Biomedical subjects

S Aglioti

Publications and source records attributed to S Aglioti.

At least 37 records · Page 2Linked to original sources

PubMed1997

Spatio-temporal properties of the pattern of evoked phantom sensations in a left index amputee patient.

In a left index finger amputee, appropriate stimulation of skin areas of the remnant left fingers or left lower face evoked veridical sensations as well as sensations localized to the phantom finger. Five months after the amputation, there was a systematic correspondence between positions of digital and facial stimuli and positions of stimuli felt on the phantom. More than 3 years after the amputation, orderly maps of the phantom index on the ipsilateral fingers were still detected. By contrast, poorly organized facial maps were present only contralaterally to the amputation. The maps on the remnant fingers are likely to acquire stability because they are systematically activated during manipulations performed with the mutilated hand. The disorganization of facial maps may be related to their irrelevance for behavioral control in everyday life conditions.

Adult↗

PubMed1996

Disownership of left hand and objects related to it in a patient with right brain damage.

We describe a woman with right brain damage who denied the ownership of her left hand and of extracorporeal objects (e.g. rings) which were worn on the left hand itself. When the same objects were worn on the right hand or were held by the examiner, the patient correctly recognized them as her own. Other personal objects unrelated to the left hand (e.g. pins, earrings, comb) were always correctly recognized as her own. Thus, by inference, the mental image of one's body may include inanimate objects which had been in contact or in close proximity with the body itself. These findings provide, for the first time, experimental support to the speculative notion of an extended body schema.

Aged↗

PubMed1996

Thumb-pointing is humans after damage to somatic sensory cortex.

Three patients with a severe somatosensory deficit consequent on damage of the right somatosensory cortices were required, while blindfolded, to point with their insensate thumb to select positions on the other left fingers. Given the absence of feedback, the motor performance of the insensate thumb appeared grossly impaired in all patients. However, all patients attained end-points with an accuracy greater than chance. This result suggests that spatial accuracy may not rely entirely on sensory feedback. A good accuracy of pointing was evinced also in potentially facilitating conditions where somatosensory and motor cues coming from the intact side during simultaneous movement of both thumbs, vision of stimulated point and final thumb position, and visuomotor imagery were available. Furthermore, in one patient, the accuracy of the insensate thumb in cued conditions was higher than in a reference baseline condition, thus indicating that motor and cognitive cues can help the motor performance of patients with cortical somatosensory lesions.

Aged↗

PubMed1996

Spatial stimulus-response compatibility in callosotomy patients and subjects with callosal agenesis.

Subjects with partial or complete defects of the corpus callosum, either congenital or acquired, performed a choice reaction time (RT) task involving a right or left key-press response to a light presented at random in the right or left hemifield. Like normal subjects, all of them exhibited two additive effects typical of these tasks: the spatial stimulus-response compatibility effect (faster RT for stimuli and responses matched for side), and the hand placement effect (longer RT for responses performed with crossed hands). Two subjects with a complete callosal defect, one acquired and the other congenital, showed a third effect, not present in normal subjects, consisting of a marked advantage for RT of responses with hand anatomically ipsilateral to the stimulus, independent of both stimulus-response compatibility and hand placement. These findings can be interpreted according to a hierarchical model of information processing assuming that, in the absence of the corpus callosum, the matching of the mental codes for the stimulus and response sets takes place solely in the hemisphere receiving the stimulus, with a subsequent rapid-intrahemispheric or slow-interhemispheric transmission of the response command to the appropriate motor centers.

Adult↗

PubMed1996

Overt and covert processing of left-side information in unilateral neglect investigated with chimeric drawings.

Overt and covert processing of contralesional information was investigated in 6 right-brain-damaged (RBD) patients with or without left hemispatial neglect by using three bedside tests that require the analysis of whole, half, and chimeric drawings. In the first task, patients named these stimuli. In the second task, patients designated as "same" or "different" drawings in a pair where one drawing was always whole and the other could be whole, half, or chimeric. In the third task, patients pointed to the more veridical, complete drawing that was presented with one half drawing, and two chimeric drawings. Although patients with no neglect performed without error in all conditions, patients with severe neglect based their performance on the analysis of the right side of the stimuli. In patients with mild neglect, not only did performance rely upon the right side of stimuli but it was also modulated by left-side information acquired either overtly or unconsciously.

Adult↗

PubMed1996

Neurolinguistic and follow-up study of an unusual pattern of recovery from bilingual subcortical aphasia.

