Ian Reeves

The neural basis of visuomotor deficits in hemispatial neglect

We have recently reported that patients with hemispatial neglect demonstrate increased terminal errors when performing delayed leftward reaches and that right-brain damaged patients (irrespective of neglect) take longer to complete their movements [Rossit, S., Muir, K., Reeves, I., Duncan, G., Birschel, P., & Harvey, M. (2009). Immediate and delayed reaching in hemispatial neglect. Neuropsychologiaa 47, 1563-1573]. Here we conducted an initial voxel-based lesion-symptom analysis to examine the neural basis of such deficits in 21 right-brain damaged subjects with 11 patients suffering from hemispatial neglect (2 more than in Rossit et al. [Rossit S., Muir K., Reeves I., Duncan, G., Birschel, P., & Harvey, M. (2009). Immediate and delayed reaching in hemispatial neglect. Neuropsychologia 47, 1563-1573] and 10 control patients without the condition. We found that the accuracy impairments in delayed leftward reaches were associated with damage to occipito-temporal areas. In contrast, the movement time slowing was related to more anterior lesions in the frontal lobe. These findings agree with the view that neglect affects actions thought to depend on the processing carried out by the ventral visual stream. In addition, we suggest that the timing impairments which are not neglect-specific maybe be driven by frontal structures.

No Neglect-Specific Deficits in Reaching Tasks

It is well established that patients with hemispatial neglect present with severe visuospatial impairments, but studies that have directly investigated visuomotor control have revealed diverging results, with some studies showing that neglect patients perform relatively better on such tasks. The present study compared the visuomotor performance of patients with and without neglect after right-hemisphere stroke with those of age-matched controls. Participants were asked to point either directly towards targets or halfway between two stimuli, both with and without visual feedback during movement. Although we did not find any neglect-specific impairment, both patient groups showed increased reaction times to leftward stimuli as well as decreased accuracies for open loop leftward reaches. We argue that these findings agree with the view that neglect patients code spatial parameters for action veridically. Moreover, we suggest that lesions in the right hemisphere may cause motor deficits irrespective of the presence of neglect and we performed an initial voxel-lesion symptom analysis to assess this. Lesion-symptom analysis revealed that the reported deficits did not result from damage to neglect-associated areas alone, but were further associated with lesions to crucial nodes in the visuomotor control network (the basal ganglia as well as occipito-parietal and frontal areas).

The role of right temporal lobe structures in off-line action:Evidence from lesion-behavior mapping in stroke patients

Recent evidence suggests the possibility that not all action modes depend on dorsal visual stream processing but that off-line nontarget-directed actions, such as antipointing, require additional and even distinct neural networks when compared with target-directed online actions. Here, we explored this potential dissociation in a group of 11 patients with left visual neglect, a syndrome characterized by a loss of awareness of the contralesional side of space. Ten healthy participants and 10 right hemisphere-damaged patients without neglect served as controls. Participants had to point either directly toward targets presented on their left or right (i.e., propointing) or to the mirror position in the opposite hemispace (i.e., antipointing). Compared with both control groups, neglect patients showed reduced accuracy when antipointing but not propointing. Lesion-behavior mapping revealed that the areas critically associated with these deficits were located in the middle and superior temporal and parahippocampal gyri. We argue that neglect patients present specific deficits only when the visuomotor task taps into more perceptual representations thought to rely on ventral visual stream processing and that our results indicate that right temporal brain regions are implicated in these off-line actions.

Non-lateralised deficits in anti-saccade performance in patients with hemispatial neglect

We tested patients suffering from hemispatial neglect on the anti-saccade paradigm to assess voluntary control of saccades. In this task participants are required to saccade away from an abrupt onset target. As has been previously reported, in the pro-saccade condition neglect patients showed increased latencies towards targets presented on the left and their accuracy was reduced as a result of greater undershoot. To our surprise though, in the anti-saccade condition, we found strong bilateral effects: the neglect patients produced large numbers of erroneous pro-saccades to both left and right stimuli. This deficit in voluntary control was present even in patients whose lesions spared the frontal lobes. These results suggest that the voluntary control of action is supported by an integrated network of cortical regions, including more posterior areas. Damage to one or more components within this network may result in impaired voluntary control.

Implementation of a stroke thrombolysis service within a tertiary neurosciences centre in the United Kingdom

BACKGROUND Intravenous alteplase is licensed for treatment of ischaemic stroke within 3 h of onset. Up to one-third of patients in the UK present to hospital within this time window but few are treated. AIMS To examine the effect of a stroke thrombolysis protocol on service provision for an acute stroke service in the UK, jointly run by Neurology and Medicine for the Elderly providing a comprehensive stroke service to a local population of 370,000. DESIGN Prospective observational study. METHODS Data collected prospectively for all thrombolysis referrals over a 12-month period beginning July 2004. RESULTS One hundred and eighty-eight patients were referred for potential thrombolysis, 129 transferred, 102 had an ischaemic stroke and 49 received intravenous thrombolysis. Referral rates from primary care and accident and emergency increased after guideline dissemination. Forty-three percent of the 49 patients treated with intravenous rt-PA achieved independence (modified Rankin Scale score 0-2) at 3months. CONCLUSION A high proportion of ischaemic stroke patients can be treated with alteplase within 3 h of onset with organized hospital services and dissemination of a simple referral protocol to local primary and secondary care services.

