Asymmetrical distractibility of global and focal visuospatial attention during segmental and total compound line bisections.

BACKGROUND/OBJECTIVES: Compound horizontal lines are composed of 2 segments of unequal length and width. Line bisection requires that the participants attend to the entire line (global attention). The longer segment often distracts participants, suggesting that attention directed to this segment (focal attention) disrupts the allocation of global attention. This study attempted to learn whether the allocation of focal attention to a line segment is distracted by global attention allocated to the entire line and whether there are right-left distraction asymmetries when allocating focal or global attention. METHOD: Twenty-four healthy adults (12 > 65 years old) attempted to bisect horizontal lines composed of 2 segments of unequal length, with the larger segment placed to the right or left. They were also asked to bisect the longer segment of these lines. RESULTS: When allocating focal attention to the larger segment, healthy participants were more distracted when the smaller segment was on the left than on the right. In contrast, when attempting to allocate global attention to the entire line, participants were more distracted when the larger segment was on the right side. There were no significant differences between older and younger participants. CONCLUSIONS: The asymmetrical global distraction during segment bisection might be related to the right hemisphere's dominance in mediating global attention and allocating attention leftward. In contrast, the asymmetrical focal distraction during full-line bisection might be related to the left hemisphere's dominance in mediating focal attention and allocating attention toward the right. (PsycINFO Database Record (c) 2018 APA, all rights reserved).

Background distraction during vertical solid and character line bisections.

Background-objectives: When vertical lines are positioned above or below the center of the page, line bisection deviates toward the center of the page, suggesting that the edges of the page distract the allocation of attention to the line. A letter-character line (LCL) bisection requires both global and focal attention, to identify the target letter closest to the line's center. If more focal and less global attention is allocated to a LCL, more global attentional resources may be available and inadvertently allocated to the page. Alternatively, if the allocation of focal attention to a LCL inhibits global attentional processing, there may be less distraction by the page. METHOD: Twenty-four healthy adults (12 older) bisected vertical solid and character lines centered, or positioned closer to the top or bottom of the page. RESULTS: There was no difference between bisection of solid and character lines centered on the page. Page-related deviations were greater with character lines than solid line bisections, and greater for lines positioned toward the top than the bottom of the page. With lines positioned toward the top, the older participants' attempted bisections were higher than those of the younger participants. CONCLUSIONS: These results suggest that the allocation of focal attention increases global attentional distractibility and that global-background attentional distraction is greater when the vertical lines are placed in the upper part of the page. Older participants appeared to be less distracted when lines were placed toward the top of the page, but the reason for this age difference requires further research.

Effects of aging on action-intentional programming.

BACKGROUND: Action-intentional programs control "when" we initiate, inhibit, continue, and stop motor actions. The purpose of this study was to learn if there are changes in the action-intentional system with healthy aging, and if these changes are asymmetrical (right versus left upper limb) or related to impaired interhemispheric communication. METHODS: We administered tests of action-intention to 41 middle-aged and older adults (61.9 ± 12.3 years). RESULTS: Regression analyses revealed that older age predicted a decrement in performance for tests of crossed motor response inhibition as well as slower motor initiation with the left hand. CONCLUSION: Changes in action-intention with aging appear to be related to alterations of interhemispheric communication and/or age-related right hemisphere dysfunction; however, further research is needed to identify the mechanisms for age-related changes in the brain networks that mediate action-intention.

Callosal disconnection neglect: reassessment after 34 years.

In 1984, Watson and Heilman reported a patient with a partial callosal disconnection following an infarction of the anterior portion of her corpus callosum. This woman's performance on line-bisection tasks revealed "callosal disconnection neglect." The objective of this research is to reexamine this woman 34 years after her callosal disconnection to gain information about her recovery. The patient completed visual line-bisection tasks in which horizontal lines were placed in the right, left, and center hemispaces and she performed these bisections using her right or left hand. Unlike her performance 34 years ago in which each hand deviated to its ipsilateral hemispace, with greater deviation when lines were placed in the contralateral rather than ipsilateral hemispace, currently, there were no significant main effects for hand or spatial position. Thus, there were notable differences between this woman's most recent performance on the line bisection and her previous performance 34 years ago. Unlike her prior testing 34 years back, this woman's most recent performance resembled the performance of a previous tested healthy control group for whom differences in hand and hemispace were not found. It remains unclear whether her callosal disconnection neglect improved because each hemisphere learned to allocate ipsilateral spatial attention or because she learned a compensatory strategy in which she turned her body so that the lines placed in her right or left hemispace were now toward her midline.

