ORCID Profile
0000-0002-8149-1352
Current Organisations
King's College London
,
University of Sussex
,
University College London
,
Ospedale Veris Delli Ponti Scorrano
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Publications
Does Stroke Imaging Provide Insights into the Neural Basis of Cognition?
Publisher: Springer Science and Business Media LLC
Date: 23-06-2015
DOI: 10.1007/S11910-015-0570-0
Abstract: 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.
Dependence of GAMA galaxy halo masses on the cosmic web environment from 100 deg2of KiDS weak lensing data
Publisher: Oxford University Press (OUP)
Date: 20-07-2016
The effects of motivational reward on the pathological attentional blink following right hemisphere stroke.
Publisher: Elsevier BV
Date: 11-2016
DOI: 10.1016/J.NEUROPSYCHOLOGIA.2016.03.037
Abstract: 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.
Dynamic attentional modulation of vision across space and time after right hemisphere stroke and in ageing
Publisher: Elsevier BV
Date: 07-2013
Self-perspective in episodic memory after parietal damage and in healthy ageing
Publisher: Elsevier BV
Date: 02-2019
DOI: 10.1016/J.NEUROPSYCHOLOGIA.2018.12.013
Abstract: Although there is strong support from functional imaging studies for lateral parietal lobe involvement in episodic memory, patients with damage to these regions do not appear to suffer from severe deficits in this cognitive domain. As such there has been no definitive explanation of this area's precise involvement. Here, we hypothesised that parietal regions play a crucial role in episodic memory - specifically in recollecting details from an egocentric perspective. In order to test this hypothesis systematically, we designed a novel experimental task utilising a head-mounted camera to record images from the participant's perspective, enabling us to evaluate the integrity of memory from the in idual's own point of view. In the first study we examined patients with parietal damage and in a second study, using fMRI, we examined young and older healthy participants. Right-hemisphere patients with parietal damage were able to recall information accurately when recollecting what items had been present and where these items had been. However, patients were significantly impaired when attempting to judge from which perspective they had viewed the scenes. Critically, the patient group showed no evidence of impairment on standard tests of episodic and working memory. Examination of healthy participants in the second study utilised multi-voxel pattern analysis on neural activity during the recognition phase of a similar task. This revealed sensitivity to be highest around the angular gyrus of the lateral parietal cortex for our critical comparison - that is, when viewing stimuli that were the same as their egocentric view during encoding versus the identical scene but presented from an alternative angle. Our results provide important evidence that parietal cortex is directly involved in egocentric spatial perspective aspects of episodic memory and demonstrate for the first time a specific deficit in episodic memory in patients with right parietal damage.
Reward modulates spatial neglect
Publisher: BMJ
Date: 15-10-2013
The masses of satellites in GAMA galaxy groups from 100 square degrees of KiDS weak lensing data
Publisher: Oxford University Press (OUP)
Date: 28-10-2015
The Atacama Cosmology Telescope: A Catalog of >4000 Sunyaev–Zel’dovich Galaxy Clusters
Publisher: American Astronomical Society
Date: 16-02-2021
Abstract: We present a catalog of 4195 optically confirmed Sunyaev–Zel’dovich (SZ) selected galaxy clusters detected with signal-to-noise ratio in 13,211 deg 2 of sky surveyed by the Atacama Cosmology Telescope (ACT). Cluster candidates were selected by applying a multifrequency matched filter to 98 and 150 GHz maps constructed from ACT observations obtained from 2008 to 2018 and confirmed using deep, wide-area optical surveys. The clusters span the redshift range 0.04 z 1.91 (median z = 0.52). The catalog contains 222 z 1 clusters, and a total of 868 systems are new discoveries. Assuming an SZ signal versus mass-scaling relation calibrated from X-ray observations, the s le has a 90% completeness mass limit of M 500c 3.8 × 10 14 M ⊙ , evaluated at z = 0.5, for clusters detected at signal-to-noise ratio in maps filtered at an angular scale of 2.′4. The survey has a large overlap with deep optical weak-lensing surveys that are being used to calibrate the SZ signal mass-scaling relation, such as the Dark Energy Survey (4566 deg 2 ), the Hyper Suprime-Cam Subaru Strategic Program (469 deg 2 ), and the Kilo Degree Survey (825 deg 2 ). We highlight some noteworthy objects in the s le, including potentially projected systems, clusters with strong lensing features, clusters with active central galaxies or star formation, and systems of multiple clusters that may be physically associated. The cluster catalog will be a useful resource for future cosmological analyses and studying the evolution of the intracluster medium and galaxies in massive clusters over the past 10 Gyr.
