Biomedical subjects

S Aglioti

Publications and source records attributed to S Aglioti.

At least 19 recordsLinked to original sources

PubMed2001

Transient inhibition of the human motor cortex by capsaicin-induced pain. A study with transcranial magnetic stimulation.

Motor evoked potentials (MEPs) to transcranial magnetic stimulation (TMS) of the left motor cortex were recorded from the right first dorsal interosseous (FDI), abductor pollicis brevis (APB), abductor digiti minimi (ADM), flexor carpi radialis (FCR), extensor carpi radialis (ECR) in 17 normal subjects, before and after painful application of capsaicin on the skin overlying the right FDI and FCR muscles. The amplitude of MEPs from the FDI and FCR was significantly reduced from 20 to 30 min after the application of capsaicin over the FDI and FCR muscles, respectively, then progressively returned to the basal values. A similar trend of MEPs inhibition was observed for APB and FCR muscles, but this reduction was not significant. Indices of peripheral nerve (M-wave) and spinal cord excitability (F and H waves) did not change throughout the experiments. Motor cortex inhibition induced by tonic cutaneous pain is maximal to muscles adjacent to the painful area. This inhibition may be due to the activation of the C fibres which mediate 'slow' nociception and might be important to alert subject to possible phasic nociceptive events that may occur close to the painful area.

Adult↗

PubMed2000

The rehabilitation of limb apraxia: a study in left-brain-damaged patients.

OBJECTIVE: To assess the effectiveness of a rehabilitative training program for patients with limb apraxia. DESIGN: Randomized, controlled trial. SETTING: Neurologic rehabilitation unit of a university hospital. PATIENTS: Thirteen patients with acquired brain injury and limb apraxia (lasting more than 2 months) as a result of lesions involving the left cerebral hemisphere. Patients were assigned to a study group or to a control group following a randomization scheme. The study group underwent an experimental training for limb apraxia. The control group received conventional treatment for aphasia. INTERVENTION: A behavioral training program consisting of gesture-production exercises. The rehabilitative program was made up of 3 sections dedicated to the treatment of gestures with or without symbolic value and related or nonrelated to the use of objects. Thirty-five experimental sessions, each lasting 50 minutes, were given. MAIN OUTCOME MEASURES: Neuropsychologic tests for assessment of aphasia, verbal comprehension, "general intelligence," oral apraxia, constructional apraxia, and 3 tests concerning limb praxic function (ideational apraxia, ideomotor apraxia, gesture recognition). Scores related to each test were used to measure the outcome. Video recordings of ideational and ideomotor apraxia tests allowed us to register type and number of praxic errors. All outcome measures, except the aphasia test, were recorded before and after the experimental (or control) treatment time interval. RESULTS: The patients in the study group achieved a significant improvement of performance in both ideational (p = .039) and ideomotor (p = .043) apraxia tests. They also showed a significant reduction of errors in ideational (p = .001) and ideomotor (p < .001) apraxia tests. A trend toward improvement was found in the gesture comprehension test (p = .058), while other outcome measures did not show any significant amelioration. Control patients did not show any significant change in performance. CONCLUSIONS: The results show the possible effectiveness of a specific training program for the treatment of limb apraxia.

Aged↗

PubMed2000

Pathological switching between languages after frontal lesions in a bilingual patient.

Cerebral lesions may alter the capability of bilingual subjects to separate their languages and use each language in appropriate contexts. Patients who show pathological mixing intermingle different languages within a single utterance. By contrast, patients affected by pathological switching alternate their languages across different utterances (a self contained segment of speech that stands on its own and conveys its own independent meaning). Cases of pathological mixing have been reported after lesions to the left temporoparietal lobe. By contrast, information on the neural loci involved in pathological switching is scarce. In this paper a description is given for the first time of a patient with a lesion to the left anterior cingulate and to the frontal lobe-also marginally involving the right anterior cingulate area-who presented with pathological switching between languages in the absence of any other linguistic impairment. Thus, unlike pathological mixing that typically occurs in bilingual aphasia, pathological switching may be independent of language mechanisms.

Aphasia↗

PubMed2000

Incomplete gustatory lateralization as shown by analysis of taste discrimination after callosotomy.

