The ability of using a large variety of tools is important in our daily life. Behind human tool-use abilities lays the brain capacity to incorporate tools into the body representation for action (Body Schema, BS), thought to rely mainly on proprioceptive information. Here we tested whether tool incorporation is possible in absence of proprioception by studying a patient with right upper-limb deafferentation. We adopted a paradigm sensitive to changes of the Body Schema and analysed the kinematics of free-hand movements before (...) and after tool-use, in three sessions over a period of two years. In the first session, before tool-use, the kinematics of the deafferented hand was disrupted. Similarly, the first movements with the tool (a mechanical grabber elongating the arm by ∼40cm) showed an abnormal profile that tended to normalize at the end of the session. Subsequent free-hand movements were also normalised. At session 2, 6 months later, the patient exhibited normal free-hand kinematic profiles, additionally showing changes in grasping kinematics after tool-use, but no sign of tool incorporation. A follow-up two years later, further confirmed the normalized kinematic profile but the absence of tool incorporation. This first description of tool-use in absence of proprioception shows the fundamental role of proprioception in the update of the Body Schema. These results provide an important further step in understanding human motor control and have implications for future development of rehabilitation programs for patients with sensory deficits. (shrink)

Humans, being highly social creatures, rely heavily on the ability to perceive what others are doing and to infer from gestures and expressions what others may be intending to do. These perceptual skills are easily mastered by most, but not all, people, in large part because human action readily communicates intentions and feelings. In recent years, remarkable advances have been made in our understanding of the visual, motoric, and affective influences on perception of human action, as well as in the (...) elucidation of the neural concomitants of perception of human action. This article reviews those advances and, where possible, draws links among those findings.Acronyms and DefinitionsApparent motion: perception of smooth motion from brief, successive exposures of static imagesChameleon effect: tendency for people to mimic the actions of others without even knowing itCommon coding principle: theory that perceiving and acting share common mental representationsDynamic noise: an array of randomly positioned dots that can camouflage perception of PL animations when the noise dots are sufficiently denseEvent-related potential : electrical brain activity registered from the scalpExtrastriate body area : brain region activated when a person views a human body or body partsFunctional magnetic resonance imaging : widely used technique that reveals brain activation patterns based on hemodynamic responses to neural activityInversion effect: difficulty of perceiving PL animations when they are shown upside downKinematics: analysis of the motions of objects without regard to the forces producing themMirror neurons: brain cells responsive when an animal engages in an activity or when it watches another animal engaged in that activityPoint-light animations: biological activity portrayed by small light tokens placed on the major body parts of an actorPositron emission tomography : brain imaging technique that uses radioactively labeled tracers to allow visualization of active brain areasSpatiotemporal jitter: means of degrading perception of PL animations, where the relative timing and positions of the moving dots are perturbedSuperior temporal sulcus : region of the cortex the posterior portion of which contains neurons selectively responsive to human activityTemplate-matching model: theory that perception of biological motion results from concatenation of static views of the bodyTranscranial magnetic stimulation : technique producing a brief disruption of neural processing. (shrink)

There seems to be no dimension of bodily awareness that cannot be disrupted. To account for such variety, there is a growing consensus that there are at least two distinct types of body representation that can be impaired, the body schema and the body image. However, the definition of these notions is often unclear. The notion of body image has attracted most controversy because of its lack of unifying positive definition. The notion of body schema, onto which there seems to (...) be a more widespread agreement, also covers a variety of sensorimotor representations. Here, I provide a conceptual analysis of the body schema contrasting it with the body image as well as assess whether the body schema can be specifically impaired, while other types of body representation are preserved; and the body schema obeys principles that are different from those that apply to other types of body representation. (shrink)

Discusses the possibility of reconciling different articulations of intentionality from a neurobiological perspective. The author analyzes the relationship between agency and representation and how representation is intrinsically related to action control. The author also presents a new account of action, arguing against what is still commonly held as its proper definition, namely the final outcome of a cascade-like process that starts from the analysis of sensory data, incorporates the result of decision processes, and ends up with responses (actions) to externally-or (...) internally-generated stimuli. The author discusses recent findings from the investigation of neural mechanisms that are at the basis of sensorimotor integration. (shrink)