Lopsidedness as a tracer of early galactic assembly history
Publisher: Oxford University Press (OUP)
Date: 04-09-2023
A deficit of spatial remapping in constructional apraxia after right-hemisphere stroke
Publisher: Oxford University Press (OUP)
Date: 04-2010
DOI: 10.1093/BRAIN/AWQ052
Abstract: Constructional apraxia refers to the inability of patients to copy accurately drawings or three-dimensional constructions. It is a common disorder after right parietal stroke, often persisting after initial problems such as visuospatial neglect have resolved. However, there has been very little experimental investigation regarding mechanisms that might contribute to the syndrome. Here, we examined whether a key deficit might be failure to integrate visual information correctly from one fixation to the next. Specifically, we tested whether this deficit might concern remapping of spatial locations across saccades. Right-hemisphere stroke patients with constructional apraxia were compared to patients without constructional problems and neurologically healthy controls. Participants judged whether a pattern shifted position (spatial task) or changed in pattern (non-spatial task) across two saccades, compared to a control condition with an equivalent delay but without intervening eye movements. Patients with constructional apraxia were found to be significantly impaired in position judgements with intervening saccades, particularly when the first saccade of the sequence was to the right. The importance of these remapping deficits in constructional apraxia was confirmed through a highly significant correlation between saccade task performance and constructional impairment on standard neuropsychological tasks. A second study revealed that even single saccades to the right can impair constructional apraxia patients' perception of location shifts. These data are consistent with the view that rightward eye movements result in loss of remembered spatial information from previous fixations, presumably due to constructional apraxia patients' damage to the right-hemisphere regions involved in remapping locations across saccades. These findings provide the first evidence for a deficit in remapping visual information across saccades underlying right-hemisphere constructional apraxia.
Dark matter halo properties of GAMA galaxy groups from 100 square degrees of KiDS weak lensing data
Publisher: Oxford University Press (OUP)
Date: 06-08-2015
The stellar-to-halo mass relation of GAMA galaxies from 100 deg2of KiDS weak lensing data
Publisher: Oxford University Press (OUP)
Date: 12-04-2016
DOI: 10.1093/MNRAS/STW747
A giant radio halo in a low-mass SZ-selected galaxy cluster: ACT-CL J0256.5+0006
Publisher: Oxford University Press (OUP)
Date: 29-04-2016
DOI: 10.1093/MNRAS/STW795
Lensing without borders – I. A blind comparison of the amplitude of galaxy–galaxy lensing between independent imaging surveys
Publisher: Oxford University Press (OUP)
Date: 14-12-2021
Abstract: Lensing without borders is a cross-survey collaboration created to assess the consistency of galaxy–galaxy lensing signals (ΔΣ) across different data sets and to carry out end-to-end tests of systematic errors. We perform a blind comparison of the litude of ΔΣ using lens s les from BOSS and six independent lensing surveys. We find good agreement between empirically estimated and reported systematic errors which agree to better than 2.3σ in four lens bins and three radial ranges. For lenses with zL & 0.43 and considering statistical errors, we detect a 3–4σ correlation between lensing litude and survey depth. This correlation could arise from the increasing impact at higher redshift of unrecognized galaxy blends on shear calibration and imperfections in photometric redshift calibration. At zL & 0.54, litudes may additionally correlate with foreground stellar density. The litude of these trends is within survey-defined systematic error budgets that are designed to include known shear and redshift calibration uncertainty. Using a fully empirical and conservative method, we do not find evidence for large unknown systematics. Systematic errors greater than 15 per cent (25 per cent) ruled out in three lens bins at 68 per cent (95 per cent) confidence at z & 0.54. Differences with respect to predictions based on clustering are observed to be at the 20–30 per cent level. Our results therefore suggest that lensing systematics alone are unlikely to fully explain the ‘lensing is low’ effect at z & 0.54. This analysis demonstrates the power of cross-survey comparisons and provides a promising path for identifying and reducing systematics in future lensing analyses.
