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ABSTRACT: Objects grasped by an agent have a value not only for the acting agent, but also for an individual observing the grasping act. The value that the observer attributes to the object that is grasped can be pivotal for selecting a possible behavioral response. Mirror neurons in area F5 of the monkey premotor cortex have been suggested to play a crucial role in the understanding of action goals. However, it has not been addressed if these neurons are also involved in representing the value of the grasped object. Here we report that observation-related neuronal responses of F5 mirror neurons are indeed modulated by the value that the monkey associates with the grasped object. These findings suggest that during action observation F5 mirror neurons have access to key information needed to shape the behavioral responses of the observer.
Proceedings of the National Academy of Sciences 07/2012; 109(29):11848-53. · 9.68 Impact Factor
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ABSTRACT: Mirror neurons are a class of visuomotor neurons in the monkey premotor and parietal cortices that discharge during the execution and observation of goal-directed motor acts. They are deemed to be at the basis of primates' social abilities. In this review, the authors provide a fresh view about two still open questions about mirror neurons. The first question is their possible functional role. By reviewing recent neurophysiological data, the authors suggest that mirror neurons might represent a flexible system that encodes observed actions in terms of several behaviorally relevant features. The second question concerns the possible developmental mechanisms responsible for their initial emergence. To provide a possible answer to question, the authors review two different aspects of sensorimotor development: facial and hand movements, respectively. The authors suggest that possibly two different "mirror" systems might underlie the development of action understanding and imitative abilities in the two cases. More specifically, a possibly prewired system already present at birth but shaped by the social environment might underlie the early development of facial imitative abilities. On the contrary, an experience-dependent system might subserve perception-action couplings in the case of hand movements. The development of this latter system might be critically dependent on the observation of own movements.
The Neuroscientist 04/2011; 17(5):524-38. · 4.57 Impact Factor
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ABSTRACT: Prospective memory (PM) describes the ability to execute a previously planned action at the appropriate point in time. Although behavioral studies clearly showed that prospective memory performance is affected by the emotional significance attributed to the intended action, no study so far investigated the brain mechanisms subserving the modulatory effect of emotional salience on PM performance. The general aim of the present study was to explore brain regions involved in prospective memory processes when PM cues are associated with emotional stimuli. In particular, based on the hypothesised critical role of the prefrontal cortex in prospective memory in the presence of emotionally salient stimuli, we expected a stronger involvement of aPFC when the retrieval and execution of the intended action is cued by an aversive stimulus. To this aim BOLD responses of PM trials cued by aversive facial expressions were compared to PM trials cued by neutral facial expressions. Whole brain analysis showed that PM task cued by aversive stimuli is differentially associated with activity in the right lateral prefrontal area (BA 10) and in the left caudate nucleus. Moreover a temporal shift between the response of the caudate nucleus that preceded that of aPFC was observed. These findings suggest that the caudate nucleus might provide an early analysis of the affective properties of the stimuli, whereas the anterior lateral prefrontal cortex (BA10) would be involved in a slower and more deliberative analysis to guide goal-directed behaviour.
PLoS ONE 01/2011; 6(10):e26290. · 4.09 Impact Factor
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ABSTRACT: Converging experimental evidence indicates that mirror neurons in the monkey premotor area F5 encode the goals of observed motor acts [1-3]. However, it is unknown whether they also contribute to encoding the perspective from which the motor acts of others are seen. In order to address this issue, we recorded the visual responses of mirror neurons of monkey area F5 by using a novel experimental paradigm based on the presentation of movies showing grasping motor acts from different visual perspectives. We found that the majority of the tested mirror neurons (74%) exhibited view-dependent activity with responses tuned to specific points of view. A minority of the tested mirror neurons (26%) exhibited view-independent responses. We conclude that view-independent mirror neurons encode action goals irrespective of the details of the observed motor acts, whereas the view-dependent ones might either form an intermediate step in the formation of view independence or contribute to a modulation of view-dependent representations in higher-level visual areas, potentially linking the goals of observed motor acts with their pictorial aspects.
Current biology: CB 01/2011; 21(2):144-8. · 10.99 Impact Factor
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ABSTRACT: Human movements, besides entailing the presence of a body shape, comply with characteristic kinematic laws of motion. Psychophysical studies show that low-level motion perception is biased toward stimuli complying with these laws. However, the neuronal structures that are sensitive to the kinematic laws of observed bodily movements are still largely unknown. We investigated this issue by dissociating, by means of computer-generated characters, form and motion information during the observation of human movements. In a functional imaging experiment, we compared the levels of blood oxygen level-dependent activity elicited by human actions complying with or violating the kinematic laws of human movements. Actions complying with normal kinematic laws of motion differentially activated the left dorsal premotor and dorsolateral prefrontal cortex as well as the medial frontal cortex. These findings suggest that the kinematic laws of human movements specifically modulate the responses of neuronal circuits also involved in action recognition and that are predominantly located in the left frontal lobe.
