[show abstract][hide abstract] ABSTRACT: It is well established that the mental simulation of actions involves visual and/or somato-motor representations of those imagined actions. In order to investigate if the total absence of vision affects the brain activity associated to the retrieval of motor representations, we recorded the readiness potential (RP), a marker of motor preparation, preceding the execution as well as the motor imagery of the right middle-finger extension in the first-person (imagining oneself performing the movement, 1P) and in the third-person (imagining the experimenter performing the movement, 3P) modes in 19 sighted and 10 congenitally blind subjects. Our main result was found for the single RP slope values at the Cz channel (corresponding likely to the supplementary motor area). No difference in RP slope was found between 1P and 3P in the sighted group, suggesting that similar motor preparation networks are recruited to simulate our own and other people's actions in spite of explicit instructions to perform the task in 1P or 3P. Conversely, reduced RP slopes in 3P as compared to 1P found in the blind group indicated that they might have used an alternative, non-motor strategy to perform the task in 3P. Moreover, movement imagery ability accessed both by means of mental chronometry and of a modified version of the Movement Imagery Questionnaire (MIQ-R) indicated that blind and sighted individuals had similar motor imagery performance. Taken together, these results suggest that complete visual loss early in life modifies the brain networks that associate with other's action representations.
Journal of Neurophysiology 01/2013; 109:405-414. · 3.30 Impact Factor
[show abstract][hide abstract] ABSTRACT: Contemporary theories of motor control propose that motor planning involves the prediction of the consequences of actions. These predictions include the associated costs as well as the rewarding nature of movements' outcomes. Within the estimation of these costs and rewards would lie the valence, that is, the pleasantness or unpleasantness of a given stimulus with which one is about to interact. The aim of this study was to test if motor preparation encompasses valence.
The readiness potential, an electrophysiological marker of motor preparation, was recorded before the grasping of pleasant, neutral and unpleasant stimuli. Items used were balanced in weight and placed inside transparent cylinders to prompt a similar grip among trials. Compared with neutral stimuli, the grasping of pleasant stimuli was preceded by a readiness potential of lower amplitude, whereas that of unpleasant stimuli was associated with a readiness potential of higher amplitude.
We show for the first time that the sensorimotor cortex activity preceding the grasping of a stimulus is affected by its valence. Smaller readiness potential amplitudes found for pleasant stimuli could imply in the recruitment of pre-set motor repertoires, whereas higher amplitudes found for unpleasant stimuli would emerge from a discrepancy between the required action and their aversiveness. Our results indicate that the prediction of action outcomes encompasses an estimate of the valence of a stimulus with which one is about to interact.
PLoS ONE 01/2012; 7(9):e45235. · 3.73 Impact Factor
[show abstract][hide abstract] ABSTRACT: The authors collected and compared mechanomyo-graphic (MMG) signal behavior from the biceps brachii of left and right arms of right-handed men (n = 19) and women (n = 20) who performed isometric contractions at 5 contraction levels. Mean frequency (MF) and RMS values were calculated from the MMG signals that arose from lateral oscillations of muscle fibers. Across genders and arms, RMS values increased with contraction level and MF values decreased with increase in muscle contraction. The authors found no significant difference in those parameters between dominant and nondominant arms. Therefore, summation of muscle twitches obtained from the MMG signal collected in biceps brachii muscle does not reveal any difference between dominant and nondominant arms.
Journal of Motor Behavior 04/2008; 40(2):83-9. · 1.04 Impact Factor
[show abstract][hide abstract] ABSTRACT: The ability to identify safety and danger is critical to survival. However, not much is known about human somatic body reactions in these contexts. We performed a posturographic study comparing body reactions to the sight of pictures of smiling babies and families (affiliative) versus matched neutral people, and to pictures depicting body envelope violations (mutilation) versus matched neutral people. The participants stood on a force platform and heart rate and displacement of the center of pressure were recorded while the pictures were presented. Pictures of mutilation induced a freezing-like reaction consisting of a medial-lateral (M-L) decrease in the amplitude of sway (immobility) and increase of the mean power frequency (rigidity), associated with bradycardia. Affiliative stimuli also induced an immobility and rigidity behavior but in the anterior-posterior (A-P) axis. This resembles the "immobility-without-fear reaction" proposed to occur when, upon detection of safety cues, mammals including humans are involved in pro-social activities. We conclude that the sight of visual cues of affiliation and danger produce distinct body somatic reactions.
