Ipsilesional Stimuli Research Articles

Monocular eye patching modulates reorienting of covert attention in patients with unilateral middle cerebral artery stroke

Unilateral brain lesions can lead to impaired contralesional attention and reduced ipsilesional and enhanced contralesional superior colliculus (SC) activity. We aimed to investigate whether modulation of SC activation via monocular eye patching can improve contralesional attention. Twenty left-hemispheric (LH) and 20 right-hemispheric (RH) patients with an acute or subacute middle cerebral artery (MCA) stroke completed an endogenous version of the Posner cueing task twice, while the left or right eye was covered with an eye patch. The LH and RH patients showed significantly slower reactions to contralesional than to ipsilesional stimuli. In addition, the eye patch modulated responses to invalidly but not those to validly cued stimuli. Post hoc analyses could not discriminate whether this effect pertained to a particular target side or eye patch position. However, exploratory analyses indicated that the observed eye patch effect might affect the RH group more than the LH group. As predicted 36 years ago, monocular eye patching modulates visuospatial attention, presumably due to differences in SC activation between the two eye patch conditions. However, this modulation seems too weak and unspecific, and therefore possibly not strong enough to be a treatment option for patients with visuospatial attention impairments.

Detection of Stroke-Induced Visual Neglect and Target Response Prediction Using Augmented Reality and Electroencephalography.

We aim to build a system incorporating electroencephalography (EEG) and augmented reality (AR) that is capable of identifying the presence of visual spatial neglect (SN) and mapping the estimated neglected visual field. An EEG-based brain-computer interface (BCI) was used to identify those spatiospectral features that best detect participants with SN among stroke survivors using their EEG responses to ipsilesional and contralesional visual stimuli. Frontal-central delta and alpha, frontal-parietal theta, Fp1 beta, and left frontal gamma were found to be important features for neglect detection. Additionally, temporal analysis of the responses shows that the proposed model is accurate in detecting potentially neglected targets. These targets were predicted using common spatial patterns as the feature extraction algorithm and regularized discriminant analysis combined with kernel density estimation for classification. With our preliminary results, our system shows promise for reliably detecting the presence of SN and predicting visual target responses in stroke patients with SN.

Pupil dilation during orienting of attention and conscious detection of visual targets in patients with left spatial neglect

Right Brain-Damaged patients (RBD) with left spatial neglect (N+), are characterised by deficits in orienting and re-orienting attention to stimuli in the contralesional left side of space. In a recent ERPs study with visual stimuli (Lasaponara et al., 2018) we have pointed out that the pathological attentional bias of N+ is matched with exaggerated novelty reaction and contextual updating of targets in the right ipsilesional space and reduced novelty reaction and contextual updating of targets in the left contralesional space. To characterise further the attentional performance of N+, here we measured Pupil Dilation (PDil), which is a reliable marker of noradrenergic-locus coeruleus activity and response to unexpected events/rewards. Compared to Neutral and Valid targets, N+ patients displayed a pathological reduction of PDil in response to infrequent Invalid targets in the left side of space, while in Healthy Controls (HC) and RBD without neglect (N-) the same targets enhanced PDil with respect to Neutral and frequent Valid targets. Invalid targets in the right side of space enhanced PDil in all experimental groups. Interestingly, both N- and N+ showed a consistent number of target omissions both in the left and right side of space. With respect to seen targets, N- showed reduced PDil in response to unseen targets both in the left and right side of space. In contrast, N+ had reduced PDil in response to unseen targets in the left side of space though not in the right side, where seen and unseen targets evoked comparable levels of PDil. These results disclose, for the first time, the PDil correlates of spatial attention in left spatial neglect and suggest that the pathological attentional bias suffered by N+ might enhance the autonomic responses reflected in PDil to unseen ipsilesional stimuli. This enhancement can contribute to biasing contextual updating and predictive coding of stimuli in the ipsilesional space, thus worsening the pathological attentional bias of N+.

