Activation of Cerebellum, Basal Ganglia and Thalamus During Observation and Execution of Mouth, hand, and foot Actions.

Humans and monkey studies showed that specific sectors of cerebellum and basal ganglia activate not only during execution but also during observation of hand actions. However, it is unknown whether, and how, these structures are engaged during the observation of actions performed by effectors different from the hand. To address this issue, in the present fMRI study, healthy human participants were required to execute or to observe grasping acts performed with different effectors, namely mouth, hand, and foot. As control, participants executed and observed simple movements performed with the same effectors. The results show that: (1) execution of goal-directed actions elicited somatotopically organized activations not only in the cerebral cortex but also in the cerebellum, basal ganglia, and thalamus; (2) action observation evoked cortical, cerebellar and subcortical activations, lacking a clear somatotopic organization; (3) in the territories displaying shared activations between execution and observation, a rough somatotopy could be revealed in both cortical, cerebellar and subcortical structures. The present study confirms previous findings that action observation, beyond the cerebral cortex, also activates specific sectors of cerebellum and subcortical structures and it shows, for the first time, that these latter are engaged not only during hand actions observation but also during the observation of mouth and foot actions. We suggest that each of the activated structures processes specific aspects of the observed action, such as performing internal simulation (cerebellum) or recruiting/inhibiting the overt execution of the observed action (basal ganglia and sensory-motor thalamus).

Amygdalar connections of the macaque areas 45A and 45B.

In the present study, based on injections of retro- or retro-anterograde tracers at the cortical level, we analyzed the amygdalar connections of the caudal ventrolateral prefrontal areas 45A and 45B of the macaque and compared them with those of the adjacent areas 8/FEF, 8r, 46v, and 12r. The results showed that areas 45A and 45B display reciprocal amygdalar connections, which appear to be considerably richer than those of their neighboring areas. Specifically, these two areas are a target of differentially weighted projections originating predominantly from the magnocellular and the intermediate subdivisions of the basal nucleus and are a source of projections mostly directed to the magnocellular subdivision of the basal nucleus and the dorsal part of the lateral nucleus. The present data, together with previous data on the thalamic connectivity of areas 45A and 45B (Contini et al. Eur J Neurosci 32:1337-53, 2010), suggest that direct and indirect-trans-thalamic-amygdalar connectivity is a characterizing connectional feature of these two areas. Specifically, the amygdalar connections of area 45A, for which a role in communication behavior has been proposed, could convey information on the emotional significance of communicative signals to this area, where it could play a crucial role in guiding appropriate social interactions. Furthermore, the amygdalar connections of area 45B, possibly involved in higher-order aspects of visual guidance of gaze, could convey information related to the relevance of visual stimuli, which could contribute to a representation of priority maps in this VLPF area.

Thalamic projections to the macaque caudal ventrolateral prefrontal areas 45A and 45B.

We studied the sources of thalamic projections to the caudal ventrolateral prefrontal areas 45A and 45B, which display markedly distinct cortical connections [M. Gerbella et al. (2010) Cereb. Cortex, 20, 141-168], and compared them with those to area 8/FEF (frontal eye field). Both areas 45A and 45B were the targets of highly predominant projections from the mediodorsal nucleus (MD) and of additional projections, mostly from the magnocellular ventral anterior and the medial pulvinar nucleus. The projection profiles from different MD subdivisions clearly distinguished these two areas from one another and from area 8/FEF. Area 45A was the target of predominant projections from parvicellular MD and of minor, albeit robust, projections from magnocellular MD. The opposite was true for area 45B: magnocellular MD was the major source of projections and parvicellular MD contributed minor, albeit robust, projections. Furthermore, area 45B, but not area 45A, was targeted by robust projections from multiform MD, the principal thalamic nucleus for area 8/FEF. These results provide further evidence for the distinctiveness of areas 45A and 45B, and support the idea that area 45B is affiliated with the frontal oculomotor system, challenging the proposed homology of this area with part of the human language-related area 45 (rostral part of Broca's region). Furthermore, the present data provide evidence for potentially robust trans-thalamic (via magnocellular MD) afferent, as well as direct and reciprocal, amygdaloid connections of areas 45A and 45B, suggesting the contribution of emotional information to the differential role of these two areas in non-spatial information processing.