We report on the neuropsychological and neurolinguistic features of a bilingual patient, E.M., who presented with an uncommon pattern of aphasic deficit consequent to subcortical lesions mainly involving the left basal ganglia. Not only are reports of bilingual subcortical aphasia rare, but E.M.'s deficit is particularly uncommon for it concerns the most used mother tongue (Venetian) much more than a less practiced second language (standard Italian). In this patient, the linguistic deficit in mother tongue production has been observed in spontaneous speech and in cross language translation tasks, where an asymmetrical paradoxical performance has been revealed. Indeed, unlike neurologically intact subjects, E.M. has more difficulties when translating into her mother tongue than into her second language. Although E.M.'s mother tongue is prevalently an oral language, the asymmetrical translation pattern is similar in written and oral translation tasks, thus ruling out the possibility that the deficit simply reflects differences between written and oral language codes. Finally, another remarkable feature of E.M.'s impairment is its stability over almost 5 years from the stroke. We propose that this unusual type of recovery in E.M. is related to the higher degree of automatization of the first language with respect to the second one. This proposal fits with the role of basal ganglia in automatized motor and cognitive performance.

Aged↗

PubMed1995

Size-contrast illusions deceive the eye but not the hand.

BACKGROUND: When we reach out to pick up an object, not only do we direct our moving limb towards the location of the object, but the opening between our fingers and thumb is scaled in flight to the object's size. Evidence obtained from patients with neurological disorders has shown that the visual processing underlying the calibration of grip aperture and other movement parameters during grasping is mediated by visual mechanisms located in the cerebral cortex that are quite distinct from those underlying the experiential perception of object size and other object features. Under appropriate conditions, such dissociations can also be observed in individuals with normal vision. Here we present evidence that the calibration of grasp is quite refractory to pictorial illusions that have large effects on perceptual judgements of size. RESULTS: We used a variation of the familiar 'Titchener circles' illusion in which two target circles of equal size, each surrounded by a circular array of either smaller or larger circles, are presented side by side. Subjects typically report that the target circle surrounded by the array of smaller circles appears to be larger than the target surrounded by larger circles. In our test, two thin 'pokerchip' discs were used as the target circles. The relative size of the two discs was randomly varied so that on some trials the discs appeared perceptually different but were physically equivalent in size, and on other trials they were physically different but appeared perceptually equivalent. The perceptual judgements made by the 14 subjects in our experiment were strongly affected by this size-contrast illusion. However, when asked to pick up a disc, the scaling of the subjects grip aperture (measured opto-electronically before contact with the disc) was largely determined by the true size of the target disc and not its illusory size. CONCLUSIONS: It would seem that the automatic and metrically accurate calibrations required for skilled actions are mediated by visual processes that are separate from those mediating our conscious experiential perception. Earlier studies on patients with neurological deficits suggest that these two types of processing may depend on quite separate, but interacting, visual pathways in the cerebral cortex.

Adult↗

PubMed1995

The McCollough effect reveals orientation discrimination in a case of cortical blindness.

BACKGROUND: The McCollough effect is a colour after-effect that is contingent on the orientation of the patterns used to induce it. To produce the effect, two differently oriented grating patterns--such as a red-and-black vertical grating and a green-and-black horizontal grating--are viewed alternatively for a few minutes. After this period of adaptation, if the black-and-white test gratings are viewed in the same orientation as the adaptation patterns, the white sections of the vertical grating will appear pale green and the white sections of the horizontal grating will appear pink. The McCollough effect indicates that colour- and orientation-coding mechanisms interact at some point during visual processing; but the question remains as to whether this interaction occurs at an early or later stage in the cortical visual pathways. In an attempt to answer this question, we studied a patient who had suffered extensive damage to extrastriate visual areas of the brain, which had left him able to see colour but little else. RESULTS: Neuropsychological and perceptual tests demonstrated that the patient, P.B., has a profound impairment in form perception and is even unable to discriminate between 90 degrees differences in the orientation of grating stimuli. He is also unable to use orientation information to control his reaching or grasping. Nevertheless, P.B. can name and discriminate different colours reliably, including those used to induce the McCollough effect. After adaptation with red-and-green gratings, P.B. appropriately reported the orientation-contingent aftereffect colours, even though he continued to be unable to discriminate the orientations of the test patterns. CONCLUSIONS: These results indicate that at some level in P.B.'s visual system orientation is being coded, but it is at a level that he is unable to use in making orientation judgements or in visuomotor control. Given the massive insult to the extrastriate cortex in P.B., it is likely that the anatomical locus of the mechanisms underlying the McCollough effect is within primary visual cortex or even earlier in the visual pathway.

