Diana Torta

Cognitive aspects of nociception and pain: bridging neurophysiology with cognitive psychology

The event-related brain potentials (ERPs) elicited by nociceptive stimuli are largely influenced by vigilance, emotion, alertness, and attention. Studies that specifically investigated the effects of cognition on nociceptive ERPs support the idea that most of these ERP components can be regarded as the neurophysiological indexes of the processes underlying detection and orientation of attention toward the eliciting stimulus. Such detection is determined both by the salience of the stimulus that makes it pop out from the environmental context (bottom-up capture of attention) and by its relevance according to the subjects goals and motivation (top-down attentional control). The fact that nociceptive ERPs are largely influenced by information from other sensory modalities such as vision and proprioception, as well as from motor preparation, suggests that these ERPs reflect a cortical system involved in the detection of potentially meaningful stimuli for the body, with the purpose to respond adequately to potential threats. In such a theoretical framework, pain is seen as an epiphenomenon of warning processes, encoded in multimodal and multiframe representations of the body, well suited to guide defensive actions. The findings here reviewed highlight that the ERPs elicited by selective activation of nociceptors may reflect an attentional gain apt to bridge a coherent perception of salient sensory events with action selection processes.

Phase-locked and non-phase-locked EEG responses to pinprick stimulation before and after experimentally-induced secondary hyperalgesia

OBJECTIVE Pinprick-evoked brain potentials (PEPs) have been proposed as a technique to investigate secondary hyperalgesia and central sensitization in humans. However, the signal-to-noise (SNR) of PEPs is low. Here, using time-frequency analysis, we characterize the phase-locked and non-phase-locked EEG responses to pinprick stimulation, before and after secondary hyperalgesia. METHODS Secondary hyperalgesia was induced using high-frequency electrical stimulation (HFS) of the left/right forearm skin in 16 volunteers. EEG responses to 64 and 96mN pinprick stimuli were elicited from both arms, before and 20min after HFS. RESULTS Pinprick stimulation applied to normal skin elicited a phase-locked low-frequency (<5Hz) response followed by a reduction of alpha-band oscillations (7-10Hz). The low-frequency response was significantly increased when pinprick stimuli were delivered to the area of secondary hyperalgesia. There was no change in the reduction of alpha-band oscillations. Whereas the low-frequency response was enhanced for both 64 and 96mN intensities, PEPs analyzed in the time domain were only significantly enhanced for the 64mN intensity. CONCLUSIONS Time-frequency analysis may be more sensitive than conventional time-domain analysis in revealing EEG changes associated to secondary hyperalgesia. SIGNIFICANCE Time-frequency analysis of PEPs can be used to investigate central sensitization in humans.

Central Sensitization: Explanation or Phenomenon?:

Central sensitization (CS) is a popular concept that is frequently used to explain pain hypersensitivity in a large number of pain conditions. However, the concept of CS is now also increasingly used to explain nonpain symptoms. In the present commentary, we argue that CS, as defined by the International Association for the Study of Pain, refers to changes in nociceptive neurons only and therefore cannot be applied to enhanced responses to stimuli other than nociceptive and/or pain. Moreover, the evidence for CS in widespread pain (other than secondary hyperalgesia) and many other conditions is scarce to absent. As a consequence, CS is a descriptive label for the explanandum rather than an explanation and, as such, suffers the risk of being a circular explanation. Finally, cognitive and emotional factors should also be considered as potential mechanisms for the wide range of phenomena that are currently interpreted as evidence for CS.