Visual exploration of emotional body language: a behavioural and eye-tracking study.

Bodily postures are essential to correctly comprehend others' emotions and intentions. Nonetheless, very few studies focused on the pattern of eye movements implicated in the recognition of emotional body language (EBL), demonstrating significant differences in relation to different emotions. A yet unanswered question regards the presence of the "left-gaze bias" (i.e. the tendency to look first, to make more fixations and to spend more looking time on the left side of centrally presented stimuli) while scanning bodies. Hence, the present study aims at exploring both the presence of a left-gaze bias and the modulation of EBL visual exploration mechanisms, by investigating the fixation patterns (number of fixations and latency of the first fixation) of participants while judging the emotional intensity of static bodily postures (Angry, Happy and Neutral, without head). While results on the latency of first fixations demonstrate for the first time the presence of the left-gaze bias while scanning bodies, suggesting that it could be related to the stronger expressiveness of the left hand (from the observer's point of view), results on fixations' number only partially fulfil our hypothesis. Moreover, an opposite viewing pattern between Angry and Happy bodily postures is showed. In sum, the present results, by integrating the spatial and temporal dimension of gaze exploration patterns, shed new light on EBL visual exploration mechanisms.

Beholders' sensorimotor engagement enhances aesthetic rating of pictorial facial expressions of pain.

The present study addresses a novel issue by investigating whether beholders' sensorimotor engagement with the emotional content of works of art contributes to the formation of their objective aesthetic judgment of beauty. To this purpose, participants' sensorimotor engagement was modulated by asking them to overtly contract the Corrugator Supercilii facial muscles or to refrain from any voluntary facial movement while judging the aesthetic value of painful and neutral facial expressions in select examples of Renaissance and Baroque paintings. Results demonstrated a specific increase in the aesthetic rating of paintings showing painful facial expressions during the congruent activation of the Corrugator Supercilii muscles. Furthermore, participants' empathetic traits and expertise in art were found to correlate directly with the amplitude of the motor enactment effect on aesthetic judgments. For the first time, we show the role of bottom-up bodily driven sensorimotor processes in the objective aesthetic evaluation of works of art.

When pliers become fingers in the monkey motor system.

The capacity to use tools is a fundamental evolutionary achievement. Its essence stands in the capacity to transfer a proximal goal (grasp a tool) to a distal goal (e.g., grasp food). Where and how does this goal transfer occur? Here, we show that, in monkeys trained to use tools, cortical motor neurons, active during hand grasping, also become active during grasping with pliers, as if the pliers were now the hand fingers. This motor embodiment occurs both for normal pliers and for "reverse pliers," an implement that requires finger opening, instead of their closing, to grasp an object. We conclude that the capacity to use tools is based on an inherently goal-centered functional organization of primate cortical motor areas.

I know what you are doing. a neurophysiological study.

In the ventral premotor cortex of the macaque monkey, there are neurons that discharge both during the execution of hand actions and during the observation of the same actions made by others (mirror neurons). In the present study, we show that a subset of mirror neurons becomes active during action presentation and also when the final part of the action, crucial in triggering the response in full vision, is hidden and can therefore only be inferred. This implies that the motor representation of an action performed by others can be internally generated in the observer's premotor cortex, even when a visual description of the action is lacking. The present findings support the hypothesis that mirror neuron activation could be at the basis of action recognition.

Decoding the activity of grasping neurons recorded from the ventral premotor area F5 of the macaque monkey.

Many neurons in the monkey ventral premotor area F5 discharge selectively when the monkey grasps an object with a specific grip. Of these, the motor neurons are active only during grasping execution, whereas the visuomotor neurons also respond to object presentation. Here we assessed whether the activity of 90 task-related F5 neurons recorded from two macaque monkeys during the performance of a visually-guided grasping task can be used as input to pattern recognition algorithms aiming to decode different grips. The features exploited for the decoding were the mean firing rate and the mean interspike interval calculated over different time spans of the movement period (all neurons) or of the object presentation period (visuomotor neurons). A support vector machine (SVM) algorithm was applied to the neural activity recorded while the monkey grasped two sets of objects. The original set contained three objects that were grasped with different hand shapes, plus three others that were grasped with the same grip, whereas the six objects of the special set were grasped with six distinctive hand configurations. The algorithm predicted with accuracy greater than 95% all the distinct grips used to grasp the objects. The classification rate obtained using the first 25% of the movement period was 90%, whereas it was nearly perfect using the entire period. At least 16 neurons were needed for accurate performance, with a progressive increase in accuracy as more neurons were included. Classification errors revealed by confusion matrices were found to reflect similarities of hand grips used to grasp the objects. The use of visuomotor neurons' responses to object presentation yielded grip classification accuracy similar to that obtained from actual grasping execution. We suggest that F5 grasping-related activity might be used by neural prostheses to tailor hand shape to the specific object to be grasped even before movement onset.

