Transcranial alternating current stimulation to areas associated with the human mirror neuron system reveals modulation to mu-suppression and corresponding behaviour

This study was carried out in order to validate the use of EEG mu (μ) suppression as an index of human mirror neuron system (hMNS) related activity. The hMNS is characterized by neuronal activity that responds to both action observation and execution of the same movement. This activity has been directly observed in both macaque monkeys and in humans. There is an abundance of studies using indirect measures of neuronal activity to indicate hMNS-related activity such as TMS, fMRI/PET and EEG/MEG. However, relating indirect indices of neuronal activity to a conceptual group of neurons is controversial because the activity observed could also reflect other neuronal processes. Therefore, the current thesis was designed to establish more direct and causal evidence for the use of EEG in indicating hMNS-related activity through the use of transcranial alternating current stimulation (tACS). This was achieved in six experiments; the first three established an efficient protocol to induce μ-suppression during action observation, and the last three demonstrated by means of tACS that activity in hMNS-related areas is directly related to μ-reactivity during observation of motor movements and in relation to imitation of the movement observed. To this extent, μ-suppression was related to both action observation, and the ability to perform the movement observed. This is interpreted as evidence that EEG μ-suppression is a valid indicator of hMNS-related activity.