Posterior Parietal Lesions Research Articles

Peripheral and bimanual reaching in a stroke survivor with left visual neglect and extinction

Whether attentional deficits are accompanied by visuomotor impairments following posterior parietal lesions has been debated for quite some time. This single-case study investigated reaching in a stroke survivor (E.B.) with left visual neglect and visual extinction following right temporo-parietal-frontal strokes. Unlike most neglect patients, E.B. did not present left hemiparesis, homonymous hemianopia nor show evidence of motor neglect or extinction allowing us to examine, for the first time, if lateralised attentional deficits co-occur with deficits in peripheral and bimanual reaching. First, we found a classic optic ataxia field effect: E.B.’s accuracy was impaired when reaching to peripheral targets in her neglected left visual field (regardless of the hand used). Second, we found a larger bimanual cost for movement time in E.B. than controls when both hands reached to incongruent locations. E.B.’s visuomotor profile is similar to the one of patients with optic ataxia showing that attentional deficits are accompanied by visuomotor deficits in the affected field.

Single-Case Neuropsychological Assessment of a Patient with a Posterior Parietal Lesion Using Behavioral Testing and Resting-State fMRI

This study integrated functional connectivity measures using resting-state fMRI and behavioral data from a single-case observation of patient (PER) one year after right-hemispheric hemorrhage in the intraparietal sulcus and superior parietal lobule (IPS/SPL). PER showed no sign of clinical neglect. Her behavioral performance in the visuo-manual pointing task and in the letter discrimination task under conditions of endogenous and exogenous attentional cueing was compared between the left (affected) and right (unaffected/control) peripheral visual fields. The resting-state fMRI demonstrated an imbalance between the right and left hemispheric frontoparietal functional connectivity within the dorsal attentional and motor networks. Although the frontal and occipital cortices were not structurally damaged, specific fronto-occipital functional connectivity was imbalanced, which was strongly associated with the behavioral changes. First, the activity in the right frontal eye field showed weaker correlations with the activity in the right inferior occipital area compared to the correlation with the activity in the left inferior occipital area. This imbalanced fronto-occipital functional connectivity was accompanied by a specific impairment in endogenous covert attention in the left visual field. Second, the activity within M1 in both hemispheres showed weaker correlations with the activity of the right cuneus compared to the correlation with the activity in the left cuneus. The imbalanced fronto-occipital functional connectivity was associated with the impairment of the reaching movement of the left and right hands towards the left visual field (optic ataxia). Altogether, our results showed that a lesion to the posterior parietal cortex affects the relationship between distal regions underlying the sensorimotor and attentional abilities

Structural representations of fingers rely on both anatomical and spatial reference frames.

Finger agnosia refers to a neurological condition in which patients with left posterior parietal lesions fail to identify their fingers, despite having relatively preserved abilities in sensation and skilled action. This dissociation suggests that the structural body representations (BSRs) may be distinct from sensorimotor representations. However, recent research has reported that postural changes modulate representation of hand structure, revealing dynamic interactions between structural and sensorimotor body representations. However, it is unknown how and to what extent anatomical and spatial proximity contribute to shape the hand structural representation. We investigate this question using the "in-between" test in which participants estimate how many unstimulated fingers are in between 2 touched fingers of the left hand placed palm down. The first phalange of the participants' fingers was touched on the left or right side. Judged finger numerosity was greater when fingers were stimulated on far sides (i.e., opposite sides of the 2 fingers) compared to when they were stimulated on close (i.e., sides facing each other's) or middistance (i.e., sides facing in the same direction) sides. Therefore, finger identification was modulated by anatomical and spatial proximity in external space between touches. This demonstrates that BSRs rely on both anatomical and external reference frames. (PsycINFO Database Record (c) 2020 APA, all rights reserved).

Cerebral lesion correlates of sympathetic cardiovascular activation in multiple sclerosis.

