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Mental chronometry is a well-established method for analyzing dynamic mental images. The present study extends a previous focus on closed skills to include the open skill of badminton sequences. Accuracy of mental duration was examined as a function of task complexity and expertise level in a total of 45 participants of varying expertise (novices, intermediates, and experts from national leagues). They had to both play and mentally rehearse defined badminton sequences of five, seven, and nine strokes. Results showed a systematic reduction of mental duration for all expertise levels. Although task experience reduced mental timing errors, this did not depend on expertise itself. Correlational data revealed individual strategies in both actual and mental durations but not across the two. It is argued that exact mental durations of badminton rallies are not an essential part of the mental routines used by athletes, because varying conditions offer visual cues that can be used to anticipate play. [ABSTRACT FROM AUTHOR]

On the basis of the simulation theory, Jeannerod (1994) suggested shared representations for so-called S-states (i.e., action observation, action imagery) and action execution. Neurophysiological studies have found neural overlap between motor imagery and execution in motor-related areas (Decety & Grèzes, 1999). Several aspects, however, proved to influence activation patterns, such as expertise (Calvo-Merino et al., 2005) or instructions during observing. Our own fMRI study showed that instructions for observation strongly modified activity in the supplementary motor area, demonstrating that the specific context of observing is relevant for the involvement of motor areas (Zentgraf et al., 2005). Participants viewed identical gymnastic sequences with the instruction to either judge movement accuracy of the model or to perform a first-person-perspective imagery of the observed movements later on. Also, our design allowed us to compare activity patterns during observation and imagery on the basis of the same movements. In spite of partially overlapping motor activation during imagery and observation, there is also differential activation in the insula, the cerebellum, and the anterior cingulate gyrus. This finding points toward specific networks in externally triggered visual-related processes (observation) and internally generated motor cognition processes (imagery) due to different processing and attentional focusing. For observational learning to occur, it might be essential to study the contextual factors that produce the most similar activation patterns during S-states and action execution. [ABSTRACT FROM AUTHOR]

Abstract Background Action observation leads to neural activation of the human premotor cortex. This study examined how the level of motor expertise (expert vs. novice) in ballroom dancing and the visual viewpoint (internal vs. external viewpoint) influence this activation within different parts of this area of the brain. Results Sixteen dance experts and 16 novices observed ballroom dance videos from internal or external viewpoints while lying in a functional magnetic resonance imaging scanner. A conjunction analysis of all observation conditions showed that action observation activated distinct networks of premotor, parietal, and cerebellar structures. Experts revealed increased activation in the ventral premotor cortex compared to novices. An internal viewpoint led to higher activation of the dorsal premotor cortex. Conclusions The present results suggest that the ventral and dorsal premotor cortex adopt differential roles during action observation depending on the level of motor expertise and the viewpoint.

Research on motor imagery and action observation has become increasingly important in recent years particularly because of its potential benefits for movement rehabilitation and the optimization of athletic performance (Munzert et al., 2009). Motor execution, motor imagery, and action observation have been shown to rely largely on a similar neural network in motor and motor-related cortical areas (Jeannerod, 2001). Given that motor imagery is a covert stage of an action and its characteristics, it has been assumed that modifying the motor task in terms of, for example, effort will impact neural activity. With this background, the present study examined how different force requirements influence corticospinal excitability (CSE) and intracortical facilitation during motor imagery and action observation of a repetitive movement (dynamic force production). Participants were instructed to kinesthetically imagine or observe an abduction/adduction movement of the right index finger that differed in terms of force requirements. Trials were carried out with single- or paired-pulse transcranial magnetic stimulation. Surface electromyography was recorded from the first dorsal interosseous (FDI) and the abductor digiti minimi (ADM). As expected, results showed a significant main effect on mean peak-to-peak motor-evoked potential (MEP) amplitudes in FDI but no differences in MEP amplitudes in ADM muscle. Participants’ mean peak-to-peak MEPs increased when the force requirements (movement effort) of the imagined or observed action were increased. This reveals an impact of the imagined and observed force requirements of repetitive movements on CSE. It is concluded that this effect might be due to stronger motor neuron recruitment for motor imagery and action observation with an additional load. That would imply that the modification of motor parameters in movements such as force requirements modulates CSE. [ABSTRACT FROM AUTHOR]

Experimental and theoretical studies on ratchet effects in graphene with a lateral superlattice excited by alternating electric fields of terahertz frequency range are presented. A lateral superlattice deposited on top of monolayer graphene is formed either by periodically repeated metal stripes having different widths and spacings or by interdigitated comblike dual-grating-gate (DGG) structures. We show that the ratchet photocurrent excited by terahertz radiation and sensitive to the radiation polarization state can be efficiently controlled by the back gate driving the system through the Dirac point as well as by the lateral asymmetry varied by applying unequal voltages to the DGG subgratings. The ratchet photocurrent includes the Seebeck thermoratchet effect as well as the effects of "linear" and "circular" ratchets, sensitive to the corresponding polarization of the driving electromagnetic force. The experimental data are analyzed for the electronic and plasmonic ratchets taking into account the calculated potential profile and the near field acting on carriers in graphene. We show that the photocurrent generation is based on a combined action of a spatially periodic in-plane potential and the spatially modulated light due to the near-field effects of the light diffraction. [ABSTRACT FROM AUTHOR]