The lateral organization of the gustatory pathway in man is incompletely understood. Majority of the studies support an uncrossed projection from each side of the tongue to the cortex, but reports of an opposite crossed organization continue to appear in the neurological literature. We studied the lateral organization of the gustatory pathway in normal controls, a man with a complete callosal agenesis, and a man with a complete section of the corpus callosum, a right anterior-frontal lesion, and language in the left hemisphere. Sapid solutions were applied to one or the other side of the tongue, and subjects reported the taste of the stimulus either verbally or by manually pointing to the name of the taste. There were no differences in accuracy and reaction time between the right and left hemitongues of the controls and the genetically acallosal observer. By contrast, the callosotomy subject showed a constant marked advantage of the left hemitongue over the right for both accuracy and speed of response, though performance with right stimuli was clearly above chance. The left advantage can be attributed to the left hemisphere being favored by the essentially verbal nature of the task, or to the presence of a lesion in cortical gustatory areas in the right hemisphere, or to both factors. Whichever of these hypotheses turns out to be correct, the results unequivocally reject the notion of an exclusively crossed organization of the gustatory pathway from the tongue to the cortex, and favor the notion of a bilaterally distributed organization of this pathway with a marked predominance of the uncrossed over the crossed component.

Adult↗

PubMed2000

Spatial stimulus-response compatibility and coding of tactile motor events: influence of distance between stimulated and responding body parts, spatial complexity of the task and sex of subject.

We studied spatial stimulus response compatibility in the somatosensory modality by instructing 16 men and 16 women to press a key using the left or the right thumb in response to a nonnoxious electric stimulation delivered either to the left or to the right little finger or, in different blocks, to the left or to the right malleolar region. The task was performed in compatible (stimulus and key-response on the same side of the corporeal midline) and in incompatible conditions (stimulus and key-response on opposite sides of the corporeal midline). In Exp. 1 subjects were tested while keeping their limbs in anatomic position; in Exp. 2 subjects performed the task while keeping the left upper and lower limbs on the right side and the right limbs on the left side of the bodily midline (crossed position). The compatibility effect was observed in both experiments and was higher for stimuli delivered to the little finger than to the malleolar region. This suggests that the cost of inhibiting compatible responses is maximal when stimulated and responding body parts are contiguous. Moreover, in the spatially most demanding task (Exp. 2) men outperformed women for both speed and accuracy suggesting a sex related specialisation in the spatial processing of somatosensory information.

Adult↗

PubMed2000

Right-sided neglect following a left subcortical lesion.

Unilateral spatial neglect is, in humans, typically consequent to lesions of the right hemisphere and pertains to the left hemispace. Although neglect is maximally frequent after right cortical lesions, it may also ensue from lesions confined to right subcortical structures. By contrast, hemispatial neglect consequent to left hemispheric lesions occurs less frequently. Reports of neglect following lesions to left subcortical structures are even more rare and largely anecdotal. Here we report on a right-handed man who had two successive left-sided brain lesions at an interval of 10 years from one another. The first lesion, centered upon the occipital lobe, induced a contralateral hemianopia, but no signs of hemispatial neglect; by contrast, the second lesion, a capsulo-thalamic hemorrhage, did induce a florid and persistent right-sided neglect. This finding would suggest that left subcortical structures may be important nodes in the network subserving spatial representations.

Attention↗

PubMed1999

Unconscious letter discrimination is enhanced by association with conscious color perception in visual form agnosia.

Adaptive behavior guided by unconscious visual cues occurs in patients with various kinds of brain damage as well as in normal observers, all of whom can process visual information of which they are fully unaware [1] [2] [3] [4] [5] [6] [7] [8]. Little is known on the possibility that unconscious vision is influenced by visual cues that have access to consciousness [9]. Here we report a 'blind' letter discrimination induced through a semantic interaction with conscious color processing in a patient who is agnosic for visual shapes, but has normal color vision and visual imagery. In seeing the initial letters of color names printed in different colors, it is normally easier to name the print color when it is congruent with the initial letter of the color name than when it is not [10]. The patient could discriminate the initial letters of the words 'red' and 'green' printed in the corresponding colors significantly above chance but without any conscious accompaniment, whereas he performed at chance with the reverse color-letter mapping as well as in standard tests of letter reading. We suggest that the consciously perceived colors activated a representation of the corresponding word names and their component letters, which in turn brought out a partially successful, unconscious processing of visual inputs corresponding to the activated letter representations.