Cardiovascular autonomic dysfunction is common in multiple sclerosis (MS) and contributes significantly to disability. We hypothesized that cerebral MS‐lesions in specific areas of the central autonomic network might account for imbalance of the sympathetic and parasympathetic cardiovascular modulation. Therefore, we used voxel‐based lesion symptom mapping (VLSM) to determine associations between cardiovascular autonomic dysfunction and cerebral MS‐related lesion sites. In 74 MS‐patients (mean age 37.0 ± 10.5 years), we recorded electrocardiographic RR‐intervals and systolic and diastolic blood pressure. Using trigonometric regressive spectral analysis, we assessed low (0.04–0.15 Hz) and high (0.15–0.5 Hz) frequency RR‐interval‐and blood pressure‐oscillations and determined parasympathetically mediated RR‐interval–high‐frequency modulation, mainly sympathetically mediated RR‐interval–low‐frequency modulation, sympathetically mediated blood pressure‐low‐frequency modulation, and the ratios of sympathetic and parasympathetic RR‐interval‐modulation as an index of sympathetic‐parasympathetic balance. Cerebral MS‐lesions were analyzed on imaging scans. We performed a VLSM‐analysis correlating parameters of autonomic dysfunction with cerebral MS‐lesion sites. The VLSM‐analysis showed associations between increased RR‐interval low‐frequency/high‐frequency ratios and lesions most prominently in the left insular, hippocampal, and right frontal inferior opercular region, and a smaller lesion cluster in the right middle cerebellar peduncle. Increased blood pressure‐low‐frequency powers were associated with lesions primarily in the right posterior parietal white matter and again left insular region. Our data indicate associations between a shift of cardiovascular sympathetic‐parasympathetic balance toward increased sympathetic modulation and left insular and hippocampal lesions, areas of the central autonomic network. The VLSM‐analysis further distinguished between right inferior fronto‐opercular lesions disinhibiting cardiac sympathetic activation and right posterior parietal lesions increasing sympathetic blood pressure modulation.

Revisited: Impaired binocular fusion as a cause of “flat vision” after right parietal brain damage – A case study

The complete loss of binocular depth perception (“flat vision”) was first thoroughly described by Holmes and Horrax (1919), and has been occasionally reported thereafter in patients with bilateral posterior-parietal lesions. Though partial spontaneous recovery occurred in some cases, the precise cause(s) of this condition remained obscure for almost a century. Here, we describe a unique patient (EH) with a large right-sided occipito-parietal hemorrhage showing a complete loss of visual depth perception for several months post-stroke. EH could well simultaneously describe multiple visual objects – hence did not show simultanagnosia – but at the same time was completely unable to estimate their distance from him. In every 3-D visual scene objects appeared equidistant to him, thus experiencing a total loss of depth perception (“flat vision”). Neurovisual assessments revealed normal functions of the eyes. EH showed bilateral lower field loss and a severely impaired binocular convergent fusion, but preserved stereopsis. Perceptual re-training of binocular fusion resulted in a progressive and finally complete recovery of objective binocular fusion values and subjective binocular depth perception in a far-to-near-space, gradient-like manner. In parallel, visual depth estimation of relative distances improved, whereas stereopsis remained unchanged. Our results show that a complete loss of 3-D depth perception can result from an isolated impairment in binocular fusion. On a neuroanatomical level, this connection could be explained by a selective lesion of area V6/V6A in the medial occipito-parietal cortex that has been associated with the integration of visual space coordinates and sustained eye-positions into a cyclopean visual 3-D percept.

Imaging Evaluation of Pediatric Sensorineural Hearing Loss in Potential Candidates for Cochlear Implantation.