Functional reorganization during the recovery of contralesional target selection deficits after prefrontal cortex lesions in macaque monkeys

Visual extinction has been characterized by the failure to respond to a visual stimulus in the contralesional hemifield when presented simultaneously with an ipsilesional stimulus (Corbetta and Shulman, 2011). Unilateral damage to the macaque frontoparietal cortex commonly leads to deficits in contralesional target selection that resemble visual extinction. Recently, we showed that macaque monkeys with unilateral lesions in the caudal prefrontal cortex (PFC) exhibited contralesional target selection deficits that recovered over 2–4 months (Adam et al., 2019). Here, we investigated the longitudinal changes in functional connectivity (FC) of the frontoparietal network after a small or large right caudal PFC lesion in four macaque monkeys. We collected ultra-high field resting-state fMRI at 7-T before the lesion and at weeks 1–16 post-lesion and compared the functional data with behavioural performance on a free-choice saccade task. We found that the pattern of frontoparietal network FC changes depended on lesion size, such that the recovery of contralesional extinction was associated with an initial increase in network FC that returned to baseline in the two small lesion monkeys, whereas FC continued to increase throughout recovery in the two monkeys with a larger lesion. We also found that the FC between contralesional dorsolateral PFC and ipsilesional parietal cortex correlated with behavioural recovery and that the contralesional dorsolateral PFC showed increasing degree centrality with the frontoparietal network. These findings suggest that both the contralesional and ipsilesional hemispheres play an important role in the recovery of function. Importantly, optimal compensation after large PFC lesions may require greater recruitment of distant and intact areas of the frontoparietal network, whereas recovery from smaller lesions was supported by a normalization of the functional network.

Attention as the ‘glue’ for object integration in parietal extinction

Patients with unilateral, parietal brain damage frequently show visual extinction, which manifests in a failure to identify contralesional stimuli when presented simultaneously with other, ipsilesional stimuli (but full awareness for single stimulus presentations). Extinction reflects an impairment of spatial selective attention, leaving basic preattentive processing unaffected. For instance, access to bilaterally grouped objects is usually spared in extinction, suggesting that grouping occurs at a stage preceding (in the patients: abnormally biased) spatial-attentional selection. Here, we reinvestigated this notion by comparing (largely between participants, but also within a single-case participant) conditions with objects that varied in their dominant direction of grouping: from the attended to the non-attended hemifield (data from Conci et al., 2009) versus from the non-attended to the attended hemifield (new data). We observe complete absence of extinction when shape completion extended from the attended hemifield. By contrast, extinction was not diminished when object groupings propagate from the unattended hemifield. Moreover, we found the individual severity of the attentional impairment (assessed by a standard “inattention” test) to be directly related to the degree of completion in the unattended hemifield. This pattern indicates that grouping can overcome visual extinction only when object integration departs from the attended visual field, implying, contrary to many previous accounts, that attention is crucial for grouping to be initiated.

EXTINCTION: POSSIBLE INTERFERENCE OF TOP-DOWN INFORMATION. A CASE STUDY

Brain-damaged patients showing extinction are able to process stimuli presented on either hemispace, but fail to report contralesional stimuli when simultaneously presented with an ipsilesional stimulus. Extinction may occur stimuli of the same modality or between stimuli of different modalities (such as visual and tactile). This phenomenon has been interpreted as supramodal imbalance in stimulus competition for attention selection. However, recent studies have reported the existence of a complex interaction of competition-facilitation between visual and tactile information. We describe a patient (RP) who suffered from a brain damage on the right occipito-temporal cortical area. RP showed severe visual neglect associated with a rare case of extinction. He performed at ceiling on tactile extinction tasks when his eyes were closed, but showed dramatic tactile extinction when he looked directly at the hand being touched. The results as reflecting the existence of top-down mechanisms whereby the “absence” of visual information caused by visual neglect might have exacerbated underlying latent attentional biases.

Neuroplasticity for spontaneous functional recovery after neonatal hypoxic ischemic brain injury in rats observed by functional MRI and diffusion tensor imaging

