Aperiodic activity masks sensorimotor mu suppression during human action observation

Area of Science:

• Neuroscience
• Cognitive Science
• Social Neuroscience

Background:

• The mu rhythm (8-14 Hz) in electroencephalography (EEG) typically decreases during action execution (AE).
• Mu suppression during action observation (AO) has been proposed to reflect a 'mirror neuron' system, crucial for social perception.
• Previous AO studies show mixed results, potentially due to methodological issues and confounds like attention and perception, as well as the influence of underlying aperiodic neural activity.

Purpose of the Study:

• To investigate the influence of aperiodic neural activity on mu suppression during both AE and AO.
• To clarify the role of the mu rhythm in social perception by controlling for confounds and aperiodic noise.
• To re-evaluate the robustness of mu suppression during AO in a large sample.

Main Methods:

• Utilized 128-channel EEG in a large sample (N=109) during both AE and AO tasks.
• Implemented appropriate visual and attentional controls during the AO task.
• Analyzed the EEG power spectrum, specifically examining the impact of removing the aperiodic (1/f-like) component on periodic oscillations like the mu rhythm.

Main Results:

• Consistent mu suppression was observed during AE.
• Initial analysis of AO data did not reveal significant mu suppression, suggesting attentional and perceptual confounds.
• After removing the aperiodic neural activity component, significant mu suppression was restored over central electrodes during AO.
• The observed mu suppression during AO was less robust than previously reported, with aperiodic activity contributing to variability.

Conclusions:

• Aperiodic neural activity can significantly influence the estimation of mu suppression in EEG.
• While mu suppression during AO is present, its effect is less pronounced than previously assumed, challenging its role as a direct index of motor contributions to social perception.
• Careful methodological considerations, including accounting for aperiodic activity, are crucial for accurate interpretation of mu rhythm changes during action observation.