Adam D. Falchook

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.

Radiographic and pathologic findings in an atypical brainstem variant of reversible posterior leukoencephalopathy syndrome.

Background:Reversible posterior leukoencephalopathy syndrome (RPLS) and hypertensive encephalopathy (HE) are terms generally used interchangeably to describe a syndrome characterized by encephalopathy, focal deficits, and vasogenic edema seen on magnetic resonance imaging, which are potentially reversible with treatment. The underlying pathologic changes are less well defined. Previously, the only pathologic data available came from a single autopsy series. Results from a recent biopsy report differ with the autopsy series leading to the suggestion that RPLS and HE may be distinct. Case Report:We report a markedly hypertensive patient with encephalopathy and hemiparesis and focal edema in the brainstem visualized on magnetic resonance imaging. A biopsy was performed that demonstrated pathologic changes associated with RPLS. With treatment of hypertension, the patients symptoms resolved completely. Conclusions:We report an unusual brainstem variant of RPLS, adding to the neuropathologic features of this syndrome, and supporting the predominant view that RPLS and HE have a shared pathologic basis.

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.

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.

Nitrous Oxide Abuse and Vitamin B12 Action in a 20-Year-Old Woman: A Case Report

Herein, we report a case of a 20-year-old (ethnicity not reported) woman with a history of nitrous oxide abuse and clinical symptoms consistent with spinal cord subacute combined degeneration with associated low serum concentrations of vitamin B12, elevated methylmalonic acid levels, and radiologic evidence of demyelination of the dorsal region of the spinal column. The health of the patient improved dramatically with B12 supplementation. In this case, we discuss the interaction of nitrous oxide with the enzymatic pathways involved in the biochemistry of vitamin B12.

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.

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.

Callosal apraxia: a 34-year follow-up study

ABSTRACT 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.

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.

Neuroplasticity, neurotransmitters and new directions for treatment of anomia in Alzheimer disease

Background: Anomia is often one of the earliest signs of Alzheimer disease (AD), and progressive language impairment remains a major source of disability throughout the disease course. Aims: This article reviews the potential uses of pharmacological adjuvants to augment neuroplasticity during speech and language therapy. Main Contribution: We begin with a discussion of the nature of anomia in AD from the perspective of classical aphasia models and in terms of a parallel distributed processing model of language. Physiological functions of acetylcholine, norepinephrine and dopamine are reviewed. We consider how pharmacological manipulation of these neurotransmitters in combination with speech and language therapy has the potential to promote maintenance and restoration of the functional connectivity within the lexical, semantic and phonological networks that are the basis of propositional language. Conclusions: AD is a disease of synaptic loss. People with AD are able to reacquire knowledge, and pharmacological modulation of acetylcholine, norepinephrine and dopamine can influence the maintenance and reformation of neuronal networks.