Activation of cerebellum and basal ganglia during the observation and execution of manipulative actions

Studies on action observation mostly described the activation of a network of cortical areas, while less investigation focused specifically on the activation and role of subcortical nodes. In the present fMRI study, we investigated the recruitment of cerebellum and basal ganglia during the execution and observation of object manipulation performed with the right hand. The observation conditions consisted in: (a) observation of manipulative actions; (b) observation of sequences of random finger movements. In the execution conditions, participants had to perform the same actions or movements as in (a) and (b), respectively. The results of conjunction analysis showed significant shared activations during both observation and execution of manipulation in several subcortical structures, including: (1) cerebellar lobules V, VI, crus I, VIIIa and VIIIb (bilaterally); (2) globus pallidus, bilaterally, and left subthalamic nucleus; (3) red nucleus (bilaterally) and left thalamus. These findings support the hypothesis that the action observation/execution network also involves subcortical structures, such as cerebellum and basal ganglia, forming an integrated network. This suggests possible mechanisms, involving these subcortical structures, underlying learning of new motor skills, through action observation and imitation

Contribution of the posterior parietal cortex in reaching, grasping, and using objects and tools

Neuropsychological and neuroimaging data suggest a differential contribution of posterior parietal regions during the different components of a transitive gesture. Reaching requires the integration of object location and body position coordinates and reaching tasks elicit bilateral activation in different foci along the intraparietal sulcus. Grasping requires a visuomotor match between the object's shape and the hand's posture. Lesion studies and neuroimaging confirm the importance of the anterior part of the intraparietal sulcus for human grasping. Reaching and grasping reveal bilateral activation that is generally more prominent on the side contralateral to the hand used or the hemifield stimulated. Purposeful behavior with objects and tools can be assessed in a variety of ways, including actual use, pantomimed use, and pure imagery of manipulation. All tasks have been shown to elicit robust activation over the left parietal cortex in neuroimaging, but lesion studies hav e not always confirmed these findings. Compared to pantomimed or imagined gestures, actual object and tool use typically produces activation over the left primary somatosensory region. Neuroimaging studies on pantomiming or imagery of tool use in healthy volunteers revealed neural responses in possibly separate foci in the left supramarginal gyrus. In sum, the parietal contribution of reaching and grasping of objects seems to depend on a bilateral network of intraparietal foci that appear organized along gradients of sensory and effector preferences. Dorsal and medial parietal cortex appears to contribute to the online monitoring/adjusting of the ongoing prehensile action, whereas the functional use of objects and tools seems to involve the inferior lateral parietal cortex. This functional input reveals a clear left lateralized activation pattern that may be tuned to the integration of acquired knowledge in the planning and guidance of the transitive movement

Neural basis of motor planning for object-oriented actions: the role of kinematics and cognitive aspects

The project I have carried out in these three years as PhD student pursued the aim of describing the motor preparation activity related to the object oriented actions actually performed. The importance of these studies comes from the lack of literature on EEG and complex movements actually executed and not just mimed or pantomimed. Using the term ‘complex’ here we refer to actions that are oriented to an object with the intent to interact with it. In order to provide a broader idea about the aim of the project, I have illustrated the complexity of the movements and cortical networks involved in their processing and execution. Several cortical areas concur to the plan and execution of a movement, and the contribution of these different areas changes according to the complexity, in terms of kinematics, of the action. The object-oriented action seems to be a circuit apart: besides motor structures, it also involves a temporo-parietal network that takes part to both planning and performing actions like reaching and grasping. Such findings have been pointed out starting from studies on the Mirror neuron system discovered in monkeys at the beginning of the ‘90s and subsequently extended to humans. Apart from all the speculations this discovery has opened to, many different researchers have started investigating different aspects related to reaching and grasping movements, describing different areas involved, all belonging to the posterior parietal cortex (PPC), and their connections with anterior motor cortices through different paradigms and techniques. Most of the studies investigating movement execution and preparation are studies on monkey or fMRI studies on humans. Limits of this technique come from its low temporal resolution and the impossibility to use self-paced movement, that is, movement performed in more ecological conditions when the subject decides freely to move. On the few studies investigating motor preparation using EEG, only pantomime of action has been used, more than real interactions with objects. Because all of these factors, we decided to get through the description of the motor preparation activity for goal oriented actions pursuing two aims: in the first instance, to describe this activity for grasping and reaching actions actually performed toward a cup (a very ecological object); secondly, we wanted to verify which parameters in these kind of movements are taken into account during their planning and preparation: because of all the variables involved in grasping and reaching movements, like the position of the objects, its features, the goal of the action and its meaning, we tried to verify how these variables could affect motor preparation creating two different experiments. In the first one, subjects were requested to perform a grasping and a reaching action toward a cup and in a third condition we tied up their hands as fist in order to verify what it could happen when people are in the condition of turning an ordinary and easy action into a new one to accomplish the final task requested. In the second experiment, we better accounted for the cognitive aspects beyond the motor preparation of an action. Here, indeed, we tested a very simple action like a key press in two different conditions. In the first one the button press was not related to any kind of consequence, whereas in the second case the same action triggered a video on a screen showing a hand moving toward a cup and grasping it (giving like a video-game effect). Both the experiments have shown results straightening the role cognitive processes have in motor planning. In particular, it seemed that the goal of the action, along with the object we are going to interact with, could create a particular response and activity starting very early in the posterior parietal cortex. Finally, because of the actions used in these experiments, it was important testing the hypothesis that our findings could be generalized even to the observation of those same actions. As I mentioned before, object-oriented actions have received great attention starting from the discovery of the mirror neuron system which showed a correspondence between the cortical activity of the person performing the action with the one produced in the observer. Such a finding allowed to describe our brain as a social brain, able to create a mental representation of what the other person is doing which allows us to understand others gesture and intentions. What we wanted to test in this project was the possibility that such a correspondence between the observer and the actor would had been extended even to the motor preparation period of an upcoming action, giving credit to the hypothesis of considering the human brain as able to even predict others actions and intentions besides understanding them. In the last experiment I carried out in my project, thus, I used the same actions involved in the first experiment but asking this time to observe them passively instead of performing them. The results provided in this study confirmed the cognitive, rather than motor, role the PPC plays in action planning. Indeed, even when no movements are involved, the same structure are active reflecting the activity found in the execution experiment. The main result I have reported in this dissertation is related to the suggestion of a new model to understand the role the PPC has in object-oriented movements. Unlike previous hypothesis and models suggesting the contribution of PPC in extracting affordances from the objects or monitoring and transforming coordinates between us and the object into intention for acting, we suggest here that the role of the parietal areas is more to make a judge about the appropriate match of the action goal with the affordances provided by the object. When actually the action we are going to perform fits well with the object features, the PPC starts its activity, elaborating all those coordinates representation and monitoring the execution and programming phases of movement. This model is well supported by results from both our experiments and well combines the two previous models, but putting more emphasis on the ‘goal-object matching’ function of the PPC and the Superior parietal lobe (SPL) in particular