The self and social cognition: the role of cortical midline structures and mirror neurons Lucina Q. Uddin1,2, Marco Iacoboni3, Claudia Lange4 and Julian Paul Keenan4 1 Department of Psychology, University of California, Los Angeles, Box 951563, 1285 Franz Hall, Los Angeles, CA 90095, USA 2 The Phyllis Green and Randolph Cowen Institute for Pediatric Neuroscience, New York University Child Study Center, New York, NY10016, USA 3 Ahmanson-Lovelace Brain Mapping Center, Department of Psychiatry and Biobehavioral Sciences, Neuropsychiatric Institute, Brain Research Institute, David Geffen School of Medicine at the University of California, Los Angeles, 660 Charles E. Young Drive South, Los Angeles, CA 90095, USA 4 Cognitive Neuroimaging Laboratory, 219 Dickson Hall, Department of Psychology, Montclair State University, Upper Montclair, NJ 07043, USA Recent evidence suggests that there are at least two large-scale neural networks that represent the self and others. Whereas frontoparietal mirror-neuron areas pro- vide the basis for bridging the gap between the physical self and others through motor-simulation mechanisms, cortical midline structures engage in processing infor- mation about the self and others in more abstract, evaluative terms. This framework provides a basis for reconciling findings from two separate but related lines of research: self-related processing and social cognition. The neural systems of midline structures and mirror neurons show that self and other are two sides of the same coin, whether their physical interactions or their most internal mental processes are examined. Introduction The search for the neural correlates of self-related cognition has developed at an almost feverish pitch. In their attempts to isolate specific brain regions or networks, researchers have identified several strong candidates for creating, sup- porting and maintaining the self. In parallel, researchers in the domain of social-cognitive neuroscience have described several brain regions that support various aspects of social interaction and representation of others [1���4]. A network composed of cortical midline structures (CMS), including the medial prefrontal cortex, the anterior cingulate cortex and the precuneus (Box 1), has been associated with self-processing [5] and social cognition [6]. Moreover, a right-lateralized frontoparietal network that overlaps with mirror-neuron areas (Box 2) seems to be involved with self- recognition [2] and socialunderstanding [7]. Anoutstanding question concerns how to tease apart the relative contri- butionsofthemirror-neuronsystem(MNS)andCMSinself- and other-representation across different domains. Here, we propose a unifying model that accounts for extant data on self and social cognition as supported by the MNS and CMS. We review evidence that suggests that a right-lateralized MNS is involved in understanding the multimodal embodied self (e.g. its face and its voice), whereas CMS seem to represent a less bodily grounded self as shaped by its social relationships. Interactions between these two systems are likely to be crucial to social functioning and might be compromised in conditions such as autism, where self-awareness and social cognition are impaired [3]. The right frontoparietal network and self History and neuropsychology of self-recognition A growing body of research suggests that a network of right frontoparietal structures is vital for generating self-aware- ness. The importance of the right hemisphere in terms of supporting the self was suggested by early researchers who presented pictures of the self-face to patients following split-brain surgery. Whereas Sperry found that the right hemisphere could recognize the self-face, Preilowski dis- covered that the right hemisphere provided a greater physiological reaction to the own-face compared with other faces and compared with left-hemisphere responses to the own-face [8]. Much progress has been made in the past 30 years, including the emergence of imaging techniques such as fMRI and transcranial magnetic stimulation (TMS). These techniques helped to reveal the special role that the right hemisphere has in self-representation and also highlighted the need for more precise definitions and con- structs. Both conceptual and methodological issues account for much of the earlier incongruent evidence with regards to laterality of self-recognition (discussed in Refs [2,8]). Patient data provide further evidence of a right frontoparietal bias for self-face and self-body processing. Mirror-sign, a condition in which patients misidentify their own face while retaining the ability to identify other faces, occurs following right frontoparietal damage [9]. Damage and clinically applied anesthesia to the right hemisphere results in anosognosia (denial that a limb is paralyzed) and asomotognosia (misidentification of one���s own limb). Stimulation of right parietal regions results in autoscopic Opinion TRENDS in Cognitive Sciences Vol.11 No.4 Corresponding author: Keenan, J.P. (keenanj@mail.montclair.edu). Available online 14 February 2007. www.sciencedirect.com 1364-6613/$ ��� see front matter �� 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.tics.2007.01.001

delusions in which one feels outside of one���s own body, or the experience that certain body parts extend or shrink. Data collected using TMS confirm these findings. TMS delivered to the right inferior parietal cortex disrupts the recognition of self-faces whereas TMS delivered to the left inferior parietal has no such influence [10]. Additional support for a localized network that enables self-awareness is derived from patients who, following a brain insult, experience either a loss of self-identity or an alteration of personality [11]. Neuroimaging of self-recognition The self-face is the most obvious embodied representation of the self. Thus, it has been most commonly used in the attempt to operationalize the term ���self��� and to investigate the brain correlates of self-awareness. When participants are presented with their own face, right frontal and right parietal networks are typically activated when compared with viewing other familiar faces [2,12���14]. Several ver- sions of this paradigm have been used, including present- ing participants with ���morphed��� (i.e. combined) versions of the self-face (Figure 1). These different forms of face pres- entation reveal a