[show abstract][hide abstract] ABSTRACT: Mental simulation of movements has been widely used to infer about representational aspects of action. On a daily basis, motor planning and execution depends crucially both upon vision and kinesthesia. What if the former is lost? In this study we investigate the physiological changes induced during a mental simulation task in subjects with early and late onset blindness, analyzing simultaneously stabilometric (body sway), electromyographic (EMG, lateral gastrocnemius) and eletrocardiographic (ECG) signals. Subjects were asked to stand up on a force platform and instructed either to: rest during 20s; count mentally from 1 to 15; imagine themselves executing a bilateral plantar flexion 15 times and execute the same movement 15 times. Discriminant analysis was employed to have access to the differences in the groups with respect to heart rate variability (HRV), EMG and body sway measurements for each condition. We found an overall correct classification of 100 and 90.9%, respectively, for the stabilometric parameters and HRV. This result was found only for the mental simulation task (p<0.05), being absent for resting, counting and executing. Previous studies have shown that motor simulation in a kinesthetic mode strongly associates with somatic and autonomic changes. In late blind subjects, however, movement simulation would tend to unfold with the use of both visual and kinesthetic representations. Thus, our results suggest that early and late blind subjects make use of distinct body representations during motor imagery.
[show abstract][hide abstract] ABSTRACT: Emotion can be functionally considered as action dispositions preparing the organism for either avoidance- or approach- related behaviors. In order to prepare an appropriate behavioral output, the organism has to be efficient in the encoding of relevant stimuli. We herein present evidence from neuroimaging studies that seeing emotional and arousing pictures leads to greater activation in visual cortex than seeing neutral ones. In addition to this facilitation of sensory processing, emotional stimuli prompt somatic and vegetative reactions. Recordings of postural oscillations and heart rate while participants visualized a block of unpleasant pictures, revealed a significant reduction of body sway and bradycardia. A parallel investigation showed that reaction time also slows down after the visualization of negative pictures. Taken together, immobility, bradycardia and slower reaction time in the laboratory experimental set may reflect the engagement of the defensive system, resembling the defensive reactions to distant threatening stimuli in natural contexts. In summary, the affective system operates at an early level of sensory encoding and at the motor output favoring dispositions for appropriate actions.
Revista Brasileira de Psiquiatria 01/2004; 25 Suppl 2:29-32, 78. · 1.86 Impact Factor
[show abstract][hide abstract] ABSTRACT: A emoção pode ser funcionalmente considerada como uma disposição à ação que prepara o organismo para comportamentos relacionados à aproximação e esquiva. Para preparar uma saída motora apropriada, o organismo tem que ser eficiente na codificação de estímulos relevantes. Neste trabalho, apresentamos evidências a partir de estudos de neuroimagem que revelam que a visualização de imagens emocionais promove uma maior ativação do córtex visual do que a observação de figuras neutras. Além desta facilitação do processamento sensorial, os estímulos emocionais desencadeiam reações somáticas e vegetativas. Registros da dinâmica postural e da freqüência cardíaca enquanto voluntários assistiam a um bloco de figuras desagradáveis revelou uma redução significativa na oscilação corporal e bradicardia. Uma investigação paralela mostrou que o tempo de reação também lentifica após a visualização de figuras negativas. Este conjunto de respostas - imobilidade, bradicardia e tempo de reação mais lento - pode refletir o engajamento do sistema defensivo, similar às reações defensivas desencadeadas em ambiente natural por estímulos ameaçadores distantes. Em resumo, o sistema afetivo influencia um nível precoce de codificação sensorial e a saída motora favorecendo, portanto, disposições para as ações apropriadas.