For infants and children, an incredible resilience from injury is often observed. There is growing evidence that functional recovery after brain injury might well be a consequence of the reorganization of the neural network as a process of neuroplasticity. We demonstrate the presence of neuroplasticity at work in spontaneous recovery after neonatal hypoxic ischemic (HI) injury, by elucidating a precise picture in which such reorganization takes place using functional MRI techniques. For all 12 siblings, 6 rats were subjected to severe HI brain injury and 6 rats underwent sham operation only. Severe HI brain injury was induced to postnatal day 7 (p7) Sprague–Dawley rats according to the Rice–Vannucci model (right carotid artery occlusion followed by 150min of hypoxia with 8% O2 and 92% of N2). Brain activation maps along with anatomical and functional connectivity maps related to the sensory motor function were obtained at adult (p63) using blood oxygen level dependent (BOLD)-functional MRI (fMRI), resting state-functional MRI (rs-fMRI) and diffusion tensor imaging (DTI); each of these MRI data was related to sensory motor functional outcome. In-depth investigation of the functional MRI data revealed: 1) intra-hemispheric expansion of BOLD signal activation in the contralesional undamaged hemisphere for ipsilesional forepaw stimuli to include the M2 and Cg1 in addition to the S1 and M1 wide spreading in the anterior and posterior directions, 2) inter-hemispheric transfer of BOLD signal activation for contralesional forepaw stimuli, normally routed to the injured hemisphere, to analogous sites in the contralesional undamaged hemisphere, localized newly to the M1 and M2 with a reduced portion of the S1, 3) inter-hemispheric axonal disconnection and axonal rewiring within the undamaged hemisphere as shown through DTI, and 4) increased functional interactions within the cingulate gyrus in the HI injured rats as shown through rs-fMRI. The BOLD signal amplitudes as well as DTI and rs-fMRI data well correlate with behavioral tests (tape to remove). We found that function normally utilizing what would be the injured hemisphere is transferred to the uninjured hemisphere, and functionality of the uninjured hemisphere remains not untouched but is also rewired in an expansion corresponding to the newly formed sensorimotor function from both the contralesional and the ipsilesional sides. The conclusion drawn from the data in our current study is that enhanced motor function in the contralesional hemisphere governs both the normal and damaged sides, indicating that active plasticity with brain laterality was spontaneously generated to overcome functional loss and established autonomously through normal experience via modification of neural circuitry for neonatal HI injured brain.

Early sensory processing in right hemispheric stroke patients with and without extinction

While extinction is most commonly viewed as an attentional disorder and not as a consequence of a failure to process contralesional sensory information, it has been speculated that early sensory processing of contralesional targets in extinction patients might not be fully normal. We used a masked visuo-motor response priming paradigm to study the influence of both contralesional and ipsilesional peripheral subliminal prime stimuli on central target performance, allowing us to compare the strength of the early sensory processing associated with these prime stimuli between right brain damaged patients with and without extinction as well as healthy elderly subjects. We found that the effect of an informative subliminal prime in the left contralesional visual field on central target performance was significantly reduced in both right brain damaged patients with and without extinction. The results suggest that a low-level early sensory deterioration of the neural representation for contralesional prime stimuli is a general consequence of right hemispheric brain damage unrelated to the presence or absence of extinction. This suggests that the presence of a spatial bias against contralesional information is not sufficient to elicit extinction. For extinction to occur, this spatial bias might need to be accompanied by a pathological (non-directional) reduction of attentional capacity.

Temporal grouping modulates ipsilateral capture in right visual neglect

The current study assessed the performance of a patient with right neglect (M.A.H.) across various manipulations of the flanker paradigm. When required to identify a central target in the presence of a unilateral flanker, M.A.H. responded to the flanking distractor on the left (ipsilesional) side as if it were the target, even when the flanker appeared at left peripheral locations. A right (contralesional) flanker did not affect central identification performance (Experiment 1). The “ipsilesional capture” effect persisted when pretrial location markers were introduced to make the flanker and target locations more clearly defined (Experiment 2). However, when the ipsilesional flanker appeared simultaneously with a contralesional flanker, central target detection improved to ceiling (Experiment 3). Interestingly, with these three-stimulus displays, congruency effects in reaction time only occurred in relation to the flanker on the contralesional side (Experiment 3), suggesting impaired response selectivity to ipsilesional stimuli. Congruency effects were produced on both sides only when the two flanking distractors grouped together (by both onset and offset, Experiment 4) and when the ipsilesional flanking distractor grouped with the target by onset (lone contra offset, Experiment 4). The results are attributed to ipsilesional capture in central target detection, which is offset by temporal grouping processes when another stimulus appears on the contralateral side.

