Theory-of-mind engages brain autobiographical memory mechanisms when inferring the mental states of familiar people

Theory of mind refers to one’s ability to infer mental states of other persons (what they think, feel, know and do not know, their intentions etc) that is arguably one of the most fascinating of human cognitive abilities. The constituent processes of theory of mind ability (such as being able to retrieve relevant person-specific information from memory) have remained less well known. Previous neuroimaging studies that have utilized theory-of-mind tasks have reported that there is an overlap between brain regions that are activated during theory-of-mind and autobiographical memory tasks, thus suggesting that one retrieves past personal experiences when inferring mental states of other persons. In contrast, however, brain lesions studies have shown that theory of mind ability is not necessarily disrupted in amnesic patients.

In their recent neuroimaging study, Rabin and Rosenbaum (2012) addressed the question of whether the reliance on autobiographical memory during theory-of-mind tasks depends on whether or not the person about whom inferences are made is personally known. The authors requested healthy volunteers to 1) remember past experiences when presented with personal photos and 2) to imagine experiences of others to photos who were personally familiar vs. 3) unfamiliar. A spatiotemporal partial least squares analysis of the functional magnetic resonance imaging data that were acquired during these tasks revealed neural activation patterns associated with the autobiographical memory, and theory of mind tasks during the personally familiar and unfamiliar conditions.

Interestingly, there was overlap between brain activity patterns in the autobiographical memory condition and in the theory-of-mind condition that involved inference of mental states of personally known others. In contrast, brain regions associated with social semantic memory were activated during inference of mental states of unfamiliar others. Taken together the results of Rabin and Rosenbaum reveal important information about the constituent processes of theory-of-mind ability and the underlying neural mechanisms; it seems that theory-of-mind engages autobiographical memory when personally familiar others are the subjects of mental state inference, and general social semantic memory when the subject of mental state inference is an unknown person.

Reference:

Rabin JS, Rosenbaum RS. Familiarity modulates the functional relationship between theory of mind and autobiographical memory. Neuroimage (2012, available online prior to printed publication). http://dx.doi.org/10.1016/j.neuroimage.2012.05.002

Phase-synchrony metrics allow inspection of inter-subject similarity at high temporal resolution

Recent studies have demonstrated that it is possible to use feature films (see Hasson et al. 2010) and music (Alluri et al. 2012) as highly dynamic naturalistic stimuli in functional magnetic resonance imaging studies. This constitutes a highly significant step forward as it enables one to study cognitive functions that would otherwise be difficult to engage under the neuroimaging laboratory conditions such as emotions, social perception and cognition, and perception of higher-order musical features. Analysis of the resulting highly multidimensional neuroimaging data is not trivial and while functional brain activity under naturalistic viewing conditions has been successfully analyzed by calculating inter-subject correlations of hemodynamic data, inspection of temporal dynamics of inter-subject similarity using inter-subject correlation has been challenging as the correlations have to be calculated over sliding time windows of ~10-20 seconds.

Glerean et al. 2012 show that it is possible to increase temporal resolution by using instantaneous phase synchronization rather than inter-subject correlation as the measure of dynamic (time-varying) functional connectivity. In their study, Glerean et al. applied inter-subject phase-synchrony on a functional magnetic resonance imaging dataset obtained while 12 healthy volunteers watched a feature film. In addition, they compared across-subject similarities of phase-synchrony that take place between brain areas (similarly to the widely used seed-voxel correlation method that also suffers from compromised temporal accuracy), denoting this as seed-based inter-subject phase-synchrony.

The findings of Glerean et al. suggest that the tested phase-synchrony metrics yield results that are consistent with both seed-based correlation and inter-subject correlation methods when inspected over the whole duration of the movie, but provide superior (an order of magnitude better) temporal resolution for estimates of how similarly brains of individual subjects are processing the various features and events of the movie. These results thus provide a significant methodological step forward in making it possible to use highly naturalistic stimuli in neuroimaging studies and remarkably broaden the possibilities of cognitive neuroimaging. The matlab algorithms for calculating the phase-synchrony metrics of functional magnetic resonance imaging data are freely downloadable from http://becs.aalto.fi/bml/software.html

References: 

Alluri V, Toiviainen P, Jääskeläinen IP, Glerean E, Sams M, Brattico E.Large-scale brain networks emerge from dynamic processing of musical timbre, key and rhythm. Neuroimage (2012) 59: 3677-3689. http://dx.doi.org/10.1016/j.neuroimage.2011.11.019

Glerean E, Salmi J, Lahnakoski JM, Jääskeläinen IP, Sams M. FMRI phase synchronization as a measure of dynamic functional connectivity. Brain Connectivity (2012) (epublication ahead of print May 4). http://dx.doi.org/10.1089/brain.2011.0068

Hasson U, Malach R, Heeger DJ. Reliability of cortical activity during natural stimulation. Trends in Cognitive Sciences (2010) 14: 40-48. http://dx.doi.org/10.1016/j.tics.2009.10.011

Inter-individual differences in human dopamine systems predict individual differences in decision-making

Dopamine has been identified in a large number of studies as a neurotransmitter that plays a central role in decision-making. In animal studies, for example, when healthy rats are to choose between freely available less desirable food and exerting effort to obtain more desirable food, they tend to choose the latter; and blocking the dopamine system decreases, and enhancing the dopaminergic system further increases, preference to exert effort to obtain the better-tasting food. What has been less clear is whether inter-individual differences in dopamine function in humans can predict variability in decision-making.

