Biomedical subjects

G Vallar

Publications and source records attributed to G Vallar.

At least 37 records · Page 2Linked to original sources

PubMed1996

Modulation of neglect hemianesthesia by transcutaneous electrical stimulation.

The effects of transcutaneous electrical stimulation on deficits of tactile perception contralateral to a hemispheric lesion were investigated in 10 right brain-damaged patients and in four left brain-damaged patients. The somatosensory deficit recovered, transiently and in part, after stimulation of the side of the neck contralateral to the side of the lesion, in all 10 patients with lesions in the right hemisphere, both with (six cases) and without (four cases) left visuo-spatial hemineglect, and in one left brain-damaged patient with right hemineglect. In three left brain-damaged patients without hemineglect, the treatment had no detectable effects. In one right brain-damaged patient, the stimulation of the side of the neck ipsilateral to the side of the lesion temporarily worsened the somatosensory deficit. These effects of transcutaneous electrical stimulation are similar to those of vestibular stimulation. The suggestion is made that these treatments modulate, through afferent sensory pathways, higher-order spatial representations of the body, which are pathologically distorted toward the side of the lesion. The modulatory effect is direction-specific: the defective internal representation of the contralesional side may be either partly restored, improving the disorder of tactile perception, or further impoverished, worsening the deficit. The possible neural basis of this modulation is discussed.

Adult↗

PubMed1996

Left neglect dyslexia and the processing of neglected information.

A patient (ES) with a right fronto-temporo-parieto-occipital lesion, and left neglect dyslexia, is reported. ES performed reading and association tasks on written words, composed of two embedded words, one to the left and one to the right of the division point. The meaning of the whole stimulus differed from that of the embedded words, and could not be inferred from either of them. ES produced appropriate associations even to those stimuli on which she made neglect paralexic errors. This dissociation reflects a distinction between processes which use co-ordinate spatial systems and subserve perceptual awareness, impaired in hemineglect, and processes which do not. The latter analyse left-sided information to a large extent, without reaching awareness.

Aged↗

PubMed1995

Gravity and hemineglect.

Spatial cognition requires the integration of visual inputs with proprioceptive and vestibular information about the position of the eye, the head and the body. All these sources are used by the brain to produce multiple higher-order (e.g. egocentric) representations of space, subserving accurate spatial behaviour. Such spatial representations are disrupted by unilateral cerebral damage producing neglect in the contralateral side of space. In eight brain-damaged patients with left unilateral neglect the manipulation of gravitational-otolithic information, obtained by placing patients in a supine position, produced a significant reduction of the rightward directional error in the line bisection task in all cases. This finding suggests that, in patients with neglect, gravitational information is processed in a non-symmetrical fashion, with a rightward bias towards the side of the lesion. This is the first study showing that manipulation of gravitational input affects neuropsychological disorders of visuo-spatial processing.

Aged↗

PubMed1995

Modulation of conscious experience by peripheral sensory stimuli.

Lack of awareness of touch associated with brain damage may transiently recover after stimulation of the vestibular system. We used positron emission tomographic regional cerebral blood flow measurements to study the neurophysiological effect of vestibular stimulation on touch imperception in a subject with a right brain lesion. We tested the hypothesis that the vestibular system aids conscious tactile perception by introducing a bias in the neural system subserving body representation. We show that in normal subjects touch and vestibular signals share projections to the putamen, insula, somatosensory area II, premotor cortex and supramarginal gyrus. In our patient a subset of these regions (right putamen and insula) was spared by the lesion and was maximally active when touch and vestibular stimulations were combined. These results support the suggestion that our phenomenological consciousness is associated with activation in circumscribed brain areas specific to the particular sensation of which we are aware.

Adult↗

PubMed1995

Improvement of left visuo-spatial hemineglect by left-sided transcutaneous electrical stimulation.

