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ABSTRACT: We tested here the hypothesis that observing others' actions can facilitate basic aspects of motor performance, such as force production, even if subjects are not required to immediately reproduce the observed actions and if they are not aware that observation can form the basis for procedural training. To this end, we compared in healthy volunteers the effects of repeated actual execution (MOV) or observation (OBS) of a simple intransitive movement (abduction of the right index and middle fingers). In a first experiment, we found that both actual and observational training significantly increased the finger abduction force of both hands. In the MOV group, force increases over pre-training values were significantly higher in the trained than in the untrained hand (50% versus 33%), whereas they were similar for the two hands in the OBS group (32% versus 30%). No force change was found in the control, untrained group. In a second experiment, we found that both training conditions significantly increased the isometric force exerted during right index finger abduction, whereas no post-training change in isometric force was found during abduction of the right little finger. Actual performance, imagination and, to a lower extent, observation of fingers movement enhanced the excitability of the corticospinal system targeting the first dorsal interosseus muscle, as tested by transcranial magnetic stimulation; pre- and post-training effects were of similar magnitude. These results show a powerful, specific role of action observation in motor training, likely exerted through premotor areas, which may prove useful in physiological and rehabilitative conditions.
Neuropsychologia 11/2007; 45(13):3114-21. · 3.64 Impact Factor
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ABSTRACT: The cortical system underlying perceptual ability to localize tactile and noxious cutaneous stimuli in humans is still incompletely understood. We used transcranial magnetic stimulation (TMS) to transiently interfere with the function of the parietal cortex, at different times after the beginning of noxious or non-noxious mechanical stimulation of the hairy skin overlying the dorsal surface of the first metacarpal of the contralateral hand. Peripheral stimuli consisted of rounded (1mm diameter) or sharp (0.2 mm) metal tips; skin contact lasted on average 242 ms (noxious) and 228 ms (non-noxious). Brief (80 ms, 25 Hz) TMS trains, given at 150 ms after the onset of cutaneous stimulation, significantly impaired subjects' ability in localizing non-nociceptive, tactile input, an effect which was not observed when TMS was applied at 300 ms after cutaneous stimulation. In contrast, brief TMS trains given at 300 ms after the onset of cutaneous stimulation significantly impaired subjects' ability in localizing nociceptive input, an effect which was not observed when TMS was applied at 150 ms after cutaneous stimulation. No impairment in stimulus detection was found in comparison with control sham TMS. The timing of parietal TMS interference with the ability to localize tactile and painful stimuli is compatible with known time differences in the arrival of non-noxious and noxious information in the postcentral gyrus. On these grounds, our findings support the existence of overlapping cortical populations in the contralateral parietal lobe, exerting a role in spatial discriminative aspects of touch and mechanically induced pain.
Behavioural Brain Research 04/2007; 178(2):183-9. · 3.42 Impact Factor
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ABSTRACT: In this paper, we review blood oxygenation level-dependent (BOLD) functional magnetic resonance imaging (fMRI) studies addressing the neural correlates of touch, thermosensation, pain and the mechanisms of their cognitive modulation in healthy human subjects. There is evidence that fMRI signal changes can be elicited in the parietal cortex by stimulation of single mechanoceptive afferent fibers at suprathreshold intensities for conscious perception. Positive linear relationships between the amplitude or the spatial extents of BOLD fMRI signal changes, stimulus intensity and the perceived touch or pain intensity have been described in different brain areas. Some recent fMRI studies addressed the role of cortical areas in somatosensory perception by comparing the time course of cortical activity evoked by different kinds of stimuli with the temporal features of touch, heat or pain perception. Moreover, parametric single-trial functional MRI designs have been adopted in order to disentangle subprocesses within the nociceptive system. Available evidence suggest that studies that combine fMRI with psychophysical methods may provide a valuable approach for understanding complex perceptual mechanisms and top-down modulation of the somatosensory system by cognitive factors specifically related to selective attention and to anticipation. The brain networks underlying somatosensory perception are complex and highly distributed. A deeper understanding of perceptual-related brain mechanisms therefore requires new approaches suited to investigate the spatial and temporal dynamics of activation in different brain regions and their functional interaction.