Sound Localization Performance Improves After Canaloplasty in Unilateral Congenital Aural Atresia Patients

To investigate the changes in sound localization ability in the horizontal plane after canaloplasty in unilateral congenital aural atresia (CAA) patients. Prospective interventional study. Tertiary referral center. Twenty-eight patients with unilateral CAA were enrolled. All patients had unilateral conductive hearing loss. Canaloplasty. Pure tone audiometry, sound localization test, and the Speech, Spatial, and Quality questionnaire (SSQ) were administered preoperatively, 6 and 12 months postoperatively. For the sound localization test, 8 loudspeakers were positioned in a circle at 45-degree intervals, and patients were instructed to identify the speaker from which sound was coming. Mean correct response rate and mean error degree were calculated for each patient. The correct lateralization rate to the ipsilesional/contralesional stimuli was also calculated. Mean hearing threshold decreased from preoperatively 63.8 to 39.4 dB 12 months after canaloplasty. Mean correct response rate and error degree at preoperative evaluation were 26.0% and 60.7 degrees, respectively, and these were respectively improved to 58.5% and 27.8 degrees postoperatively. Respective mean correct lateralization rate to ipsilesional stimuli after canaloplasty improved from 20.6% to 84.0%, and that to contralesional stimuli slightly improved from 93.8% to 98.8%. Patients with good postoperative hearing (<40 dBHL) showed better sound localization results. In addition, self-assessment scores of spatial domain in the SSQ questionnaire were significantly improved after the operation. Sound localization performance improved significantly after canaloplasty. Canaloplasty could provide better localization benefit and subjective improvement in spatial sensation to unilateral CAA patients.

Spatial and non-spatial aspects of neglect

Spatial and non-spatial aspects of neglect

Anti-Extinction in the Tactile Modality

Patients with extinction fail to report a contralesional stimulus when it is presented at the same time as an ipsilesional stimulus, and patients with unilateral neglect fail to report a contralesional stimulus even when there is no competing ipsilesional stimulus. Whereas extinction and neglect are common following stroke, the related phenomenon of anti-extinction is rare--there are four cases of anti-extinction in the literature, and all four cases demonstrated anti-extinction in the visual modality. Patients with anti-extinction do report a contralesional stimulus when it is presented at the same time as an ipsilesional stimulus; but, like patients with neglect, they fail to report a contralesional stimulus when there is no competing ipsilesional stimulus. We present the first case ofanti-extinction in the tactile modality.

Extinction and anti-extinction: The “attentional waiting” hypothesis.

Patients with visual extinction have difficulty detecting a single contralesional stimulus when a second stimulus is simultaneously presented on the ipsilesional side. The rarely reported phenomenon of visual anti-extinction describes the opposite behavior, in which patients show greater difficulty in reporting a stimulus presented in isolation than they do in reporting 2 simultaneously presented stimuli. S. J. Goodrich and R. Ward (1997, Anti-extinction following unilateral parietal damage, Cognitive Neuropsychology, Vol. 14, pp. 595-612) suggested that visual anti-extinction is the result of a task-specific mechanism in which processing of the ipsilesional stimulus facilitates responses to the contralesional stimulus; in contrast, G. W. Humphreys, M. J. Riddoch, G. Nys, and D. Heinke (2002, Transient binding by time: Neuropsychological evidence from anti-extinction, Cognitive Neuropsychology, Vol. 19, pp. 361-380) suggested that temporal binding groups contralesional and ipsilesional stimuli together at brief exposure durations. We investigated extinction and anti-extinction phenomena in 3 brain-damaged patients using an extinction paradigm in which the stimulus exposure duration was systematically manipulated. Two patients showed both extinction and anti-extinction depending on the exposure duration of stimuli. Data confirmed the crucial role of duration in modulating the effect of extinction and anti-extinction. However, contrary to Humphreys and colleagues' (2002) single case, our patients showed extinction for short and anti-extinction for long exposure durations, suggesting that different mechanisms might underlie our patients' pattern of data. We discuss a novel "attentional waiting" hypothesis, which proposes that anti-extinction may be observed in patients showing extinction if the exposure duration of stimuli is increased.