Computerized tomography (CT) and magnetic resonance (MR) are complementary in the imaging of the labyrinth, the internal auditory canal and the brain in children with sensorineural hearing loss who are being evaluated for cochlear implantation. An accurate anatomical description of the inner ear is essential in the preoperative work up. Computerized tomography visualizes the bony structures, whereas MR can discern soft-tissue components including intra labyrinthine fluid, cerebrospinal fluid (CSF), nerves, and vessels within the IAC. This prospective study was conducted in the Department of Otorhinolaryngology, Head & Neck Surgery, Government Medical College, Srinagar. 40 children in the age group of 1-16years with unidentified causes of bilateral SNHL were analysed radiologically over the period of 2years from Dec 2011 to Jan 2014. Each patient underwent MRI and high resolution CT scanning of temporal bone in axial and coronal planes. Out of the 40 patients 22 were males (55%) and 18 were females (45%). 30 patients (72.5%)in our study had normal radiological scans. Five patients (12.5%) had B/L large vestibular aqueduct and two patients (5%) had internal auditory canal stenosis with cochlear nerve hypoplasia on CT and MR imaging. Cochlear dysplasia was present in two patients (5%) and semicircular canal dysplasia was present in one patient (2.5%) as an isolated finding on HRCT. In addition isolated cochlear nerve hypoplasia was present in one patient (2.5%). Hyperintense basal ganglia lesion suggestive of kernicterus was present in one patient (2.5%) and hyperintense posterior parietal and occipital white matter lesions suggestive of congenital CMV infection was present in one patient (2.5%) on MR imaging. Arachnoid cysts of middle cranial fossa was an incidental finding present in one patient. Radiological abnormalities of the inner ear are not uncommon. Computerized tomography and MRI are important modalities to analyze the inner ear in children with unexplained SNHL. MRI with an extremely small field of view should be used to study possible abnormalities of the vestibulocochlear nerves.

Neural correlates of finger gnosis.

Neuropsychological studies have described patients with a selective impairment of finger identification in association with posterior parietal lesions. However, evidence of the role of these areas in finger gnosis from studies of the healthy human brain is still scarce. Here we used functional magnetic resonance imaging to identify the brain network engaged in a novel finger gnosis task, the intermanual in-between task (IIBT), in healthy participants. Several brain regions exhibited a stronger blood oxygenation level-dependent (BOLD) response in IIBT than in a control task that did not explicitly rely on finger gnosis but used identical stimuli and motor responses as the IIBT. The IIBT involved stronger signal in the left inferior parietal lobule (IPL), bilateral precuneus (PCN), bilateral premotor cortex, and left inferior frontal gyrus. In all regions, stimulation of nonhomologous fingers of the two hands elicited higher BOLD signal than stimulation of homologous fingers. Only in the left anteromedial IPL (a-mIPL) and left PCN did signal strength decrease parametrically from nonhomology, through partial homology, to total homology with stimulation delivered synchronously to the two hands. With asynchronous stimulation, the signal was stronger in the left a-mIPL than in any other region, possibly indicating retention of task-relevant information. We suggest that the left PCN may contribute a supporting visuospatial representation via its functional connection to the right PCN. The a-mIPL may instead provide the core substrate of an explicit bilateral body structure representation for the fingers that when disrupted can produce the typical symptoms of finger agnosia.

The Sitting Position in Neurosurgery: A Clinical Study in 30 Cases

Objective: Sitting position for operation of posterior fossa lesions, occipital and posterior parietal lesions, foramen magnum, upper cervical spinal lesions provides an excellent visualization because of slack of brain due to gravity drainage of CSF and blood. Hence gross total tumour removal relatively easy and less complicative.Methods: From January 2008 to march 2010 total 30 cases underwent neurosurgical procedure in sitting position. Physical characteristics including patients age, sex, size of the tumour and histological diagnosis were collected. The post operative image were studied to see the extent of tumour removal and early detection of complications. Almost all patients required peroperative cerebral venous line or peripheral inserted central venous line, precordial doppler sound, ETCO2, O2 saturation and close monitoring of blood pressure.Results: Venous air embolism were detected in two cases (6.6%). Total tumour removal was possible in 17 (56.6%) cases and subtotal in 11 (36.6%) cases. There were 4 (13.33%) mortality in thirty cases, two cases from CP angle tumour and another case from petroclival meningioma and another from pineal region tumour. There was pneumocephalus in almost all cases and post-operative new facial paresis in 10 (33.3%) cases. Fifth cranial nerve palsy developed in 3 (10%) cases. Temporary lower cranial nerve palsy developed in 2 cases. Post-operative tumour bed haematoma developed in 4 (13.33%) cases. Most of the patient had good outcome (GOS 5).Conclusion: Sitting position can be safely done with good preoperative physiological, peroperative close monitoring of the patient regarding blood pressure, ETCO2 and oxygen saturation. However postoperative complication like tumour bed haematoma, pneumocephalus, cranial nerve palsy have to be bring in mind.Bangladesh Journal of Neuroscience 2012; Vol. 28 (1): 45-51

