Ipsilesional Side Research Articles

Object-based Neglect Varies with Egocentric Position

Different reference frames have been identified to influence neglect behavior. In particular, neglect has been demonstrated to be related to the contralesional side of the subject's body (egocentric reference frames) as well as to the contralesional side of individual objects irrespective of their position to the patient (object-based reference frame). There has been discussion whether this distinction separates neglect into body- and object-based forms. The present experiment aimed to prove possible interactions between object-based and egocentric aspects in spatial neglect. Neglect patients' eye and head movements were recorded while they explored objects at five egocentric positions along the horizontal dimension of space. The patients showed both egocentric as well as object-based behavior. Most interestingly, data analysis revealed that object-based neglect varied with egocentric position. Although the neglect of the objects' left side was strong at contralesional egocentric positions, it ameliorated at more ipsilesional egocentric positions of the objects. The patients showed steep, ramp-shaped patterns of exploration for objects located on the far contralesional side and a broadening of these patterns as the locations of the objects shifted more to the ipsilesional side. The data fitted well with the saliency curves predicted by a model of space representation, which suggests that visual input is represented in two modes simultaneously: in veridical egocentric coordinates and in within-object coordinates.

Neuropsychological evidence for an interaction between endogenous visual and motor-based attention

We report data examining the relations between endogenous allocation of visual attention and effects of motor-preparation on attention. We tested a patient with a spatial bias in perceptual report following damage to the left inferior parietal lobe and superior temporal gyrus. Previously we have shown that the spatial bias in report can be reduced when a movement is planned to where a target falls in the contralesional field, while the bias is exacerbated when a movement is planned to the ipsilesional side (Kitadono & Humphreys, 2007, Cognitive Neuropsychology, 24). Here we pitted the effects of planning a movement to the contra- or ipsilesional side against the effects of endogenous visual attention, manipulated by varying the probability of where a target would fall. In a no-movement baseline, there was better identification of contralesional targets when there was a good likelihood of targets appearing on the contralesional side (the 20–80 and 50–50 conditions) compared with when targets had a low probability of occurring there (the 80–20 condition). This sensitivity to target probability interacted with the effects of planning a movement to the contra- or ipsilesional side. When the target had a good probability of falling in the contralesional field (the 20–80 and 50–50 conditions), planning a movement to the ipsilesional side disrupted contralesional report. When there was a high probability of an ipsilesional target (the 80–20 condition), planning a movement to a congruent side improved contralesional report. The results indicate that effects of endogenous attention and of motor-based attention influence a common system controlling visual orienting.

Shifting attention in viewer- and object-based reference frames after unilateral brain injury

The aims of the present study were to investigate the respective roles that object- and viewer-based reference frames play in reorienting visual attention, and to assess their influence after unilateral brain injury. To do so, we studied 16 right hemisphere injured (RHI) and 13 left hemisphere injured (LHI) patients. We used a cueing design that manipulates the location of cues and targets relative to a display comprised of two rectangles (i.e., objects). Unlike previous studies with patients, we presented all cues at midline rather than in the left or right visual fields. Thus, in the critical conditions in which targets were presented laterally, reorienting of attention was always from a midline cue. Performance was measured for lateralized target detection as a function of viewer-based (contra- and ipsilesional sides) and object-based (requiring reorienting within or between objects) reference frames. As expected, contralesional detection was slower than ipsilesional detection for the patients. More importantly, objects influenced target detection differently in the contralesional and ipsilesional fields. Contralesionally, reorienting to a target within the cued object took longer than reorienting to a target in the same location but in the uncued object. This finding is consistent with object-based neglect. Ipsilesionally, the means were in the opposite direction. Furthermore, no significant difference was found in object-based influences between the patient groups (RHI vs. LHI). These findings are discussed in the context of reference frames used in reorienting attention for target detection.