Sound Localization after Canaloplasty

Objective: Unilateral congenital aural atresia (CAA) is much more common than bilateral atresia, and subsequent unilateral hearing loss usually leads to poor sound localization. The objective of this study was to investigate the change in sound localization after canaloplasty for correction of the unilateral hearing loss. Method: Twenty patients with unilateral CAA, who underwent canaloplasty, were enrolled. Pure tone audiometry, sound localization test, and Speech, Spatial, and Quality (SSQ) questionnaire were administered preoperatively and 6 months postoperatively. For sound localization test, 8 loudspeakers were positioned around the patient, and patients were instructed to identify the sound source. Results: Mean air-bone gap decreased from preoperatively 54.6 dB to 25.3 dB 6 months after canaloplasty. In sound localization test, mean correct response rate and error degree at preoperative evaluation were 27.40% and 60.7°, respectively, and these were improved to 57.5% and 26.2° postoperatively. Mean correct response rate to ipsilesional stimuli following canaloplasty (left/right discrimination) improved from 29.5% to 88.2%, and that to contralesional stimuli improved from 90.0% to 98.7%. In addition, scores in the spatial domain of the SSQ questionnaire improved significantly from 6.6 to 7.5 after canaloplasty ( P = .014). Conclusion: Sound localization performance including right-left discrimination ability improved significantly 6 months following canaloplasty. Canaloplasty could restore a binaural hearing ability and may be a good treatment option to improve sound localization ability in unilateral CAA patients.

The effect of stimulus duration and motor response in hemispatial neglect during a visual search task.

Patients with hemispatial neglect exhibit a myriad of profound deficits. A hallmark of this syndrome is the patients' absence of awareness of items located in their contralesional space. Many studies, however, have demonstrated that neglect patients exhibit some level of processing of these neglected items. It has been suggested that unconscious processing of neglected information may manifest as a fast denial. This theory of fast denial proposes that neglected stimuli are detected in the same way as non-neglected stimuli, but without overt awareness. We evaluated the fast denial theory by conducting two separate visual search task experiments, each differing by the duration of stimulus presentation. Specifically, in Experiment 1 each stimulus remained in the participants' visual field until a response was made. In Experiment 2 each stimulus was presented for only a brief duration. We further evaluated the fast denial theory by comparing verbal to motor task responses in each experiment. Overall, our results from both experiments and tasks showed no evidence for the presence of implicit knowledge of neglected stimuli. Instead, patients with neglect responded the same when they neglected stimuli as when they correctly reported stimulus absence. These findings thus cast doubt on the concept of the fast denial theory and its consequent implications for non-conscious processing. Importantly, our study demonstrated that the only behavior affected was during conscious detection of ipsilesional stimuli. Specifically, patients were slower to detect stimuli in Experiment 1 compared to Experiment 2, suggesting a duration effect occurred during conscious processing of information. Additionally, reaction time and accuracy were similar when reporting verbally versus motorically. These results provide new insights into the perceptual deficits associated with neglect and further support other work that falsifies the fast denial account of non-conscious processing in hemispatial visual neglect.

Hemispheric differences in VEPs to lateralised stimuli are a marker of recovery from neglect

Visual-evoked potentials (VEPs) were recorded in seventeen patients with unilateral lesions of the right hemisphere (RH) and visuospatial neglect. Hemispheric differences were detected for VEP components in the time window from 130 to 280 msec; this result replicates data from a previous study using a larger group of patients (Di Russo et al., 2008). Three patients were tested twice; their hemispheric differences, i.e., the differences in latency and amplitude of VEPs to ipsilesional and contralesional stimuli, were evaluated at the beginning and end of visuospatial rehabilitation training for neglect. The hemispheric differences were limited to components anterior N1 (N1a), posterior N1 (N1p) and P2 (not C1 and P1) and showed a significant decrease after training; amelioration at the behavioural level was also observed. Fourteen patients were tested only once, at different steps of their training. For the overall group, we determined the correlation between VEP hemispheric differences and the number of sessions attended by the patients at the time of VEP recording. The correlation was negative, the higher the number of sessions, the lower the hemispheric asymmetry, and high, ranging from .45 to .64, for both the latency and amplitude of the N1p and P2 components, and for the amplitude of the N1a component. The correlation between VEP hemispheric differences and time from onset (TFO) of the pathological event was not significant. Overall, the hemispheric differences between specific components of the VEP responses to lateralised stimuli appear to be a good marker of recovery from neglect.