Long Term Improvements in Activities of Daily Living in Patients with Hemispatial Neglect

Monika Harvey, Keith Muir, Ian Reeves, George Duncan, Philip Birschel, Margaret Roberts, Katrina Livingstone, Hazel Jackson, Caroline Hogg , Pauline Castle , Gemma Learmonth and Stephanie Rossit School of Psychology, University of Glasgow, Glasgow, UK Institute of Neurological Sciences, Southern General Hospital, Glasgow, UK Department of Medicine for the Elderly, Southern General Hospital, Glasgow, UK Stroke Discharge and Rehabilitation Team, Southern General Hospital, Glasgow, UK Stroke Unit, Southern General Hospital, Glasgow, UK Mansion House Unit, Glasgow, UK Victoria Infirmary, Glasgow, UK Department of Psychology, University of Western Ontario, London, Canada

Efficacy of home-based visuomotor feedback training in stroke patients with chronic hemispatial neglect

ABSTRACT Hemispatial neglect is a severe cognitive condition frequently observed after a stroke, associated with unawareness of one side of space, disability and poor long-term outcome. Visuomotor feedback training (VFT) is a neglect rehabilitation technique that involves a simple, inexpensive and feasible training of grasping-to-lift rods at the centre. We compared the immediate and long-term effects of VFT vs. a control training when delivered in a home-based setting. Twenty participants were randomly allocated to an intervention (who received VFT) or a control group (n = 10 each). Training was delivered for two sessions by an experimenter and then patients self-administered it for 10 sessions over two weeks. Outcome measures included the Behavioural Inattention Test (BIT), line bisection, Balloons Test, Landmark task, room description task, subjective straight-ahead pointing task and the Stroke Impact Scale. The measures were obtained before, immediately after the training sessions and after four-months post-training. Significantly greater short and long-term improvements were obtained after VFT when compared to control training in line bisection, BIT and spatial bias in cancellation. VFT also produced improvements on activities of daily living. We conclude that VFT is a feasible, effective, home-based rehabilitation method for neglect patients that warrants further investigation with well-designed randomised controlled trials on a large sample of patients.

Non-lateralized impairments in anti- but not pro-pointing in patients with hemispatial neglect

It has been widely shown that hemispatial neglect manifests itself in a rightward perceptual bias, but whether this bias extends to goal-directed movements remains a matter of debate. Here we analysed the ability of 10 patients with hemispatial neglect to perform pro- and anti-pointing movements in response to left and rightwardly presented targets. A group of 10 age-matched healthy controls and 10 patients with right-hemisphere lesions but no neglect served as controls. In the pro-pointing condition, subjects were asked to point directly to the target, whereas in the anti-pointing condition they had to move in the opposite direction of the target (i.e. if a target was illuminated on the right subjects had to point to the equivalent target position on the left and vice-versa). In the pro-pointing condition, no impairments specific to patients with hemispatial neglect where found. However for anti-pointing, neglect specific deficits emerged: neglect patients showed greater directional errors (i.e. anti-pointing movements in the wrong direction) and were also severely disrupted in the end-point accuracy of their movements, in particular when anti-pointing rightwards in response to leftwardly presented targets. We relate these findings to the presence of impairments in movements that require specific location mapping and cannot be performed on-line.

Pointing and bisection in open and closed loop reaching in patients with hemispatial neglect.

It is well established that patients with hemispatial neglect present severe visuospatial impairments, but studies that have directly investigated the visuomotor control in these patients have revealed diverging results, some pointing to relatively spared visuomotor function. The present study compared the performance of 8 patients with hemispatial neglect and 10 without the disorder after right hemisphere stroke and 10 age-matched controls. Subjects were asked to point either directly towards targets or in the middle of two targets, both with and without visual feedback of the hand and target during movement. No specific impairments were observed for the neglect patients on either timing, speed and end-point accuracy measures for any of the conditions. Despite the failure of our neglect patients to react to stimuli on the contralesional side of space when assessed with paper and pencil tests, we did not find any specific deviations in their movements. Our results suggest that the perceptual distortions present in patients with neglect do not influence their performance on pointing tasks with or without visual feedback of their hand, supporting the view that such patients code spatial parameters for action veridically.

Dissociation between eye-movements and right perceptual biases in chimeric face processing in right hemisphere lesioned patients

Using blended chimeric facial stimuli, where the left and the right sides of the face are different, we have previously shown that both young and older observers tend to bias their responses significantly toward the information on the left, supposedly reflecting a right-hemisphere advantage in this task (Butler, Gilchrist, Burt, Perrett, Jones & Harvey, 2005, Neuropsychologia, 43, 52-59; Harvey & Butler, 2004, Perception, 33, 106). Analyses of the eye movement patterns further indicated a tendency for both groups to initially scan to the left side of the chimeric image, presumably reflecting the tendency to first inspect the side of the face better suited to face analysis (left side of face/right hemisphere). As expected, patients with right hemisphere lesions based their gender decisions mainly on the right side of the chimeric face and this was not only the case for patients who suffered from spatial neglect (Mattingley, Bradshaw, Phillips, Bradshaw, 1993, Brain and Cognition, 23, 145-165). More interestingly though, there was no clear relationship between perceptual and eye-movements biases to chimeric stimuli. Although most patients showed more right-sided saccades and longer rightward fixations this was not necessarily reflected in the rightward perceptual bias. One patient in particular showed rightward saccades only, yet based his gender decision on the left hemi-face half the time when he should have shown 100% rightward hemi-face judgements. We would argue that although in healthy subjects face biases and eye-movement biases are tightly coupled, this relationship breaks down with brain damage and that for such patients eye-movement patterns are not a good indicator of perceptual processing (see also Ferber, Danckert, Joanisse, Goltz, Goodale, 2003, Neurology, 60 1826-1829 and Harvey, Olk, Muir, K, 2003, Neuropsychologia, 41, 1114-1121 for supporting evidence).