Spatial localization in patients with unilateral posterior left or right hemisphere lesions

In this study, perceptual and visuomotor spatial localization were examined in patients with unilateral right (RH) or left (LH) hemisphere lesions and in a group of control subjects. Perceptual localization was measured with a position-discrimination task; in the visuomotor localization task, subjects had to point to a visual target. Both tasks were investigated in conditions with or without background visibility and with central and peripheral targets. In the visuomotor task, hand visibility was also manipulated. In both tasks, targets were presented in the left and right visual hemifield. The perceptual task revealed impairments for both LH and RH patients in the contra-lateral visual hemifield. RH patients also revealed slightly larger impairments in conditions without a visual background. In the visuomotor task, the LH patients were not impaired, whereas the RH patients were impaired in conditions without hand visibility and/or background visibility. Hence, our data strengthen the idea that spatial localization is not a unitary function and that perceptual and visuomotor localization can be selectively impaired. We suggest that one of the important factors distinguishing between localization impairments in RH and LH patients might be absolute versus relative localization.     

Learning postural tasks in hemiparetic patients with lesions of left versus right hemisphere

There are a number of studies concerning difference of postural control following left or right hemisphere lesions. Few studies, however, compare the role of the right and left hemisphere in learning new postural tasks. This study aimed to address this question. Twenty patients with hemiparesis after ischemic stroke in the middle cerebral artery territory (11 with a right and 9 with a left hemispheric lesion) were investigated. All subjects were trained using two different tasks during ten training sessions. In both tasks, the subjects stood on a force platform and were taught to change the position of the center of pressure (COP) presented as a cursor on a monitor screen in front of the patient. The subjects were instructed to align the COP with the target and then move the target by shifting the COP in the indicated direction. In the “Balls” task, the position of the target (a ball) varied randomly, so the subject had to learn a general strategy of voluntary COP control. In “Bricks”, the subject always had to move the target in a single direction (downward) from the top to the bottom of the screen, so that a precise postural coordination had to be learned. The number of correctly performed trials for a session was scored. The task performance and its rate were analyzed and compared with respect to the lesion lateralization between two patient groups. The voluntary control of the COP position and learning course were initially impaired in all groups of patients in both tasks. In “Balls”, there were no differences between the two groups of patients. In contrast, in “Bricks”, there was a greater initial deficit in patients with right hemisphere lesions, while the rate of postural learning and the final performance level did not differ between the groups. With a lower initial deficit and similar rate of learning, the maximal level of the task performance was reached earlier (on the 5th day of training) in patients with left hemisphere lesions. This group stopped improving its performance during follow-up training. The results suggest that the motor structures of the right hemisphere are more involved in the precise control of COP trajectory, but not in learning. There is no difference between hemispheres in the initial performance and learning of the general strategy of voluntary COP control. Possibly, the control of specific COP trajectory needs more sensory feedback that is associated with greater involvement of the right hemisphere. This might be a reason for the greater initial impairment of this task after lesions in the right hemisphere.     

Lymphocyte homing after left or right brain neocortex ablation

The cerebral neocortex is known to modulate the immune system in an asymmetrical way. Ablations of the left cortex decrease, whereas symmetrical right lesions have no effect, or enhance, T cell functions measured 6-8 weeks after lesioning. However, modifications of immune responses induced by lesions of the brain neocortex could result from a lymphocyte redistribution mediated by glucocorticoids, like that observed during stress. We tested this possibility in the present experiments. Cortical lesions modulated concanavalin A-induced proliferation of both lymph node and spleen lymphocytes in a similar way. Cortical lesions of either side modified neither the lymphocyte distribution of 51Cr-labelled injected lymph node cells, nor the percentage of blood cell subsets. These results show that cortical lesions do not affect lymphocyte homing, and suggest that the brain neocortex immunomodulatory effects are not mediated by glucocorticoids.     

Figural fluency: differential impairment in patients with left versus right frontal lobe lesions.

Based on an experimental study, Jones-Gotman and Milner demonstrated that patients with right frontal lobe lesions were impaired on design fluency. We sought a clinical adaptation and developed a psychometrically sound technique for design fluency. The present study explores the validity of the Ruff Figural Fluency Test (RFFT) in discriminating patients with either right frontal or nonright frontal lobe lesions. In the first of two studies, six subjects with circumscribed focal lesions were given the RFFT and the Jones-Gotman and Milner figural fluency task. In the second study, we identified a larger sample of 30 patients with focal lesions in the right frontal, left frontal, right posterior, or left posterior cortex. The results from both studies support the validity of the RFFT as a measure which is sensitive to right anterior dysfunction.     

