Watching Dance: Kinesthetic Empathy

Transcranial Magnetic Stimulation (TMS)

Transcranial magnetic stimulation (TMS) is a non-invasive technique used to stimulate a restricted part of the cortex and has proven to be a very useful tool in understanding thefunctioning of the normal and pathological human brain.

Developed in the eighties, it was first used for clinical diagnostics but there is a growing interest in the potential for using TMS as a therapeutic tool in psychiatry, as well as an investigative tool in cognitive neuroscience.

How can TMS be used?

1)   TMS can be used in different modes depending on its application. In the Watching Dance project, we use TMS to probe cortical excitability by measuring directly the response to single-pulse TMS applied over primary cortices. In this case the evoked response (e.g. motor evoked potential for the motor cortex or phosphene intensity for the visual cortex), as well as the TMS intensity threshold necessary to elicit those responses, can be used as dependant variable.

In this way we investigate how passively watching dance movements can change the motor excitability of the observer. So we apply TMS over the motor cortex and measure the response in the muscles while participants watch dance movements.

We expect that watching movements of the hand will increase excitability in the hand motor cortex but not in the leg motor cortex, and vice versa. Critically, we expect that this effect will be modulated by the spectators’ experience of watching those specific dance movements, which would be a signature of different kinesthetic empathy.

2)  TMS can also be used to induce long-term (minutes) changes in cortical excitability and connectivity with several minutes of low frequency repetitive stimulation. In this case participants are submitted to a brain-imaging test before and after the administration of around 10-15 minutes of TMS.

In the ‘Watching Dance: Kinesthetic Empathy’ project, we use TMS in this mode to investigate which regions of the brain are critically involved in perceiving dance movements. It is crucial to localize precisely the area stimulated by TMS and this is achieved by identifying this area on the high-resolution magnetic resonance image (MRI) of the participant and using a frameless stereotaxy system (Brainsight Inc) to position the TMS coil.

We first use fMRI to identify brain regions that are engaged while people watch expressive dance movements, then we apply repetitive TMS so that the peak of electric field is localized on the desired area while observers watch the same movements.  By this method we are able to assess how TMS changes their evaluation of those movements.

3) TMS can also be used to interfere briefly with ongoing cortical activity with single pulse or short trains of high frequency repetitions. In this case TMS is applied while the participant is engaged in a behavioural task. This mode is not necessary for our purposes.