Neural correlates of individual differences in manual imitation fidelity

Abstract

Imitation is crucial for social learning, and so it is important to identify what determines between-subject variability in imitation fidelity. This might help explain what makes some people, like those with social difficulties such as in autism spectrum disorder (ASD), significantly worse at performance on these tasks than others. A novel paradigm was developed to provide objective measures of imitation fidelity in which participants used a touchscreen to imitate videos of a model drawing different shapes. Comparisons between model and participants' kinematic data provided three measures of imitative fidelity. We hypothesized that imitative ability would predict variation in BOLD signal whilst performing a simple imitation task in the MRI-scanner. In particular, an overall measure of accuracy (correlation between model and imitator) would predict activity in the overarching imitation system, whereas bias would be subject to more general aspects of motor control. Participants lying in the MRI-scanner were instructed to imitate different grips on a handle, or to watch someone or a circle moving the handle. Our hypothesis was partly confirmed as correlation between model and imitator was mediated by somatosensory cortex but also ventromedial prefrontal cortex, and bias was mediated mainly by cerebellum but also by the medial frontal and parietal cortices and insula. We suggest that this variance differentially reflects cognitive functions such as feedback-sensitivity and reward-dependent learning, contributing significantly to variability in individuals' imitative abilities as characterized by objective kinematic measures.

Keywords: correlated activity; fMRI BOLD; kinematics; manual imitation; mirror neuron areas.

Figure 1

Video stills of Rest (A) and Move/Watch (B) stimuli.

Figure 2

Still frame of video-clip showing model drawing stimuli.

Figure 3

Imitate BOLD contrast (p < 0.05 FWE-corr.).

Figure 4

(A) The two significant clusters in the negative correlation between speed accuracy (R) and BOLD response in Imitate (p < 0.05 FWE-corr.). (B) Scatter-plots for both ROIs show how speed “R” correlates to BOLD signal across participants. Average BOLD response for each condition was calculated over a 5 mm sphere around the peak of the ROI, after which Rest was subtracted from Move for each participant to reflect differential activation during Imitate.

Figure 5

Group activation found in the negative correlation between the BOLD Imitate contrast and rate of change in speed “m” (14 participants, p < 0.05 FWE-corr.).

Figure 6

Group BOLD response in positive correlation with speed RMSE data (p < 0.05 FWE-corr.).