Biomedical subjects

L Pizzamiglio

Publications and source records attributed to L Pizzamiglio.

At least 19 recordsLinked to original sources

PubMed2001

Linguistic and nonlinguistic priming in aphasia.

Studies of real-time processing in aphasia suggest that linguistic symptoms may be due to deficits in activation dynamics rather than loss of linguistic knowledge. To investigate the domain specificity of such processing deficits, we compared performance by Italian-speaking fluent aphasics, nonfluent aphasics, and normal controls in a linguistic priming task (grammatical gender) with their performance in a color-priming task that requires no verbal mediation. Normal or larger than normal color-priming effects were demonstrated in both aphasic groups. Gender priming did not reach significance in either group, even though the patients displayed above-chance sensitivity to gender class and gender agreement in their accuracy scores. The demonstration of spared gender knowledge despite impaired gender priming underscores the utility of on-line techniques in the study of aphasia. The demonstration of spared color priming suggests that priming deficits in aphasia are either (1) specific to speech and language or (2) specific only to those sensorimotor and attentional processes that language shares with other nonlinguistic systems.

Adult↗

PubMed2000

TENS modulates spatial reorientation in neglect patients.

The existence of separate systems for processing geometric and non-geometric spatial information was studied. Twelve neglect patients were asked to reorient themselves in a room using only geometric information or to integrate this information with relevant visual cues both in the presence and in the absence of transcutaneous electrical neural stimulation (TENS). In the absence of TENS, all patients were greatly impaired in coding geometric information, and they had difficulty in coding non-geometric information. TENS significantly improved the ability to code shape-based representation, but is ineffective with non-geometric representations (such as color). The data support previous findings on neglect patients suggesting the presence of separate, independent neural systems subserving different types of space representation.

Attention↗

PubMed2000

The neural basis of egocentric and allocentric coding of space in humans: a functional magnetic resonance study.

The spatial location of an object can be represented in the brain with respect to different classes of reference frames, either relative to or independent of the subject's position. We used functional magnetic resonance imaging to identify regions of the healthy human brain subserving mainly egocentric or allocentric (object-based) coordinates by asking subjects to judge the location of a visual stimulus with respect to either their body or an object. A color-judgement task, matched for stimuli, difficulty, motor and oculomotor responses, was used as a control. We identified a bilateral, though mainly right-hemisphere based, fronto-parietal network involved in egocentric processing. A subset of these regions, including a much less extensive unilateral, right fronto-parietal network, was found to be active during object-based processing. The right-hemisphere lateralization and the partial superposition of the egocentric and the object-based networks is discussed in the light of neuropsychological findings in brain-damaged patients with unilateral spatial neglect and of neurophysiological studies in the monkey.

Adult↗

PubMed2000

Psychophysical properties of line bisection and body midline perception in unilateral neglect.

Past research associated unilateral neglect with a systematic ipsilesional shift of the perceived position of the body midline; however, this was not confirmed by recent experiments. We used the constant stimuli method to control for potential artifacts intrinsic to the techniques used in previous studies. Body midline perception was measured in the visual and proprioceptive modalities in ten patients with left unilateral neglect, ten control patients and ten normal subjects and compared with a visual line bisection task, also using the constant stimuli method. Neglect patients showed a significant rightward bias in the line bisection task, but no consistent directional bias either in the proprioceptive or in the visual body midline task. These results clearly counter the association between neglect and an ipsilesional shift of the body midline. However, in the body midline tasks neglect patients made more errors in judgement on both sides of their subjective midline, both with respect to the control groups and with respect to the line bisection task. This may imply that a specific impairment of body-centered representations is indeed present and manifests as a non directional increase in response variability, rather than as a systematic shift. It is suggested that body- and object-related tasks (such as line bisection) may be processed by independent cognitive computations. This interpretation is discussed with reference to a recent neuroimaging study investigating the same kinds of tasks.

Aged↗

PubMed1999

A fronto-parietal system for computing the egocentric spatial frame of reference in humans.

