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Abstract Functional magnetic resonance imaging (fMRI) was used to localize brain areas that were active during the observation of actions made by another individual. Object- and non-object-related actions made with different effectors (mouth, hand and foot) were presented. Observation of both object- and non-object-related actions determined a somatotopically organized activation of premotor cortex. The somatotopic pattern was similar to that of the classical motor cortex homunculus. During the observation of object-related actions, an activation, also somatotopically organized, was additionally found in the posterior parietal lobe. Thus, when individuals observe an action, an internal replica of that action is automatically generated in their premotor cortex. In the case of object-related actions, a further object-related analysis is performed in the parietal lobe, as if the subjects were indeed using those objects. These results bring the previous concept of an action observation/execution matching system (mirror system) into a broader perspective: this system is not restricted to the ventral premotor cortex, but involves several somatotopically organized motor circuits. [ABSTRACT FROM AUTHOR]

Very little is known about the action observation network and the mirror neuron system (AON/MNS) in children and its age-related properties compared with those observed in adults. In the present fMRI study we explored the activation of areas belonging to the AON/MNS in children and adults during observation of complex hand-grasping actions, as compared to observation of simple grasping acts executed with the left and the right hand, seen from a first person perspective. The results indicate that during the action observation tasks in children there was activation of a cortical network similar to that found in adults, including the premotor cortex, the posterior part of the inferior frontal gyrus and the posterior parietal lobe. However, the activation in children was more widespread and showed a higher inter-subject variability compared with adults. Furthermore, the activated network seems more lateralized to the left hemisphere in adults and more bilateral in children, with a linear growth of lateralization index as a function of age. Finally, in children the activation in the anterior intraparietal cortex (AIP) of each hemisphere was higher during observation of the contralateral hand (hand identity effect) and during the observation of complex actions relative to simple grasping acts, confirming the role of AIP for action-related hand identity previously described in adults. These results support the assumption that structure and size of action representations are sensitive to mechanisms of development and show physiological plasticity. These properties of the AON/MNS could constitute a powerful tool for spontaneous reorganization and recovery of motor deficits after brain injury in children and in adults, as well as for specific rehabilitation programmes., (© 2015 John Wiley & Sons Ltd.)

Grasping actions require the integration of two neural processes, one enabling the transformation of object properties into corresponding motor acts, and the other involved in planning and controlling action execution on the basis of contextual information. The first process relies on parieto-premotor circuits, whereas the second is considered to be a prefrontal function. Up to now, the prefrontal cortex has been mainly investigated with conditional visuomotor tasks requiring a learned association between cues and behavioural output. To clarify the functional role of the prefrontal cortex in grasping actions, we recorded the activity of ventrolateral prefrontal (VLPF) neurons while monkeys (Macaca mulatta) performed tasks requiring reaching-grasping actions in different contextual conditions (in light and darkness, memory-guided, and in the absence of abstract learned rules). The results showed that the VLPF cortex contains neurons that are active during action execution (movement-related neurons). Some of them showed grip selectivity, and some also responded to object presentation. Most movement-related neurons discharged during action execution both with and without visual feedback, and this discharge typically did not change when the action was performed with object mnemonic information and in the absence of abstract rules. The findings of this study indicate that a population of VLPF neurons play a role in controlling goal-directed grasping actions in several contexts. This control is probably exerted within a wider network, involving parietal and premotor regions, where the role of VLPF movement-related neurons would be that of activating, on the basis of contextual information, the representation of the motor goal of the intended action (taking possession of an object) during action planning and execution., (© 2015 Federation of European Neuroscience Societies and John Wiley & Sons Ltd.)

Mirror neurons (MNs) of the monkey ventral premotor cortex (area F5) are a class of cells that match the visual descriptions of others' actions with correspondent motor representations in the observer's brain. Several human studies suggest that one's own motor representations activated during action observation play a role in directing proactive eye movements to the site of the upcoming hand-target interaction. However, there are no data on the possible relationship between gaze behaviour and MN activity. Here we addressed this issue by simultaneously recording eye position and F5 MN activity in two macaques during free observation of a grasping action. More than half of the recorded neurons discharged stronger when the monkey looked at the action than when it did not look at it, but their firing rate was better predicted by 'when' rather than by 'how long' the monkey gazed at the location of the upcoming hand-target interaction. Interestingly, the onset of MN response was linked to the onset of the experimenter's movement, thus making motor representations potentially exploitable to drive eye movements. Furthermore, MNs discharged stronger and earlier when the gaze was 'proactive' compared with 'reactive', indicating that gaze behaviour influences MN activity. We propose that feedforward, automatic representations of other's actions could lead eye movements that, in turn, would provide the motor system with feedback information that enhances the neural representations of the ongoing action., (© 2013 Federation of European Neuroscience Societies and John Wiley & Sons Ltd.)