An Elderly Woman With Difficulty Reading and Abnormal Eye Movements

An Elderly Woman With Difficulty Reading and Abnormal Eye Movements

The neural basis of inhibitory effects of semantic and phonological neighbors in spoken word production.

Theories of word production and word recognition generally agree that multiple word candidates are activated during processing. The facilitative and inhibitory effects of these "lexical neighbors" have been studied extensively using behavioral methods and have spurred theoretical development in psycholinguistics, but relatively little is known about the neural basis of these effects and how lesions may affect them. This study used voxel-wise lesion overlap subtraction to examine semantic and phonological neighbor effects in spoken word production following left hemisphere stroke. Increased inhibitory effects of near semantic neighbors were associated with inferior frontal lobe lesions, suggesting impaired selection among strongly activated semantically related candidates. Increased inhibitory effects of phonological neighbors were associated with posterior superior temporal and inferior parietal lobe lesions. In combination with previous studies, these results suggest that such lesions cause phonological-to-lexical feedback to more strongly activate phonologically related lexical candidates. The comparison of semantic and phonological neighbor effects and how they are affected by left hemisphere lesions provides new insights into the cognitive dynamics and neural basis of phonological, semantic, and cognitive control processes in spoken word production.

Virtual Lesion of Angular Gyrus Disrupts the Relationship between Visuoproprioceptive Weighting and Realignment

Posterior parietal cortex is thought to be involved in multisensory processes such as sensory weighting (how much different modalities are represented in sensory integration) and realignment (recalibrating the estimates given by unisensory inputs relative to each other, e.g., when viewing the hand through prisms). Sensory weighting and realignment are biologically independent but can be correlated such that the lowest-weighted modality realigns most. This is important for movement precision because it results in the brain's estimate of hand position favoring the more reliable (higher-weighted) modality. It is unknown if this interaction is an emergent property of separate neural pathways for weighting and realignment or if it is actively mediated by a common substrate. We applied disruptive TMS to the angular gyrus near the intraparietal sulcus (PGa) before participants performed a task with misaligned visual and proprioceptive information about hand position. Visuoproprioceptive weighting and realignment were unaffected. However, the relationship between weighting and realignment, found in control conditions, was absent after TMS in the angular gyrus location. This suggests that a specific region in the angular gyrus actively mediates the interaction between visuoproprioceptive weighting and realignment and may thus play a role in the decreased movement precision associated with posterior parietal lesions.

Neurocysticercosis masquerading psychotic disorder: A case report

Psychotic manifestations are uncommon in neurocysticercosis. This article describes a ten year girl presented with manic–psychotic manifestation for which she was under treatment with antipsychotics for eight months. Eventually she developed generalized tonic clonic seizure and CT scan of brain revealed small isodense right posterior parietal lesion of 5 mm size with perifocal edema. CECT revealed intense nodular post contrast enhancement. This highlights the possible misdiagnosis of a case of neurocysticercosis as an organic psychotic disorder so it should be considered as a differential diagnosis in patients with neurological as well as psychiatric manifestations in endemic area like India.

Memory in ASD: have we been barking up the wrong tree?

In this theoretical note, possible neural causes of episodic memory impairment in individuals with ASD and currently normal intellectual and linguistic function are considered. The neural causes most commonly argued for are hippocampal or prefrontal cortex dysfunction, associated with impaired neural connectivity. It is argued here that a hippocampal dysfunction hypothesis is weakened by differences in cued recall and paired associate learning in individuals with ASD compared with individuals with developmental or acquired hippocampus-related amnesia, and that recent findings on patients with posterior parietal lesions (PPC) offer a better fit with the dissociation between free and cued recall observed in ASD. The PPC forms part of the default system subserving mindreading, among other functions, and an association between PPC dysfunction and memory impairment in ASD is consistent with recent suggestions that neural disconnectivity within the default system underlies behaviours diagnostic of ASD.