Cerebral Cortex 11/2009; 20(7):1647-55. · 6.54 Impact Factor
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ABSTRACT: Actions performed by others may have different relevance for the observer, and thus lead to different behavioral responses, depending on the regions of space in which they are executed. We found that in rhesus monkeys, the premotor cortex neurons activated by both the execution and the observation of motor acts (mirror neurons) are differentially modulated by the location in space of the observed motor acts relative to the monkey, with about half of them preferring either the monkey's peripersonal or extrapersonal space. A portion of these spatially selective mirror neurons encode space according to a metric representation, whereas other neurons encode space in operational terms, changing their properties according to the possibility that the monkey will interact with the object. These results suggest that a set of mirror neurons encodes the observed motor acts not only for action understanding, but also to analyze such acts in terms of features that are relevant to generating appropriate behaviors.
Science 05/2009; 324(5925):403-6. · 31.20 Impact Factor
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ABSTRACT: Early in life, visual experience influences the refinement of the preferential response for specific stimulus features exhibited by neurons in the primary visual cortex. A striking example of this influence is the reduction in cortical direction selectivity observed in cats reared under high-frequency stroboscopic illumination. Although various mechanisms have been proposed to explain the maturation of individual properties of neuronal responses, a unified account of the joint development of the multiple response features of cortical neurons has remained elusive. In this study, we show that Hebbian synaptic plasticity accounts for the simultaneous refinement of orientation and direction selectivity under both normal and stroboscopic rearing, if one takes into account the spatiotemporal input to the retina during oculomotor activity. In a computational model of the LGN and V1, eye movements are sufficient to establish the patterns of thalamocortical activity required for a Hebbian refinement of both direction- and orientation-selective responses during exposure to natural stimuli. Furthermore, we show that consideration of fixational eye movements explains the simultaneous loss of direction selectivity and preservation of orientation selectivity observed as a consequence of stroboscopic rearing. These results further support a role for oculomotor activity in the refinement of the response properties of V1 neurons.
Network Computation in Neural Systems 01/2009; 20(4):197-232. · 1.53 Impact Factor
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Computer Analysis of Images and Patterns, 13th International Conference, CAIP 2009, Münster, Germany, September 2-4, 2009. Proceedings; 01/2009
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Artificial Neural Networks - ICANN 2008, 18th International Conference, Prague, Czech Republic, September 3-6, 2008, Proceedings, Part II; 01/2008
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ABSTRACT: Behavioral and modeling studies have established that curved and drawing human hand movements obey the 2/3 power law, which dictates a strong coupling between movement curvature and velocity. Human motion perception seems to reflect this constraint. The functional MRI study reported here demonstrates that the brain's response to this law of motion is much stronger and more widespread than to other types of motion. Compliance with this law is reflected in the activation of a large network of brain areas subserving motor production, visual motion processing, and action observation functions. Hence, these results strongly support the notion of similar neural coding for motion perception and production. These findings suggest that cortical motion representations are optimally tuned to the kinematic and geometrical invariants characterizing biological actions.
Proceedings of the National Academy of Sciences 01/2008; 104(51):20582-7. · 9.68 Impact Factor
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ABSTRACT: Under natural viewing conditions, the physiological instability of visual fixation keeps the projection of the stimulus on the retina in constant motion. After eye opening, chronic exposure to a constantly moving retinal image might influence the experience-dependent refinement of cell response characteristics. The results of previous modeling studies have suggested a contribution of fixational instability to the Hebbian maturation of the receptive fields of V1 simple cells (Rucci, Edelman, & Wray, 2000; Rucci & Casile, 2004). This letter examines the origins of such a contribution. Using quasilinear models of lateral geniculate nucleus units and V1 simple cells, we derive analytical expressions for the second-order statistics of thalamocortical activity before and after eye opening. We show that in the presence of natural stimulation, fixational instability introduces a spatially uncorrelated signal in the retinal input, which strongly influences the structure of correlated activity in the model. This input signal produces a regime of thalamocortical activity similar to that present before eye opening and compatible with the Hebbian maturation of cortical receptive fields.
Neural Computation 03/2006; 18(3):569-90. · 1.88 Impact Factor
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ABSTRACT: Experimental evidence suggests a link between perception and the execution of actions . In particular, it has been proposed that motor programs might directly influence visual action perception . According to this hypothesis, the acquisition of novel motor behaviors should improve their visual recognition, even in the absence of visual learning. We tested this prediction by using a new experimental paradigm that dissociates visual and motor learning during the acquisition of novel motor patterns. The visual recognition of gait patterns from point-light stimuli was assessed before and after nonvisual motor training. During this training, subjects were blindfolded and learned a novel coordinated upper-body movement based only on verbal and haptic feedback. The learned movement matched one of the visual test patterns. Despite the absence of visual stimulation during training, we observed a selective improvement of the visual recognition performance for the learned movement. Furthermore, visual recognition performance after training correlated strongly with the accuracy of the execution of the learned motor pattern. These results prove, for the first time, that motor learning has a direct and highly selective influence on visual action recognition that is not mediated by visual learning.