Reward sensitivity predicts dopaminergic response in spatial neglect
Publisher: Elsevier BV
Date: 2020
DOI: 10.1016/J.CORTEX.2018.09.002
Abstract: It has recently been revealed that spatial neglect can be modulated by motivational factors including anticipated monetary reward. A number of dopaminergic agents have been evaluated as treatments for neglect, but the results have been mixed, with no clear anatomical or cognitive predictors of dopaminergic responsiveness. Given that the effects of incentive motivation are mediated by dopaminergic pathways that are variably damaged in stroke, we tested the hypothesis that the modulatory influences of reward and dopaminergic drugs on neglect are themselves related. We employed a single-dose, double-blind, crossover design to compare the effects of Co-careldopa and placebo on a modified visual cancellation task in patients with neglect secondary to right hemisphere stroke. Whilst confirming that reward improved visual search in this group, we showed that dopaminergic stimulation only enhances visual search in the absence of reward. When patients were ided into REWARD-RESPONDERs and REWARD-NON-RESPONDERs, we found an interaction, such that only REWARD-NON-RESPONDERs showed a positive response to reward after receiving Co-careldopa, whereas REWARD-RESPONDERs were not influenced by drug. At a neuroanatomical level, responsiveness to incentive motivation was most associated with intact dorsal striatum. These findings suggest that dopaminergic modulation of neglect follows an 'inverted U' function, is dependent on integrity of the reward system, and can be measured as a behavioural response to anticipated reward.
Motivation and attention following hemispheric stroke.
Publisher: Elsevier
Date: 2016
Harnessing motivation to alleviate neglect
Publisher: Frontiers Media SA
Date: 2013
GMRT 610 MHz observations of galaxy clusters in the ACT equatorial sample
Publisher: Oxford University Press (OUP)
Date: 27-03-2019
DOI: 10.1093/MNRAS/STZ823
Abstract: We present Giant Metrewave Radio Telescope (GMRT) 610 MHz observations of 14 Atacama Cosmology Telescope (ACT) clusters, including new data for nine. The s le includes 73 per cent of ACT equatorial clusters with M500 & 5 × 1014 M⊙. We detect diffuse emission in three of these (27$^{+20}_{-14}$ per cent): we detect a radio minihalo in ACT-CL J0022.2–0036 at z = 0.8, making it the highest redshift minihalo known we detect potential radio relic emission in ACT-CL J0014.9–0057 (z = 0.533) and we confirm the presence of a radio halo in low-mass cluster ACT-CL J0256.5+0006, with flux density S610 = 6.3 ± 0.4 mJy. We also detect residual diffuse emission in ACT-CL J0045.9–0152 (z = 0.545), which we cannot conclusively classify. For systems lacking diffuse radio emission, we determine radio halo upper limits in two ways and find via survival analysis that these limits do not significantly affect radio power scaling relations. Several clusters with no diffuse emission detection are known or suspected mergers, based on archival X-ray and/or optical measures given the limited sensitivity of our observations, deeper observations of these disturbed systems are required in order to rule out the presence of diffuse emission consistent with known scaling relations. In parallel with our diffuse emission results, we present catalogues of in idual radio sources, including a few interesting extended sources. Our study represents the first step towards probing the occurrence of diffuse emission in high-redshift (z ≳ 0.5) clusters, and serves as a pilot for statistical studies of larger cluster s les with the new radio telescopes available in the pre-SKA era.
The evolution in the stellar mass of brightest cluster galaxies over the past 10 billion years
Publisher: Oxford University Press (OUP)
Date: 19-05-2016
Related Organisations
King's College London
Location: United Kingdom of Great Britain and Northern Ireland
University Of Sussex
Location: United Kingdom of Great Britain and Northern Ireland
University College London Institute Of Cognitive Neuroscience
Location: United Kingdom of Great Britain and Northern Ireland
Fondazione Santa Lucia Istituto Di Ricovero E Cura A Carattere Scientifico
Location: Italy
Brunel University
Location: United Kingdom of Great Britain and Northern Ireland
University College London
Location: United Kingdom of Great Britain and Northern Ireland
Related Funding Activities
No related grants have been discovered for Cristóbal Sifón.