The ventral agranular frontal cortex of the macaque monkey is formed by a mosaic of anatomically distinct areas. Although each area has been explored by several neurophysiological studies, most of them focused on small sectors of single areas, thus leaving to be clarified which is the general anatomo-functional organization of this wide region. To fill this gap, we studied the ventral convexity of the frontal cortex in two macaque monkeys (Macaca nemestrina) using intracortical microstimulation and extracellular recording. Functional data were then matched with the cytoarchitectonic parcellation of the recorded region. The results demonstrated the existence of a dorso-ventral functional border, encompassing the anatomical boundary between areas F4 and F1, and a rostro-caudal anatomo-functional border between areas F5 and F4. The ventral subdivision of areas F4 and F1 was highly electrically excitable, represented simple mouth movements and lacked visual properties; in contrast, their dorsal counterpart showed a higher stimulation threshold, represented forelimb and mouth motor acts and hosted different types of visual properties. The data also showed that area F5 was scarcely excitable, and displayed various motor specificity (e.g. for the type of grip) and complex visual (i.e. mirror responses) properties. Overall, the posterior areas F4 and F1 appear to be involved in organizing and controlling goal-directed mouth motor acts and simple movements within different parts of the external (dorsal sector) and internal (ventral sector) space, whereas area F5 code motor acts at a more abstract level, thus enabling the emergence of higher order socio-cognitive functions., (© 2012 The Authors. European Journal of Neuroscience © 2012 Federation of European Neuroscience Societies and Blackwell Publishing Ltd.)

The general view on the functional role of the monkey inferior parietal lobule (IPL) convexity mainly derives from studies carried out more than two decades ago and does not account for the functional complexity suggested by more recent neuroanatomical findings. We investigated this issue by recording multi- and single units in the IPL convexity of two monkeys and characterizing their somatosensory, visual and motor responses, using a naturalistic (ethologically relevant) approach. These properties were then matched with IPL cytoarchitectonic parcellation. A further aim of this study was to describe the general properties and the localization of IPL mirror neurons, until now not investigated in detail. Results showed that each studied cytoarchitectonic subdivision of the IPL (PF, PFG, PG) is characterized by specific sensory and motor properties. A key feature of the recorded motor neurons is that of coding goal-directed motor acts. Motor responses are somatotopically organized in a rostro-caudal fashion, with mouth, hand and arm represented in PF, PFG and PG, respectively, with a certain degree of overlap between adjacent representations. In each subdivision the motor activity is associated with specific somatosensory and visual responses, suggesting that each area organizes motor acts in different space sectors. Mirror neurons have been found mainly in area PFG and their general features appear to be very similar to those of ventral premotor mirror neurons. The present data suggest that the IPL plays an important role in both action organization and action understanding and should be considered part of the motor system.

In the ventral premotor cortex (area F5) of the monkey there are neurons that discharge both when the monkey performs specific motor actions and when it observes another individual performing a similar action (mirror neurons). Previous studies on mirror neurons concerned hand actions. Here, we describe the mirror responses of F5 neurons that motorically code mouth actions. The results showed that about one-third of mouth motor neurons also discharge when the monkey observes another individual performing mouth actions. The majority of these 'mouth mirror neurons' become active during the execution and observation of mouth actions related to ingestive functions such as grasping, sucking or breaking food. Another population of mouth mirror neurons also discharges during the execution of ingestive actions, but the most effective visual stimuli in triggering them are communicative mouth gestures (e.g. lip smacking). Some also fire when the monkey makes communicative gestures. These findings extend the notion of mirror system from hand to mouth action and suggest that area F5, the area considered to be the homologue of human Broca's area, is also involved in communicative functions.