Longitudinal Changes of Resting-State Functional Connectivity During Motor Recovery After Stroke

Functional MRI (fMRI) studies could provide crucial information on the neural mechanisms of motor recovery in patients with stroke. Resting-state fMRI is applicable to patients with stroke who are not capable of proper performance of the motor task. In this study, we explored neural correlates of motor recovery in patients with stroke by investigating longitudinal changes in resting-state functional connectivity of the ipsilesional primary motor cortex (M1). A longitudinal observational study using repeated fMRI experiments was conducted in 12 patients with stroke. Resting-state fMRI data were acquired 4 times over a period of 6 months. Patients participated in the first session of fMRI shortly after onset and thereafter in subsequent sessions at 1, 3, and 6 months after onset. Resting-state functional connectivity of the ipsilesional M1 was assessed and compared with that of healthy subjects. Compared with healthy subjects, patients demonstrated higher functional connectivity with the ipsilesional frontal and parietal cortices, bilateral thalamus, and cerebellum. Instead, functional connectivity with the contralesional M1 and occipital cortex were decreased in patients with stroke. Functional connectivity between the ipsilesional and contralesional M1 showed the most asymmetry at 1 month after onset to the ipsilesional side. Functional connectivity of the ipsilesional M1 with the contralesional thalamus, supplementary motor area, and middle frontal gyrus at onset was positively correlated with motor recovery at 6 months after stroke. Resting-state fMRI elicited distinctive but comparable results with previous task-based fMRI, presenting complementary and practical values for use in the study of patients with stroke.

Hemianopia and Neglect Influence on Straight-Ahead Perception

In spatial neglect, the pathological ipsilesional deviation of the subjective straight ahead (SSA) received both ‘translational’ and ‘rotational’ interpretations. Furthermore, hemianopia per se could also influence straight-ahead (SA) perception. Here, we aimed at disentangling the relative effects of neglect and hemianopia on the SSA by using a method analyzing translation and rotation in parallel. We included patients with a right hemisphere stroke. Ten had neglect and hemianopia, 6 neglect only, 3 hemianopia only, and 12 neither one nor the other. 15 were controls. Participants had to adjust a bar, movable in translation and rotation, SA of the navel, in darkness. Patients with spatial neglect showed systematic rightward translation, greater when hemianoptic. The rotation component appeared more variable and was influenced by the presence of a visual field defect, as most of the patients with hemianopia showed an anticlockwise rotation and most of the patients without hemianopia a clockwise rotation. Non-neglect patients and control subjects demonstrated a fair performance level. In conclusion, both neglect and hemianopia resulted in a translation error of the SSA to the ipsilesional side. In neglect patients, additional hemianopia resulted in a counterclockwise rotation. Furthermore, rotation and translation errors appeared dissociated, suggesting a different coding of these dimensions by the right posterior hemisphere.

Hyperventilation-Induced Nystagmus in Patients with Vestibular Neuritis in the Acute and Follow-Up Stages

Objective: Our purposes were to characterize hyperventilation-induced nystagmus (HVIN) in patients with unilateral vestibular neuritis (VN) through follow-up examinations and to determine the effects of hyperventilation on vestibular imbalance in patients with VN. Materials and Methods: The horizontal eye movements in 35 patients with acute VN were recorded. The eye movements were analyzed and the maximum value of slow-phase eye velocity (SPV) was obtained during and after hyperventilation. Nineteen of 35 patients underwent follow-up examinations around 7 weeks later. When spontaneous nystagmus was present, the SPV of spontaneous nystagmus was subtracted from that of HVIN. A maximum SPV of HVIN of ≧4°/s was considered abnormal. The direction and SPV of HVIN were analyzed. Results: The incidence of HVIN in patients with VN was significantly higher in the acute stage (18 of 35; 51%) than the follow-up stage (4 of 19; 21%). The direction of HVIN present in the follow-up stage was entirely towards the contralesional side (contralesional HVIN). However, the direction of HVIN in the acute stage was mixed, towards the contralesional side (10 of 35; 28%) and towards the ipsilesional side (8 of 35; 23%). The SPVs (49 ± 56°/s) of ipsilesional HVIN were significantly greater than the contralesional HVIN in the acute stage (8 ± 3°/s). Robust nystagmus (SPV ≧25°/s) was entirely ipsilesional HVIN, which was observed only in the acute stage. Conclusions: Our findings indicate that hyperventilation can result in aggravation of vestibular imbalance in the acute and follow-up stages in different ways. Hyperventilation resulted in contralesional HVIN in both the acute and follow-up stages, each in approximately a fourth of the patients, which suggests a disruption of central static compensatory mechanisms. However, ipsilesional HVIN was elicited only in the acute stage (in approximately a fourth of the patients). About half of the patients with ipsilesional HVIN showed robust responses, which is a characteristic finding, suggesting a transient intense increase in vestibular activity on the lesional side.