Spatial orientation is based on coordinates referring to the subject's body. A fundamental principle is the mid-sagittal plane, which divides the body and space into the left and right sides. Its neural bases were investigated by functional magnetic resonance imaging (fMRI). Seven normal subjects pressed a button when a vertical bar, moving horizontally, crossed the subjective mid-sagittal plane. In the control condition, the subjects' task was to press a button when the direction of the bar movement changed, at the end of each leftward or rightward movement. The task involving the computation of the mid-sagittal plane yielded increased signal in posterior parietal and lateral frontal premotor regions, with a more extensive activation in the right cerebral hemisphere. This direct evidence in normal human subjects that a bilateral, mainly right hemisphere-based, cortical network is active during the computation of the egocentric reference is consistent with neuropsychological studies in patients with unilateral cerebral lesions. Damage to the right hemisphere, more frequently to the posterior-inferior parietal region, may bring about a neglect syndrome of the contralesional, left side of space, including a major rightward displacement of the subjective mid-sagittal plane. The existence of a posterior parietal-lateral premotor frontal network concerned with egocentric spatial reference frames is also in line with neurophysiological studies in the monkey.

Adult↗

PubMed1999

Cortical control of optokinetic nystagmus in humans: a positron emission tomography study.

Positron emission tomography (PET) was used to address the issue of physiological changes in the cerebral cortex associated to optokinetic nystagmus (OKN) in humans. We studied regional cerebral blood flow in eight volunteers during reflexive induction of OKN by a pattern of dots moving unidirectionally (toward the left side). We used two control conditions, with subjects passively viewing either stationary or incoherently moving dots. This paradigm was designed in order to differentiate the OKN-related activations from blood flow changes related to visual motion. When compared with the stationary condition, OKN activated a set of occipital areas known to be sensitive to visual motion. Bilateral activation was found in the striate cortex (V1) and the parieto-occipital fissure, while area V5, the intraparietal sulcus, and the pulvinar were activated only in the left hemisphere. When compared with incoherent motion, OKN activated the V1 and the parieto-occipital fissure bilaterally and the right lingual gyrus, while a signal decrease was observed in the V5 region in both hemispheres. No significant signal changes were found in areas implicated in saccades or in processing vestibular information. These results indicate that processing of OKN-related information is associated with neural activity in a specific set of visual motion areas and suggest that this network can be asymmetrically activated by a strictly unidirectional stimulation. Results are also discussed in terms of the specific kinds of OKN-related information processing subserved by each area in this network.

Adult↗

PubMed1998

Recovery of neglect after right hemispheric damage: H2(15)O positron emission tomographic activation study.

BACKGROUND: The neural correlates of recovery of unilateral neglect (ULN), as well as of other consequences of focal brain damage, are largely unknown. Functional neuroimaging methods (in particular, positron emission tomography [PET]) can be applied to the in vivo study of recovery mechanisms in neurologic patients. OBJECTIVE: To evaluate the functional cerebral correlates of recovery from ULN in patients with right-sided lesions, with the use of a PET activation paradigm. METHODS: Study of 3 patients with cerebrovascular lesions that involved corticosubcortical (patient 1) or subcortical (patients 2 and 3) areas of the right hemisphere. Unilateral neglect was tested twice, before and after completion of a 2-month rehabilitation program, after which all 3 patients showed considerable improvement. Similarly, 2 PET examinations were performed, before and after recovery, during the performance of a visuospatial task requiring the patients to detect and respond to visual targets moving on a computer screen from the right to the left visual hemifield (experimental condition). The cerebral activation was compared with a baseline task in which subjects responded to a black dot flashing in a fixed position of the right hemifield. RESULTS: The brain areas activated by the performance of the visuospatial task before and after recovery were compared. In all 3 patients, the regions notably more active after recovery were almost exclusively found in right-sided cortical areas and largely overlapped with those observed in a group of 4 normal subjects performing the same task. Other areas, which have been shown to be involved in attentional and oculomotor tasks in other PET studies, were also activated in patients with ULN. CONCLUSIONS: The behavioral recovery of ULN in these patients with predominantly subcortical lesions is mainly associated with cerebral activations in cortical regions similar to those observed in normal subjects. There is some evidence of functional reorganization in individual subjects, which involves other areas related to space representation and exploration.

Aged↗

PubMed1998

Somatosensory stimulation improves imagery disorders in neglect.

A group of 9 right brain damaged patients with unilateral neglect performed a set of tasks involving mental imagery with and without a transcutaneous electrical neural stimulation (TENS) to both sides of the neck. Results showed that TENS on the left side of the neck produced significant improvements of performances on the left side of mental representations of objects (drawing, shape comparison) as well as on left side of mental images of space (description of squares). The results suggest that the modification induced by TENS may affect the imagery systems involved in objects as well as in space representation.

Aged↗

PubMed1998

Evidence for separate allocentric and egocentric space processing in neglect patients.