Adult↗

PubMed1999

The neurological basis of conscious color perception in a blind patient.

We have studied patient PB, who, after an electric shock that led to vascular insufficiency, became virtually blind, although he retained a capacity to see colors consciously. For our psychophysical studies, we used a simplified version of the Land experiments [Land, E. (1974) Proc. R. Inst. G. B. 47, 23-58] to learn whether color constancy mechanisms are intact in him, which amounts to learning whether he can assign a constant color to a surface in spite of changes in the precise wavelength composition of the light reflected from that surface. We supplemented our psychophysical studies with imaging ones, using functional magnetic resonance, to learn something about the location of areas that are active in his brain when he perceives colors. The psychophysical results suggested that color constancy mechanisms are severely defective in PB and that his color vision is wavelength-based. The imaging results showed that, when he viewed and recognized colors, significant increases in activity were restricted mainly to V1-V2. We conclude that a partly defective color system operating on its own in a severely damaged brain is able to mediate a conscious experience of color in the virtually total absence of other visual abilities.

Blindness↗

PubMed1999

Temporal discrimination of somesthetic stimuli is impaired in dystonic patients.

Clinical and experimental evidence documents abnormal somatosensory functions in dystonia. Despite the fact that somatosensory processing is inherently temporal, mainly spatial aspects of somatosensory functions have so far been assessed in dystonic patients. Seven patients with idiopathic dystonia and nine healthy controls were given pairs of non-noxious electrical stimuli separated by different time intervals and asked to report if they perceived single or double stimuli. Somesthetic temporal discrimination thresholds (STDT) were obtained by computing the shortest time interval at which stimuli, applied to the left or the right hand, were perceived as separate. STDT were significantly higher in dystonic than in controls thus showing for the first time that temporal and not only spatial somatosensory processing is altered in dystonia.

Adult↗

PubMed1999

Frames of reference for mapping tactile stimuli in brain-damaged patients.

Twelve normal controls, twelve left-brain-damaged patients, and thirty-six right-brain-damaged patients with or without tactile extinction or tactile neglect were asked to report light touches delivered to the left or the right hand or simultaneously to both hands. The hands could be in anatomic position or one hand could cross over the other. Moreover, the two hands could be in the left or the right hemispace or across the corporeal midline. Controls and nontactile-extinction groups performed better when the hands were in anatomical than in crossed position. By contrast, patients with tactile extinction detected contralesional stimuli with higher accuracy in crossed than in anatomical position. This result suggests that, in these patients, impairments in detecting contralesional stimuli can be due not only to sensory but also to spatial factors contingent upon the position of the hands. There was no interaction between the effect of crossing the hands and the hemispace where the crossing took place. This suggests that coding the position of a hand as left or right does not necessarily occur in relation to the bodily midline, but it may arise from the computation of the position of the other hand.

Brain Damage, Chronic↗

PubMed1999

Possible recoding of visual space in covert orienting tasks.

Reaction time to lateralized light targets is longer if targets are preceded by light stimuli in the same visual hemifield compared to when they are preceded by light stimuli in the opposite visual hemifield. The effect is probably caused by interactions between implicit oculomotor tendencies and covert shifts of attention. We show here that a similar, but much smaller, ipsilateral RT inhibition can be observed when all stimuli are presented in a display completely lateralized to one hemifield, where ipsilateral and contralateral are defined with respect to the midpoint of the display. The persistence of ipsilateral inhibition with unilateral stimulus displays can be accounted for by a recoding of visual space predicated on the centering of covert attention on the display midpoint rather than on the fixation point. The recoding seems to affect the control of covert attention and perhaps oculomotor control as well.

Adult↗

PubMed1998

Motor representation of the hand in the human cortex: an f-MRI study with a conventional 1.5 T clinical unit.