Voluntary activation failure contributes more to plantar flexor weakness than antagonist coactivation and muscle atrophy in chronic stroke survivors

The contributions of nervous system muscle activation and muscle atrophy to poststroke weakness have not been evaluated together in the same subject. Maximal voluntary contraction (MVC) torque, voluntary activation (twitch interpolation), and electromyographic (EMG) amplitude were determined bilaterally in the plantar flexors of seven chronic stroke survivors (40-63 yr, 24-51 mo poststroke). Volumes of the plantar flexor muscles were determined bilaterally with magnetic resonance imaging (MRI). The mean (±SD) contralesional (paretic) MVC torque was less than one-half of the ipsilesional leg: 56.7 ± 57.4 vs. 147 ± 35.7 Nm (P = 0.006). Contralesional voluntary activation was only 48 ± 36.9%, but was near complete in the ipsilesional leg, 97 ± 1.9% (P = 0.01). The contralesional MVC EMG amplitude (normalized to the maximum M-wave peak-to-peak amplitude) of the gastrocnemii and soleus were 36.0 ± 28.5 and 36.0 ± 31.0% of the ipsilesional leg. Tibialis anterior (TA) EMG coactivation was not different between the contralesional (23.2 ± 24.0% of TA MVC EMG) and ipsilesional side (12.3 ± 5.7%) (P = 0.24). However, TA EMG coactivation was excessive (71%) in one subject and accounted for ~8% of her weakness based on the estimated antagonist torque. Relative (%ipsilesional leg) plantar flexor and gastrocnemii volumes were 88 ± 6% (P = 0.004) and 76 ± 15% (P = 0.01), respectively. Interlimb volume differences of the soleus, deep plantar flexors, and peronei were not significant. Preferred walking speed (0.83 ± 0.33 m/s) was related to the contralesional MVC torque (r(2) = 0.57, P = 0.05, N = 7), but the two subjects with the greatest weakness walked faster than three others. Our findings suggest that plantar flexor weakness in mobile chronic stroke survivors reflects mostly voluntary activation failure, with smaller contributions from antagonist activity and atrophy.

Ocular vestibular-evoked myogenic potentials to bone-conducted vibration in superior vestibular neuritis show utricular function

Objective To determine whether the first negative component (n10) of the ocular vestibular-evoked myogenic potential (oVEMP) to bone-conducted vibration (BCV) is due primarily to activation of the utricular macula. Study Design The n10 was recorded in response to brief BCV at the midline of the forehead at the hairline (Fz). If the n10 is due primarily to utricular activation, then diseases that affect only the superior division of the vestibular nerve in which all utricular afferents course (i.e., superior vestibular neuritis [SVN]) should reduce or eliminate n10 beneath the contralesional eye, whereas the n10 beneath the ipsilesional eye and the sacculo-collic cervical vestibular-evoked myogenic potential (cVEMP) on the ipsilesional side should be preserved. Setting A prospective study at a tertiary neurotological referral center. Subjects and Methods The n10 component of the oVEMP was measured in 133 patients with unilateral SVN but with inferior vestibular nerve function preserved, as shown by ipsilesional cVEMPs. Results The n10 to Fz BCV of 133 SVN patients was reduced beneath the contralesional eye relative to the ipsilesional eye so that there was an n10 asymmetry that was significantly greater than the n10 asymmetry in the 50 healthy subjects. In terms of predicting the affected side (shown by canal paresis), using an n10 asymmetry ratio (asymmetry ratio for the relative size of the n10 of the oVEMPs for the two eyes [AR]) of 46.5 percent, the n10 AR has a diagnostic accuracy of 94 percent. Conclusion The n10 component of the oVEMP to BCV is probably mediated by the superior vestibular nerve and so mainly by the utricular receptors. The n10 AR is almost as good as canal paresis in identifying the affected side in patients.

