Modulation of somatosensory processing by action.

Psychophysical evidence suggests that sensations arising from our own movements are diminished when predicted by motor forward models and that these models may also encode the timing and intensity of movement. Here we report a functional magnetic resonance imaging study in which the effects on sensation of varying the occurrence, timing and force of movements were measured. We observed that tactile-related activity in a region of secondary somatosensory cortex is reduced when sensation is associated with movement and further that this reduction is maximal when movement and sensation occur synchronously. Motor force is not represented in the degree of attenuation but rather in the magnitude of this region's response. These findings provide neurophysiological correlates of previously-observed behavioural forward-model phenomena, and advocate the adopted approach for the study of clinical conditions in which forward-model deficits have been posited to play a crucial role

Sensory attenuation in Parkinson’s disease is related to disease severity and dopamine dose

Abnormal initiation and control of voluntary movements are among the principal manifestations of Parkinson’s disease (PD). However, the processes underlying these abnormalities and their potential remediation by dopamine treatment remain poorly understood. Normally, movements depend on the integration of sensory information with the predicted consequences of action. This integration leads to a suppression in the intensity of predicted sensations, reflected in a ‘sensory attenuation’. We examined this integration process and its relation to dopamine in PD, by measuring sensory attenuation. Patients with idiopathic PD (n = 18) and population-derived controls (n = 175) matched a set of target forces applied to their left index finger by a torque motor. To match the force, participants either pressed with their right index finger (‘Direct’ condition) or moved a knob that controlled a motor through a linear potentiometer (‘Slider’ condition). We found that despite changes in sensitivity to different forces, overall sensory attenuation did not differ between medicated PD patients and controls. Importantly, the degree of attenuation was negatively related to PD motor severity but positively related to individual patient dopamine dose, as measured by levodopa dose equivalent. The results suggest that dopamine could regulate the integration of sensorimotor prediction with sensory information to facilitate the control of voluntary movements

Predicted action consequences are perceptually facilitated before cancellation

Models of action control suggest that predicted action outcomes are “cancelled” from perception, allowing agents to devote resources to more behaviorally relevant unexpected events. These models are supported by a range of findings demonstrating that expected consequences of action are perceived less intensely than unexpected events. A key assumption of these models is that the prediction is subtracted from the sensory input. This early subtraction allows preferential processing of unexpected events from the outset of movement, thereby promoting rapid initiation of corrective actions and updating of predictive models. We tested this assumption in three psychophysical experiments. Participants rated the intensity (brightness) of observed finger movements congruent or incongruent with their own movements at different timepoints after action. Across Experiments 1 and 2, evidence of cancellation—whereby congruent events appeared less bright than incongruent events—was only found 200 ms after action, whereas an opposite effect of brighter congruent percepts was observed in earlier time ranges (50 ms after action). Experiment 3 demonstrated that this interaction was not a result of response bias. These findings suggest that “cancellation” may not be the rapid process assumed in the literature, and that perception of predicted action outcomes is initially “facilitated.” We speculate that the representation of our environment may in fact be optimized via two opposing processes: The primary process facilitates perception of events consistent with predictions and thereby helps us to perceive what is more likely, but a later process aids the perception of any detected events generating prediction errors to assist model updating

¿Cómo entender los fenómenos de pasividad?

Desde 1980, C. D. Frith ha venido investigando sobre la esquizofrenia, explicando síntomas centrales como las alucinaciones, con miras a aclarar cuál es el déficit de base y originario de este trastorno mental. A lo largo de estos años, Frith ha propuesto su hipótesis centrada en el concepto de consciencia, y ha venido elaborándola como parte del desarrollo científico contemporáneo: parte de la aplicación de modelos neurocognitivos de control motor, según los cuales el déficit se atribuye al concepto de copia eferente y su función, luego la actualiza y complementa con evidencia de imagen cerebral de la atenuación de la actividad cortical parietal, como efecto derivado de la copia eferente; por último, adiciona el concepto de sentido de agencia, y el componente de cognición social, intentando integrar la experiencia del paciente y la relevancia del ámbito inter-subjetivo a su propuesta, ambos aspectos recientemente populares.Since 1980, C. D. Frith has been working on schizophrenia, and explaining central symptoms such as hallucinations, in an attempt to clarify the basic deficits of this mental disorder. Frith has put forth a hypothesis based on the concept of consciousness, and has been adjusting it alongside contemporary scientific developments. Infirst place, it begins with the use of neurocognitive models of motor control, according to which the deficit is attributable to the concept of efferent copy and its function. In second place, he updated the model by including neuroimaging evidence of attenuation in parietal activity, as a consequence of the efferent copy. In third place, he added the concept of sense of agency, and the social cognition component, trying to integrate to his proposal the patient’s experience and the relevance of the intersubjective aspect. The current paper, which critically reviews Frith’s hypothesis, it’s divided in four parts: First, the hypothesis’ evolution is synthesized; second, the main arguments are summarized; third, the main critical points are presented; and,finally, some general conclusions are drawn

