Publications
116 results found
Arshad Q, Nigmatullina Y, Roberts RE, et al., 2016, Perceived state of self during motion can differentially modulate numerical magnitude allocation., European Journal of Neuroscience, Vol: 44, Pages: 2369-2374, ISSN: 1460-9568
Although a direct relationship between numerical-allocation and spatial-attention has been proposed, recent research suggests these processes are not directly coupled. In keeping with this, spatial attention shifts induced either via visual or vestibular motion can modulate numerical allocation in some circumstances but not in others. In addition to shifting spatial attention, visual or vestibular motion-paradigms also (i) elicit compensatory eye-movements which themselves can influence numerical-processing and (ii) alter the perceptual-state of-"self", inducing changes in bodily self-consciousness impacting upon cognitive mechanisms. Thus, the precise mechanism by which motion modulates numerical-allocation remains unknown. We sought to investigate the influence that different perceptual experiences of motion have upon numerical magnitude allocation whilst controlling for both eye-movements and task-related effects. We first used optokinetic visual-motion stimulation (OKS) to elicit the perceptual experience of either "visual world" or "self"-motion during which eye movements were identical. In a second experiment we used a vestibular protocol examining the effects of perceived and subliminal angular rotations in darkness, which also provoked identical eye movements. We observed that during the perceptual experience of "visual-world" motion, rightward OKS biased judgments towards smaller numbers, whereas leftward OKS biased judgments towards larger numbers. During the perceptual experience of "self-motion", judgments were biased towards larger numbers irrespective of the OKS direction. Contrastingly, vestibular motion perception was found not to modulate numerical magnitude allocation, nor was there any differential modulation when comparing "perceived" versus "subliminal" rotations. We provide a novel demonstration that magnitude-allocation can be differentially modulated by the perceptual state
Arshad Q, Bonsu A, Malhotra PA, et al., 2016, Influence of lateralised hemispheric asymmetries upon numerical cognition and its influence upon pro-social decision making in Parkinson's disease, Publisher: WILEY, Pages: 97-97, ISSN: 1351-5101
Li K, Russell C, Balaji N, et al., 2016, The effects of motivational reward on the pathological attentional blink following right hemisphere stroke, Neuropsychologia, Vol: 92, Pages: 190-196, ISSN: 1873-3514
Recent work has shown that attentional deficits following stroke can be modulated by motivational stimulation, particularly anticipated monetary reward. Here we examined the effects of anticipated reward on the pathological attentional blink (AB), an index of temporal selective attention, which is prolonged in patients with right hemisphere damage and a history of left neglect. We specifically compared the effects of reward versus feedback-without-reward on the AB in 17 patients. We found that the patients all manifested impaired performance compared to healthy controls and that reward modulated the pathological blink in the patient group, but only in the second experimental session. When the performance of patients whose neglect had recovered was compared with that of patients who had ongoing or persistent neglect, reward appeared to only influence the AB in the former. These results have implications for our understanding of motivation-attention interactions following right hemisphere stroke, and how they may impact upon recovery from spatial neglect.
Arshad Q, Bronstein A, 2016, Bidirectional modulation of numerical magnitude, Cerebral Cortex, Vol: 26, Pages: 2311-2324, ISSN: 1460-2199
Numerical cognition is critical for modern life; however, the precise neural mechanisms underpinning numerical magnitude allocation in humans remain obscure. Based upon previous reports demonstrating the close behavioral and neuro-anatomical relationship between number allocation and spatial attention, we hypothesized that these systems would be subject to similar control mechanisms, namely dynamic interhemispheric competition. We employed a physiological paradigm, combining visual and vestibular stimulation, to induce interhemispheric conflict and subsequent unihemispheric inhibition, as confirmed by transcranial direct current stimulation (tDCS). This allowed us to demonstrate the first systematic bidirectional modulation of numerical magnitude toward either higher or lower numbers, independently of either eye movements or spatial attention mediated biases. We incorporated both our findings and those from the most widely accepted theoretical framework for numerical cognition to present a novel unifying computational model that describes how numerical magnitude allocation is subject to dynamic interhemispheric competition. That is, numerical allocation is continually updated in a contextual manner based upon relative magnitude, with the right hemisphere responsible for smaller magnitudes and the left hemisphere for larger magnitudes.