Line Bisection Error and Its Anatomic Correlate

Patients with chronic visual field defects typically show a contralesional line bisection error (LBE). However, in the acute phase of the disease, it has been suggested that the LBE points to the ipsilesional side. The aims of the current study were first, to test whether specific lesions are associated with LBE, and second, to determine whether there is a difference in the LBE between the acute and the chronic phase. Twenty-two patients with visual field defects due to stroke without neglect were tested for line bisection and for the anatomic lesion site by voxelwise lesion-behavior mapping analysis. Patients with visual field defects in the acute and chronic phases differed in neither the direction nor the extent of their LBE. An association between lesions of the lingual gyrus, the cuneus, and the extent of contralesional LBE was found. Present data support the view that a contralesional LBE is due rather to lesions of the lingual gyrus and the cuneus and not to an adaptive attentional mechanism over time.

Symmetrical kinematic changes in highly functioning older patients post-stroke during obstacle-crossing

With the advances in stroke care, the number of high-functioning patients after stroke is increasing. However, existing clinical tools may not be sensitive enough to identify the residual deficits in these patients. The current study aimed to investigate the control of the pelvis, and the joints and end-point of the lower limbs in high-functioning older patients post-stroke during obstacle-crossing using motion analysis techniques. Twenty-four high-functioning older patients following unilateral stroke and fifteen healthy controls walked and crossed obstacles of three different heights. End-point variables (leading toe-clearance and trailing toe-obstacle distance) and crossing pelvic and joint angles were obtained for both limbs during leading limb crossing. Whether leading with the contralesional or ipsilesional limb, the stroke group exhibited significantly different joint kinematics from the controls mainly in the frontal and transverse planes, with greater leading toe-clearance, trailing toe-obstacle distance, and posterior pelvic tilt. None of the end-point and joint variables were significantly different between limbs. High-functioning patients post-stroke appeared to have acquired a specific symmetric kinematic strategy with increased leading toe-clearance during obstacle-crossing, most likely in order to prevent tripping. This symmetric strategy, possibly a consequence of brain reorganization, may help in performing functional activities during which symmetric performance between the contralesional and ipsilesional sides is required. Obstacle-crossing training with both limbs leading alternately may be helpful for the development of this symmetric strategy. It is suggested that computerized motion analysis of obstacle-crossing can be a sensitive assessment tool for distinguishing the motor performance between normal and high-functioning patients post-stroke.

Repetitive exploration towards locations that no longer carry a target in patients with neglect

About 50% of neglect patients show ipsilesional target re-exploration on neglect tasks and in daily life. The present study examines whether omissions and revisitings are due to disengagement failure from visible stimuli on the ipsilesional side. Thirteen patients with neglect and nine healthy controls were tested with three versions of the Bells test on touch screen, i.e. a standard cancellation in which targets have to be marked, an erase cancellation in which targets have to be erased, and a condition in which all items (including distracters) have to be erased. Whereas omissions decreased in the full-erase condition, revisitings were the most prominent in this condition. Our study shows that neglect patients also return to previously visited locations which no longer carry a target.

