Dopaminergic drugs such as levodopa, bromocriptine and apomorphine have been reported to have positive effects in some individuals, simply the studies are extremely pocket-size and reported responses variable (Fleet et al., 1987; Geminiani et al., 1998; Grujic et al., 1998; Mukand et al., 2001). The α2-noradrenergic agonist, guanfacine, which has been used successfully in some children with attention arrears hyperactivity disorder, may also be benign in some individuals with neglect (Malhotra et al., 2006). Again, the extent of brain damage and the integrity of critical brain regions may exist factors which account for response variability.

There has been no reported attempt to combine behavioural or device-based interventions with neuropharmacological modulation. In the hereafter, such concurrent handling might potentially be a very powerful approach if at that place were synergistic effects.

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Internal references

Larry Weiskrantz (2007) Blindsight. Scholarpedia, two(4):3047.

Keith Rayner and Monica Castelhano (2007) Eye movements. Scholarpedia, ii(10):3649.

Jeremy Wolfe and Todd S. Horowitz (2008) Visual search. Scholarpedia, three(vii):3325.

Steven J. Luck (2007) Visual short term memory. Scholarpedia, 2(six):3328.

Kimron 50. Shapiro, Jane Raymond and Karen Arnell (2009) Attentional blink. Scholarpedia, iv(half dozen):3320.

External links

Effigy five: Masud Husain.

Author's webpages:

Husain Lab Institute of Cognitive Neuroscience webpage
Husain Lab Institute of Neurology webpage
Vision@UCL

Other labs:

Bartolomeo Lab
Berti Lab
Buxbaum lab
Behrmann Lab
Chatterjee Lab
Corbetta Lab
Coslett Lab
Danckert Lab
Driver Lab
Ferber Lab
Fink Lab
Goodale Lab
Halligan Lab
Humphreys Lab
Jackson Lab
Karnath Lab
Mattingley Lab
Milner Lab
Rafal Lab
Rees Lab
Riddoch Lab
Rizzolatti Lab
Ian Robertson's Lab
Lynn Robertson'southward Lab
Rossetti Lab
Vuilleumier Lab
Walker Lab

Occupational Therapy Anchoring During Reading for Unilateral Neglect

Contents

Chief sensory and motor representations may be intact in neglect

A gradient of fail

Unconscious or implicit processing of neglected information

Measuring neglect: neuropsychological tests

Neuroanatomy of fail

Mechanisms underlying neglect

Spatial or directional attention deficits

Deficits in spatial frames of reference

Spatial or directional motor deficits

Spatial working memory deficits

Non-spatial attention deficits

Attempts to modulate or treat neglect

Behavioural or device-mediated therapies

Neuropharmacological modulation

References

Recommended reading

External links

See also

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