Recent studies of corticospinal excitability during observation of grasping and lifting of objects of different weight have highlighted the role of agent's kinematics in modulating observer's motor excitability. Here, we investigate whether explicit weight-related information, provided by written labels on the objects, modulate the excitability of the observer's motor system and how this modulation is affected when there is a conflict between label and object's weight. We measured TMS-evoked motor potentials (MEPs) from right hand intrinsic muscles, while subjects were observing an actor lifting objects of different weights, in some trials labeled (heavy/light) in congruent or incongruent way. Results confirmed a weight-related modulation of MEPs based on kinematic cues. Interestingly, any conflict between the labels and the actual weight (i.e., explicit versus implicit information), although never consciously noticed by the observer, deeply affected the mirroring of others' actions. Our findings stress the automatic involvement of the mirror-neuron system.

In many parts of the vertebrate nervous system, synaptic connections are remodeled during early postnatal life. Neural activity plays an important role in regulating one such rearrangement, synapse elimination, in the developing neuromuscular system, but there is little direct evidence on roles of pre-or postsynaptic activity in regulating synapse elimination in the developing brain. To address this issue, we expressed a chloride channel-yellow fluorescent protein fusion in cerebellar Purkinje cells (PCs) of transgenic mice to decrease their excitability. We then assessed elimination of supernumerary climbing fiber inputs to PCs. Individual PCs are innervated by multiple climbing fibers at birth; all but one are eliminated during the first three postnatal weeks in wild-type mice, but multiple innervation persists for at least three months in the transgenic mice. The normal redistribution of climbing fiber synapses from PC somata to proximal dendrites was also blunted in transgenics. These results show that normal electrical activity of the postsynaptic cell is required for it to attain a mature innervation pattern.chloride channel ͉ climbing fiber ͉ Purkinje cell T hroughout the vertebrate nervous system, neurons receive more inputs early in development than they maintain in adulthood. During a circumscribed period in early postnatal life, supernumerary inputs are removed by a process called synapse elimination, and the remaining inputs then become stronger. This process has been analyzed in greatest detail at a peripheral synapse, the skeletal neuromuscular junction, at which all motor axons but one are eliminated, leaving each muscle fiber with a single input. There, the process has been shown to be activity dependent and competitive, with the relative activities of the inputs playing a decisive role in the outcome (1-4).Neural activity also regulates synaptic rearrangements in the developing central nervous system (5-8). In the cerebellar cortex, one of the best-studied systems in this respect, each Purkinje cell (PC) is innervated by multiple climbing fibers at birth. Between postnatal day (P) 5 and P15-20, supernumerary climbing fibers are withdrawn, leaving each PC innervated by just a single climbing fiber (7-10). In parallel, climbing fiber terminations are redistributed on the PC, with a loss of perisomatic synapses and an increase in number of synapses on proximal dendrites (10, 11). Early studies showed that supernumerary climbing fiber inputs were retained in mutants with developmental defects in cerebellar maturation (12)(13)(14)(15), and subsequent analysis demonstrated a critical role for the other main input to PCs, the parallel fibers, in the elimination of redundant inputs (9,(16)(17)(18)(19)(20)(21)(22)(23)(24)(25). Conversely, harmaline administration to inferior olivary neurons, from which climbing fibers arise, leads to synchronous activation and to the persistence of multiple innervation (26).Limitations of these studies are that most of them involved perturbation of a particular neurotran...

Background: Time information processing relies on memory, which greatly supports the operations of hypothetical internal timekeepers. Scalar Expectancy Theory (SET) postulates the existence of a memory component that is functionally separated from an internal clock and other processing stages. SET has devised several experimental procedures to map these cognitive stages onto cerebral regions and neurotransmitter systems. One of these, the time bisection procedure, has provided support for a dissociation between the clock stage, controlled by dopaminergic systems, and the memory stage, mainly supported by cholinergic neuronal networks. This study aimed at linking the specific memory processes predicted by SET to brain mechanisms, by submitting time bisection tasks to patients with probable Alzheimer's disease (AD), that are known to present substantial degeneration of the fronto-temporal regions underpinning memory.

The ability to swiftly and smoothly switch from one task set to another is central to intelligent behavior, because it allows an organism to flexibly adapt to ever changing environmental conditions and internal needs. For this reason, researchers interested in executive control processes have often relied on task-switching paradigms as powerful tools to uncover the underlying cognitive and brain architecture. In order to gather fundamental information at the single-cell level, it would be greatly helpful to demonstrate that non-human primates, especially the macaque monkey, share with us similar behavioral manifestations of task-switching and therefore, in all likelihood, similar underlying brain mechanisms. Unfortunately, prior attempts have provided negative results (e.g., Stoet & Snyder, 2003b), in that it was reported that macaques do not show the typical signature of task-switching operations at the behavioral level, represented by switch costs. If confirmed, this would indicate that the macaque cannot be used as a model approach to explore human executive control mechanisms by means of task-switching paradigms. We have therefore decided to re-explore this issue, by conducting a comparative experiment on a group of human participants and two macaque monkeys, whereby we measured and compared performance costs linked to task switching and resistance to interference across the two species. Contrary to what previously reported, we found that both species display robust task switching costs, thus supporting the claim that macaque monkeys provide an exquisitely suitable model to study the brain mechanisms responsible for maintaining and switching task sets.