The aging brain: Movement speed and spatial control.

BACKGROUND/OBJECTIVES: With aging, people commonly develop motor slowing (bradykinesia). Although this slowness with aging may be entirely related to degradation of the cerebral networks important in motor programing, it is possible that, at least in part, it may be a learned procedure for enhancing the accuracy and/or precision of movements. The goal of this study is to test these contradictory hypotheses. METHODS: Twenty-four healthy adults, 12 younger than age 26 and 12 older than age 65 were asked to make alternative marks with a pen between a card centered in front of them and a series of circles distributed across a page. Performance was timed, and participants were instructed to complete the task as quickly as possible while not sacrificing accuracy for speed. The circle sizes and hand used varied by trial. RESULTS: The older adults performed the task more slowly for all target circle diameters. As the circles decreased in size, the younger adults performed the task more rapidly than did the older participants, but the younger participants also had a greater decline in accuracy. CONCLUSIONS: During this aiming task, healthy older adults were less likely than younger adults to sacrifice accuracy for speed. Thus, at least in part, their slowing may be a learned adaptive strategy.

Callosal apraxia: a 34-year follow-up study.

Loss of ability of the left upper limb (LUL) to correctly produce spatial and temporal components of skilled purposeful movements was reported 34 years ago in a woman with a callosal infarction. To learn about recovery, we recently reexamined this woman. This woman was tested for ideomotor apraxia by asking her to pantomime to command and to seeing pictures of tools. Whereas she performed normally with her right upper limb, her LUL remained severely apraxic, making many spatial (postural and movement) errors. Initially, she did not reveal loss of finger-hand deftness (limb-kinetic apraxia), and when tested again with the coin rotation task, her left hand performance was normal. Without vision, she could name objects placed in her left hand but not name numbers written in this hand. Since this woman had a callosal lesion, failure to recover cannot be accounted for by left hemisphere inhibition of her right hemisphere. Although failure for her LUL to improve may have been related to not using her LUL for skilled actions, her right hemisphere was able to observe transitive actions, and this failure of her LUL to produce skilled purposeful movements suggests her right hemisphere may have not had the capacity to learn these movement representations. Without vision, her ability to recognize objects with her left hand, but not numbers written on her left palm, suggests graphesthesia may require that her left hand did not have access to movement representations important for programming these numbers when writing.

Allocentric But Not Egocentric Pseudoneglect of Peripersonal Space.

BACKGROUND AND OBJECTIVE: Healthy adults often deviate leftward on line bisection tasks (allocentric pseudoneglect) but rightward on body part bisection tasks (egocentric pseudoneglect). People visually estimate distance in peripersonal space by comparing the distance to the length of a body part such as an arm's length (an egocentric reference) or using standard units of distance such as inches (an allocentric reference). Our objective was to learn whether people have pseudoneglect when estimating distances in peripersonal space using egocentric versus allocentric reference frames. METHODS: Twelve healthy participants standing either next to or 5 feet away from a wall were asked to move away from or toward the wall such that their shoulder would be what they judged to be an arm's length or a distance of 1, 2, or 3 feet from the wall. RESULTS: The participants estimated their arm's length more accurately than the standard units of distance (possibly related to learning and practice). Participants were more precise when estimating the length of their left than their right arm. When estimating standard units of distance, participants underestimated the distances on their left side more than on their right. CONCLUSIONS: Our results support the postulate that left pseudoneglect is an allocentric phenomenon related to a hemispheric asymmetry in computing allocentric distances. The participants underestimated 2 and 3 feet, but overestimated 1 foot. This dichotomy may relate to using focused versus distributed attention. The brain mechanisms leading to these asymmetries remain to be determined.