Kaski D, Quadir S, Nigmatullina Y, et al., 2015, Temporoparietal encoding of space and time during vestibular-guided orientation, Brain, Vol: 139, Pages: 392-403, ISSN: 0006-8950
When we walk in our environment, we readily determine our travelled distance and location using visual cues. In the dark, estimating travelled distance uses a combination of somatosensory and vestibular (i.e. inertial) cues. The observed inability of patients with complete peripheral vestibular failure to update their angular travelled distance during active or passive turns in the dark implies a privileged role for vestibular cues during human angular orientation. As vestibular signals only provide inertial cues of self-motion (e.g. velocity, °/s), the brain must convert motion information to distance information (a process called ‘path integration’) to maintain our spatial orientation during self-motion in the dark. It is unknown, however, what brain areas are involved in converting vestibular-motion signals to those that enable such vestibular-spatial orientation. Hence, using voxel-based lesion–symptom mapping techniques, we explored the effect of acute right hemisphere lesions in 18 patients on perceived angular position, velocity and motion duration during whole-body angular rotations in the dark. First, compared to healthy controls’ spatial orientation performance, we found that of the 18 acute stroke patients tested, only the four patients with damage to the temporoparietal junction showed impaired spatial orientation performance for leftward (contralesional) compared to rightward (ipsilesional) rotations. Second, only patients with temporoparietal junction damage showed a congruent underestimation in both their travelled distance (perceived as shorter) and motion duration (perceived as briefer) for leftward compared to rightward rotations. All 18 lesion patients tested showed normal self-motion perception. These data suggest that the cerebral cortical regions mediating vestibular-motion (‘am I moving?’) and vestibular-spatial perception (‘where am I?’) are distinct. Furthermore, the congruent contralesiona
Li LM, Leech R, Scott GT, et al., 2015, The effect of oppositional parietal transcranial direct current stimulation on lateralized brain functions, European Journal of Neuroscience, Vol: 42, Pages: 2904-2914, ISSN: 1460-9568
Cognitive functions such as numerical processing and spatial attention show varying degrees of lateralization. Transcranial direct current stimulation (tDCS) can be used to investigate how modulating cortical excitability affects performance of these tasks. This study investigated the effect of bi-parietal tDCS on numerical processing, spatial and sustained attention. It was hypothesized that tDCS would have distinct effects on these tasks because of varying lateralization (numerical processing left, spatial attention right) and that these effects are partly mediated by modulation of sustained attention. A single-blinded, crossover, sham-controlled study was performed. Eighteen healthy right-handed participants performed cognitive tasks during three sessions of oppositional parietal tDCS stimulation: sham; right anodal with left cathodal (RA/LC); and right cathodal with left anodal (RC/LA). Participants performed a number comparison task, a modified Posner task, a choice reaction task (CRT) and the rapid visual processing task (RVP). RA/LC tDCS impaired number comparison performance compared with sham, with slower responses to numerically close numbers pairs. RA/LC and RC/LA tDCS had distinct effects on CRT performance, specifically affecting vigilance level during the final block of the task. No effect of stimulation on the Posner task or RVP was found. It was demonstrated that oppositional parietal tDCS affected both numerical performance and vigilance level in a polarity-dependent manner. The effect of tDCS on numerical processing may partly be due to attentional effects. The behavioural effects of tDCS were specifically observed under high task demands, demonstrating the consequences of an interaction between stimulation type and cognitive load.