Neuroanatomical Dissections of Unilateral Visual Neglect Symptoms: ALE Meta-Analysis of Lesion-Symptom Mapping

Unilateral visual neglect is commonly defined as impaired ability to attend to stimuli presented on the side of visual space contralateral to the brain lesion. However, behavioral analyses indicate that different neglect symptoms can dissociate. The neuroanatomy of the syndrome has been hotly debated. Some groups have argued that the syndrome is linked to posterior parietal cortex lesions, while others report damage within regions including the superior temporal gyrus, insula, and basal ganglia. Several recent neuroimaging studies provide evidence that heterogeneity in the behavioral symptoms of neglect can be matched by variations in the brain lesions, and that some of the discrepancies across earlier findings might have resulted from the use of different neuropsychological tests and/or varied measures within the same task for diagnosing neglect. In this paper, we review the evidence for dissociations between both the symptoms and the neural substrates of unilateral visual neglect, drawing on ALE (anatomic likelihood estimation) meta-analyses of lesion-symptom mapping studies. Specifically, we examine dissociations between neglect symptoms associated with impaired control of attention across space (in an egocentric frame of reference) and within objects (in an allocentric frame of reference). Results of ALE meta-analyses indicated that, while egocentric symptoms are associated with damage within perisylvian network (pre- and postcentral, supramarginal, and superior temporal gyri) and damage within sub-cortical structures, more posterior lesions including the angular, middle temporal, and middle occipital gyri are associated with allocentric symptoms. Furthermore, there was high concurrence in deficits associated with white matter lesions within long association (superior longitudinal, inferior fronto-occipital, and inferior longitudinal fasciculi) and projection (corona radiata and thalamic radiation) pathways, supporting a disconnection account of the syndrome. Using this evidence we argue that different forms of neglect link to both distinct and common patterns of gray and white matter lesions. The findings are discussed in terms of functional accounts of neglect and theoretical models based on computational studies of both normal and impaired attention functions.

Ataxic hemiparesis in a patient with posterior cortical borderzone infarction

Dear Sir, A 76-year-old woman was admitted to our institution with weakness and lack of coordination along the left side of her body. Review of her medical history revealed that she had hypertension and diabetes mellitus, had undergone stent-assisted coil embolization for a saccular aneurysm on the right distal internal carotid artery, and had taken aspirin, antihypertensive drugs, and glucose-lowering medication. Physical examination revealed a blood pressure of 150/90 mmHg, but no other specific findings were noted. Neurological examination indicated a slight impairment of motor power in the patient’s left arm (Medical Research Council grade 4?) and leg (grade 4?). With regard to cerebellar function, finger-to-nose and heel-to-shin tests showed observable dysmetria of the arm and leg, respectively. All aspects of the sensory system including proprioception were normal. Tandem gait was affected; the patient tended to tilt slightly towards the left. These findings suggested ataxic hemiparesis (AH), and hence, lacunar stroke was strongly suspected. However, the results of magnetic resonance imaging performed on admission and on the fourth day after admission showed distinct right posterior cortical borderzone infarction between the middle and posterior cerebral arterial territories (Fig. 1a). A wedge-shaped lesion was seen on the right posterior parietal area (Fig. 1b) alongside a lesion resembling a ‘string of beads’ on the right posterior centrum semiovale. The previously undertaken stent-assisted coil embolization was evident from the initial computerized tomographic angiography results (Fig. 2a); thereafter, irregular stenosis in the stent was observed on magnetic resonance angiography performed on the fourth day after admission (Fig. 2b). We carried out cardiac evaluation procedures, including electrocardiography and transthoracic echocardiography, but there was no indication of cardioembolism. Finally, we concluded that the posterior cortical borderzone infarction was caused by thromboembolism from the stenotic lesion in the stent. The patient fully recovered and was discharged on the seventh day after admission. Dual antiplatelets with aspirin and clopidogrel were prescribed for secondary prevention. This is the first reported case of AH caused by cortical borderzone infarction; a thorough review of literature indicated no reports of borderzone infarction causing AH [1]. In this study, we deduced that hemiparesis is associated with the lesion on the centrum semiovale, which involves the pyramidal tract. Ataxia was assumed to be associated with a wedge-shaped posterior parietal lesion. This is a common site for the occurrence of cortical borderzone infarctions [2]. Previously, kinetic ataxia has been reported in a patient with an acute posterior parietal infarction [3]. This association is very rare, but the interruption of cerebellar projections on the cortex was postulated as a possible mechanism [3]. Prior to this study, an autopsy report showed parietal ataxia related to the right postcentral gyrus in the arm [4]. In this article, however, proprioceptive impairment rather than dysmetria was regarded as the neurological basis of ataxia [4]. The neurologic deficits in our patient suggest pyramidal involvement near the centrum semiovale and kinetic ataxia due to a posterior parietal lesion, both of which represent AH. This association of AH with posterior cortical borderzone infarction is novel; AH is traditionally D. H. Shin S. W. Lee Y. H. Hong J. M. Hong J. S. Lee (&) Department of Neurology, Ajou University Medical Center, Ajou University School of Medicine, San 5, Wonchondong, Suwon, Youngtonggu 443-721, South Korea e-mail: jinsoo22@gmail.com

