Istvan Molnar-Szakacs

Music and mirror neurons: from motion to ’e’motion

The ability to create and enjoy music is a universal human trait and plays an important role in the daily life of most cultures. Music has a unique ability to trigger memories, awaken emotions and to intensify our social experiences. We do not need to be trained in music performance or appreciation to be able to reap its benefits-already as infants, we relate to it spontaneously and effortlessly. There has been a recent surge in neuroimaging investigations of the neural basis of musical experience, but the way in which the abstract shapes and patterns of musical sound can have such profound meaning to us remains elusive. Here we review recent neuroimaging evidence and suggest that music, like language, involves an intimate coupling between the perception and production of hierarchically organized sequential information, the structure of which has the ability to communicate meaning and emotion. We propose that these aspects of musical experience may be mediated by the human mirror neuron system.

Observing complex action sequences: The role of the fronto-parietal mirror neuron system.

A fronto-parietal mirror neuron network in the human brain supports the ability to represent and understand observed actions allowing us to successfully interact with others and our environment. Using functional magnetic resonance imaging (fMRI), we wanted to investigate the response of this network in adults during observation of hierarchically organized action sequences of varying complexity that emerge at different developmental stages. We hypothesized that fronto-parietal systems may play a role in coding the hierarchical structure of object-directed actions. The observation of all action sequences recruited a common bilateral network including the fronto-parietal mirror neuron system and occipito-temporal visual motion areas. Activity in mirror neuron areas varied according to the motoric complexity of the observed actions, but not according to the developmental sequence of action structures, possibly due to the fact that our subjects were all adults. These results suggest that the mirror neuron system provides a fairly accurate simulation process of observed actions, mimicking internally the level of motoric complexity. We also discuss the results in terms of the links between mirror neurons, language development and evolution.

Do You See What I Mean? Corticospinal Excitability During Observation of Culture-Specific Gestures

People all over the world use their hands to communicate expressively. Autonomous gestures, also known as emblems, are highly social in nature, and convey conventionalized meaning without accompanying speech. To study the neural bases of cross-cultural social communication, we used single pulse transcranial magnetic stimulation (TMS) to measure corticospinal excitability (CSE) during observation of culture-specific emblems. Foreign Nicaraguan and familiar American emblems as well as meaningless control gestures were performed by both a Euro-American and a Nicaraguan actor. Euro-American participants demonstrated higher CSE during observation of the American compared to the Nicaraguan actor. This motor resonance phenomenon may reflect ethnic and cultural ingroup familiarity effects. However, participants also demonstrated a nearly significant (p = 0.053) actor by emblem interaction whereby both Nicaraguan and American emblems performed by the American actor elicited similar CSE, whereas Nicaraguan emblems performed by the Nicaraguan actor yielded higher CSE than American emblems. The latter result cannot be interpreted simply as an effect of ethnic ingroup familiarity. Thus, a likely explanation of these findings is that motor resonance is modulated by interacting biological and cultural factors.

Self-processing and the default mode network: interactions with the mirror neuron system

Recent evidence for the fractionation of the default mode network (DMN) into functionally distinguishable subdivisions with unique patterns of connectivity calls for a reconceptualization of the relationship between this network and self-referential processing. Advances in resting-state functional connectivity analyses are beginning to reveal increasingly complex patterns of organization within the key nodes of the DMN – medial prefrontal cortex and posterior cingulate cortex – as well as between these nodes and other brain systems. Here we review recent examinations of the relationships between the DMN and various aspects of self-relevant and social-cognitive processing in light of emerging evidence for heterogeneity within this network. Drawing from a rapidly evolving social-cognitive neuroscience literature, we propose that embodied simulation and mentalizing are processes which allow us to gain insight into another’s physical and mental state by providing privileged access to our own physical and mental states. Embodiment implies that the same neural systems are engaged for self- and other-understanding through a simulation mechanism, while mentalizing refers to the use of high-level conceptual information to make inferences about the mental states of self and others. These mechanisms work together to provide a coherent representation of the self and by extension, of others. Nodes of the DMN selectively interact with brain systems for embodiment and mentalizing, including the mirror neuron system, to produce appropriate mappings in the service of social-cognitive demands.

Self in time: imagined self-location influences neural activity related to mental time travel

Conscious awareness of the self as continuous through time is attributed to the human ability to remember the past and to predict the future, a cogitation that has been called “mental time travel” (MTT). MTT allows one to re-experience ones own past by subjectively “locating” the self to a previously experienced place and time, or to pre-experience an event by locating the self into the future. Here, we used a novel behavioral paradigm in combination with evoked potential mapping and electrical neuroimaging, revealing that MTT is composed of two different cognitive processes: absolute MTT, which is the location of the self to different points in time (past, present, or future), and relative MTT, which is the location of ones self with respect to the experienced event (relative past and relative future). These processes recruit a network of brain areas in distinct time periods including the occipitotemporal, temporoparietal, and anteromedial temporal cortices. Our findings suggest that in addition to autobiographical memory processes, the cognitive mechanisms of MTT also involve mental imagery and self-location, and that relative MTT, but not absolute MTT, is more strongly directed to future prediction than to past recollection.

