PAIN MECHANISMS: Labeled Lines Versus Convergence in Central Processing

Abstract

The issue of whether pain is represented by specific neural elements or by patterned activity within a convergent somatosensory subsystem has been debated for over a century. The gate control theory introduced in 1965 denied central specificity, and since then most authors have endorsed convergent wide-dynamic-range neurons. Recent functional and anatomical findings provide compelling support for a new perspective that views pain in humans as a homeostatic emotion that integrates both specific labeled lines and convergent somatic activity.

Nonlinear neurobiological probability weighting functions for aversive outcomes

“…The anterior insula, in particular, has been previously associated with anticipatory responses to painful stimuli (Craig, 2003;Koyama et al, 2005;Ploghaus et al, 1999;Tracey, 2005). Although this region was identified by its monotonically increasing response to expected magnitude, it also showed a significantly nonlinear NPRR (Fig.…”

“…Moreover, no comparable data exist in monkeys using aversive paradigms. The ACC is an integral component of the cortical pain matrix, and current evidence suggests that the ACC integrates several dimensions of the subjective pain experience, including emotional and attentional components (Craig, 2003;Ploghaus et al, 1999;Vogt, 2005). Interestingly, studies of positive financial incentives have also shown a significant interaction of probability and magnitude in the ACC (Knutson et al, 2005).…”

Three studies on the neuroeconomics of decision-making when payoffs are real and negative

“…This would also account for a willingness to bring adverse outcomes forward in time, if possible. In the experiment described here, these two explanations imply a different time course of activation in the pain matrix, a network of brain regions associated with unpleasant or noxious stimuli (Ploghaus et al, 1999;Koyama, McHaffie, Laurienti, & Coghill, 2005;Rajj et al, 2005;Tracy, 2001;Craig, 2003;Peyron et al, 2000). Measuring the time profile of activation allows us to distinguish between the two explanations.…”

“…Both SI and SII have generally been associated with the physical intensity of noxious stimulation (Tracy, 1999;Craig, 2003;Petrovic, Petersson, Hansson, & Ingvar, 2002;Bentley et al, 2004), whereas the caudal ACC has been associated with the attentive component of pain (Vogt, 2005;Bentley, Derbyshire, Youell, & Jones, 2003). The localization of dread to the posterior elements of the matrix suggests that dread has a substantial attentive component.…”

“…Moreover, it was the significantly different dread factor in the posterior divisions that most clearly distinguished mild from extreme dreading behavior when individuals subsequently had to make decisions regarding wait times. With regard to nociceptive inputs, both SI and SII receive afferent signals from the posterior portion of the ventromedial nucleus of the thalamus, whereas the ACC receives input from the mediodorsal nucleus (Craig, 2003). As the terminal fields from the spinothalamic system, these regions naturally show activations that track stimulation voltage.…”