Biomedical subjects

Angela Sirigu

Publications and source records attributed to Angela Sirigu.

23 records · Page 2Linked to original sources

PubMed2003

Production and perception of grip force without proprioception: is there a sense of effort in deafferented subjects?

We assessed the ability of healthy subjects (n = 7) and a patient deprived of proprioception (GL) to produce and assess different levels of isometric forces. They first produced a target force with one hand (the reference control hand) and then, after a delay of 3 s, they attempted to match it with the other hand (the experimental matching hand). Despite abnormal variations in motor outputs, we found that GL could, as could the control subjects, maintain a constant relationship between the force exerted by the control hand and the force exerted by the experimental hand. As GL was deprived of proprioceptive cues, these results suggest that she indirectly perceived muscular force through central effort. Interestingly, when carrying out the task the patient reported neither feelings of fatigue nor awareness of how hard she tried to perform the matches. Hence, under certain circumstances (such as in our motor task), it seems possible to assess and scale muscular force on the basis of endogenous signals only. However, internally generated signals related to the size of the motor command may need to interact with afferent input to gain full access to consciousness.

Adult↗

PubMed2002

Face or hand, not both: perceptual correlates of reafferentation in a former amputee.

The topography of the somatosensory maps of our body can be largely shaped by alterations of peripheral sensory inputs. Following hand amputation, the hand cortical territory becomes responsive to facial cutaneous stimulation. Amputation-induced remapping, however, reverses after transplantation, as the grafted hand (re)gains its sensorimotor representation. Here, we investigate hand tactile perception in a former amputee by touching either grafted hand singly or in combination with another body part. The results showed that tactile sensitivity recovered rapidly, being remarkably good 5 months after transplant. In the right grafted hand, however, the newly acquired somatosensory awareness was strikingly hampered when the ipsilateral face was touched simultaneously, i.e., right face perception extinguished right hand perception. Ipsilateral face-hand extinction was present in the formerly dominant right hand 5 months after transplant and eventually disappeared 6 months afterwards. Control conditions' results showed that right hand tactile awareness was not extinguished either by contralateral left face and left hand stimulation or ipsilateral stimulation of the arm, which is bodily close to, but cortically far from, the hand. We suggest that ipsilateral face-hand extinction is a perceptual counterpart of the remapping that occurs after allograft and eyewitnesses the inherently competitive nature of sensory representations.

Adult↗

PubMed2002

Distinct areas in parietal cortex involved in long-term and short-term action planning: a PET investigation.

The sequential organization of events within a script, can be considered as a means to explore the cognitive mechanisms involved in action planning. Scripts are composed of goal-oriented sequences of events that typically occur in a specific and systematic order. The purpose of this study was to investigate the effect of temporal variation between script events (short-term versus long-term) on neural activity in normal volunteers. Subjects were required to judge whether the chronological order of three events was correct or not, while regional cerebral blood flow was measured using positron emission tomography. The modality of script presentation (graphic versus lexical) was manipulated. In the left hemisphere, the supramarginal gyrus, the middle frontal gyrus, the inferior temporal gyrus, and the middle occipital gyrus were more activated in the short-term script conditions, while the angular gyrus, the medial superior frontal gyrus, the precuneus bilaterally, the anterior cingulate gyrus and the inferior and middle temporal gyrus on the left were more involved during long-term scripts processing. The occipito-temporal junction (MT/V5) was significantly more activated in the graphic conditions as compared to the lexical ones, and in the short-term scripts conditions as compared to the long-term ones although all stimuli were static. Our results support the notion that two distinct frontal-parietal networks are engaged in short-term and long-term script processing. In addition, our study demonstrates two kinds of dissociations in the parietal lobe. A macro-dissociation between the anterior and the posterior portion of the inferior parietal lobe was found which accounts for processing short-term and long-term scripts respectively, as well as a micro-dissociation in each of these regions which is associated with distinct processing depending on the presentation modalities. These results may help to better understand apraxia at the neurophysiological level.

Adult↗

PubMed2002

Laterality effects on motor awareness.

The ability to perceive self-produced movements and to correctly attribute an action to its proper agent is a natural task and a basic requirement to human social communication. Recent experiments suggest that this apparently simple phenomenon is related to the mechanisms of motor production, raising the question whether recognition of self-produced movement is affected by asymmetries similar to those present in motor skills. In this study, right- and left-handed subjects decided whether a moving hand presented on a screen was the image of their own hand or of that of another person. Two experimental conditions were tested: either subjects saw their own moving hand (subject condition) or they were shown the experimenter's hand pantomiming their movement (experimenter condition); a glove masked morphological differences between the two hands. Verbal responses and response times were analysed. Results showed that all subjects were more accurate in recognising their preferred hand with respect to their non-preferred hand. Right-handers responded faster than left-handers did, the latter group being especially slowed down in the experimenter condition. On the contrary, in the right-handers group, response times did not differ among conditions. The present data indicate that the ability to recognise self-generated movements is affected by motor dominance, thus suggesting that conscious knowledge of self-produced movements is closely related to the motor system.

Adolescent↗

PubMed2002

Sensation of effort is altered in Huntington's disease.

In this study, we investigated sensation of effort in Huntington disease (HD). We tested the hypothesis that the basal ganglia are involved in processing effort sensation. The experimental paradigm consisted in a contralateral matching procedure where normal subjects (N=6) and HD patients (N=6) were required to lift a reference weight with their non-dominant index, and then compare the target-weight with variable weights lifted by the dominant index. Two kinds of sequences were administered: (1) increasing, where the first weight was lighter than the reference weight and progressively increased in 20g steps, (2) decreasing, where trials started with a heavier weight and progressively decreased. We calculated the discrimination threshold (DT) across sequences as the weight for which the subject's response changed sign. The difference between the higher and the lower threshold was defined as "uncertain area". We predicted that controls should overestimate the reference weight lifted by their non-dominant hand because the same effort produces more force when applied to stronger muscles. If the basal ganglia mediates sensation of effort, patients' capability to discriminate weights should be degraded. As expected, normal subjects overestimated the reference weight lifted by their non-dominant index and showed a restricted uncertain area, thus, indicating that were able to discriminate minimal differences in generated forces. By contrast, patients with HD underestimated the reference weight lifted by their non-dominant hand and showed a broad uncertain area, thus, demonstrating that they could detect only important differences in the matched efforts. These results suggest that effort sensation critically involves the basal ganglia. In normal conditions, in parallel with the efferent command of force, an efferent copy reflecting the magnitude of the voluntary motor command is transmitted to sensory centres. This signal and/or the integration of sensory feedback which generates what is experienced as the sense of effort, would be altered in HD.

Adult↗