Crossmodal visual‐tactile extinction: Modulation by posture implicates biased competition in proprioceptively reconstructed space

Extinction is a common consequence of unilateral brain injury: contralesional events can be perceived in isolation, yet are missed when presented concurrently with competing events on the ipsilesional side. This can arise crossmodally, where a contralateral touch is extinguished by an ipsilateral visual event. Recent studies showed that repositioning the hands in visible space, or making visual events more distant, can modulate such crossmodal extinction. Here, in a detailed single-case study, we implemented a novel spatial manipulation when assessing crossmodal extinction. This was designed not only to hold somatosensory inputs and hand/arm-posture constant, but also to hold (retinotopic) visual inputs constant, yet while still changing the spatial relationship of tactile and visual events in the external world. Our right hemisphere patient extinguished left-hand touches due to visual stimulation of the right visual field (RVF) when tested in the usual default posture with eyes/head directed straight ahead. But when her eyes/head were turned to the far left (and any visual events shifted along with this), such that the identical RVF retinal stimulation now fell at the same external location as the left-hand touch, crossmodal extinction was eliminated. Since only proprioceptive postural cues could signal this changed spatial relationship for the critical condition, our results show for the first time that such postural cues alone are sufficient to modulate crossmodal extinction. Identical somatosensory and retinal inputs can lead to severe crossmodal extinction, or none, depending on current posture.

The one that does, leads: Action relations influence the perceived temporal order of graspable objects.

Perception and action are influenced by the "possibilities for action" in the environment. Neuropsychological studies (e.g., Riddoch, Humphreys, Edwards, Baker, & Willson, 2003) have demonstrated that objects that are perceived to be interacting (e.g., a corkscrew going toward the top of a wine bottle) are perceptually integrated into a functional unit, facilitating report of both objects. In addition, patients with parietal damage tend to report the "active" item of the pair (the corkscrew in the above example) when the objects are positioned for action, overriding their spatial bias toward the ipsilesional side. Using a temporal order judgment task we show for the first time that normal viewers judge that active objects appear earlier when they are positioned correctly for action. This effect is not dependent on a learned relationship between objects, or on the active object being integrated at a perceptual level with the object it is paired with. The data suggest that actions afforded by a correctly positioned active object permeate normal perceptual judgments.

Perfusion Imaging in Pusher Syndrome to Investigate the Neural Substrates Involved in Controlling Upright Body Position

Brain damage may induce a dysfunction of upright body position termed “pusher syndrome”. Patients with such disorder suffer from an alteration of their sense of body verticality. They experience their body as oriented upright when actually tilted nearly 20 degrees to the ipsilesional side. Pusher syndrome typically is associated with posterior thalamic stroke; less frequently with extra-thalamic lesions. This argued for a fundamental role of these structures in our control of upright body posture. Here we investigated whether such patients may show additional functional or metabolic abnormalities outside the areas of brain lesion. We investigated 19 stroke patients with thalamic or with extra-thalamic lesions showing versus not showing misperception of body orientation. We measured fluid-attenuated inversion-recovery (FLAIR) imaging, diffusion-weighted imaging (DWI), and perfusion-weighted imaging (PWI). This allowed us to determine the structural damage as well as to identify the malperfused but structural intact tissue. Pusher patients with thalamic lesions did not show dysfunctional brain areas in addition to the ones found to be structurally damaged. In the pusher patients with extra-thalamic lesions, the thalamus was neither structurally damaged nor malperfused. Rather, these patients showed small regions of abnormal perfusion in the structurally intact inferior frontal gyrus, middle temporal gyrus, inferior parietal lobule, and parietal white matter. The results indicate that these extra-thalamic brain areas contribute to the network controlling upright body posture. The data also suggest that damage of the neural tissue in the posterior thalamus itself rather than additional malperfusion in distant cortical areas is associated with pusher syndrome. Hence, it seems as if the normal functioning of both extra-thalamic as well as posterior thalamic structures is integral to perceiving gravity and controlling upright body orientation in humans.