Visual Puzzles, Figure Weights, and Cancellation: Some Preliminary Hypotheses on the Functional and Neural Substrates of These Three New WAIS-IV Subtests

In this study, five consecutive patients with focal strokes and/or cortical excisions were examined with the Wechsler Adult Intelligence Scale and Wechsler Memory Scale—Fourth Editions along with a comprehensive battery of other neuropsychological tasks. All five of the lesions were large and typically involved frontal, temporal, and/or parietal lobes and were lateralized to one hemisphere. The clinical case method was used to determine the cognitive neuropsychological correlates of mental rotation (Visual Puzzles), Piagetian balance beam (Figure Weights), and visual search (Cancellation) tasks. The pattern of results on Visual Puzzles and Figure Weights suggested that both subtests involve predominately right frontoparietal networks involved in visual working memory. It appeared that Visual Puzzles could also critically rely on the integrity of the left temporoparietal junction. The left temporoparietal junction could be involved in temporal ordering and integration of local elements into a nonverbal gestalt. In contrast, the Figure Weights task appears to critically involve the right temporoparietal junction involved in numerical magnitude estimation. Cancellation was sensitive to left frontotemporal lesions and not right posterior parietal lesions typical of other visual search tasks. In addition, the Cancellation subtest was sensitive to verbal search strategies and perhaps object-based attention demands, thereby constituting a unique task in comparison with previous visual search tasks.

Similarities and differences between parietal and frontal patients in autobiographical and constructed experience tasks

Recent findings suggest that constructed experience, the ability to envision future events, activates the same cortical network as recollection of past events. For example, damage to one key area, the hippocampus, impairs patients’ ability to remember the past and to imagine novel experiences (Hassabis, Kumaran, Vann, & Maguire, 2007). Here, we investigated whether damage to two other areas, posterior parietal cortex and prefrontal cortex, also impairs this ability. Patients with bilateral posterior parietal lesions or unilateral prefrontal lesions were tested in their ability to describe imaginary future events. Only parietal patients were impaired at freely describing autobiographical memories, but both patient groups were impaired when elaborating constructed experiences. This dissociation suggests that parietal and prefrontal structures are differentially involved in constructed experience. Current tasks may impose overly broad cognitive demands making it impossible to specify the deficient cognitive component in any patient group. These findings provide additional constraints regarding the mechanistic role of the parietal cortex in memory.