Cognitive-motor dysfunction after severe traumatic brain injury: A cerebral interhemispheric disconnection syndrome.

BACKGROUND/OBJECTIVES: In most right-handed people, the left hemisphere is dominant for programming the temporal and spatial "how" (praxis) aspects of purposeful skilled movements, and the right hemisphere is dominant for control of the intentional "when" aspects of actions that mediate initiation, persistence, termination, and inhibition. Since the interhemispheric axons of the corpus callosum are especially susceptible to shearing from torsional forces during traumatic brain injury (TBI), the goal of this study was to learn whether participants with a history of severe traumatic brain injury demonstrate three types of cognitive-motor impairments that may result from callosal injury: ideomotor apraxia of the left hand, limb kinetic apraxia of the left hand, and hypokinesia of the right hand in response to left hemispatial stimuli. METHOD: Nine participants with severe TBI and nine healthy control participants were studied for the presence of ideomotor apraxia, limb kinetic apraxia, and hypokinesia. RESULTS: When compared to the control participants, the participants with TBI revealed ideomotor apraxia and limb kinetic apraxia of the left hand and hypokinesia in response to left-sided visual stimuli when tested with the right hand. CONCLUSIONS: TBI appears to cause unilateral disorders of cognitive-motor functions. Future research is needed to understand how these cognitive-motor disorders are related to interhemispheric disconnection most likely induced by injury to the corpus callosum.

Abnormal tactile pressure perception in Parkinson's disease.

BACKGROUND/OBJECTIVE: Some of the behavioral disorders associated with Parkinson's disease (PD), such as the reduced magnitude of actions (hypometria) may be related to an impairment in cognitive disengagement. A reduced ability to disengage attention from previous sensory stimuli will alter perception with a reduced range of estimated stimulus magnitudes (contraction to the mean). To test this disengagement hypothesis, participants with PD were tested to learn whether they had abnormal sensory perception with overestimation of the relative magnitude of weaker tactile stimuli and underestimation of the relative magnitude of stronger tactile stimuli in relation to a reference stimulus. DESIGN/METHOD: The participants were 12 people with PD and 12 healthy adults. Test stimuli were applied to the palm using Semmes-Weinstein monofilaments (SWM) of 6 magnitudes, 3 greater and 3 less than a standard stimulus. In each trial, after being stimulated with the reference (standard) stimulus, a test monofilament was applied, and the participant was asked to provide a numerical estimate of the magnitude of the second stimulus relative to the standard. RESULTS: Compared to the control group, participants with PD overestimated the magnitudes of the tactile stimuli below the standard stimulus and underestimated the magnitudes of stimuli above the standard stimulus. CONCLUSIONS: These results demonstrate that people with PD likely have a reduced ability to estimate the relative magnitudes of tactile sensory stimuli. Whereas deafferentation would alter perception in one direction, the impairment of these participants with PD may result from a disorder of disengagement, and disorders of disengagement are often due to frontal-executive dysfunction.

Global attentional neglect of segmented lines in Parkinson's disease.

Global attention requires disengagement from focal elements of stimuli. Since people with Parkinson's disease (PD) may reveal impaired disengagement, this study attempted to learn if people with PD may be impaired at allocating global attention. Healthy adults and people with PD attempted to bisect lines of uniform thickness and lines composed of two segments of unequal thickness and length. When the longer line segment was to the right of the shorter segment, the group with PD demonstrated an increased deviation toward the longer segment, supporting the postulate that people with PD have an impaired ability to disengage focal attention and engage global spatial attention.

Functional Brain Correlates of Upper Limb Spasticity and Its Mitigation following Rehabilitation in Chronic Stroke Survivors.

