Mental rotation strategies reflected in event-related ( de ) synchronization of alpha and mu power

During a mental rotation task of hands, participants mentally rotate their hand into the orientation of the shown hand. These mental movements are subject to the body’s biomechanical constraints. In this study, we investigated whether the involvement of motor processes during the mental rotation process, as reflected in mu-power desynchronization, is also influenced by one’s movement capabilities. We performed an EEG study and used a delayed response mental rotation task of hands to examine the event-related desynchronization differences between movements that are biomechanically easy and difficult to perform. Our results show an increase in event-related desynchronization of the mu power for biomechanically easy compared to difficult-to-adopt postures. These findings provide further evidence for the notion that motor simulations can only be performed for movements that can already be performed overtly. Descriptors: Mental rotation, Motor imagery, EEG, Event-related desynchronization, Event-related synchronization During a mental rotation task, participants mentally rotate a shown stimulus, for example, a hand, in order to judge whether that stimulus is a left or a right hand. During the mental rotation of hands, participants typically imagine moving their own hand into the orientation of the shown stimulus in order to judge its laterality (Parsons, 1987, 1994; Sekiyama, 1982, 1987). The participant’s performance during a mental rotation task of hands is influenced by one’s own body posture (de Lange, Hagoort, & Toni, 2005; de Lange, Helmich, & Toni, 2006; Helmich, de Lange, Bloem, & Toni, 2007; Ionta & Blanke, 2009; Ionta, Fourkas, Fiorio, & Aglioti, 2007; Sirigu & Duhamel, 2001), movement constrictions (i.e., biomechanical constraints) (Parsons, 1987, 1994; ter Horst, van Lier, & Steenbergen, 2010, 2011; Tomasino & Rumiati, 2004), and pathologies related to the motor system (de Lange, Roelofs, & Toni, 2008; Funk & Brugger, 2008; Harris, Harris, & Caine, 2002; Helmich et al., 2007; Lust, Geuze, Wijers, & Wilson, 2006; Moseley et al., 2008; Mutsaarts, Steenbergen, & Bekkering, 2007; Nico, Daprati, Rigal, Parsons, & Sirigu, 2004; Sirigu & Duhamel, 2001; ter Horst, Cole, van Lier, & Steenbergen, 2012). These findings exemplify the embodied nature of the mental process during the mental rotation task of hands. This process is also referred to as motor imagery (MI). During MI, an action is internally simulated including the kinesthetic sensations but without the overt movement part (Decety, 1996a, 1996b; Guillot & Collet, 2010; Jeannerod, 1994). As stated in the simulation theory (Jeannerod, 2001), MI is similar to actual movements and has been shown to activate similar neuronal processes as actual movement (Jeannerod, 1994, 2001; see, for review, Jeannerod, 2006). In contrast to motor imagery, visual imagery (VI) encompasses mental visual transformations of (non-)corporeal objects without a kinesthetic sensation (Guillot & Collet, 2010). Consequently, VI is not subject to biomechanical constraints or postural changes (de Lange et al., 2005). The influences of the biomechanical constraints on the mental rotation of hands has been studied extensively on a behavioral level by Parsons (1987, 1994). It was shown that participants are faster in judging the laterality of hands oriented in anatomically easier-toadopt postures (i.e., medial rotations) than more difficult-to-adopt postures (i.e., lateral rotations). Medial and lateral rotations are hands rotated towards and away from the body’s midsagittal plane, respectively, see Figure 1. The influence of biomechanical constraints on the mental rotation process is seen as evidence for the use of MI (Parsons, 1987, 1994; ter Horst, Jongsma, Janssen, van Lier, & Steenbergen, 2012; ter Horst et al., 2010, 2011). Parsons (1987) scrutinized the influence of the biomechanical constraints on the mental movements by showing that participants are likely to use different mental movement paths for internally rotating one’s hands medially or laterally. The selection of a movement path is based on anatomically induced movement constraints. Medial rotations, especially when rotating one’s hand with the palm in view, are biomechanically easy to perform. In contrast, lateral rotations are biomechanically difficult or even impossible to perform. From the literature, it is already known that experience with performing a movement is mandatory to be able to internally simulate that movement (Munzert, Lorey, & Zentgraf, 2009). Consequently, for medial rotations, it is likely that the corresponding motor simulations can be performed. For lateral rotations, on the other hand, experience with the movement is lacking, and hence it is unlikely that an accompanying motor simulation can be performed. The Address correspondence to: Arjan C. ter Horst, Radboud University Nijmegen, Donders Institute for Brain, Cognition, and Behaviour, Centre for Cognition, P.O. Box 9104, 6500 HE Nijmegen, The Netherlands. E-mail: a.terhorst@donders.ru. nl bs _b s_ ba nn er Psychophysiology, 50 (2013), 858–863. Wiley Periodicals, Inc. Printed in the USA. Copyright © 2013 Society for Psychophysiological Research DOI: 10.1111/psyp.12076