Vision-related quality of life in first stroke patients with homonymous visual field defects

BackgroundTo evaluate vision-related and health-related quality of life (VRQoL, HRQoL) in first stroke patients with homonymous visual field defects (VFD) with respect to the extent of the lesion. Since VFD occur in approximately 10% of stroke patients the main purpose of the study was to investigate the additional impact of VFD in stroke patients hypothesizing that VFD causes diminished VRQoL.MethodsIn 177 first stroke patients with persisting VFD 2.5 years after posterior-parietal lesions VRQoL was assessed by the National-Eye-Institute-Visual-Functioning-Questionnaire (NEI-VFQ) and HRQoL by the Medical-Outcome-Study Short-Form-36 Health-Survey (SF-36). Questionnaire results of VFD-patients were compared with age- and sex-matched healthy controls and with general non-selected stroke samples as published elsewhere. VFD-type and visual acuity were partially correlated with questionnaire results.ResultsCompared to healthy controls VFD-patients had lower NEI-VFQ scores except ocular pain (Z-range -11.34 to -3.35) and lower SF-36 scores except emotional role limitations (Z-range -7.21 to -3.34). VFD-patients were less impaired in SF-36 scores than general stroke patients one month post lesion (6/8 subscales) but had lower SF-36 scores compared to stroke patients six months post lesion (5/8 subscales). Visual acuity significantly correlated with NEI-VFQ scores (r-range 0.27 to 0.48) and VFD-type with SF-36 mental subscales (r-range -0.26 to -0.36).ConclusionsVFD-patients showed substantial reductions of VRQoL and HRQoL compared to healthy normals, but better HRQoL compared to stroke patients one month post lesion. VFD-patients (although their lesion age was four times higher) had significantly lower HRQoL than a general stroke population at six months post-stroke. This indicates that the stroke-related subjective level of HRQoL impairment is significantly exacerbated by VFD. While VRQoL was primarily influenced by visual acuity, mental components of HRQoL were influenced by VFD-type with larger VFD being associated with more distress.

Simulating posterior parietal damage in a biologically plausible framework: Neuropsychological tests of the search over time and space model

The search over time and space (sSoTS) model attempts to simulate both the spatial and the temporal aspects of human visual search using spiking level neurons, which incorporate some biologically plausible aspects of neuronal firing. The model contains pools of units that (a) code basic features of objects, presumed to reside in the ventral visual stream, and (b) respond in a feature-independent way to stimulation at their location, presumed to operate in the posterior parietal cortex. We examined the effects of selective lesioning neurons responding to one side of the location map. Unilateral damage introduced spatial biases into selection that affected conjunction more than single-feature search. In addition, there was an impaired ability to segment stimuli over time as well as space (e.g., in preview search). These results match previously reported data on patients with posterior parietal lesions. In addition we show that spatial biases in selection increase under conditions in which there is decreased activity from excitatory neurotransmitters, mimicking effects of reduced arousal. Further simulations explored the effects of time and of visual grouping on extinction, generating predictions that were then tested empirically. The model provides a framework for linking behavioural data from patients with neural-level determinants of visual attention.

Attention for action?: Examining the link between attention and visuomotor control deficits in a patient with optic ataxia

The classic definition of ‘pure’ optic ataxia suggests that these patients’ visuomotor impairments are independent of perceptual or attentional deficits. More recent work suggests that some patients with optic ataxia also have difficulty attending to targets in their ataxic field. Thus, an important question is whether these attentional deficits might be related to the well-known problems in visuomotor control evident in these patients. To investigate this question we had controls (N=5) and CF, a patient with optic ataxia in his left visual field, perform tasks that required them to detect or reach towards targets presented in either central vision, or at different target eccentricities in the periphery. As expected, CF was less accurate than controls when reaching to targets in his ataxic (left) visual field, and was much slower than controls to detect the presence of targets in his ataxic field. The reaction times to lift the hand in the pointing and the detecting conditions were correlated in the ataxic field of patient CF, suggesting a common attentional deficit in both tasks. Importantly, although CF was slower to detect targets in the ataxic field, and less accurate to reach towards those same targets, the two deficits did not follow the same pattern. Specifically, only reaching errors in the ataxic field were strongly modulated by target eccentricity. These results suggest that dorsal posterior parietal lesions result in attention and visuomotor control problems in optic ataxia that arise from damage to independent mechanisms.