Background. Arm spasticity is a challenge in the care of chronic stroke survivors with motor deficits. In order to advance spasticity treatments, a better understanding of the mechanism of spasticity-related neuroplasticity is needed. Objective. To investigate brain function correlates of spasticity in chronic stroke and to identify specific regional functional brain changes related to rehabilitation-induced mitigation of spasticity. Methods. 23 stroke survivors (>6 months) were treated with an arm motor learning and spasticity therapy (5 d/wk for 12 weeks). Outcome measures included Modified Ashworth scale, sensory tests, and functional magnetic resonance imaging (fMRI) for wrist and hand movement. Results. First, at baseline, greater spasticity correlated with poorer motor function (P = 0.001) and greater sensory deficits (P = 0.003). Second, rehabilitation produced improvement in upper limb spasticity and motor function (P < 0.0001). Third, at baseline, greater spasticity correlated with higher fMRI activation in the ipsilesional thalamus (rho = 0.49, P = 0.03). Fourth, following rehabilitation, greater mitigation of spasticity correlated with enhanced fMRI activation in the contralesional primary motor (r = -0.755, P = 0.003), premotor (r = -0.565, P = 0.04), primary sensory (r = -0.614, P = 0.03), and associative sensory (r = -0.597, P = 0.03) regions while controlling for changes in motor function. Conclusions. Contralesional motor regions may contribute to restoring control of muscle tone in chronic stroke.

Praxis and writing in a right-hander with crossed aphasia.

Studies of patients with brain lesions have demonstrated that language and praxis are mediated by dissociable networks. However, language has the capacity to influence the selection of purposeful actions. The abilities to use language and to program purposeful movements are often mediated by networks that have anatomic proximity. With hemispheric injury, the diagnosis of apraxia is often confounded by the specific influence of language impairments on the ability to select and produce transitive gestures. We report a patient who illustrates this confound. This patient is a right-handed man who developed global aphasia and neglect after a right hemispheric stroke. His right hand remained deft, and when asked to produce specific transitive gestures (pantomimes), he often performed normally but did make some body part as object and perseverative errors. However, he did not demonstrate the temporal or spatial errors typical of ideomotor apraxia. He also had a perseverative agraphia. Our patient's left hemisphere praxis system appeared to be intact, and the error types demonstrated during production of transitive gestures cannot be attributed to a degradation of postural and movement (praxis) programs mediated by his left hemisphere. The praxis errors types are most consistent with a deficit in the ability to select the necessary praxis programs. Thus, our patient appeared to have dissociation between language and praxis programs that resulted in body part as object and perseverative errors.

Hypometric allocentric and egocentric distance estimates in Parkinson disease.

OBJECTIVE AND BACKGROUND: Persons with Parkinson disease (PD) show hypometric movements and make hypometric estimates of imagined actions. These deficits may be related to misestimates of the length of body parts. Our objective was to learn whether patients with PD are impaired in their estimations of their arm's length and standard units of distance. METHODS: We tested 20 patients with PD, all on therapeutic doses of dopaminergic medications, and 13 healthy controls. In half of the trials, the participants stood so that either their right or left shoulder was adjacent to a wall; in the other half, their right or left shoulder was 5 feet from the wall. In the egocentric testing condition, they were asked to move their body toward or away from the wall to what they considered was an arm's length from the wall. In the allocentric testing condition, they were to move toward or away from the wall so that their proximal shoulder was a standard unit distance of 1, 2, or 3 feet from the wall. RESULTS: The patients with PD made much greater hypometric (too close to the wall) errors. Since at 5 feet from the wall they had to move farther to underestimate distances, their errors cannot be explained by hypometric movements. The results did not differ significantly by egocentric or allocentric estimation, side of shoulder proximity, or side of PD onset. CONCLUSIONS: Our findings support the idea that the egocentric and allocentric hypometria associated with PD is a perceptual rather than motor disorder.

Hemispheric differences in ischemic stroke: is left-hemisphere stroke more common?

