Avoiding pain: cortical responses to nociceptive stimuli and defensive movements
Neuroimaging and neurophysiological studies in humans have shown that transient nociceptive stimuli causing pain elicit responses in an extensive network of cortical structures. This network, often referred to as the “pain matrix”, has been assumed to be specifically reflecting nociceptive processing, and extensively used in the past 30 years to gain knowledge about the cortical mechanisms underlying nociception and pain perception in humans. In the first part of this talk I will provide evidence that, in contrast with this dominant view, these brain responses are not specific for the perception of pain. These results indicate that it is incorrect to refer to these responses as originating from a “pain matrix”, and question the appropriateness of relying on them to infer that in individual is in pain, or to build models of where and how nociceptive input is processed in the human brain to generate painful percepts. Instead, I will suggest that the largest part of pain-evoked brain responses are related to detection of environmental threats - they represent a basic mechanism through which the individual detects, reorients attention and reacts to sensory events threatening the integrity of the body, regardless of the sensory channel conveying this information. In the second part of this talk I will illustrate the rules that the nervous system obeys to identify threatening changes in the sensory environment, and provide evidence that the brain responses elicited by a salient stimuli are sensitive to behaviourally relevant changes in the location of a potential threat with respect to the body. I will finally show that the brain responses elicited by transient nociceptive stimuli are related to the execution of defensive movements, aimed to protect the body from threats in the sensory environment. Furthermore, by exploring the dependence of such responses on the position of the threatening stimulus in space, I will show evidence supporting the existence of a part of space surrounding the body (a “defensive” peripersonal space, DPPS) representing a safety margin advantageous for survival.