Bronstein AM, Arshad Q, Siddiqui S, et al., 2015, Right hemisphere dominance directly predicts both baseline V1 cortical excitability and the degree of top-down modulation exerted over low-level brain structures, Neuroscience, Vol: 311, Pages: 484-489, ISSN: 0306-4522
Right hemisphere dominance for visuo-spatial attention is characteristically observed in most right-handed individuals. This dominance has been attributed to both an anatomically larger right fronto-parietal network and the existence of asymmetric parietal interhemispheric connections. Previously it has been demonstrated that interhemispheric conflict, which induces left hemisphere inhibition, results in the modulation of both (i) the excitability of the early visual cortex (V1) and (ii) the brainstem-mediated vestibular–ocular reflex (VOR) via top-down control mechanisms. However to date, it remains unknown whether the degree of an individual’s right hemisphere dominance for visuospatial function can influence, (i) the baseline excitability of the visual cortex and (ii) the extent to which the right hemisphere can exert top-down modulation. We directly tested this by correlating line bisection error (or pseudoneglect), taken as a measure of right hemisphere dominance, with both (i) visual cortical excitability measured using phosphene perception elicited via single-pulse occipital trans-cranial magnetic stimulation (TMS) and (ii) the degree of trans-cranial direct current stimulation (tDCS)-mediated VOR suppression, following left hemisphere inhibition. We found that those individuals with greater right hemisphere dominance had a less excitable early visual cortex at baseline and demonstrated a greater degree of vestibular nystagmus suppression following left hemisphere cathodal tDCS. To conclude, our results provide the first demonstration that individual differences in right hemisphere dominance can directly predict both the baseline excitability of low-level brain structures and the degree of top-down modulation exerted over them.
Malhotra PA, Russell C, 2015, Does stroke imaging provide insights into the neural basis of cognition?, Current Neurology and Neuroscience Reports, Vol: 15, ISSN: 1534-6293
Since the advent of in vivo imaging, first with CT, and then MRI, structural neuroimaging in patients has been widely used as a tool to explore the neural correlates of a wide variety of cognitive functions. Findings from studies using this methodology have formed a core component of current accounts of cognition, but there are a number of problematic issues related to inferring cognitive functions from structural imaging data in stroke and more generally, lesion-based neuropsychology as a whole. This review addresses these concerns in the context of spatial neglect, a common disorder most frequently encountered following right hemisphere stroke. Recent literature, including attempts to address some of these questions, is discussed. Novel approaches and findings from related fields that may help to put stroke-based lesion-mapping studies into perspective are reviewed, allowing critical but constructive evaluation of previous work in the field.
Li K, Malhotra PA, 2015, Spatial Neglect, Practical Neurology, Vol: 15, Pages: 333-339, ISSN: 1474-7766
The syndrome of visuospatial neglect is acommon consequence of unilateral brain injury.It is most often associated with stroke and ismore severe and persistent following righthemisphere damage, with reported frequenciesin the acute stage of up to 80%. Neglect isprimarily a disorder of attention whereby patientscharacteristically fail to orientate, to report or torespond to stimuli located on the contralesionalside. Neglect is usually caused by large strokes inthe middle cerebral artery territory and isheterogeneous, such that most patients do notmanifest every feature of the syndrome.A number of treatments may improve neglect,but there is no widely accepted universalapproach to therapy. Although most patientsrecover spontaneously, the evidence suggeststhat they continue to have significant cognitiveimpairments, particularly relating to attention.
Malhotra PA, Bronstein AM, 2015, Antisaccades and executive dysfunction in PD: Two sides of the same coin?, MOVEMENT DISORDERS, Vol: 30, Pages: 745-746, ISSN: 0885-3185
Adams G, Brown A, Burnside A, et al., 2015, An undiagnosed stupor in the acute medical unit: a case of malignant catatonia, QJM-AN INTERNATIONAL JOURNAL OF MEDICINE, Vol: 108, Pages: 335-336, ISSN: 1460-2725
Kamourieh S, Braga RM, Leech R, et al., 2015, Neural systems involved when attending to a speaker, Cerebral Cortex, Vol: 25, Pages: 4284-4298, ISSN: 1460-2199
Remembering what a speaker said depends on attention. During conversational speech, the emphasis is on working memory, but listening to a lecture encourages episodic memory encoding. With simultaneous interference from background speech, the need for auditory vigilance increases. We recreated these context-dependent demands on auditory attention in 2 ways. The first was to require participants to attend to one speaker in either the absence or presence of a distracting background speaker. The second was to alter the task demand, requiring either an immediate or delayed recall of the content of the attended speech. Across 2 fMRI studies, common activated regions associated with segregating attended from unattended speech were the right anterior insula and adjacent frontal operculum (aI/FOp), the left planum temporale, and the precuneus. In contrast, activity in a ventral right frontoparietal system was dependent on both the task demand and the presence of a competing speaker. Additional multivariate analyses identified other domain-general frontoparietal systems, where activity increased during attentive listening but was modulated little by the need for speech stream segregation in the presence of 2 speakers. These results make predictions about impairments in attentive listening in different communicative contexts following focal or diffuse brain pathology.