BACKGROUND AND PURPOSE: Understanding the mechanisms underlying stroke can aid the development of therapies and improve the final outcome. The purposes of this study were to establish whether there are characteristic mechanistic differences in the frequency, severity, functional outcome, and mortality between left- and right-hemisphere ischemic stroke and, given the velocity differences in the carotid circulation and direct branching of the left common carotid artery from the aorta, whether large-vessel ischemia (including cardioembolism) is more common in the territory of the left middle cerebral artery. METHODS: Trial cohorts were combined into a data set of 476 samples. Using Trial of Org 10172 in Acute Stroke Treatment criteria, ischemic strokes in a total 317 patients were included in the analysis. Hemorrhagic stroke, stroke of undetermined etiology, cryptogenic stroke, and bilateral ischemic strokes were excluded. Laterality and vascular distribution were correlated with outcomes using a logistic regression model. The etiologies of the large-vessel strokes were atherosclerosis and cardioembolism. RESULTS: The overall event frequency, mortality, National Institutes of Health Stroke Scale (NIHSS) score, Glasgow Coma Scale score, and rate of mechanical thrombectomy interventions differed significantly between the hemispheres. Left-hemispheric strokes (54%) were more common than right-hemispheric strokes (46%; p=0.0073), and had higher admission NIHSS scores (p=0.011), increased mortality (p=0.0339), and higher endovascular intervention rates (p≤0.0001). ischemic strokes were more frequent in the distribution of the left middle cerebral artery (122 vs. 97; p=0.0003) due to the higher incidence of large-vessel ischemic stroke in this area (p=0.0011). CONCLUSIONS: Left-hemispheric ischemic strokes appear to be more frequent and often have a worse outcome than their right-hemispheric counterparts. The incidence of large-vessel ischemic strokes is higher in the left middle cerebral artery distribution, contributing to these hemispheric differences. The hemispheric differences exhibit a nonsignificant trend when strokes in the middle cerebral artery distribution are excluded from the analysis.

Vertical line quadrisection: "what" it represents and who gets the upper hand.

BACKGROUND: Normal adults demonstrate a slight upward bias (vertical pseudoneglect) when attempting vertical line bisection. The mechanism for this bias is unknown. Activation of the allocentric (object-centered) ventral visual system during attempted bisection may induce this bias. This object-centered ventral stream may also mediate focal attention. As compared to bisection, when normal participants perform a vertical line quadrisection task that requires more focal attention, they may have a greater upward bias. METHODS: Sixteen participants bisected and quadrisected vertical lines. RESULTS: The mean upward bias (deviation error) for the quadrisection tasks was significantly higher than the mean error for the line bisections. CONCLUSIONS: These results are consistent with the hypothesis that activation of the ventral stream by a task that requires focal allocentric attention can induce an upward vertical bias that is greater than the upward bias observed with allocentric line bisection, a task that requires more global attention.

Sign language aphasia from a neurodegenerative disease.

While Alois Alzheimer recognized the effects of the disease he described on speech and language in his original description of the disease in 1907, the effects of Alzheimer's disease (AD) on language in deaf signers has not previously been reported. We evaluated a 55-year-old right-handed congenitally deaf woman with a 2-year history of progressive memory loss and a deterioration of her ability to communicate in American Sign Language, which she learned at the age of eight. Examination revealed that she had impaired episodic memory as well as marked impairments in the production and comprehension of fingerspelling and grammatically complex sentences. She also had signs of anomia as well as an ideomotor apraxia and visual-spatial dysfunction. This report illustrates the challenges in evaluation of a patient for the presence of degenerative dementia when the person is deaf from birth, uses sign language, and has a late age of primary language acquisition. Although our patient could neither speak nor hear, in many respects her cognitive disorders mirror those of patients with AD who had normally learned to speak.

The relationship between semantic knowledge and conceptual apraxia in Alzheimer disease.