Aberrant force processing in schizophrenia

Initially considered as mere side effects of antipsychotic medication, there is now evidence that motor and somatosensory disturbances precede the onset of the illness and can be found in drug-naive patients. However, research on the topic is scarce. Here, we were interested in assessing the accuracy of the neural signal in detecting parametric variations of force linked to a voluntary motor act and a received tactile sensation, either self-generated or externally generated. Patients with a diagnosis of schizophrenia and healthy controls underwent functional magnetic resonance imaging while asked to press, or abstain from pressing, a lever in order to match a visual target force. Forces, exerted and received, varied on 10 levels from 0.5 N to 5 N in 0.5 N increments. Healthy participants revealed a positive correlation between force and activity in contralateral primary somatosensory area (S1) when performing a movement as well as when receiving a tactile sensation but only when this was externally, and not self-, generated. Patients showed evidence of altered force signaling in both motor and tactile conditions, as well as increased correlation with force when tactile sensation was self-generated. Findings are interpreted in line with accounts of predictive and sensory integration mechanisms and point toward alterations in the encoding of parametric forces in the motor and somatosensory domain in patients affected by schizophrenia

Action enhances predicted touch

It is widely believed that predicted tactile action outcomes are perceptually attenuated. The present experiments determined whether predictive mechanisms necessarily generate attenuation, or instead can enhance perception – as typically observed in sensory cognition domains outside of action. We manipulated probabilistic expectations in a paradigm often used to demonstrate tactile attenuation. Participants produced actions and subsequently rated the intensity of forces on a static finger. Experiment 1 confirmed previous findings that action outcomes are perceived less intensely than passive stimulation but demonstrated more intense perception when active finger stimulation was removed. Experiments 2 and 3 manipulated prediction explicitly and found that expected touch during action is perceived more intensely than unexpected touch. Computational modelling suggested that expectations increase the gain afforded to expected tactile signals. These findings challenge a central tenet of prominent motor control theories and demonstrate that sensorimotor predictions do not exhibit a qualitatively distinct influence on tactile perception

Physiological and perceptual sensory attenuation have different underlying neurophysiological correlates

Sensory attenuation, the top-down filtering or gating of afferent information, has been extensively studied in two fields: physiological and perceptual. Physiological sensory attenuation is represented as a decrease in the amplitude of the primary and secondary components of the somatosensory evoked potential (SEP) before and during movement. Perceptual sensory attenuation, described using the analogy of a persons’ inability to tickle oneself, is a reduction in the perception of the afferent input of a self-produced tactile sensation due to the central cancellation of the reafferent signal by the efference copy of the motor command to produce the action. The fields investigating these two areas have remained isolated, so the relationship between them is unclear. The current study delivered median nerve stimulation to produce SEPs during a force-matching paradigm (used to quantify perceptual sensory attenuation) in healthy human subjects to determine whether SEP gating correlated with the behavior. Our results revealed that these two forms of attenuation have dissociable neurophysiological correlates and are likely functionally distinct, which has important implications for understanding neurological disorders in which one form of sensory attenuation but not the other is impaired. Time–frequency analyses revealed a negative correlation over sensorimotor cortex between gamma-oscillatory activity and the magnitude of perceptual sensory attenuation. This finding is consistent with the hypothesis that gamma-band power is related to prediction error and that this might underlie perceptual sensory attenuation