Treadway et al. (2012) recently studied the role of dopamine in effort-based decision-making is healthy humans. In their study, healthy volunteers were scanned with positron emission tomography (using [¹⁸F]fallypride and d-amphetamine) to quantify inter-individual differences in dopaminergic function. The same subjects also underwent a so-called effort expenditure for rewards task. In this task, subjects can choose between high-effort and low-effort trials that require different amounts of speeded button presses. If successful, the participants earn a lower monetary reward in the low-effort condition, and a higher reward in the high-effort condition; however, each successfully completed trial is not rewarded, as there are no-win trials. Before making their choice between the low and high effort conditions, the subjects are indicated the probability of winning (if successful) that varies between “high” (88% of successful trials rewarded), “medium” (50%), and “low” (12%).

The positron emission tomography data showed that there were inter-individual differences in dopamine function in multiple brain structures that correlated with the results of the behavioral task. Inter-individual variation in dopamine function in the left striatum and bilateral ventromedial prefrontal cortex correlated positively with the willingness to exert greater effort to obtain larger rewards in cases where the probability of reward receipt was lower. Insula, in contrast, showed a negative correlation between dopamine function and decision-making. This latter finding is in line with findings in previous studies suggesting that insula plays a central role in processing of response costs. Taken together, these highly interesting findings show that inter-individual differences in dopamine function explain individual differences in cost-benefit decision-making in human volunteers.

Reference: Treadway MT, Buckholtz JW, Cowan RL, Woodward ND, Li R, Ansari MS, Baldwin RM, Schwartzman AN, Kessler RM, Zald DH. Dopaminergic mechanisms of individual differences in human effort-based decision-making. J Neurosci (2012) 32: 6170-6176. http://dx.doi.org/10.1523/JNEUROSCI.6459-11.2012

The six basic emotions are not culturally universal after all

In everyday life we use a plethora of words to describe various emotional states (and facial expressions) such as “upset”, “nervous”, “delighted”, “contended”, and “flabbergasted”. One of the most intriguing questions in emotion research has been which of (and to what extent) these emotions are culturally shaped, and to what extent facial expressions are universal across cultures, driven more by “nature” (i.e., human biology) than “nurture”. To solve this question, emotion researchers have looked for culturally shared basic emotions and it has become a more or less consensual view that there are six culturally universal basic emotions: happy, surprised, fearful, disgusted, angry, and sad.

In their highly interesting study, Jack et al. (in PNAS early view) report findings that challenge the view of culturally universal basic emotions. In their study, Western Caucasian and Eastern Asian subjects perceived 4800 computer-generated random facial expressions (that were based on simulated contractions of facial muscles, for a short video example of a random expression, see http://www.pnas.org/content/suppl/2012/04/12/1200155109.DCSupplemental/sm01.avi). The task of the  subjects was to categorize each of the facial expressions as either one of the six basic emotions or “don’t know” and, in case one of the six basic emotions was detected, also rate the intensity of the emotion. Based on these ratings facial action unit (muscle group) models for the six basic emotions (as well as for emotion intensity) were generated for the two cultures.

Comparison of the Western Caucasian and East Asian models revealed that the two groups perceived the six basic emotions differently and, furthermore, the intensity ratings of the emotional expressions also differed between the cultures. Specifically, Western Caucasian subjects appeared to perceive each of the six basic emotions based on a distinct set of facial muscles (as predicted based on previous studies). In contrast, in the East Asian subjects the emotion categories considerably overlapped; furthermore, for the perceived intensity of emotions, early movements of the eyes appeared to be important cues for Eastern Asian subjects in contrast to the Western Caucasian subjects. For video examples of Western Caucasian and East Asian facial expressions see http://www.psy.gla.ac.uk/~rachael/4D_FoE_Culture/. These results constitute an important step forward in emotion research and potentially also help explain misunderstandings that may arise in social interactions between representatives from different cultural backgrounds.

Reference: Jack RE, Garrod OG, Yu H, Caldara R, Schyns PG. Facial expressions of emotion are not culturally universal. Proc Natl Acade Sci USA (2012). http://dx.doi.org/10.1073/pnas.1200155109