BACKGROUND: Conceptual apraxia (CA), a feature of Alzheimer disease (AD), can be detected by asking participants to identify the correct tool to act on an object. Assessment can be based on either learned associations (a tool selection test) or the mechanical properties that the tool needs to alter the target object (an alternative tool selection test). OBJECTIVES: We wanted to determine whether knowledge of semantic taxonomic relations (intrinsic properties shared by items) correlated with performance on tests for CA in people with AD or amnestic mild cognitive impairment (aMCI). METHODS: We tested 10 participants with AD, 12 with aMCI, and 18 healthy older adults for CA using an alternative tool selection test, a tool selection test, and a test of taxonomic relations. RESULTS: The aMCI group did not differ from the control group on the CA tests. The patients with AD were impaired on all tests except tool selection; their performance on the alternative tool selection test correlated significantly with their performance on the taxonomic relations test. CONCLUSIONS: The correlation between performances on the alternative tool selection test and the taxonomic relations test in AD suggests a common pathophysiologic substrate, either impairment in accessing conceptual-semantic representations or a degradation of these representations.

Famous faces but not remembered spaces influence vertical line bisections.

Whereas the ventral visual processing stream mediates facial and object recognition, the dorsal stream mediates recognition of spatial relationships. In addition, ventral lesions have been reported to induce visual inattention to the upper visual field and dorsal lesions inattention to the lower field. The purpose of this study is to test the hypothesis that activation of the ventral stream will induce an upward attentional bias and activation of the dorsal stream, a downward bias, as assessed by vertical line bisection tests. Twelve healthy right-handed individuals performed vertical line bisections. During these trials, either pictures of famous faces or dots in different spatial locations were presented above and below the line. The participants were asked to recognize and remember the faces or locations of dots while they performed the bisections. In control trials, they were no faces or dots. An upward bias was observed in all conditions. This upward bias was significantly increased in the face recognition and recall condition, but not altered in the dot location condition. Although the face task appeared to activate the ventral stream and increase the upward vertical bias, the failure of the dot localization task to alter the bias may be related task selection. Dorsolateral lesions cause optic ataxia, a disorder of the egocentric "where" system, and the dot location task in this study was allocentric. Thus, further research will be needed to learn whether an egocentric spatial localization task, with a memory component, will alter the vertical attentional bias.

Right up there: hemispatial and hand asymmetries of altitudinal pseudoneglect.

BACKGROUND: Pseudoneglect is a normal left sided spatial bias observed with attempted bisections of horizontal lines and a normal upward bias observed with attempted bisections of vertical lines. Horizontal pseudoneglect has been attributed to right hemispheric dominance for the allocation of attention. The goal of this study was to test the hypothesis that the upward bias in vertical line bisection may also relate to right hemispheric dominance for the allocation of attention and/or action-intention. METHODS: Twenty right handed healthy adults were asked to bisect vertical lines presented in the midsagittal plane (center space) and in sagittal planes to the left and right of the midsagittal plane (left and right hemispace) when using a pen held in either the right or left hand. RESULTS: Vertical line bisections were biased upward in all three sagittal planes and higher in left than right hemispace. However, bisections made with the left hand were lower than those made with the right hand. DISCUSSION: Whereas these results suggest a left hemispace-right hemispheric visuospatial attentional upward bias and a relative left hemispheric-right hand upward action-intentional bias, further studies are needed to document this intentional versus attentional bias and to understand the brain mechanisms that produce these biases.

Alternate but do not swim: a test for executive motor dysfunction in Parkinson disease.

The objective of this study is to learn if participants with Parkinson disease (PD), when compared to normal controls, are impaired in making simultaneous but independent right and left hand movements. Participants were tested with Luria's Alternating Hand Postures (AHP) test and modified AHP tests. Twelve PD participants without dementia and twelve matched controls were assessed for their ability to perform the parallel AHP test (both hands remaining in the same coronal plane) and with modifications of this test into swimming (alternative arm extension with finger extension and arm flexion with finger flexion) and reverse swimming (alternative arm extension-finger flexion and arm flexion-finger extension) movements. The participants with PD were significantly impaired when performing the parallel and the reverse swimming movements AHP tests, but not impaired on the swimming movements AHP test. Swimming movements may be phylogenetically and ontogenetically more primitive and not as heavily dependent on frontal-basal ganglia networks; thus performance of swimming movements during the parallel AHP test may decrease this test's sensitivity.