Chronic electrical stimulation of the contralesional lateral cerebellar nucleus enhances recovery of motor function after cerebral ischemia in rats

Novel neurorehabilitative strategies are needed to improve motor outcomes following stroke. Based on the disynaptic excitatory projections of the dentatothalamocortical pathway to the motor cortex as well as to anterior and posterior cortical areas, we hypothesize that chronic electrical stimulation of the contralesional dentate (lateral cerebellar) nucleus output can enhance motor recovery after ischemia via augmentation of perilesional cortical excitability. Seventy-five Wistar rats were pre-trained in the Montoya staircase task and subsequently underwent left cerebral ischemia with the 3-vessel occlusion model. All survivors underwent stereotactic right lateral cerebellar nucleus (LCN) implantation of bipolar electrodes. Rats were then randomized to 4 groups: LCN stimulation at 10 pps, 20 pps, 50 pps or sham stimulation, which was delivered for a period of 6 weeks. Performance on the Montoya staircase task was re-assessed over the last 4 weeks of the stimulation period. On the right (contralesional) side, motor performance of the groups undergoing sham, 10 pps, 20 pps and 50 pps stimulation was, respectively, 2.5 ± 2.7; 2.1 ± 2.5; 6.0 ± 3.9 ( p < 0.01) and 4.5 ± 3.5 pellets. There was no difference on the left (ipsilesional) side motor performance among the sham or stimulation groups, varying from 15.9 ± 6.7 to 17.2 ± 2.1 pellets. We conclude that contralesional chronic electrical stimulation of the lateral cerebellar nucleus at 20 pps but not at 10 or 50 pps improves motor recovery in rats following ischemic strokes. This effect is likely to be mediated by increased perilesional cortical excitability via chronic activation of the dentatothalamocortical pathway.

Spatial gradient for unique-feature detection in patients with unilateral neglect: Evidence from auditory and visual search

Patients with unilateral spatial neglect following right hemisphere damage are impaired in detecting contralesional targets in both visual and haptic search tasks, and often show a graded improvement in detection performance for more ipsilesional spatial locations. In audition, multiple simultaneous sounds are most effectively perceived if they are distributed along the frequency dimension. Thus, attention to spectro-temporal features alone can allow detection of a target sound amongst multiple simultaneous distracter sounds, regardless of whether these sounds are spatially separated. Spatial bias in attention associated with neglect should not affect auditory search based on spectro-temporal features of a sound target. We report that a right brain damaged patient with neglect demonstrated a significant gradient favouring the ipsilesional side on a visual search task as well as an auditory search task in which the target was a frequency modulated tone amongst steady distractor tones. No such asymmetry was apparent in the auditory search performance of a control patient with a right hemisphere lesion but no neglect. The results suggest that the spatial bias in attention exhibited by neglect patients affects stimulus processing even when spatial information is irrelevant to the task.

Sustained interactions between perception and action in visual extinction and neglect: Evidence from sequential pointing

Interactions between perception and action were examined by assessing the effects of action programming on extinction and neglect. In an extension of prior work, effects of sequential motor programming were assessed under conditions in which attention was first directed to an ipsilesional stimulus. Despite pointing and reporting a stimulus on the ipsilesional side first, programming a second action to the contralesional side reduced the spatial deficit on report, improving the report of contralesional stimuli (relative to when the patient just pointed to the ipsilesional side) while decreasing the report of ipsilesional items. The data suggest that perception and action interact through motor feedback to early visual coding, helping a patient overcome a lack of visual awareness to contralesional stimuli. This is effective even when attention has to be disengaged from the ipsilesional side suggesting that motor programming decreases ipsilesional capture and exerts a sustained influence on perception.