Simultaneous recording of macaque premotor and primary motor cortex neuronal populations reveals different functional contributions to visuomotor grasp.

To understand the relative contributions of primary motor cortex (M1) and area F5 of the ventral premotor cortex (PMv) to visually guided grasp, we made simultaneous multiple electrode recordings from the hand representations of these two areas in two adult macaque monkeys. The monkeys were trained to fixate, reach out and grasp one of six objects presented in a pseudorandom order. In M1 326 task-related neurons, 104 of which were identified as pyramidal tract neurons, and 138 F5 neurons were analyzed as separate populations. All three populations showed activity that distinguished the six objects grasped by the monkey. These three populations responded in a manner that generalized across different sets of objects. F5 neurons showed object/grasp related tuning earlier than M1 neurons in the visual presentation and premovement periods. Also F5 neurons generally showed a greater preference for particular objects/grasps than did M1 neurons. F5 neurons remained tuned to a particular grasp throughout both the premovement and reach-to-grasp phases of the task, whereas M1 neurons showed different selectivity during the different phases. We also found that different types of grasp appear to be represented by different overall levels of activity within the F5-M1 circuit. Altogether these properties are consistent with the notion that F5 grasping-related neurons play a role in translating visual information about the physical properties of an object into the motor commands that are appropriate for grasping, and which are elaborated within M1 for delivery to the appropriate spinal machinery controlling hand and digit muscles.

Microprobe array with low impedance electrodes and highly flexible polyimide cables for acute neural recording.

This paper reports on a novel type of silicon-based microprobes with linear, two and three dimensional (3D) distribution of their recording sites. The microprobes comprise either single shafts, combs with multiple shafts or 3D arrays combining two combs with 9, 36 or 72 recording sites, respectively. The electrical interconnection of the probes is achieved through highly flexible polyimide ribbon cables attached using the MicroFlex Technology which allows a connection part of small lateral dimensions. For an improved handling, probes can be secured by a protecting canula. Low-impedance electrodes are achieved by the deposition of platinum black. First in vivo experiments proved the capability to record single action potentials in the motor cortex from electrodes close to the tip as well as body electrodes along the shaft.

Audiovisual mirror neurons and action recognition.

Many object-related actions can be recognized both by their sound and by their vision. Here we describe a population of neurons in the ventral premotor cortex of the monkey that discharge both when the animal performs a specific action and when it hears or sees the same action performed by another individual. These 'audiovisual mirror neurons' therefore represent actions independently of whether these actions are performed, heard or seen. The magnitude of auditory and visual responses did not differ significantly in half the neurons. A neurometric analysis revealed that based on the response of these neurons, two actions could be discriminated with 97% accuracy.

Patterns of muscle activity underlying object-specific grasp by the macaque monkey.

During object grasp, a coordinated activation of distal muscles is required to shape the hand in relation to the physical properties of the object. Despite the fundamental importance of the grasping action, little is known of the muscular activation patterns that allow objects of different sizes and shapes to be grasped. In a study of two adult macaque monkeys, we investigated whether we could distinguish between EMG activation patterns associated with grasp of 12 differently shaped objects, chosen to evoke a wide range of grasping postures. Each object was mounted on a horizontal shuttle held by a weak spring (load force 1-2 N). Objects were located in separate sectors of a "carousel," and inter-trial rotation of the carousel allowed sequential presentation of the objects in pseudorandom order. EMG activity from 10 to 12 digit, hand, and arm muscles was recorded using chronically implanted electrodes. We show that the grasp of different objects was characterized by complex but distinctive patterns of EMG activation. Cluster analysis shows that these object-related EMG patterns were specific and consistent enough to identify the object unequivocally from the EMG recordings alone. EMG-based object identification required a minimum of six EMGs from simultaneously recorded muscles. EMG patterns were consistent across recording sessions in a given monkey but showed some differences between animals. These results identify the specific patterns of activity required to achieve distinct hand postures for grasping, and they open the way to our understanding of how these patterns are generated by the central motor network.