Spatial orientation was investigated in two different conditions: (a) when the shape of the enclosure was the only available information; (b) when a clearly perceivable visual cue was added. Three groups of subjects were investigated: normal controls, right brain-damaged patients without and with hemispatial neglect. The performance of the first two groups clearly demonstrated the capacity to use the geometric properties of the environment and to integrate this information with an additional visual cue. Considered as a group, patients with hemispatial neglect were able to use the shape of the environment and, to a lesser extent, the additional visual cue. However, individual differences suggest two opposite performance patterns: two patients responded randomly when the shape of the environment was the only available information, and they improved considerably when the cue was offered; two other patients showed normal competence in dealing with the geometrical properties of the environment, but were unable to take advantage of the cue. The different lesion site in these two types of patients suggests a possible dissociation of processing based upon allocentric or egocentric coding of space in humans as well as in animals.

Aged↗

PubMed1997

Neural control of fast-regular saccades and antisaccades: an investigation using positron emission tomography.

Regional cerebral blood flow changes related to the performance of two oculomotor tasks and a central fixation task were compared in ten healthy human subjects. The tasks were: (a) performance of fast-regular saccades; (b) performance of voluntary antisaccades away from a peripheral cue; (c) passive maintenance of central visual fixation in the presence of irrelevant peripheral stimulation. The saccadic task was associated with a relative increase in activity in a number of occipitotemporal areas. Compared with both the fixation and the saccadic task, the performance of antisaccades activated a set of areas including: the superior and inferior parietal lobules, the precentral and prefrontal cortex, the cingulate cortex, and the supplementary motor area. The results of the present study suggest that: (a) compared with self-determined saccadic responses the performance of fast regular, reflexive saccades produces a limited activation of the frontal eye fields; (b) in the antisaccadic task the inferior parietal lobes subserve operations of sensory-motor integration dealing with attentional disengagement from the initial peripheral cue (appearing at an invalid spatial location) and with the recomputation of the antisaccadic vector on the basis of the wrong (e.g., spatially opposite) information provided by the same cue.

Adult↗

PubMed1997

Gravitational inputs modulate visuospatial neglect.

Right brain-damaged patients with left visuospatial neglect were required to bisect a line placed in front of them in two different body positions (upright and supine) and two different light conditions (light and dark). The neglect patients, unlike right brain-damaged patients without neglect, strongly reduced their rightward directional error in the supine compared with the upright position. No systematic changes were produced by the light-dark manipulation. The present result cannot be explained with an attentional interpretation of hemispatial neglect. We suggest that the present data provide further evidence that hemineglect is the consequence of a mismatch between different afferent information integrated into an egocentric space representation. According to this model, the presence of a lateralized brain lesion produces asymmetries in some intermediate spatial representations (eye-head, head-trunk, body-environment) but not in the retinotopic one. Any experimental manipulation that reduces the asymmetry of the intermediate representation such as the reduction of gravitational inputs may improve the dynamic integration of the egocentric coordinates.

Aged↗

PubMed1997

Response bias in color priming.

Four experiments investigated the role of response bias in color priming. Subjects were shown three prime-target pair conditions: same color trials, category priming trials (in which prime and target were different colors associated with the same response category) and incongruent trials. The subjects' task ('go-no-go' vs. 'two-choice' RT, Experiments 1-2), the categorization criterion of the stimuli (Experiment 3) and the proportion of the same versus different response trials (Experiment 4) were manipulated to influence the amount of response bias. Overall, the results indicate that color priming is produced whether or not a bias is generated at the response level, suggesting that the mechanisms underlying the two effects are largely independent of each other.

Adult↗

PubMed1997

Dissociation between position sense and visual-spatial components of hemineglect through a specific rehabilitation treatment.

Current evidence suggests an association between contralesional extra-personal hemineglect, and deficits of arm position sense in patients with damage to the right cerebral hemisphere. A unitary deficit may produce both disorders, or this association may reflect the anatomical contiguity of relevant brain structures. A rehabilitation treatment, devised for visual-spatial hemineglect, was used to investigate these hypotheses in 8 patients with damage to the right cerebral hemisphere. The treatment improved hemineglect, but not the position sense deficit. The severity of the latter was however transiently reduced by optokinetic stimulation, with effects similar to those found in visual-spatial hemineglect. These effects of rehabilitation suggest that extra-personal hemineglect and the neglect-related component of the position sense disorder of the left forearm are independent, though frequently associated, deficits. Implications for the design of rehabilitation programs are discussed.

Aged↗

PubMed1997

Motor deficits and optokinetic stimulation in patients with left hemineglect.