consistent activation of the right fronto- parietal network during self-face recognition [2]. In a series of recent studies, it has been shown that both the self-face and the self-body activate the right frontoparietal network [14���16]. Such activation also seems to include the self- voice, indicating that right-hemisphere activation might not be limited to the visual domain [17]. Although not all studies indicate a clear right-hemispheric bias [18], the data collected thus far indicate that self-recognition is mostly supported by right frontoparietal regions. Three recent fMRI studies [2,13,14] on self-face recognition have suggested that the right frontoparietal areas that are associated with self-recognition overlap with areas that contain mirror neurons (Box 2 Figure 2). It has been proposed that these neurons can provide a link between self and other, enabling intersubjectivity through an intentional attunement mechanism that enables the understanding of the actions and associated mental states of others through the unreflective, automatic simulation of the actions and associated mental states of the self [19]. During self-recognition, mirror-neuron areas in the perceiv- ing subject would process the perceived self (i.e. one���s own face) using a similar simulation mechanism. Here, the perceived self is mapped onto the perceiving subject���s motor repertoire. This mapping mechanism can produce an even betterfitthanthe mappingofothers ontoself, thusresulting in increased ���resonance���, which is reflected by higher fMRI activity [2]. Thus, frontoparietal mirror-neuron areas of the humanbraincaneffectivelyfunctionasbridgesbetweenself and other, by co-opting a system for recognizing the actions of others to support self-representation functions. The simulation processes that are supported by the human mirror-neuron system go a long way towards explaining action and intention understanding. However, evidence for involvement of the MNS in more abstract forms of simulation and mentalizing is lacking. Instead, CMS structures seem to be more involved in internal aspects of representing self and others, where simple motor coding is insufficient. Cortical midline structures and self A comprehensive review of the debate concerning the definition of the term ���self��� is beyond the scope of this Box 1. The default-mode network It has been well documented that certain areas of the brain (namely, the dorsal and ventral medial prefrontal cortex, precuneus and posterior lateral cortices) are characterized by high baseline metabolic activity at rest. These regions are thought to comprise a ���default mode��� of brain function, as they exhibit decreases in activity during a variety of goal-directed behaviors. Various neuroimaging techniques (e.g. PET and fMRI) have confirmed the presence of this underlying default-mode network [33]. When subjects are explicitly engaged in attention-demanding goal-directed cognitive tasks, activity in this network is attenuated. Functional-connectivity analyses suggest that this default-mode network is inversely correlated with task-specific prefrontal activations [34]. Although the exact function of the tonic activity in the default-mode network is unknown, this activity has been linked to mental processes that have been termed ���task-unrelated imagery and thought��� (TUITs) [35]. Such thoughts often take the form of autobiographical reminis- cences, self-referential thought or inner speech. However, in some cases, increased activity, compared to rest in the default-mode network, has been documented during tasks of a social nature [26,36]. This suggests that both self-directed and socially oriented thoughts are implemented in the default-mode network. Box 2. The mirror-neuron system Mirror neurons were initially discovered in the macaque ventral premotor cortex [37]. These cells discharge during goal-oriented hand actions, such as grasping, tearing and holding. They also discharge during ingestive and communicative mouth actions, such as sucking and lip-smacking. The discharge of these cells typically occurs throughout the whole action and is not associated with the contraction of specific muscles. In addition, mirror neurons can fire during actions that are performed with different body parts. For instance, they can fire during grasping actions that are performed with the left hand, the right hand and even the mouth. However, mirror neurons often discriminate between different types of grips. Typically, mirror neurons that discharge during precision grips (i.e. the grasping of a small object that is performed with the opposition of the thumb and the index finger) do not fire during whole-hand grasps of larger objects, and vice versa [38]. Mirror neurons also discharge in association with visual and auditory stimuli. A mirror neuron that is active during the execution of a particular action will respond to the sight of similar actions. For instance, if a mirror neuron discharges during the execution of precision grips, it will also fire when the monkey observes somebody else grasping a small object with a precision grip [37,38]. The auditory stimuli that trigger the firing of mirror neurons are sounds that are associated with the actions coded by these neurons in motor terms. For instance, if a mirror neuron fires while the monkey breaks a peanut and while the monkey observes somebody else breaking a peanut, it will also fire if the monkey hears the sound of breaking a peanut [39]. The visual and auditory responses of mirror neurons are specific to these kinds of stimuli. This pattern of neuronal firing suggests that these neurons code agent-independent actions in rather abstract terms. Thus far, there is evidence for mirror neurons in two anatomically connected cortical areas in the macaque brain: area F5 in the ventral premotor cortex and area PF/PFG in the rostral part of the inferior parietal lobule [38]. The human mirror-neuron system ��� revealed by a variety of fMRI [40], magnetoencephalography (MEG) [41], transcranial magnetic stimulation (TMS) [42] and EEG [43] studies ��� is analogously composed by two cortical areas in the inferior frontal cortex and in the rostral part of the inferior parietal lobule. In humans, the mirror-neuron system is strongly associated with imitative behavior [44] and social cognition [4]. 154 Opinion TRENDS in Cognitive Sciences Vol.11 No.4 www.sciencedirect.com