Koa-Wing M, Jamil-Copley S, Ariff B, et al., 2014, Haemorrhagic cerebral air embolism from an atrio-oesophageal fistula following atrial fibrillation ablation., Perfusion, Vol: 30, Pages: 484-486, ISSN: 0935-0020
We report the case of a man found unconscious three weeks following atrial fibrillation (AF) ablation. Cranial and thoracic imaging demonstrated multiple areas of pneumo-embolic infarction secondary to an atrio-oesophageal fistula (AEF). AEF is a recognised, but rare, complication of AF ablation.(1-8) Early recognition is critical as the mortality is 100% without surgical intervention. We consider the postulated mechanisms of AEF formation, the spectrum of clinical presentation, investigations and treatment.
Bodak R, Malhotra P, Bernardi NF, et al., 2014, Reducing chronic visuo-spatial neglect following right hemisphere stroke through instrument playing, FRONTIERS IN HUMAN NEUROSCIENCE, Vol: 8, ISSN: 1662-5161
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- Citations: 22
de Bourbon-Teles J, Bentley P, Koshino S, et al., 2014, Thalamic control of human attention driven by memory and learning, Current Biology, Vol: 24, Pages: 993-999, ISSN: 0960-9822
The role of the thalamus in high-level cognition—attention, working memory (WM), rule-based learning, and decision making—remains poorly understood, especially in comparison to that of cortical frontoparietal networks [1, 2, 3]. Studies of visual thalamus have revealed important roles for pulvinar and lateral geniculate nucleus in visuospatial perception and attention [4, 5, 6, 7, 8, 9, 10] and for mediodorsal thalamus in oculomotor control [11]. Ventrolateral thalamus contains subdivisions devoted to action control as part of a circuit involving the basal ganglia [12, 13] and motor, premotor, and prefrontal cortices [14], whereas anterior thalamus forms a memory network in connection with the hippocampus [15]. This connectivity profile suggests that ventrolateral and anterior thalamus may represent a nexus between mnemonic and control functions, such as action or attentional selection. Here, we characterize the role of thalamus in the interplay between memory and visual attention. We show that ventrolateral lesions impair the influence of WM representations on attentional deployment. A subsequent fMRI study in healthy volunteers demonstrates involvement of ventrolateral and, notably, anterior thalamus in biasing attention through WM contents. To further characterize the memory types used by the thalamus to bias attention, we performed a second fMRI study that involved learning of stimulus-stimulus associations and their retrieval from long-term memory to optimize attention in search. Responses in ventrolateral and anterior thalamic nuclei tracked learning of the predictiveness of these abstract associations and their use in directing attention. These findings demonstrate a key role for human thalamus in higher-level cognition, notably, in mnemonic biasing of attention.
Kaski D, Quadir S, Nigmatullina Y, et al., 2014, Human angular path integration, timing and the temporoparietal junction, Joint Congress of European Neurology, Publisher: SPRINGER HEIDELBERG, Pages: S194-S194, ISSN: 0340-5354
Devine MJ, Bentley P, Jones B, et al., 2014, The role of the right inferior frontal gyrus in the pathogenesis of post-stroke psychosis, JOURNAL OF NEUROLOGY, Vol: 261, Pages: 600-603, ISSN: 0340-5354
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- Citations: 33
Russell C, Malhotra P, Deidda C, et al., 2013, Dynamic attentional modulation of vision across space and time after right hemisphere stroke and in ageing, Cortex, Vol: 49, Pages: 1874-1883, ISSN: 0010-9452
IntroductionAttention modulates the availability of sensory information to conscious perception. In particular, there is evidence of pathological, spatial constriction of the effective field of vision in patients with right hemisphere damage when a central task exhausts available attentional capacity. In the current study we first examined whether this constriction might be modulated across both space and time in right hemisphere stroke patients without neglect. Then we tested healthy elderly people to determine whether non-pathological ageing also leads to spatiotemporal impairments of vision under conditions of high attention load.MethodsRight hemisphere stroke patients completed a task at fixation while attempting to discriminate letters appearing in the periphery. Attentional load of the central task was modulated by increasing task difficulty. Peripheral letters appeared simultaneously with the central task or at different times (stimulus onset asynchronies, SOAs) after it. In a second study healthy elderly volunteers were tested with a modified version of this paradigm.ResultsUnder conditions of high attention load right hemisphere stroke patients have a reduced effective visual field, over a significantly extended ‘attentional blink’, worse for items presented to their left. In the second study, older participants were unable to discriminate otherwise salient items across the visual field (left or right) when their attention capacity was loaded on the central task. This deficit extended temporally, with peripheral discrimination ability not returning to normal for up to 450 msec.ConclusionsDynamically tying up attention resources on a task at fixation can have profound effects in patient populations and in normal ageing. These results demonstrate that items can escape conscious detection across space and time, and can thereby impact significantly on visual perception in these groups.
