Authors: Alena Streltsova Cristina Berchio Vittorio Gallese Maria Alessandra Umilta’
Publish Date: 2010/08/03
Volume: 205, Issue: 3, Pages: 363-373
Abstract
The main aim of the present study was to explore by means of highdensity EEG the intensity and the temporal pattern of eventrelated sensorymotor alpha desynchronization ERD during the observation of different types of hand motor acts and gestures In particular we aimed to investigate whether the sensorymotor ERD would show a specific modulation during the observation of hand behaviors differing for goalrelatedness hand grasping of an object and meaningless hand movements and social relevance communicative hand gestures and grasping within a social context Time course analysis of alpha suppression showed that all types of hand behaviors were effective in triggering sensorymotor alpha ERD but to a different degree depending on the category of observed hand motor acts and gestures Meaningless gestures and hand grasping were the most effective stimuli resulting in the strongest ERD The observation of social hand behaviors such as social grasping and communicative gestures triggered a more dynamic time course of ERD compared to that driven by the observation of simple grasping and meaningless gestures These findings indicate that the observation of hand motor acts and gestures evoke the activation of a motor resonance mechanism that differs on the basis of the goalrelatedness and the social relevance of the observed hand behaviorGastaut and coworkers first described the desynchronization of an EEG rhythm within the alpha band 8–13 Hz recorded from central electrodes occurring not only during the execution of active movements but also during their observation CohenSeat et al 1954 Gastaut and Bert 1954 This result was confirmed many years later by Cochin et al 1998 1999 Altschuler et al 1997 2000 using EEG recordings and by Hari et al 1998 using magnetoencephalography MEG In particular Hari and coworkers demonstrated that the desynchronization during action observation includes rhythms originating from the cortex inside the central sulcus Hari and Salmelin 1997 Salmelin and Hari 1994 for a review see Pineda 2005It has been proposed that the suppression of the sensorymotor alpha rhythm also termed as eventrelated desynchronization ERD during action execution and observation could be due to a neurophysiological mechanism of motor resonance the mirror mechanism likely due to the activation of neurons endowed with properties similar to those of mirror neurons discovered in the premotor and posterior parietal cortices of macaque monkeys Mirror neurons discharge both during the execution of goalrelated motor acts and during their observation when executed by others Di Pellegrino et al 1992 Gallese et al 1996 Rizzolatti et al 1996A growing body of research showing that a number of human cortical areas are activated by both action execution and observation supports the existence of a mirror mechanism in humans These cortical areas include the lower part of precentral gyrus the posterior part of inferior frontal gyrus IFG and the rostral part of the inferior parietal lobule for a review see Rizzolatti and Craighero 2004 Gallese et al 2004 Cattaneo and Rizzolatti 2009 Recently evidence at the single neuronlevel about the existence of the mirror mechanism in the human brain was provided Mukamel et al 2010Several neuroimaging studies have reported the activation of distinct cortical regions within premotor and posterior parietal cortices during the observation/execution of goalrelated hand mouth and foot actions Buccino et al 2001 AzizZadeh et al 2006 during the observation/execution of meaningless hand movements Lui et al 2008 Villarreal et al 2008 during the execution of a noisy action and listening to the corresponding sound Gazzola et al 2006 Few studies have demonstrated communicative face and hand actions showing an activation of cortical regions endowed with mirror properties Nakamura et al 1999 Nakamura et al 2004 Montgomery et al 2007 Villarreal et al 2008Recent EEG studies of the mirror mechanism have shown that the observation and execution of a motor act is accompanied by an eventrelated alpha desynchronization ERD reflected in a relative decrease in power of sensorymotor alpha 8–13 Hz and beta 13–30 Hz frequency bands Hari 2006 More generally ERD reflects a cortical deactivation which depends on the task and it is usually measured with respect to the baseline that contains a clear peak in the frequency band of interest Pfurtscheller and Lopes da Silva 1999 Klimesch 1999 It has been shown that during movement execution ERD reflects an inhibition of the motor cortex and has a premovement onset Pfurtscheller and Lopes da Silva 1999 Calmels et al 2006 for review see Pineda 2005 Several EEG studies have shown sensorymotor alpha ERD during the observation of different types of grasping Muthukumaraswamy et al 2004 Muthukumaraswamy and Johnson 2004a Perry and Bentin 2009 meaningless gestures Babiloni et al 2002 and sequential finger movements Calmels et al 2006 Recent EEG studies aiming to investigate sensorymotor alpha suppression during the observation of more complex stimuli such as social interaction scenes body movements from different perspectives and dance performance have shown that alpha ERD can be modulated by the degree of social relevance Kilner et al 2006 Oberman et al 2007b and by the motor expertise of the observer Orgs et al 2008 Babiloni et al 2009 Furthermore recent findings demonstrate the existence of an observation/execution matching system even in infants and young children Lepage and Théoret 2006 Southgate et al 2009 2010The main aim of the present study was to explore by means of highdensity EEG the sensitivity of sensorymotor ERD during the observation of different types of hand motor acts and gestures In particular we aimed to investigate the specificity of sensorymotor ERD for processing hand behaviors differing along two dimensions their goalrelatedness and social relevanceAll participants also performed a control motor execution task Similarly to other studies Muthukumaraswamy and Johnson 2004a Southgate et al 2009 2010 the aim of the motor task keypress was to identify the frequency band that was functionally related to motor activation in each individual participant
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