Magnetic Resonance Imaging 01/2005; 22(10):1539-48. · 1.99 Impact Factor
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ABSTRACT: We investigated changes in the corticospinal pattern of activity in healthy volunteers during sustained noxious and non-noxious mechanical stimulation of the first hand digit, resulting from active (self-stimulation) or passive (externally-induced) pressing against a sharp or blunted tip. The results indicate that, in order to press a finger onto a noxious stimulus with the same force generated to press onto a non-noxious one, the motor cortex adopts a peculiar strategy in terms of recruitment of motor units. This is reflected by an increase of corticospinal excitability (as revealed by motor potentials evoked by transcranial magnetic stimulation of the contralateral primary motor cortex) and EMG activity of agonist muscles, possibly related to an increase of motor unit synchronization.
Neuroscience Letters 06/2004; 361(1-3):250-3. · 2.11 Impact Factor
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ABSTRACT: Seasonal and diurnal variations in tonic pain reactions were examined in female and male CBA/J mice maintained in a 12/12 dark/light cycle, at controlled temperature and humidity conditions. Animals were injected into the dorsum of one hindpaw with a dilute (20 microl, 1%) formalin solution. Pain-related behaviors were quantified as the time spent licking the injected paw and the number of flinching episodes. The experiments were performed during the first part of the light phase (Light: from 7 to 10 a.m.) or during the first part of the dark phase of the diurnal cycle (Dark: from 7 to 10 p.m.), in two different periods of the year: Spring (March-June) and Winter (November-January). Considering all data, females showed a slightly enhanced licking response, as well as an increase in the time spent in self-grooming, in comparison with males. In Spring, the licking and flinching responses were higher during the Dark phase than during the Light phase. This held for both sexes and for both phases of the behavioral response to formalin injection. By contrast, no significant diurnal variation in pain reactions was found in Winter. These seasonal and diurnal differences were not due to nonspecific changes in motor behavior, inasmuch as locomotor activity and self-grooming showed a different pattern: during the second phase after formalin, self-grooming was higher in the Light period in the experiments performed in Spring, whereas locomotor activity showed no significant seasonal changes. These results show that the behavioral reactions to prolonged noxious input, integrated both at spinal and supraspinal sites, undergo similar seasonal and diurnal variations in both sexes, strengthening the importance of chronobiological factors in the modulation of nociception.
Life Sciences 02/2003; 72(8):897-907. · 2.53 Impact Factor
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ABSTRACT: Anticipation of pain is a complex state that may influence the perception of subsequent noxious stimuli. We used functional magnetic resonance imaging (fMRI) to study changes of activity of cortical nociceptive networks in healthy volunteers while they expected the somatosensory stimulation of one foot, which might be painful (subcutaneous injection of ascorbic acid) or not. Subjects had no previous experience of the noxious stimulus. Mean fMRI signal intensity increased over baseline values during anticipation and during actual stimulation in the putative foot representation area of the contralateral primary somatosensory cortex (SI). Mean fMRI signals decreased during anticipation in other portions of the contralateral and ipsilateral SI, as well as in the anteroventral cingulate cortex. The activity of cortical clusters whose signal time courses showed positive or negative correlations with the individual psychophysical pain intensity curve was also significantly affected during the waiting period. Positively correlated clusters were found in the contralateral SI and bilaterally in the anterior cingulate, anterior insula, and medial prefrontal cortex. Negatively correlated clusters were found in the anteroventral cingulate bilaterally. In all of these areas, changes during anticipation were of the same sign as those observed during pain but less intense ( approximately 30-40% as large as peak changes during actual noxious stimulation). These results provide evidence for top-down mechanisms, triggered by anticipation, modulating cortical systems involved in sensory and affective components of pain even in the absence of actual noxious input and suggest that the activity of cortical nociceptive networks may be directly influenced by cognitive factors.
Journal of Neuroscience 05/2002; 22(8):3206-14. · 7.11 Impact Factor