Verbal dichotic listening and manual performance in children with congenital unilateral brain lesions

The authors assessed manual performance and verbal dichotic listening performance in 16 epilepsy-free children with congenital unilateral brain lesions and normal IQ to investigate cerebral reorganization. In all children, the paretic hand had fair grip function, but reaction times were impaired, and cerebral reorganization of hand function in those with right hemiplegia was shown by the high incidence of pathological left-handedness. The dichotic listening results showed that most children with left lesions had a left ear advantage significantly related to the extent of brain damage. This finding suggests that extent of cortical damage and presence of thalamic involvement, irrespective of neuropathology, are the primary factors inducing rightward cerebral language reorganization in children with unilateral congenital brain lesions.     

Fewer brain lesions with AZT

An eleven-year Norwegian autopsy study found fewer brain lesions in people who died of AIDS complications who had used AZT until death. Previous studies contradict this result. The Norwegian researchers believe that the inclusion of data prior to AZT availability led to the inconclusive findings.     

Reactivity of the right and left hemispheres in 3.5-5-year-old children with different attention efficiency

Here we present the analysis of age-specific and individual characteristics of sensory systems of the right and left hemispheres in preschool children. We studied the role of visual, auditory, and cutaneous sensory zones of the right and left hemispheres in 3.5-5-year-old children in the structure of functional systems realizing attention processes with different efficiency. Sensorimotor parameters reflecting the structure of functional systems at the perceptive level were identified. These data are helpful for diagnostics of the causes of low efficiency of cognition abilities.     

Text comprehension after brain injury: left prefrontal lesions affect inference processes

Comprehending language in context requires inferencing, particularly for the establishment of local coherence. In the neurolinguistic literature, an inference deficit after right hemisphere brain damage has been postulated, but clinical observation and imaging data suggest that left-frontal lesions might also result in inference deficits. In the present experiment, 25 nonaphasic patients performed a coherence judgment task requiring them to indicate a pragmatic connection between 2 successively presented sentences. Patients with left-temporal or right-frontal lesions performed the task well. In contrast, patients with left- and bifrontal lesions exhibited the most severe deficit. Both error rates and response times were elevated for coherent trials as compared with incoherent trials. These results confirm that the left-frontal lobe contributes to inference processes.     

Chronic isolated brain lesions caused by respiratory viruses in children

Combined study of 48 postmortem observations of cerebral lesions caused mainly by meningococcal infection in children was carried out. In 15 cases, isolated subclinical involvement of the brain (more frequently, of the vascular plexus and meninges) caused by influenza A viruses (8 cases), B (2 cases), adenoviruses (6), parainfluenza and respiratory syncytial virus (1 each), and chlamydia (2) was found. This was proved by the presence of the appropriate antigens in the brain revealed by immunofluorescence which were absent in respiratory organs, high titres of antibody to the same agents in the cerebrospinal fluid which were lacking in 13 cases or had significantly low titres in 2 cases in the blood, virus isolation from the brain (2 cases) and detection of virus particles in 1 out of 2 cases from which the vascular plexus was examined by electron microscopy. Histological examination of the affected areas revealed structural changes of ependymocytes which were principally similar to those described in respiratory organs as well as in other organs in cases of generalization of respiratory infections. Different degrees of sclerosis of vascular plexus (2 cases) or meninges (2 cases) were also observed.     

Disorders of visuospatial orientation in the frontal plane in patients with visual neglect following right or left parietal lesions

Current models of spatial neglect focus on deficits in the patients’ horizontal or midsagittal plane. However, other evidence suggests that patients with temporoparietal lesions centered on the parieto-insular-vestibular cortex show disturbed spatial perception of the subjective visual vertical and oblique orientation discrimination in another spatial plane, the frontal plane. As the relationship between neglect and spatial orientation deficits is unclear, we examined how patients with and without visual neglect perform visuospatial tasks in the roll plane and how their performance is related to neglect. Thirteen patients with predominantly right parietal lesions and left-sided neglect, 14 control patients without neglect after right-hemispheric cerebral lesions (RBD-controls), 11 patients without neglect after left-hemispheric lesions (LBD-controls), 3 patients with right-sided neglect after left parietal lesions, and 12 normal subjects were investigated. Constant errors and difference thresholds were measured with a PC-based system when the subjects had to adjust a luminous line to their subjective visual vertical, subjective visual horizontal, and in relation to an obliquely oriented reference line. Subjects were oriented with their head and body earth-vertical while sitting in a chair in total darkness. Patients with left-sided as well as those with right-sided neglect showed a significant, in most cases contraversive, tilt of the three spatial orientations (about 5° counterclockwise in the left neglect group and 5.5°–8.5° clockwise in the right neglect group). In contrast, the two patient groups without neglect as well as the normal subjects showed nearly perfect visuospatial judgements with constant errors of less than 0.8°. Difference thresholds were significantly elevated in patients with left neglect and in two of three patients with right-sided neglect, whereas normal control subjects and both control patient groups without neglect performed indistinguishably, having thresholds of one-tenth of those of the neglect patients. Tilt of all three spatial axes was significantly related to the severity of neglect (mean r for unsigned errors, 0.74; for difference thresholds, 0.40), indicating a significant contribution to the symptomatology of left and right spatial neglect. These results indicate a close although not necessarily causal link between spatial orientation deficits in the frontal plane and hemispatial neglect in patients with left or right parietal lesions, surpassing the well-documented impairments of these patients in the horizontal plane. Received: 1 August 1997 / Accepted: 1 April 1998     