Common and distinct neural mechanisms of visual and tactile extinction: A large scale VBM study in sub-acute stroke

Extinction is diagnosed when patients respond to a single contralesional item but fail to detect this item when an ipsilesional item is present concurrently. It is considered to be a disorder of attention characterized by a striking bias for the ipsilesional stimulus at the expense of the contralesional stimulus. Extinction has been studied mainly in the visual modality but it occurs also in other sensory modalities (touch, audition) and hence can be considered a multisensory phenomenon. The functional and neuroanatomical relations between extinction in different modalities are poorly understood. It could be hypothesised that extinction deficits in different modalities emerge after damage to both common (attention specific) and distinct (modality specific) brain regions. Here, we used voxel-based morphometry to examine the neuronal substrates of visual versus tactile extinction in a large group of stroke patients (). We found that extinction deficits in the two modalities were significantly correlated (; ). Lesions to inferior parietal lobule and middle frontal gyrus were linked to visual extinction, while lesions involving the superior temporal gyrus were associated with tactile extinction. Damage within the middle temporal gyrus was linked to both types of deficits but interestingly these lesions extended into the middle occipital gyrus in patients with visual but not tactile extinction. White matter damage within the temporal lobe was associated with both types of deficits, including lesions within long association pathways involved in spatial attention. Our findings indicate both common and distinct neural mechanisms of visual and tactile extinction.

A Case of Phantom Synchiric Percepts in Touch and Vision

After being presented with an ipsilesional stimulus, individuals with synchiria report both ipsilesional and contralesional sensation. Most published reports of synchiria are limited to a single modality. We report an individual with a right frontoparietal lesion (KG_591) who demonstrated synchiria subsequent to both visual and tactile stimulation. We tested KG_591 with various tasks in which she was presented with a stimulus on the left side, right side, both sides simultaneously, or no stimulation. On tactile trials, she reported tactile synchiric percepts on approximately 40% of right hand stimulation trials. Next, we projected visual stimuli either onto or away from her hands, in order to examine whether her phantom visual sensations were limited to personal space on the body. KG_591's synchiric percepts remained constant on or off of her hands, suggesting that her deficit was not limited to her body. Furthermore, as she does not report seeing phantoms in everyday life, we examined the effect of stimu...

Objections against the view of visual extinction as an attentional disengagement deficit: The interaction between spatial position and temporal modulation

Visual extinction is a common consequence of brain injury where individuals fail to detect a contralesional target when it is presented with a competing ipsilesional target. This disorder is often seen as either a consequence of biased competitive interactions or as a consequence of an attentional disengagement deficit. A study of neurological patients by Rorden et al. (2008) found that extinction is maximal at stimulus simultaneity when the target stimuli straddle the central gaze fixation location, while it is maximal when the ipsilesional stimulus has a temporal lead on the contralesional stimulus when both target stimuli are presented in the ipsilesional visual field. The authors argued that these results are most parsimoniously explained as a consequence of low-level biased competitive interactions due to cortical magnification, but acknowledged that an attentional disengagement deficit could also accommodate the results. The present study set out to adjudicate between these models by examining the performance of neurologically healthy subjects who exhibit normal cortical magnification but do not have pathological attentional biases. We presented (a)synchronous double stimulation trials where both targets to be identified could straddle the central gaze fixation location or be presented in either the left or the right visual field. We found that in both the left and the right visual field target performance accuracy was poorest when the more peripheral stimulus led. This suggests that the findings from Rorden et al. can indeed be explained by a low-level physiological bias due to cortical magnification and argues against the notion that neurological extinction represents an attentional disengagement deficit.

Alexander's law during high-acceleration head rotations in humans

Alexander's law states that the amplitude of the spontaneous nystagmus grows with increasing gaze in the direction of the fast phase. Using the search-coil method we employed head impulses at various eye-in-orbit azimuth angles to test (i) whether the normal vestibulo-ocular reflex (VOR) in the behaviorally relevant high-frequency range has intrinsic properties that could account for Alexander's law and (ii) whether such properties can also be shown in patients with unilateral vestibulopathy. We showed that the gain of the VOR remained unaffected by eye-in-orbit position in contols and in patients, both on ipsilesional and contralesional stimuli. These findings suggest that eye-in-orbit position does not directly modulate the activity in VOR pathways, neither during unbalanced but reciprocal (in controls), nor during unbalanced and nonreciprocal natural vestibular stimulation (in patients).