Adult↗

PubMed1995

Callosotomy for intractable epilepsy from bihemispheric cortical dysplasias.

Four patients suffering for severe drug-resistant epilepsy from bihemispheric cortical dysplasias underwent anterior callosotomy. One of these patients also presented mental retardation of mild degree associated with the epileptic syndrome. There were no operative complications in this series. Clinical signs of interhemispheric disconnection were not detectable postoperatively. Twenty-eight to 53 months after surgery, the generalized seizures were completely suppressed in 2 cases, and were reduced by 89-97% in frequency in the other 2 cases. Partial seizures were less affected by callosotomy being reduced by 14-87%. In an additional fifth case of intractable epilepsy from bihemispheric cortical dysplasias with associated severe mental retardation operated upon elsewhere for callosotomy and followed at our institution, the outcome for seizures was completely unsatisfactory. Neurophysiological studies revealed that the interhemispheric transfer (IHT) of visuo-motor responses was functionally impaired after callosotomy only in one patient who harboured bilateral cortical dysplasias in the occipital lobes. This malformation might affect the pattern of axonal projection to the posterior portion of the corpus callosum which is considered of crucial importance for the integration of crossed visuo-motor responses. From this paper the following conclusions can be drawn: a) epileptic patients with severe drug-resistant epilepsy due to bihemispheric cortical dysplasias are good candidates for callosotomy, b) one-stage extensive anterior callosotomy sparing the splenium is the procedure of choice, c) associated severe mental retardation seems to contra-indicate callosotomy, d) the neurophysiological study of the IHT can yield information on the functional status of the corpus callosum.

Adult↗

PubMed1995

Corpus callosum and simple visuomotor integration.

Malcolm Jeeves was the first to demonstrate lengthened interhemispheric transmission times in subjects with agenesis of the corpus callosum by using a simple reaction time paradigm with lateralized unstructured light stimuli and crossed and uncrossed hand responses. Uncrossed responses can be integrated within one hemisphere, whereas crossed responses require a communication between the two hemispheres. In the normal brain this communication is effected rapidly by the corpus callosum, whereas in the acallosal brain it must occur much more slowly by way of less efficient alternative interhemispheric pathways. Using a similar experimental paradigm we have studied normal subjects, subjects with a complete callosal agenesis and epileptic patients with surgical callosal sections, either complete or partial. All subjects with complete callosal defects showed much lengthened interhemispheric times compared to normal controls. Virtually normal interhemispheric transmission times were found in subjects with partial callosal defects, whether anterior or posterior, suggesting a possible equipotentiality of different portions of the corpus callosum in the mediation of crossed manual responses. In both normals and acallosals there were no crossed-uncrossed differences in reaction time when responses were made unilaterally with lower limb effectors or para-axial upper limb effectors, as well as bilaterally with upper-limb proximal and para-axial effectors. Since these effectors can be controlled directly from either side of the brain via bilaterally distributed motor pathways, crossed responses using them, unlike crossed manual responses, do not require an interhemispheric integration.

Animals↗

PubMed1995

Sensory and spatial components of somaesthetic deficits following right brain damage.

We instructed patients with right brain damage (RBD) and somatosensory extinction, hemispatial neglect, or both to verbally report light touches delivered to the left hand, to the right hand, or simultaneously to both hands in two experimental situations. In the "anatomic" situation, each hand was in its homonymous hemispace; in the "crossed" one, each hand was held across the corporeal midline, in its heteronymous hemispace. Under both single and the double stimulation conditions, RBD patients detected stimuli delivered to the contralesional hand with lower accuracy in the anatomic than in the crossed position. This result suggests that somaesthetic deficits can be due not only to sensory but also to attentional factors, depending on the spatial position of the hands. Processing of sensory information in primary areas should not be influenced by the hemispatial position of the stimulated body part. These results suggest that somaesthetic deficits may stem not only from damage of primary sensory areas, as classically held, but also from damage of higher-order areas where information about stimuli, body parts, and extrapersonal space is integrated. Finally, the results show that sensory and attentional components of the deficit can be dissociated by using a very simple clinical test.