The effects of transcutaneous electrical stimulation on left visuo-spatial hemineglect, assessed by a visuo-motor exploratory task (letter cancellation), were investigated in patients with right hemisphere lesions. In Experiment 1 left neck stimulation temporarily improved the deficit in 13 out of 14 patients (93%), while stimulation of the right neck had no positive effects, worsening exploratory performance in nine patients (64%). Experiment 2 showed that left neck stimulation temporarily improved neglect also when head movements were prevented by a chin-rest. In Experiment 3, stimulation of both the left hand and left neck had comparable positive effects on visuo-spatial hemineglect. These results are interpreted in terms of: (1) non-specific activation of the right hemisphere, contralateral to the stimulation side; (2) specific directional effects of left somatosensory stimulation on the egocentric co-ordinates of extra-personal space, which in neglect patients are distorted towards the side of the brain lesion.

Adult↗

PubMed1995

Optokinetic stimulation affects both vertical and horizontal deficits of position sense in unilateral neglect.

The effects of optokinetic stimulation on the disorders of position sense in the horizontal and vertical planes were assessed in 24 patients with unilateral cerebral lesions (eight right brain-damaged patients with visuo-spatial hemineglect, eight right brain-damaged patients without neglect, eight left brain-damaged patients without neglect). In neglect patients, the position sense disorder was more severe, and affected by optokinetic stimulation in a direction-specific fashion. In both the horizontal and the vertical plane, and in both arms, stimulation with a direction of the movement contralateral to the side of the lesion improved the disorder, whereas stimulation with an ipsilateral direction worsened the deficit. The suggestion is made that in patients with neglect the disorder of position sense is produced, at least in part, by an ipsilateral distortion of an egocentric co-ordinate system, comprising both the horizontal and the vertical dimension, which may be affected by direction-specific optokinetic stimuli.

Aged↗

PubMed1995

Vestibular stimulation, spatial hemineglect and dysphasia, selective effects.

The selectivity of the effects of vestibular stimulation was investigated in a left brain-damaged patient suffering from right visuo-spatial hemineglect and severe dysplasia. Vestibular stimulation temporarily improved the former but not the latter disorder. These results support the view that this treatment improves hemineglect by a specific effect, running counter the rightward distortion of egocentric co-ordinates, rather than by a general hemispheric activation.

Aged↗

PubMed1995

Verbal short-term memory and vocabulary learning in polyglots.

Polyglot and non-polyglot Italian subjects were given tests assessing verbal (phonological) and visuo-spatial short-term and long-term memory, general intelligence, and vocabulary knowledge in their native language. Polyglots had a superior level of performance in verbal short-term memory tasks (auditory digit span and nonword repetition) and in a paired-associate learning test, which assessed the subjects' ability to acquire new (Russian) words. By contrast, the two groups had comparable performance levels in tasks assessing general intelligence, visuo-spatial short-term memory and learning, and paired-associate learning of Italian words. These findings, which are in line with neuropsychological and developmental evidence, as well as with data from normal subjects, suggest a close relationship between the capacity of phonological memory and the acquisition of foreign languages.

Adult↗

PubMed1995

Spatial hemineglect in back space.

The subjective location of the mid-sagittal plane was assessed by a free-field auditory localization task in the front and in the back half-spaces in 11 right brain-damaged patients with spatial hemineglect, 10 right brain-damaged patients without spatial hemineglect, and 11 normal control subjects. In patients with hemineglect the subjective mid-sagittal plane was found to be displaced rightwards in both half-spaces. Both patients without hemineglect and controls, in contrast, made a minor error, and showed a greater displacement towards the left side in the back half-space. In four right brain-damaged patients the rightward displacement was confined either to the front, or to the back half-space. This pattern of impairment may be explained by a rightward, ipsilesional, pathological translation of an egocentric co-ordinate system, rather than by a rotation around the vertical axis of the body.

Aged↗

PubMed1994

Identification of the central vestibular projections in man: a positron emission tomography activation study.

The cerebral representation of space depends on the integration of many different sensory inputs. The vestibular system provides one such input and its dysfunction can cause profound spatial disorientation. Using positron emission tomography (PET), we measured regional cerebral perfusion with various vestibular stimulations to map central vestibular projections and to investigate the cerebral basis of spatial disorientation. We showed that the temporoparietal cortex, the insula, the putamen, and the anterior cingulate cortex are the cerebral projections of the vestibular system in man and that the spatial disorientation caused by unilateral vestibular stimulation is associated with their asymmetric activation.