Right-hemisphere motor facilitation by self-descriptive personality-trait words

The emergent picture from the literature on the processing of self‐related information suggests that in addition to the neural mechanisms involved in recognizing ones own face, there may also be neural representations of the self that are modality independent and favour the right hemisphere. We used focal, single‐pulse transcranial magnetic stimulation in human subjects to assess cortical excitability during covert reading of self‐descriptive personality‐trait words. We hypothesized that the right hemisphere would show a greater overall facilitation to personality‐trait words than the left hemisphere. Overall, personality‐trait words led to significantly greater motor facilitation in the right hemisphere than in the left hemisphere. In addition, words rated as ‘never’ self‐characteristic yielded significant right hemisphere facilitation, and words rated as ‘always’ self‐characteristic showed a similar trend. The results are discussed in terms of the notion that the right hemisphere plays a dominant role in both self‐relevant processing and the processing of affective stimuli.

Music: a unique window into the world of autism.

Understanding emotions is fundamental to our ability to navigate the complex world of human social interaction. Individuals with autism spectrum disorders (ASD) experience difficulties with the communication and understanding of emotions within the social domain. Their ability to interpret other peoples nonverbal, facial, and bodily expressions of emotion is strongly curtailed. However, there is evidence to suggest that many individuals with ASD show a strong and early preference for music and are able to understand simple and complex musical emotions in childhood and adulthood. The dissociation between emotion recognition abilities in musical and social domains in individuals with ASD provides us with the opportunity to consider the nature of emotion processing difficulties characterizing this disorder. There has recently been a surge of interest in musical abilities in individuals with ASD, and this has motivated new behavioral and neuroimaging studies. Here, we review this new work. We conclude by providing some questions for future directions.

Disturbances of self-other distinction after stimulation of the extrastriate body area in the human brain

Abstract In a recent experiment with functional magnetic-resonance imaging, we found that brain activity in the extrastriate body area (EBA) distinguished between observed self- and other-generated movements, being significantly higher during observation of someone elses movement. Here, we investigated further the role of EBA in self–other distinctions using low-frequency repetitive transcranial magnetic stimulation (rTMS). As compared with rTMS applied over a control site, rTMS applied over the EBA increased reaction times, without affecting accuracy, for the detection of other-generated movements. Performance on a control motion-direction detection task was unaffected. These findings provide additional evidence for the role of the EBA in processing information necessary for identifying ourselves as agents of self-generated movements.

Exploring the contributions of premotor and parietal cortex to spatial compatibility using image-guided TMS.

Functional brain imaging studies have demonstrated increased activity in dorsal premotor and posterior parietal cortex when performing spatial stimulus-response compatibility tasks (SRC). We tested the specific role of these regions in stimulus-response mapping using single-pulse transcranial magnetic stimulation (TMS). Subjects were scanned using functional magnetic resonance imaging (fMRI) prior to the TMS session during performance of a task in which spatial compatibility was manipulated. For each subject, the area of increased signal within the regions of interest was registered onto their own high-resolution T1-weighted anatomic scan. TMS was applied to these areas for each subject using a frameless stereotaxic system. Task accuracy and reaction time (RT) were measured during blocks of compatible or incompatible trials and during blocks of real TMS or sham stimulation. On each trial, a single TMS pulse was delivered at 50, 100, 150, or 200 ms after the onset of the stimulus in the left or right visual field. TMS over the left premotor cortex produced various facilitatory effects, depending on the timing of the stimulation. At short intervals, TMS appeared to prime the left dorsal premotor cortex to select a right-hand response more quickly, regardless of stimulus-response compatibility. The strongest effect of stimulation, however, occurred at the 200-ms interval, when TMS facilitated left-hand responses during the incompatible condition. Facilitation of attention to the contralateral visual hemifield was observed during stimulation over the parietal locations. We conclude that the left premotor cortex is one of the cortical regions responsible for overriding automatic stimulus-response associations.

Searching for an integrated self-representation

Recent inquiries into the nature of self-representation have put forward a new and interesting conceptualization of the Self, as a “center of gravity” of one’s private and social behavior. We review recent neuroimaging work that has suggested interactions among brain regions comprising the default state network, including medial and temporo-parietal cortical regions and the mirror neuron system including lateral fronto-parietal regions as two interacting neural systems that work in concert to produce a cohesive self-representation through simulation. Simulation processes—broadly construed here as using existing representations as templates for understanding novel information—are instantiated by these brain systems across a wide range of domains including time, space, physical and social, giving rise to the multi-faceted Self that we all are. Accumulating evidence also suggests, that these simulation processes are used in a multitude of cognitions that constitute the self, including autobiographical memory and prospection, perspective taking, understanding other’s actions and mental states and embodied self-representation.