Does focusing on hand-grasping intentions modulate electroencephalogram l and a suppressions? Anat Perry a and Shlomo Bentin a,b Understanding the intentions of others presumably involves a human analog of the mirror neuron system. A putative marker of such mirror activity is the suppression of electroencephalographic oscillations in the 8–12 Hz range, which, when recorded over somatosensory areas, is associated with motor activity and labeled l rhythms. We investigated whether l-suppression can be modulated by attention to another person’s intention as expressed by her hand movement toward an object and whether this suppression is distinguished from the suppression of a waves that oscillate in the same frequency range and are modulated by attention and cognitive load. Both l and a suppressions were modulated by task difficulty, and not distinctively by intention, reflecting the recruitment of resources needed for task performance. NeuroReport 21:1050–1054  c 2010 Wolters Kluwer Health | Lippincott Williams & Wilkins. NeuroReport 2010, 21:1050–1054 Keywords: a rhythms, electroencephalography, grasping, intention, mirror neuron system, l rhythms a Department of Psychology and b Interdisciplinary Center for Neural Computation Hebrew University, Jerusalem, Israel Correspondence to Anat Perry, Department of Psychology, Hebrew University, Jerusalem, 91905 Israel Tel: + 972 2 5883589; fax: + 972 2 5825659; e-mail: anat.perry@mail.huji.ac.il Received 21 July 2010 accepted 23 August 2010 Introduction The discovery of the mirror neuron system (MNS), which is active in the monkey during the observation and the execution of an action [1–3], established the biological plausibility of a link between perception and action, which has been frequently predicated by cognitive psychologists [4]. To this end, researchers proposed that an analog MNS also exists in humans (hMNS), in whom it may have evolved into a more complex network, expanding its role to form the basis for imitation [5], language development [6], and even higher-level social skills such as understanding others’ emotions and providing the basis for empathy [7]. The contribution of a mirror-like system to efficient social interaction has received additional support from functional magnetic resonance imaging (fMRI) studies, showing that brain activity in regions corresponding to the putative hMNS are involved in understanding the intentions of observed actions [8,9]. For instance, viewing hand-grasping actions embedded in contexts that implied the intention of the action, yielded higher blood–oxygen- level-dependent signal than viewing the same hand actions without a context or viewing the context without the hand movement [8]. Furthermore, the synergy between the type of grasp observed and the type of context in which the action occurred was indicated by greater activity when the type of grasp suggested the same intention as the context than when the action and the context were incongruent [9]. These studies played an important role in linking the hMNS to the under- standing of intentions, suggesting that the motor system infers a forthcoming new goal in an automatic way, through simulation of the other’s motor acts. One aim of this study was to corroborate this link and extend the fMRI findings. Putative evidence for an hMNS has also been found using electrophysiological measures such as the modulation of motor-evoked potentials elicited by transcranial magnetic stimulation [10], intracranial single-unit recordings [11], magnetoencephalography [12], and electroencephalogra- phy (EEG). The last line of research focused particularly on the modulation of EEG oscillations within the range of 8–12 Hz. Given their presumed sources in the somato- motor cortex, these oscillations had been labeled as Rolandic or ‘m’ rhythms [13]. The suppression of m rhythms is considered to reflect event-related desynchronization of the EEG induced by an enhancement of neural activity in somato-motor and prefrontal cortex leading to asynchronous neural firing [13]. This manifestation is analogous to the desynchro- nization of EEG-a oscillations by visual input, increased attention and/or mental load [14]. It should be noted, however, that although in the same frequency range, the modulation of m rhythms differs from that of the a rhythms in several ways. First, in contrast to a rhythms, m rhythms are not modulated primarily by visual stimula- tion or attention, but rather are desynchronized and their power attenuated during motor activity [15] and, crucially, also during the observation of actions executed by other humans, but not by nonbiological motion [16–19]. Second, the modulation of m is usually seen in more anterior areas (largely recorded over the sensorymotor cortex) compared with the more posterior (parieto-occipital) distribution, in which a suppression is characteristically measured [13]. 1050 Cognitive neuroscience and neuropsychology 0959-4965  c 2010 Wolters Kluwer Health | Lippincott Williams & Wilkins DOI: 10.1097/WNR.0b013e32833fcb71 Copyright © Lippincott Williams & Wilkins. Unauthorized reproduction of this article is prohibited.