Adult↗

PubMed1994

Challenging current accounts of unilateral neglect.

Two left-neglect patients were asked (i) to bisect a 15 cm line, (ii) to bisect the empty space between the endpoints of a 15 cm virtual line, and (iii) to set the endpoints of a 15 cm virtual line, given its midpoint. With one patient, the subjective midpoint of the virtual line was found to be displaced leftwards with respect to the subjective midpoint of the real line, whereas with the other it was found to be displaced rightwards. However, in condition (iii) both patients significantly underestimated the distance from the centre of the rightmost point of the virtual line while relatively overestimating that from the centre to the left endpoint. This latter result challenges current accounts of unilateral neglect.

Aged↗

PubMed1994

Anatomical correlates of visual and tactile extinction in humans: a clinical CT scan study.

The anatomical correlates of tactile and visual extinction with double simultaneous stimulation were investigated in a series of 159 patients with right brain damage caused by stroke. Forty six patients showed extinction (22 tactile, 14 visual, 10 tactile and visual). Over 50% of the patients with extinction had deep lesions, which were found in about 25% of the patients with visuospatial neglect not associated with extinction. In the patients with extinction and cortico-subcortical damage the paraventricular occipital white matter and the dorsolateral frontal cortex were most often involved. By contrast, when neglect was also present, the lesions clustered in the inferior parietal lobule. These data suggest, from an anatomical perspective, that partly different neural mechanisms may underlie neglect and extinction. The comparatively high frequency of subcortical lesions involving the ascending pathways may be a neural correlate of a sensory component of extinction.

Adolescent↗

PubMed1994

Immunologic changes in circulating leukocytes in the presence of atherosclerotic disease.

To assess the numeric and functional changes in circulating white blood cells in the presence of severe atherosclerosis, 25 subjects with marked, angiographically assessed, atherosclerotic lesions and 29 selected controls were studied. Of the differential leukocyte counts, only monocyte count was significantly higher in the atherosclerotic than in the control subjects (449.0 +/- 115.6 (1 S.D.) vs. 344.1 +/- 138.8/mmc; P = 0.0016). By flow-cytometry no significant differences concerning monocyte surface antigens were found, except a feeble decrease in beta 2-microglobulin in the atherosclerotic subjects. As to lymphocytes, an increase in the CD8 population (33.4 +/- 6.8 vs 28.6 +/- 6.5%; P = 0.0144) and decreases in class I HLA antigen (96.6 +/- 7.3 vs 99.4 +/- 0.7%; P = 0.0049), beta 2-microglobulin (97.9 +/- 2.1 vs 99.3 +/- 1.0%; P = 0.0055) and especially in vivo DNA synthesis (3.8 +/- 1.2 vs 5.3 +/- 2.1%; P = 0.0102) percent expressions were found in the atherosclerotic patients with respect to the controls. This study shows that circulating monocytes are increased in atherosclerotic disease, possibly due to their participation in the phagocytosis of lipids in the arterial wall, with no further immunologic involvement. Conversely, the replicative activity of T lymphocytes is decreased, which might be a consequence of or a factor predisposing to atherosclerosis.

Acute Disease↗

PubMed1993

Left and right hemisphere contribution to recovery from neglect after right hemisphere damage--an [18F]FDG pet study of two cases.

A 2-[18F]-Fluoro-2-Deoxy-D-Glucose ([18F]FDG) and positron emission tomography (PET) study was performed in the acute and chronic phase of stroke in one patient with unilateral neglect due to a right hemispheric lesion. In the acute phase, severe neglect, as well as hypometabolism in both the right and in the left unaffected cerebral hemisphere, was demonstrated. At follow-up evaluation the patient showed an almost complete recovery from unilateral neglect. This was associated with a return of left hemisphere metabolism to normal values and partial metabolic recovery in the right hemisphere, where frontal and parietal areas remained functionally impaired. Another patient with an extensive right cerebral ischaemic lesion on CT and severe unilateral neglect was studied by PET in chronic phase. A severe metabolic depression in the left unaffected hemisphere and in the right cerebral areas spared by the lesion, was found. These data suggest that the remission of unilateral neglect might be associated to a functional metabolic recovery in both the undamaged left hemisphere and the unaffected regions of the right hemisphere.