Optokinetic stimulation with left direction of the movement of luminous dots temporarily improved motor weakness of the left hand in two right-brain-damaged patients with left spatial hemineglect. Stimulation to the right had no effect. In two left-brain-damaged patients, optokinetic stimulation did not affect the right motor weakness, regardless of direction of the movement of the optokinetic stimuli. We suggest that in patients with left hemineglect, contralesional motor deficits have a neglect-related component, which, as other aspects of the neglect syndrome, may be improved by optokinetic stimulation. The mechanisms may include a temporary restoration of the spatial coordinates of bodily representations, pathologically distorted towards the side of the lesion.

Aged↗

PubMed1996

Facilitatory effect of neglect rehabilitation on the recovery of left hemiplegic stroke patients: a cross-over study.

A study of the effect of specific training for visual neglect on the recovery of motor and functional impairment in stroke patients is reported. Two groups of right hemisphere stroke patients with hemispatial neglect and one group without neglect were assessed by means of three functional and neurological scales (Rivermead Mobility Index, Barthel Index, Canadian Neurological Scale). Three evaluations were made at 0, 2 and 4 months from the beginning of physical rehabilitation. During the first 2 months of physical rehabilitation one of the two groups of neglect patients was randomly assigned to specific training for neglect, and the second group to a general cognitive intervention; during the final 2 months of rehabilitation the types of training were switched in the two groups. The non-neglect patients improved steadily during physical rehabilitation. In contrast, the functional recovery of the two neglect groups was time-locked to the period of the specific training for neglect. At the time of admission, the two neglect groups performed at the same level; after 2 months of rehabilitation, the group with neglect training showed higher functional recovery than the group with only general cognitive intervention. When the latter group received neglect training, there was no longer any difference between the two neglect groups. This pattern was present for both of the functional scales used but not for the neurological scale. Motor and functional recovery of stroke patients with neglect seems to be significantly improved by the simultaneous presence of a treatment specifically focused on neglect.

Cerebrovascular Disorders↗

PubMed1996

Asymmetry of rapid eye movements in chronic unilateral neglect does not change with behavioral improvement induced by rehabilitation treatment.

A strong reduction of leftward rapid eye movements (REMs) during REM sleep was recently documented in patients with severe and chronic left unilateral neglect. The aim of the present research was to study the stability of the unilateral suppression of REMs before and after a rehabilitative treatment for neglect disorders. Six right-brain-damaged patients were tested for neglect at the beginning and at the end of a 2 month cognitive rehabilitation treatment. REMs were recorded during 1 night of undisturbed sleep before and after the training. Five out of 6 patients improved considerably their ability to attend the previously neglected left hemispace; in all patients REM asymmetry remained unchanged. The lack of relationship between the improvement of the neglect disorder and the persistence of REM asymmetry suggests that the sensorimotor mechanisms activated by rehabilitation are different from those involved in the production of REMs. It is proposed that: (a) the directional vectors of REMs are computed on the basis of the exclusive or predominant endogenous activation of the central attentional mechanisms related to vestibular input; (b) the presence of rightward and leftward saccades and the positive effects of the rehabilitation treatment are functionally linked to attentional oculomotor mechanisms that are not active in REM sleep.

Aged↗

PubMed1996

Beyond unilateral neglect.

When required to set the endpoints of an imaginary horizontal line of a given length on the basis of its midpoint printed on a sheet of paper, left neglect patients most frequently misplaced endpoints leftwards. Though giving rise to the very same disproportion usually found with these patients on canonical line bisection tasks, this behaviour cannot be accommodated by current explanations of unilateral neglect. When the task was executed during leftward optokinetic stimulation (OKS), a manoeuvre known temporarily to improve neglect symptoms, the disproportion increased instead of vanishing. We therefore suggest that unilateral neglect is a manifestation of a disorder primarily implying a horizontal anisometry of space representation and that manipulations such as OKS may remove neglect without normalizing the representational medium itself.

Adult↗

PubMed1996

Gender priming in Italian.

The goals of the present study were (1) to determine whether grammatical gender on a noun modifier can prime recognition of the following noun, (2) to determine whether the priming effect involves facilitation, inhibition, or both, and (3) to compare performance across three different tasks that vary in the degree to which explicit attention to gender is required, including word repetition, gender monitoring, and grammaticality judgment. Results showed a clear effect of gender priming, involving both facilitation and inhibition. Priming was observed whether or not the subjects' attention was directed to gender per se. Results suggest that gender priming involves a combination of controlled postlexical processing and automatic prelexical processing. Implications for different models of lexical access are discussed, with special reference to modular versus interactive-activation theories.

Adult↗