Spiroperidol reinstates asymmetries in neglect in rats recovered from left or right dorsomedial prefrontal cortex lesions

The role of dopaminergic mechanisms in spontaneous behavioral recovery from cortical neglect was examined in rats that received lesions of either the left or the right dorsomedial prefrontal cortex (PCm, also referred to as AGm). Neglect was assessed by rating the degree of head orientation to visual, auditory, or tactile stimuli. Following behavioral recovery, separate groups received 0.03, 0.05, 0.07, or 0.10 mg/kg spiroperidol or the vehicle. In accordance with the lateralization of neglect typically seen postsurgery, spiroperidol dose-dependently reinstated contralesional neglect in left PCm operates and ipsilesional neglect in right PCm operates. Neglect was reinstated by spiroperidol in right PCm operates at lower doses than in left PCm operates. Also, only right PCm operates demonstrated asymmetrical bilateral dose-dependent neglect. Spiroperidol did not produce neglect in unilaterally brain-damaged control subjects. The results indicate that dopaminergic mechanisms may underlie spontaneous recovery from cortical neglect and that these mechanisms are asymmetrical in left and right PCm operates.     

Externalising spatial knowledge in patients with right hemisphere lesions

Abstract

This study examines the performance of patients with right hemisphere lesions and neurologically intact control subjects on three spatial tasks designed to access spatial representation unconfounded by enabling skills. The three tasks were: (1) imagining a map of the United States and verbally estimating distances between all possible pairs of nine major cities, (2) locating these cities on an outline map of the United States, and (3) verbally estimating distances between all possible pairs of nine symbols which were placed on a page in the same spatial arrangment as the nine cities. The right hemisphere group performed significantly worse than controls on only the first task. Since performance on the latter two tasks was equivalent, the significant group differences cannot be due to ignorance of the city locations or inability to verbally estimate distances. Our results suggest that the visuo-spatial disorder commonly seen after right hemisphere lesions is not limited to tasks which involve spatial perception in the conventional sense, but also involves the internal representation of spatial information.     

Superdominant right coronary artery with absent left circumflex artery

Noninvasive imaging of coronary artery disease is rapidly replacing angiography as the first line of investigation. Multislice CT is the non-invasive modality of choice for imaging coronary artery disease and provides high speed with good spatial resolution. CT coronary angiography in addition to detecting and characterising atherosclerotic coronary artery disease is also a good imaging tool for evaluating anomalies of coronary arteries. Superdominant right coronary artery with absent left circumflex artery is one such rare coronary artery anomaly which is well evaluated with multislice CT angiography. The authors report one such case of superdominant right coronary artery with absent left circumflex artery imaged with 64-slice MDCT.     

Grasping with the left and right hand: a kinematic study

The goal of the present study was to compare prehension movements of the dominant and the non-dominant hand. Twenty right-handed volunteers (age 20–30 years) reached forward to grasp a cylindrical object, which was lifted and then placed into a target position in a retraction–insertion movement. The movements were performed at three different velocities (normal, deliberately fast, or slowly) both, under visual control, and in a no-vision condition. Analysis of the kinematic data revealed that the speed of hand transport influenced pre-shaping of both hands in a similar way. In the visual condition, the grip aperture increased about linearly with peak transport velocity, while it increased non-linearly with shorter movement duration. Comparison of the regression parameters showed that these relationships were nearly identical for both hands. The dominant hand was faster in inserting the object into the target position. Otherwise, no significant inter-manual differences were found. During prehension without visual control, the fingers opened more and movement duration was prolonged. Except for a larger grip aperture of the dominant hand at the end of the acceleration phase, the kinematic data of both hands were again comparable. This invariance was in contrast to performance in fine motor skills such as a pegboard test and drawing movements, where there was a clear advantage of the dominant hand. The similar pre-shaping of both hands during prehension is discussed with regard to a common motor representation of grasping.