Hemispherectomy sustained before adulthood does not cause persistent hemispatial neglect

Introduction Hemispatial neglect has been well established in adults following acute ischemic stroke, but has rarely been investigated in children and young adults following brain injury. It is known that young brains have a tremendous potential for reorganization; however, there is controversy as to whether functions are assumed by the opposite hemisphere, or perilesional areas in the same hemisphere. Patients with intractable epilepsy who undergo hemispherectomy for treatment are missing the entire cortex on one side following surgery. In these patients, only the opposite hemisphere is available to assume function. Therefore, they provide the unique opportunity to determine in what cases the left or right hemisphere can take over the spatial attention functions of the opposite hemisphere following damage. The objective of this study was to determine the incidence and types of hemispatial neglect in children and young adults following both right- and left-sided hemispherectomy; which types of spatial attention functions can be assumed by the opposite hemisphere; and whether factors like their age at time of surgery, handedness, or gender influence recovery. Methods Thirty-two children and young adults who had previously undergone hemispherectomy were administered two tests to evaluate for two types of hemispatial neglect: a gap detection test and a line cancellation test. Egocentric neglect was defined as significantly more omissions of targets on the contralesional versus ipsilesional side of the page (by chi square analysis; p < .05). Allocentric neglect was defined as significantly more errors in detecting contralesional versus ipsilesional gaps in circles. Results Only one of the patients displayed statistically significant hemispatial egocentric neglect on the line cancellation test, and none of the patients displayed statistically significant egocentric or allocentric neglect on the gap detection test. Conclusions These results imply that reorganization to the contralateral hemisphere occurs peri-hemispherectomy, as there are no perilesional areas to assume function.

Hyperexcitability of parietal-motor functional connections in the intact left-hemisphere of patients with neglect

Hemispatial neglect is common after unilateral brain damage, particularly to perisylvian structures in the right-hemisphere (RH). In this disabling syndrome, behaviour and awareness are biased away from the contralesional side of space towards the ipsilesional side. Theoretical accounts of this in terms of hemispheric rivalry have speculated that the intact left-hemisphere (LH) may become hyper-excitable after a RH lesion, due to release of inhibition from the damaged hemisphere. We tested this directly using a novel twin-coil transcranial magnetic stimulation (TMS) approach to measure excitability within the intact LH of neglect patients. This involved applying a conditioning TMS pulse over left posterior parietal cortex (PPC), in order to test its effect on the amplitude of motor evoked potentials (MEPs) produced by a subsequent test pulse over left motor cortex (M1). Twelve RH stroke patients with neglect, an age-matched group of eight RH stroke patients without neglect, and 10 healthy controls were examined. We found that excitability of left PPC-M1 circuits was higher in neglect patients than the other groups, and related to the degree of neglect on clinical cancellation tests. A follow-up found that 1 Hz repetitive TMS over left PPC normalized this over-excitability, and also ameliorated visual neglect on an experimental measure with chimeric objects. Our results provide 'direct' evidence for pathological over-excitability of the LH in the neglect syndrome, as quantified by left PPC influences on left M1, with implications for possible treatment.

When they see, they see it almost right: Normal subjective experience of detected stimuli in spatial neglect

Unilateral spatial neglect (USN) patients show reduced contrast sensitivity on their contralesional side and often miss their non-salient stimuli. What their subjective experience is when successfully reporting a stimulus remains unclear. Here, we report that despite large contrast sensitivity differences between the sides, the relative attenuation in perceived contrast measured in a contrast-matching task was small. This was true even at threshold levels where the patients missed up to 40% of the contralesional target patches, in contrast to a 100% detection rate on their ipsilesional side. When the misses were counted as zero perceived contrast events, the attenuation in perceived contrast was less than half of the sensitivity loss. When the misses were ignored, there was almost no attenuation in perceived contrast, implying that whenever the patients detected a target, they perceived it with the correct contrast. These findings suggest that contrast sensitivity reduction in USN is not due to attenuation occurring at a peripheral low-level processing stage. More likely it reflects a high-threshold added at a higher level of processing, which prevents sensory events from reaching conscious awareness. Hence, patients may often miss contralesional stimuli but see them in full contrast once they clear the high-level hurdle.