The purpose of this study was to show a gradient of possible bilateral activation for movements of the non-dominant vs. dominant hand, as well as for areas involved in complex vs. simple hand movements. A standard 1.5 T magnetic resonance imaging (MRI) system has been utilized to localize the cortical motor hand areas, using the blood oxygen level dependent contrast (BOLDc) technique and single-section fast low-angle shot (FLASH) imaging. Ten normal right-handed subjects volunteered for the study. The motor tasks consisted of simple (flexion-extension) finger movements of either hand, and complex movements (finger-to-thumb opposition in a repeating, pre-planned sequence) of the non-dominant hand. Simple movements caused contralateral activation of the primary motor area (MA); ipsilateral activation was observed for the non-dominant hand only. Supplementary motor area (SMA) was also activated, with a clear contralateral prevalence. The ratio of bilateral activation of MA did not change with complex movements of the non-dominant hand, while SMA as well as lateral premotor area were largely bilaterally activated in this task. In conclusion, the ipsilateral MA is activated for movements--even simple--performed with the non-dominant hand. There is widespread functional activity, involving both contralateral and ipsilateral SMA, for complex movements.

Adult↗

PubMed1998

Paradoxically greater interhemispheric transfer deficits in partial than complete callosal agenesis.

Symptoms of interhemispheric disconnection are typically much less severe in callosal agenesis than after surgical section of the corpus callosum. Sperry [Sperry, R. W., Plasticity of neural maturation. Developmental Biology, 1968, 2 (Suppl.), 306-327.] has attributed this difference to two interconnected factors: (1) the callosal section is usually performed after the brain has lost the maximal degree of functional plasticity associated with the early stages of development and (2) the removal of an already formed structure is more disruptive for functional brain organization than the failure of the same structure to develop. It has been suggested that functional compensation is less efficient if callosal agenesis is partial rather than complete [Dennis, M., Impaired sensory and motor differentiation with corpus callosum agenesis: A lack of callosal inhibition during ontogeny? Neuropsychologia, 1976, 14, 455-469.]. This suggestion is supported by the present findings of partial left-hand anomia, partial left-field alexia and poor tactile cross-localization in a subject with a congenital absence of the posterior part of the corpus callosum due to an arteriovenous malformation. In agreement with many previous studies, similar, though more severe, symptoms of interhemispheric disconnection were found in a subject with a complete section of the corpus callosum, but not in a subject with complete callosal agenesis. Praxic control of the left hand on verbal commands was severely deficient in the callosotomy subject, but it was normal in the subject with callosal hypogenesis. The lesser degree of compensation in partial compared to complete callosal agenesis may be explained by a reduced pressure to develop extracallosal means of interhemispheric communication, contingent on the partial existence of callosal connections, as well as by the later occurrence in development of the causes of callosal hypogenesis compared to those of total callosal agenesis.

Agenesis of Corpus Callosum↗

PubMed1998

Tactile salience influences extinction.

We delivered unilateral (left or right) or bilateral tactile stimuli to hands or feet of right-brain-damaged patients, six with tactile extinction and two without. Stimuli were simple touches or sliding stimuli directed proximo-distally (e.g., toward the fingers) or disto-proximally (e.g., toward the forearm). Patients were asked to report number (one or two), type (touch or slide), and direction (proximo-distally or disto-proximally) of the experimental stimuli. Nonextinction patients performed perfectly. Extinction patients, although accurate in reporting single stimuli, omitted left stimuli under double-stimuli conditions. However, the number of left stimuli detected consciously was related to an imbalance of the salience between left and right stimuli. Moreover, in three patients the extinguished, left-sided stimulus, even when inaccessible to consciousness, influenced implicitly the report of the features of the right stimulus. Thus, the relationships between left and right stimuli can modulate both overtly and covertly the performance of extinction patients.

Adolescent↗

PubMed1997

Influence of stimulus salience and attentional demands on visual search patterns in hemispatial neglect.

