Investigating the Cognitive Neuropsychology of Social Perception and Reasoning

Abstract

The neural processes by which we perceive and understand our complex social world are currently somewhat of a mystery. This thesis used electroencephalography (EEG) to investigate the potential involvement of the mirror neuron system (MNS) and default-mode network (DMN) in social cognition. The three experiments contained herein investigated function of these networks during a variety of social cognition tasks using two proposed EEG correlates: mu suppression for the MNS, and frontal theta suppression for the DMN. The same 20 participants were tested during all three experiments. For all experiments the general hypotheses were that both mu suppression and frontal theta suppression would be detected during social cognition. Mu power was assessed as log mean spectral power in the 7.5-12.5Hz band at electrodes C3 and C4. Frontal theta suppression was assessed using log mean spectral power in the 4-7Hz band at Fz. Additionally, Exact Low Resolution Electromagnetic Tomography (eLORETA) was used to more precisely locate the sources of differences in spectral power. Experiment 1 compared activity during a social reasoning tasks to activity during the solving of physics problems. The hypotheses were partially supported for this experiment. Mu suppression was found during social reasoning, even when the task was presented as a textual vignette. No support was found for frontal theta suppression as a correlate of DMN activity. Experiment 2 investigated activity while participants used a button press to identify emotions from facial expressions. The hypotheses were again partially supported. Robust mu suppression was associated with facial emotion processing, but no frontal theta suppression was detected. Experiment 3 investigated activity during imitation of facial expressions. Neither mu suppression nor theta suppression were associated with the facial imitation task, failing to support either hypothesis. Taken together, the results of the first two experiments offered partial support for the current model of the MNS, and the validity of mu suppression as its correlate. However no mu suppression was detected during imitation, often considered a central function of the MNS. This result indicates that the current model of the MNS and/or mu suppression may not adequately explain the social cognition process. The most likely source of the mu activity in this thesis was found by eLORETA to be the lateral postcentral gyri. No frontal theta suppression was detected during social cognition in any of the experiments, perhaps indicating that it is not a strong enough correlate to be used in EEG studies of the DMN.