Thursday, July 26, 2007

Talk to the Hand and Just Say No


A new fMRI paper (Grosbras et al., 2007) examined the hemodynamic response [an indirect reflection of neural activity] in 10 yr old children who were watching videos of angry faces and gestures (versus neutral faces and gestures and control stimuli, see Fig 1 below). The authors wanted to see whether there were differences in the way that kids who are susceptible to peer pressure respond to these stimuli, relative to those who are resistant to peer pressure. The kids who are better able to resist peer pressure [at least, as measured by self-report on Steinberg and Monahan's resistance to peer influence questionnaire] showed more "coordinated" neural activity across a network of brain regions related to decision making and the perception of action than did the more easily influenced kids.

Fig 1 (Grosbras & Paus, 2006). Stimuli. Snapshots were taken at the beginning of representative clips of each condition. The video clips were displayed at 30 frames/s. Two consecutive images on the figure are separated by five frames.

Across all 35 participants [the data from 11 were thrown out due to excessive head motion],
the observation of hand movements engaged frontoparietal and middle temporal regions. Angry hand movements also recruited part of the parietal operculum/supramarginal gyrus, the medial prefrontal cortex, and the amygdala. The observation of angry or neutral faces engaged the premotor cortex, various parts of the inferior and medial frontal cortex, the fusiform cortex, the superior temporal sulcus, and the amygdala.
Next, an inverse correlation between RPI score and increased activity while watching angry hand or face movements (relative to neutral) was noted in the right dorsal premotor cortex and the left mid-dorsolateral prefrontal cortex. This means the less able to resist peer pressure, the greater the activity in those frontal areas. Hmm.
More sensitive children might engage more attentional resources when presented with salient stimuli such as angry hand movements.
OK, then. The children with high RPI scores (better able to resist peer pressure) showed greater functional connectivity (interregional correlations as determined by partial least-square analysis) between
both (1) regions involved in action observation, from the frontoparietal as well as from the temporo-occipital system..., and (2) regions in the prefrontal cortex.
What does this mean? Didn't we see greater frontal activity in the "just say yes" children?
It is important to note the difference between the findings obtained with univariate and multivariate analyses here. Univariate, voxel-by-voxel correlation between the fMRI signal and RPI scores showed a more robust response in low-resistance children independently in the premotor cortex and the prefrontal cortex. The multivariate analysis, in contrast, revealed stronger interregional correlations, or functional connectivity, between these and other regions in high-resistance children. We speculate that these two phenomena reflect, respectively, higher sensitivity of low-resistance children to socially relevant input and higher interregional integration of such inputs in high-resistance children. It is possible that the brains of the children with high RPI engage automatically executive processes when challenged with relatively complex and socially relevant stimuli. Interestingly, the children with higher RPI were also those who performed better in (explicit) executive tasks.
SO the kids who are better able to resist peer-pressure showed better executive control functions (no surprise there) and a higher correlation between prefrontal and posterior brain activity in response to those angry hands.

References

Grosbras M, Paus T. (2006) Brain networks involved in viewing angry hands or faces. Cereb Cortex 16:1087–1096.

Grosbras M-H, Jansen M, Leonard G, McIntosh A, Osswald K, Poulsen C, Steinberg L, Toro R, Paus T. (2007). Neural Mechanisms of Resistance to Peer Influence in Early Adolescence. J. Neurosci. 27:8040-8045.

During the shift from a parent-dependent child to a fully autonomous adult, peers take on a significant role in shaping the adolescent's behavior. Peer-derived influences are not always positive, however. Here, we explore neural correlates of interindividual differences in the probability of resisting peer influence in early adolescence. Using functional magnetic resonance imaging, we found striking differences between 10-year-old children with high and low resistance to peer influence in their brain activity during observation of angry hand movements and angry facial expressions: compared with subjects with low resistance to peer influence, individuals with high resistance showed a highly coordinated brain activity in neural systems underlying perception of action and decision making. These findings suggest that the probability of resisting peer influence depends on neural interactions during observation of emotion-laden actions.

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