Aged↗

PubMed1994

Interhemispheric integration of simple visuomotor responses in patients with partial callosal defects.

Because of the organization of visual and motor pathways, simple manual responses to a light stimulus in the right or left visual hemifields are performed faster with uncrossed hand-field combinations than with crossed hand-field combinations. Uncrossed responses can be integrated within a single hemisphere, whereas crossed responses require a time-consuming interhemispheric transfer via the corpus callosum which is reflected in the difference between crossed and uncrossed reaction times. We investigated crossed-uncrossed differences (CUDs) in speed of simple visuomotor responses to lateralized flashes in seven subjects with an anterior section of the corpus callosum sparing the splenium and in one subject with an agenetic absence of the splenium due to a cerebrovascular malformation. There was no evidence of an abnormal prolongation of the CUDs in any of these subjects, in sharp contrast with the very long CUDs exhibited by an epileptic subject with a complete callosal section and two subjects with total callosal agenesis tested in the same experimental situation [1]. The normality of the CUDs in the subjects with partial callosal defects was not due to a postoperatory reorganization of interhemispheric communication, since there was no indication of an increased CUD in a patient tested as early as 5 days after the anterior callosotomy. These results are compatible with the assumption that both anterior and posterior callosal routes may subserve the integration of speeded manual responses to a visual stimulus directed to the hemisphere ipsilateral to the responding hand.

Adult↗

PubMed1994

Phantom lower limb as a perceptual marker of neural plasticity in the mature human brain.

Three lower limb amputees, who reported phantom sensations, referred somatic stimuli delivered to skin regions proximal to the stump to select points on the phantom limb. Stimuli on the rectum and anus (e.g. during defecation) and on genital areas (e.g. during sexual intercourse) induced analogous, although less precise, mislocation to the phantom limb. Although the representation of the stump in the somatosensory pathway is lateral to that of the amputated lower limb, both anus and genitals are mapped medially to the areas formerly subserving the amputated lower limb. Therefore the mislocalization phenomenon can be considered as a perceptual landmark of new functional connections between the deprived areas and the adjacent ones, thus suggesting a dynamic neural remodelling in the mature nervous system, which was previously considered as a static entity.

Adult↗

PubMed1994

Rapid sensory remapping in the adult human brain as inferred from phantom breast perception.

We provide evidence for a perceptual marker of neuroplasticity in female mastectomy patients who reported phantom breast perceptions. When tactile stimuli were delivered to dorso-thoracic, shoulder and pinna regions ipsilateral to the mastectomy, these patients (in some cases even 5 days after the operation) referred the stimuli to the amputated breast mainly to the nipple. The somatosensory representation of the stimulated regions is probably adjacent to the former representation of the amputated breast. These results suggest that input from stimulated regions of the skin can drive neurones originally driven by input from the amputated breast. The apparent functional relation between pinna and nipple might give clues to the mechanisms underlying referred sensations and pain.

Adult↗

PubMed1994

Do peripheral non-informative cues induce early facilitation of target detection?

It has been reported that simple reaction time (RT) to a peripheral visual target is faster if the target is presented within about 200 msec from the onset of a non-informative cue flashed at the same location, as compared with RT to a target presented at an uncued location. This period of facilitation is followed by a period of inhibition during which RT is longer if cue and target are shown at the same location or at different locations within the same hemifield, as opposed to contralateral cues and targets. Early facilitation has been explained by an automatic covert orienting towards the cue, while the following inhibition has been regarded as a consequence of such covert orienting. In a series of four experiments, we have investigated the dependency of these effects on the temporal and spatial relationships between cue and target. Normal, right-handed subjects responded to a target displayed for 16 msec simultaneously with, or following at stimulus-onset asynchronies (SOAs) of 60, 130, 300 or 900 msec, the onset of a non-informative cue. Both cues and targets could appear at random in one of four locations (Expts 1-3) or in one of two locations (Expt 4) disposed symmetrically across the fixation point along the horizontal meridian. Duration of the cue varied between experiments. In Expt 1 it was 16 msec. In Expt 2 the cue remained on view throughout the period of the SOA and terminated 300 msec after target onset. In the remaining two experiments cue duration was 130 msec. In the first experiment, at all cue-target SOAs RTs to target flashed either at the same location or in the same hemifield as the cue were significantly slower than RTs to contralateral cue-target combinations (RT inhibition). In the other experiments, there was no RT inhibition with targets in cued locations if the cue remained on during target presentation and outlasted target offset. Since at no SOA was RT to targets in cued locations shorter than RT to targets contralateral to cues, there was no direct evidence for facilitation. However, the facilitatory influence of these cues could be inferred from the fact that they countered and masked inhibition. RT to uncued targets ipsilateral to cues was consistently inhibited in all experimental conditions. These results show that at each cue-target SOA the consequences of a peripheral non-informative cue depend on whether or not the cue remains visible during target processing.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗

PubMed1993

Paradoxical selective recovery in a bilingual aphasic following subcortical lesions.