Current Biology 02/2006; 16(1):69-74. · 9.65 Impact Factor
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ABSTRACT: Humans can perceive the motion of living beings from very impoverished stimuli like point-light displays. How the visual system achieves the robust generalization from normal to point-light stimuli remains an unresolved question. We present evidence on multiple levels demonstrating that this generalization might be accomplished by an extraction of simple mid-level optic flow features within coarse spatial arrangement, potentially exploiting relatively simple neural circuits: (1) A statistical analysis of the most informative mid-level features reveals that normal and point-light walkers share very similar dominant local optic flow features. (2) We devise a novel point-light stimulus (critical features stimulus) that contains these features, and which is perceived as a human walker even though it is inconsistent with the skeleton of the human body. (3) A neural model that extracts only these critical features accounts for substantial recognition rates for strongly degraded stimuli. We conclude that recognition of biological motion might be accomplished by detecting mid-level optic flow features with relatively coarse spatial localization. The computationally challenging reconstruction of precise position information from degraded stimuli might not be required.
Journal of Vision 02/2005; 5(4):348-60. · 3.38 Impact Factor
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ABSTRACT: Early in life, visual experience appears to influence the refinement and maintenance of the orientation-selective responses of neurons in the primary visual cortex. After eye opening, the statistical structure of visually driven neural responses depends not only on the stimulus, but also on how the stimulus is scanned during behavior. Modulations of neural activity due to behavior may thus play a role in the experience-dependent refinement of cell response characteristics. To investigate the possible influences of eye movements on the maturation of thalamocortical connectivity, we have simulated the responses of neuronal populations in the lateral geniculate nucleus (LGN) and V1 of the cat while images of natural scenes were scanned in a way that replicated the cat's oculomotor activity. In the model, fixational eye movements were essential to attenuate neural sensitivity to the broad correlational structure of natural visual input, decorrelate neural responses, and establish a regime of neural activity that was compatible with a Hebbian segregation of geniculate afferents to the cortex. We show that this result is highly robust and does not depend on the precise characteristics of the model.
Visual Neuroscience 08/2004; 21(5):725-38. · 2.23 Impact Factor
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Artificial Neural Networks and Neural Information Processing - ICANN/ICONIP 2003, Joint International Conference ICANN/ICONIP 2003, Istanbul, Turkey, June 26-29, 2003, Proceedings; 01/2003
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Advances in Neural Information Processing Systems 14 [Neural Information Processing Systems: Natural and Synthetic, NIPS 2001, December 3-8, 2001, Vancouver, British Columbia, Canada]; 01/2001
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ABSTRACT: To recognize how people interact with objects is essential for humans and artificial systems like robots. However, this recognition task is difficult and requires the capturing of the details of effector and goal object under a wide range of image transformations, such as view or position changes. Here, we demonstrate how specific effector-object interactions can be efficiently recognized by a simple, biologically plausible neural model. In line with biological evidence, the model applies a view-based approach for the recognition of grasping sequences from videos. The model generalizes to untrained views by interpolation between stored example views. In addition, it presents a novel physiologically plausible mechanism to capture the spatial relationship between effector and object. The results support the view that where and how an object will be grasped by an agent can be predicted without estimation of the 3D structure of the scene.
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ABSTRACT: Mirror neurons are a class of neurons that have been found on the premotor cortex of monkeys, and which are active during the motor planning and the visual observation of actions. These neurons have recently received a vast amount of interest in cognitive neuroscience and robotics and have been discussed as potential basis for the imitation learning and understanding of actions. However, their visual tuning properties are only poorly understood. Most existing models assume that the tuning properties of mirror neurons might be based on a reconstruction of the three-dimensional structure of action and object, a computationally difficult problem. In line with a broad body of work on object recognition, we present a model that explains visual properties of mirror neurons without this requirement. The proposed model is based on a small number of physiologically well-established principles. In addition, it postulates novel neural mechanisms for the integration of information about object and effector movement, which can be tested in electrophysiological experiments.
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ABSTRACT: Under natural viewing conditions, small movements of the eye, head and body prevent the maintenance of a steady direction of gaze. It is known that stimuli tend to fade when they are stabilized on the retina for several seconds. However, it is unclear whether the physiological motion of the retinal image serves a visual purpose during the brief periods of natural visual fixation. This study examines the impact of fixational instability on the statistics of the visual input to the retina and on the structure of neural activity in the early visual system. We show that fixational instability introduces a component in the retinal input signals that, in the presence of natural images, lacks spatial correlations. This component strongly influences neural activity in a model of the LGN. It decorrelates cell responses even if the contrast sensitivity functions of simulated cells are not perfectly tuned to counter-balance the power-law spectrum of natural images. A decorrelation of neural activity at the early stages of the visual system has been proposed to be beneficial for discarding statistical redundancies in the input signals. The results of this study suggest that fixational instability might contribute to the establishment of efficient representations of natural stimuli.
Network Computation in Neural Systems 16(2-3):121-38. · 1.53 Impact Factor