Voluntary self-touch increases body ownership

Experimental manipulations of body ownership have indicated that multisensory integration is central to forming bodily self representation. Voluntary self touch is a unique multisensory situation involving corresponding motor, tactile and proprioceptive signals. Yet, even though self-touch is frequent in everyday life, its contribution to the formation of body ownership is not well understood. Here we investigated the role of voluntary self touch in body ownership using a novel adaptation of the rubber hand illusion (RHI), in which a robotic system and virtual reality allowed participants self-touch of real and virtual hands. In the first experiment, active and passive self-touch were applied in the absence of visual feedback. In the second experiment, we tested the role of visual feedback in this bodily illusion. Finally, in the third experiment, we compared active and passive self-touch to the classical RHI in which the touch is administered by the experimenter. We hypothesized that active self-touch would increase ownership over the virtual hand through the addition of motor signals strengthening the bodily illusion. The results indicated that active self-touch elicited stronger illusory ownership compared to passive self-touch and sensory only stimulation, and show an important role for active self-touch in the formation of bodily self

Atténuation des réafférences visuelles de la main dans le cortex pariétal lors d’un mouvement d’atteinte vers une cible.

Résumé : Il semble que le cerveau atténuerait les stimuli provenant de nos actions par rapport aux stimuli d’origine externe, ceci afin d’augmenter la pertinence des informations environnementales. Lors de la production d’un mouvement, la copie de la commande motrice serait utilisée pour anticiper les conséquences sensorielles. Les conséquences sensorielles prédites permettraient ainsi d’atténuer les réafférences réelles du mouvement. Plusieurs évidences montrent que l’activité corticale liée aux réafférences somatosensorielles et auditives est atténuée lorsque celles-ci résultent de nos propres mouvements par rapport à lorsqu’elles proviennent d’une cause externe. L’étude présentée dans ce mémoire a investigué l’existence d’une atténuation des réafférences visuelles lors d’un mouvement d’atteinte du bras vers une cible. L’expérience consistait en une tâche de pointage de la main vers une cible visuelle, pendant laquelle l’activité EEG des sujets était enregistrée. L’intervalle de temps entre la position réelle de la main et le curseur visuel associé à celle-ci était manipulé. De fait, le retour visuel était fourni soit en temps réel soit avec un retard de 150 ms. Le délai créait ainsi un décalage entre les conséquences visuelles prédites et réelles du mouvement. Les résultats montrent que l’amplitude de la composante N1 du Potentiel Évoqué Visuel (PEV) associé au retour visuel de la main était réduite dans le cortex pariétal lorsque le retour visuel était fourni en temps réel par rapport à lorsqu’il était présenté en retard. Conséquemment, ces données suggèrent que les réafférences visuelles du membre en mouvement sont atténuées au niveau cortical lorsqu’elles correspondent aux prédictions. L’association des résultats comportementaux et électrophysiologiques supportent également d’autres études qui montrent que les processus sensorimoteurs sont plus fins que la perception consciente. À la lumière de la littérature, la modulation de la composante N1 enregistrée aux électrodes pariéto-occipitales suggère l’implication des régions pariétales dans l’intégration des retours sensoriels et des prédictions motrices. En discussion, nous proposons que les retours visuels liés au contrôle en ligne du membre soient modulés au niveau pariétal en raison des prédictions motrices cérébelleuses, à l’instar des retours tactiles.Abstract : It is well established that the cortical processing of somatosensory and auditory signals is attenuated when they result from self-generated actions as compared to external events. This phenomenon is thought to result from an efference copy of motor commands used to predict the sensory consequences of an action through a forward model. The present work examined whether attenuation also takes place for visual reafferent signals from the moving limb during voluntary reaching movements. To address this issue, EEG activity was recorded in a condition in which visual feedback of the hand was provided in real time and compared to a condition in which it was presented with a 150 ms delay, thus creating a mismatch between the predicted and actual visual consequences of the movement. Results revealed that the amplitude of the N1 component of the visual ERP evoked by hand visual feedback over the parietal cortex was significantly smaller when presented in real time as compared to when it was delayed. These data suggest that the cortical processing of visual reafferent signals is attenuated when they are correctly predicted, likely as a result of a forward model