Dopaminergic stimulation in unilateral neglect

Effects of light deprivation on recovery from neglect and extinction induced by unilateral lesions of the medial agranular cortex and dorsocentral striatum

A number of previous studies have indicated that an environmental manipulation, 48 h of light deprivation (LD), produces virtually complete and permanent behavioral recovery of function from neglect induced by medial agranular cortex (AGm) lesions. LD-induced behavioral recovery from neglect is correlated with physiological changes in the dorsolateral striatum, an area that contains the projection zone of AGm efferents in the dorsocentral striatum (DCS). In this study, the behavioral effects of 48 h of LD on subjects with either unilateral DCS, AGm, or combined AGm/DCS lesions were investigated to examine whether the integrity of the DCS is crucial for behavioral recovery from neglect and whether LD will have a therapeutic effect on extinction deficits. Subjects were tested for extinction to bilateral simultaneous stimulation of the forepaws, and visual, auditory and tactile neglect. Forty-eight hours of LD failed to produce behavioral recovery from neglect in rats with DCS lesions, or a therapeutic affect on extinction deficits in any of the groups. The results of this study further support the crucial role of the DCS in recovery from neglect induced by AGm lesions and suggests that the DCS may be the crucial site for the mechanisms leading to LD-induced recovery. Further, the ineffectiveness of LD on extinction suggests that components of the neglect syndrome are dissociable and may require different therapeutic interventions.

Unilateral destruction of the dorsocentral striatum in rats produces neglect but not extinction to bilateral simultaneous stimulation

A number of previous studies have indicated that lesions of the medial agranular cortex (AGm) in rats induce multimodal neglect and extinction to bilateral simultaneous stimulation (extinction), the two major symptoms of the neglect syndrome in humans. A recent study demonstrated that lesions of dorsocentral striatum (DCS), the site of AGm projections to the striatum, produce multimodal neglect qualitatively similar to that found with AGm lesions. In the present study, the behavioral effects of unilateral DCS lesions were examined in more detail for the major manifestations of neglect: hemineglect, extinction, and allesthesia/allokinesia. Subjects were tested for extinction to bilateral simultaneous stimulation of the forepaws three times a week for 3 weeks. Neglect testing occurred twice weekly and the subjects were tested for the presence of neglect by rating the magnitude of orientation to visual, tactile, and auditory stimulation. The results indicated that DCS operates, while demonstrating severe neglect, failed to demonstrate extinction or allesthesia/allokinesia. These findings suggest that the neural mechanisms that underlie neglect and extinction are dissociable in this system. A better understanding of the neural mechanisms that underlie extinction is particularly important because humans that have recovered from neglect often continue to demonstrate the debilitating symptoms of extinction.

Visuomotor adaptation to optical prisms: a new cure for spatial neglect?

In this issue, McIntosh and colleagues show that visual and haptic deficits in spatial neglect can be improved following a brief period of visuomotor adaptation to rightward displacing optical prisms. Their paper is the latest in a series of recent studies that have demonstrated the utility of prismatic adaptation in reducing the clinical symptoms of unilateral spatial neglect (Pisella et al., 2002; Rode et al., 1999; Rossetti et al., 1998; Rossetti et al., 1999). The technique has great promise as a rehabilitative tool, and may provide unique insights into the underlying mechanisms of spatial perception and action in normality and pathology. In this article I provide an introduction to the neuropsychological syndrome of spatial neglect, highlighting the significant rehabilitative challenges it poses for clinicians. I then outline the prism adaptation procedure, and consider the possible reasons for its beneficial effects in patients with spatial neglect. I conclude with some open questions and suggestions for future research.

Treatments of unilateral neglect: a review

OBJECTIVES

To review the existing literature on treatments of unilateral neglect, to synthesize findings, and to offer recommendations for future studies.

DATA SOURCES

Computerized databases including MEDLINE and PsychINFO.

STUDY SELECTION

All studies investigating treatment(s) of unilateral neglect.

DATA EXTRACTION

Authors reviewed design and other methodologic issues.

DATA SYNTHESIS

Unilateral neglect is a common consequence of right-hemisphere stroke. It is well recognized that the disorder is heterogeneous and has numerous subtypes. There have been numerous studies showing that arousal, hemispheric activation, and spatial attention treatments may all improve neglect, at least transiently. Despite these promising outcomes, little consensus exists as to whether 1 treatment is more efficacious than others, in part because cross-study differences in methodology render meta-analyses difficult, and in part because many studies fail to document duration of treatment effects or generalization to daily activities. One possibility is that these varied and diverse treatments may all be effective, reflecting redundancy in neural circuits devoted to attention and action in space, and consequent flexibility of the spatial processing system. It remains possible, however, that different subtypes of neglect may respond differentially to treatment of various sorts. Most existing studies of neglect have relied on very small populations of neglect patients, whose neglect is characterized only generally.

CONCLUSION

Methodologic shortcomings hinder assessment of the efficacy of various types of neglect treatment. In the future, these shortcomings could be addressed with larger studies of well-characterized patients that evaluate duration of treatment effects and include functional measures. In addition, the role of overarching variables, such as reduced arousal, requires consideration. The ultimate goal of these studies might be the development of triaging strategies wherein neglect patients are assigned to treatments of most likely benefit on the basis of neuroanatomic and behavioral profiles.

Dopaminergic therapy with carbidopa L-dopa for left neglect after stroke: a case series

OBJECTIVE

To evaluate the efficacy of carbidopa L-dopa (Sinemet) in reducing left spatial neglect after stroke.

DESIGN

Case series.

SETTING

Inpatient neurorehabilitation unit in a regional rehabilitation center.

PARTICIPANTS

A convenience sample of 4 women with right brain strokes and left neglect.

INTERVENTION

A trial of carbidopa L-dopa to treat left neglect, if indicated by selected subtests of the Behavioral Inattention Test (BIT).

MAIN OUTCOME MEASURES

Baseline and posttreatment evaluation with the modified BIT and the FIM instrument.

RESULTS

Three of 4 subjects had significant improvements in their modified BIT scores (8%, 12%, 27%, respectively) and their functional status on the FIM.

CONCLUSION

With further study, carbidopa L-dopa may be shown to reduce unilateral spatial neglect and thereby improve rehabilitation outcomes.

Psychostimulant treatment of stroke and brain injury

Psychopharmacology is rapidly becoming an adjuvant treatment to traditional rehabilitation strategies for patients with stroke or brain injury because it helps to facilitate recovery in a time-efficient manner. Norepinephrine, dopamine, acetylcholine, and serotonin appear to play important roles in recovery from stroke or brain injury. Animal models have shown that blockade of these neurotransmitters inhibits recovery, whereas recovery is promoted by drugs that promote norepinephrine, dopamine, acetylcholine, and serotonin activity. Preliminary evidence from human trials supports these findings. Further study is needed, but expanded use of pharmacologic agents for stroke and brain-injured patients appears imminent.