Russell C, Li K, Malhotra PA, 2013, Harnessing motivation to alleviate neglect, FRONTIERS IN HUMAN NEUROSCIENCE, Vol: 7, ISSN: 1662-5161
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- Citations: 15
Kaski D, Stafford N, Mehta A, et al., 2013, Melanotan and the Posterior Reversible Encephalopathy Syndrome, Annals of Internal Medicine, Vol: 158, Pages: 707-708, ISSN: 0003-4819
Malhotra PA, Soto D, Li K, et al., 2013, Reward modulates spatial neglect, JOURNAL OF NEUROLOGY NEUROSURGERY AND PSYCHIATRY, Vol: 84, Pages: 366-369, ISSN: 0022-3050
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- Citations: 37
Li K, Soto D, Russell C, et al., 2013, THE EFFECTS OF REWARD ON THE ATTENTIONAL BLINK IN HEALTHY HUMANS AND PATIENTS WITH RIGHT HEMISPHERE STROKE, 20th Annual Meeting of the Cognitive-Neuroscience-Society, Publisher: MIT PRESS, Pages: 209-209, ISSN: 0898-929X
Kaski D, Malhotra P, Bronstein AM, et al., 2012, TEMPOROPARIETAL CORTEX AFFORDS SELF-LOCATION PERCEPTION BY A TEMPORAL INTEGRATION OF SENSORY SIGNALS OF MOTION, Annual Meeting of the Association-of-British-Neurologists, Publisher: BMJ PUBLISHING GROUP, ISSN: 0022-3050
Gorgoraptis N, Mah Y-H, Machner B, et al., 2012, The effects of the dopamine agonist rotigotine on hemispatial neglect following stroke, BRAIN, Vol: 135, Pages: 2478-2491, ISSN: 0006-8950
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- Citations: 61
Russell C, Spencer S, Musil AS, et al., 2012, Failure of spatial representation contributes to memory decline during aging, COGNITIVE PROCESSING, Vol: 13, Pages: S49-S50, ISSN: 1612-4782
Chica AB, Thiebaut de Schotten M, Toba M, et al., 2012, Attention networks and their interactions after right-hemisphere damage, CORTEX, Vol: 48, Pages: 654-663, ISSN: 0010-9452
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- Citations: 59
Rossit S, McIntosh RD, Malhotra P, et al., 2012, Attention in action: Evidence from on-line corrections in left visual neglect, NEUROPSYCHOLOGIA, Vol: 50, Pages: 1124-1135, ISSN: 0028-3932
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- Citations: 11
Gorgoraptis N, Mah Y-H, Machner B, et al., 2012, Effects of the Dopamine Agonist Rotigotine on Hemispatial Neglect Following Stroke, 137th Annual Meeting of the American-Neurological-Association (ANA), Publisher: WILEY-BLACKWELL, Pages: S84-S84, ISSN: 0364-5134
Rossit S, Malhotra P, Muir K, et al., 2011, The Role of Right Temporal Lobe Structures in Off-line Action: Evidence from Lesion-Behavior Mapping in Stroke Patients, CEREBRAL CORTEX, Vol: 21, Pages: 2751-2761, ISSN: 1047-3211
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- Citations: 22
Rossit S, Fraser JA, Teasell R, et al., 2011, Impaired delayed but preserved immediate grasping in a neglect patient with parieto-occipital lesions, NEUROPSYCHOLOGIA, Vol: 49, Pages: 2498-2504, ISSN: 0028-3932
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- Citations: 10
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