Seventy-five left and right brain-damaged patients, with or without hemispatial neglect, and 40 age-matched control subjects were tested on cancellation tasks with two different visual textures modeled after Julesz (1981). In one condition ("preattentive"), target elements segregated easily from background elements and were perceived effortlessly. In the other ("attentive"), target elements did not segregate easily and could be detected only after prolonged focal scrutiny. Both controls and patients were more accurate and faster on the preattentive than attentive texture. However, only neglect patients were disproportionately impaired on the attentive texture, thus suggesting that unilateral neglect is exacerbated by the low visual salience of the stimuli and a higher engagement of focal attention. Thus, a simple bedside test may help to tell apart the level of visual information processing maximally impaired in neglect patients.

Analysis of Variance↗

PubMed1997

Influence of perceptual and semantic conflicts between the two halves of chimeric stimuli on the expression of visuo-spatial neglect.

We investigated how perceptual and semantic relationships between the left and right half of chimeric stimuli influence overt and covert visual processing by asking eight right brain damaged (RBD) patients with hemispatial neglect to identify complete, half-, and chimeric drawings. Chimeric stimuli belonged in one of four categories defined according to the perceptual and semantic relatedness between the two compounding hemi-figures. Thus, the hemi-figures could be related both perceptually and semantically, only perceptually, only semantically, or neither perceptually nor semantically. Although patients often appeared to base their report on the right part of the chimerics, the number of errors was minimal when conflicts between the two hemi-figures were maximal. Moreover, perceptual conflicts, which mainly affect the perception of the shape, appeared to influence the performance more than semantic conflicts. Since the analysis of shape incongruency is probably accomplished at early levels of information processing, the result suggests that preattentive analysis is largely spared in the experimental patients and that, in our task, bottom-up factors more than top-down factors modulate the expression of left neglect.

Aged↗

PubMed1997

Rightward attentional bias and left hemisphere dominance in a cue-target light detection task in a callosotomy patient.

Six normal subjects and a callosotomized man with a prefrontal lesion, mostly on the right side, were tested in a reaction time (RT) task involving a key-pressing response to an extrafoveal light target preceded by an extrafoveal light cue. Cues and targets were presented along the horizontal meridian at 4 degrees and 12 degrees on the right and left of fixation. Fixation was maintained throughout each trial. The cue signalled the occurrence of the target within a time window extending from 200 to 4000 misec from the cue, but did not predict target location. Normal controls responded faster to medial than to lateral targets in both fields, but showed no between-field difference, and their RT was not affected by cue location. Furthermore, they showed the so-called 'ipsilateral inhibition' or 'inhibition of return' effect, their RT being longer when cues and targets occurred in the same field than when they occurred in opposite fields. The RT of the callosotomized subject showed a left-right gradient for both cue location and target location, being longest for the leftmost location and shortest for the right locations. In addition, he showed a significant advantage for the right hand regardless of cue and target location, as well as a consistent ipsilateral inhibition in the left field, whereas in the right field there was ipsilateral inhibition only at the two longest stimulus onset asynchronies. These results suggest that, at least under these experimental conditions, there was a rightward orientational bias which reflected the taking over of the control of performance by the left hemisphere. This attentional bias was reminiscent of that seen in patients with hemi-inattention from right hemisphere damage, although the callosotomized patient showed no sign of such hemi-inattention in routine clinical tests. On the basis of several considerations the rightward bias could be attributed to the callosal interhemispheric disconnection rather than to the right prefrontal lesion.

Adult↗

PubMed1997

The body in the brain: neural bases of corporeal awareness.

Recent studies have begun to unravel the brain mechanisms that underlie the mental representation of the body. Imitation of movements by neonates suggests an implicit knowledge of the body structure that antedates the adult body schema. This can include inanimate objects that bear systematic relations to the body, as shown by the elimination from self awareness of a body part and its associated paraphernalia after selective brain lesions. Dynamic aspects of the body schema are revealed by spontaneous sensations from a lost body part as well as by orderly phantom sensations elicited by stimulation of body areas away from the amputation line and even by visual stimulation. The mechanisms of the body schema exhibit stability, since some brain regions seem permanently committed to representing the corresponding body parts in conscious awareness, and plasticity, since brain regions deprived of their natural inputs from a body part become reactive to inputs from other body parts.

Adult↗