Motor Facilitation While Observing Hand Actions: Specificity of the Effect and Role of Observer's Orientation

Abstract

Maeda, Fumiko, Galit Kleiner-Fisman, and Alvaro Pascual-Leone. Motor facilitation while observing hand actions: specificity of the effect and role of observer's orientation. J Neurophysiol 87: 1329 -1335, 2002; 10.1152/jn.00773.2000. Action observation enhances cortico-spinal excitability. Here we tested the specificity of this effect and the role played by the orientation of the observer. Ten normal subjects observed video clips of right hand performing three different finger movements (thumb ab-/adduction, index ab-/adduction, index extens-/flexion) in two different orientations (Away, i.e., natural hand-orientation facing out from the observer; or Toward, i.e., unnatural hand-orientation facing toward the observer). Motor-evoked potentials (MEPs) induced by transcranial magnetic stimulation (TMS) were recorded from the abductor pollicis brevis (APB) and the first dorsal interosseus (FDI) muscles. Movement direction of the index finger was recorded using force transducers. Facilitation of MEP size was significantly greater for APB during observation of thumb movements and for FDI during observation of index finger movements. Facilitation of MEP size was significantly greater when the hand presented on screen was facing out from and corresponding to that of the observer (Away orientation). The direction of the index finger movement evoked by TMS shifted toward extension/flexion versus ab-/adduction matching the observed movement. Our results give further evidence that observation of a movement enhances motor output to the muscles involved in the movement and facilitates the observed action. In addition, we provide novel evidence about the high degree of specificity of this observation-induced motor cortical modulation. The degree of modulation depends on hand orientation. The modulation is maximal when the observed action corresponds to the orientation of the observer.

Transcranial alternating current stimulation to the inferior parietal lobe decreases mu suppression to egocentric, but not allocentric hand movements

“…In addition, our results support a neurophysiological advantage for self-related stimuli (Jackson, Meltzoff, & Decety, 2006;Maeda, Kleiner-Fisman, & Pascual-Leone, 2002) as subsequent to IPL-stimulation, -suppression only decreased for the egocentric hands movements. Given that we observed no effect on -suppression during observation of allocentric hands movements subsequent to stimulation, we suggest that other neural mechanisms are involved in the processing of allocentric hands movements.…”

“…Typically, correlational studies investigating perspectives as an indication of self-other differentiation have shown that egocentric stimuli induce greater neurophysiological and behavioural responses compared to allocentric stimuli. For example, it has been observed: greater cortical activity in the sensorymotor cortex (Jackson et al, 2006), greater visuomotor interference (Bortoletto et al, 2013;Vogt et al, 2003) and larger motor-evoked potentials (MEPs) as induced by transcranial magnetic stimulation (TMS) during the observation of egocentric movements (Maeda et al, 2002). However, these correlational reports have not always been consistent; Alaerts and colleagues (2009) reported that MEPs are not necessarily larger for egocentric movements per se; rather, MEP's are larger for an egocentric right hand and for an allocentric left hand.…”

The functional role of the parieto-frontal mirror circuit: interpretations and misinterpretations

“…both these assumptions are hard to reconcile with what is known about the organization of the cerebral cortex. Most importantly, TMS studies have shown a clear congruence between the observed motor act and the activated motor representation [32][33][34][35][36] . Thus, if higher-order sensory information describing a motor act reaches motor neurons that encode that same motor act, these motor neurons are mirror neurons by definition.…”

“…The initial evidence for this mechanism was based on TMS experiments which indicated that the observation of the movements of others results in an activation of the muscles involved in the execution of those movements [32][33][34][35][36] . Additional support comes from eeG and MeG studies showing that the observation of movements without a goal desynchronizes the rhythms recorded from motor areas [57][58][59][60][61][62][63][64] .…”

Release of premotor activity after repetitive transcranial magnetic stimulation of prefrontal cortex

“…This internal PMC representation is probably used for their understanding Fadiga, Fogassi, Pavesi, & Rizzolatti, 1995;Grafton, Arbib, Fadiga, & Rizzolatti, 1996;Grè zes, Armony, Rowe, & Passingham, 2003;Grè zes, Costes, & Decety, 1999;Hari et al, 1998;Iacoboni et al, 1999;Kohler et al, 2002;Maeda, Kleiner-Fisman, & Pascual-Leone, 2002). This passive automatic activation of PMC-motor circuits, without the production of an actual movement, seems to be the counterpart of the compelling tendency to move of the PFC-lesioned patients.…”