Pain is a negative feeling that we want to get rid of as soon as possible. In order to protect our bodies, we react for example by withdrawing the hand. This action is usually understood as a consequence of the perception of pain.

A team from the Technical University of Munich (TUM) has now shown that perception, the impulse to act and provision of energy to take the place in the brain simultaneously and not, as was expected, one after the other.

Led by Markus Ploner, Heisenberg Professor for Human Pain Research, scientists from the Department of Neurology of the university hospital TUM Klinikum rechts der Isar investigated in detail how a painful event is processed in the brain. 

For the first time, they were able to show that the brain yields at least three different responses to a painful stimulus and that these responses are simultaneous and independent of one another. The results may have significant repercussions for the understanding of pain and treatment of pain patients.

Pain embodies at least three factors: Perception of pain, an action such as withdrawing the hand from a hot stove, and a response of the autonomic nervous system which provides the necessary energy for the work. The autonomic nervous system controls essential functions such as heart rate, breathing, digestion, and metabolism.

Combination of behavioral and EEG measurements

In their experiments, the researchers applied little pain stimuli of varying strengths to the back of the hand of healthy volunteers. The perception of pain was determined based on the participant's evaluation of the stimulus on a rating scale. 

The team, led by Markus Ploner, investigated the action component based on the reaction time the subjects needed to withdraw their fingers in response to the stimulus. Moreover, to determine the reaction of the autonomic nervous system, the team measured the sweat production at the interior surface of the hand.

For the entire duration of the experiment, brain activity was measured using electroencephalography (EEG). This method provides highly precise information on when and how nerve cells react to pain stimuli.

Pain components arise independently of one another 

Ploner and his team applied a statistical method known as mediation analysis to the data. The technique has been well established in the social sciences for some time now; however, this was its first application to EEG data. The team was thus able to find out which brain responses serve the three pain components, and when exactly they take place.

The results of the evaluations surprised the researchers: "For the first time we were able to see that the brain responses to the pain components did not take place one after the other, but rather in part simultaneously," explains Laura Tiemann, the study's lead author.

"This means that the preparation for action and the provision of energy are not entirely dependent on the perception of pain; instead, they are in part triggered independently of one another," said Tiemann.