Aged↗

PubMed1993

Deficits of position sense, unilateral neglect and optokinetic stimulation.

The effects of optokinetic stimulation on position sense disorders were investigated in a series of 30 patients with unilateral vascular lesions (10 right brain-damaged patients with visuospatial hemineglect, 10 right brain-damaged patients without visuo-spatial hemineglect, 10 left brain-damaged patients), and 10 control subjects. The position sense deficit was more severe in right brain-damaged patients with neglect, where both the contralateral and the ipsilateral arm were involved. Optokinetic stimulation was effective only in right brain-damaged patients with neglect: stimulation with a leftward movement (contralateral to the side of the hemispheric lesion) improved the position sense deficit, while stimulation with a rightward (ipsilateral) movement produced a worsening of the performance level. These findings suggest that in right brain-damaged patients with neglect the position sense deficit has a nonsensory component, related to neglect, which may be affected by optokinetic stimulation. The role of the derangement of sensory and perceptual-egocentric representations of the body and of extrapersonal space in producing position sense disorders is discussed.

Aged↗

PubMed1993

Preserved vocabulary acquisition in Down's syndrome: the role of phonological short-term memory.

We report the study of a 23-year-old Italian girl, FF, with Down's syndrome (trisomy 21). FF showed a remarkably good developmental acquisition of Italian language and vocabulary and was able to learn English and French, although the latter with less proficiency. FF showed an entirely preserved function of the phonological short-term store and articulatory rehearsal components of verbal short-term memory. By contrast, she was impaired in a wide range of tasks assessing verbal and non-verbal reasoning, visuo-spatial perception and memory, and verbal long-term memory. These findings, in line with evidence from brain-damaged patients, normal subjects and children, suggest that phonological short-term memory plays a crucial role in vocabulary acquisition, which may occur in the presence of substantial deficits of general intelligence and episodic memory.

Adult↗

PubMed1993

Exploring somatosensory hemineglect by vestibular stimulation.

The effects of vestibular stimulation upon somatosensory deficits or tactile extinction contralateral to a hemispheric lesion were investigated in 20 right brain-damaged patients and 11 left brain-damaged patients. After stimulation, right brain-damaged patients showed a temporary partial recovery from left hemianaesthesia or extinction. Conversely, right somatosensory deficits associated with left brain damage were virtually unaffected by vestibular stimulation. Temporary recovery from somatosensory deficits was independent of the presence of visuo-spatial hemineglect. The suggestion is made that somatosensory deficits and extinction produced by right brain damage have an important non-sensory or perceptual component, that may be positively affected by vestibular stimulation. The mechanisms whereby this treatment may ameliorate somatosensory deficits may involve the restoration of the normal correspondence between somatotopic and egocentric representations of the body.

Adolescent↗

PubMed1993

Evidence of multiple memory systems in the human brain. A [18F]FDG PET metabolic study.

Patients with global amnesia of different aetiologies (n = 11), and patients with probable Alzheimer's disease of recent onset and mild to moderate severity (n = 18) underwent extensive neuropsychological examination, which included the evaluation of multiple components of memory, and a measurement of regional cerebral glucose metabolism with [18F]fluoro-deoxyglucose ([18F]FDG) and PET. In the neuropsychological tests, both global amnesia and Alzheimer's disease patients had impaired episodic long-term memory, while deficits of short-term, semantic and implicit memory were present only in Alzheimer's disease. When local metabolic rates for glucose were compared with values from age- and education-matched normal controls, a common pattern of bilateral hypometabolism was present in the hippocampus, cingulate and frontal basal cortex of both global amnesia and Alzheimer's disease patients. On the other hand, significant hypometabolism was found in the thalamus in only global amnesia, and in the frontal, parietal and temporal associative cortex in only Alzheimer's disease. The results of a multivariate regression analysis of test scores with metabolic data indicated that different clusters of cerebral areas were associated with each of the main components of memory function. These data are in agreement with 'neural network' models of the neural basis of cognition, according to which complex functions are subserved by multiple interconnected cortical and subcortical structures.

Aged↗