In monolinguals, not only cortical areas but also specific subcortical structures are crucial for language and speech processing. While the role of the left basal ganglia in monolingual aphasia has been defined, its relevance in bilingual and polyglot aphasia is still unknown. Data have now been obtained on a patient who, following an ischaemic lesion not involving cortical structures and mainly confined to the left basal ganglia, showed severe impairments in mother tongue production, with significantly better performance in her hardly spoken second language. This dissociation remained stable for over a year and was observed both in spontaneous speech and in translation tasks. This pattern of linguistic performance, which has never been described in relation to subcortical lesions, suggests that the left basal ganglia play a relevant role in the output of a highly automatized language.

Aged↗

PubMed1993

Hemispheric control of unilateral and bilateral responses to lateralized light stimuli after callosotomy and in callosal agenesis.

Normally, simple digital or manual responses to a light stimulus in the right or left visual hemifields are performed faster with uncrossed hand-field combinations than with crossed hand-field combinations. Because of the organization of visual and motor pathways, the integration of uncrossed responses is assumed to occur within a single hemisphere, whereas a time-consuming interhemispheric transfer via the corpus callosum is considered to be necessary for the integration of crossed responses. However, callosal transfer may be dispensable for those crossed responses which can be controlled through ipsilaterally descending motor pathways by the hemisphere receiving the visual stimulus. We investigated crossed-uncrossed differences (CUDs) in speed of simple visuomotor responses to lateralized flashes in one subject with total section of the corpus callosum and two subjects with complete callosal agenesis. We recorded the reaction times as well as the premotor times, as indicated by the electromyographic latencies of the prime movers, of three types of responses: a distal response involving a thumb flexion, a proximal response chiefly involving a forearm flexion and an axial response involving a shoulder elevation. Further, the three types of responses to a single lateralised flash were performed both unilaterally and bilaterally. The three acallosal subjects showed CUDs greatly exceeding normal values on distal responses, either unilateral or bilateral, and on unilateral proximal responses. These abnormally long CUDs stood in sharp contrast to the insignificant CUDs exhibited by the same subjects on bilateral proximal responses and on unilateral and bilateral axial responses in agreement with correspondingly insignificant CUDs reported for normal subjects. These results confirm that a callosal contribution is important for the execution of fast distal and unilateral proximal responses to a visual stimulus directed to the hemisphere ipsilateral to the responding hand. By contrast, the other types of crossed responses appear to be efficiently coordinated across the midline without the aid of the corpus callosum. This is in keeping with the hypothesis that they are governed by a bilaterally distributed motor system which is preferentially activated for the execution of symmetrical bilateral movements, employing axial and proximal limb muscles.

Accidents, Traffic↗

PubMed1991

Bilateral hemispheric control of foot distal movements: evidence from normal subjects.

Normal subjects have been tested for interhemispheric transfer (IT) of visuo-motor information using a simple reaction time (RT) paradigm and lateralized stimuli and responses (the so-called Poffenberger paradigm). In this paradigm IT time is assumed to correspond to the RT difference between crossed and uncrossed stimulus-response combinations (CUD). In Experiment 1, two types of movements were used: a unilateral flexion of the thumb and a unilateral plantar flexion of the big toe. A reliable CUD (7.4 msec) was found only with manual responses. Changing stimulus retinal eccentricity (10 degrees vs. 70 degrees) or attentional demands (blocked vs. random stimulus presentation) did not result in any reliable effect on the CUD. In Experiment 2 the number of RTs for each subject was considerably increased and several visual field sites (from areas close to the vertical meridian to the monocular crescent) were tested. Notwithstanding these modifications, this experiment confirmed the lack of CUD found for foot responses in Exp. 1. Taken together, these results are in keeping with a less lateralized hemispheric control of distal foot movements in comparison to hand movements.

Acoustic Stimulation↗