Physical inactivity is now universally accepted as the biggest public health problem of the 21st century in Western societies. Physical inactivity and the resulting physical deconditioning are associated with a host of chronic diseases of which non-specific chronic back pain (CLBP) may be one.

Abstract: Patients with major depressive disorder have repeatedly been described to exhibit increased thresholds upon experimentally applied pain stimuli to the skin as compared to respective controls. Since the sensory-discriminative component of stimulus perception, e.g. for warmth, cold and vibration, appears to be unaltered in depression, higher central nervous centres have been assumed to cause this phenomenon. To date, hardly any attention has been paid to the efferent components of the noxious reflex loop. Here, we aimed to assess the autonomic reaction upon a painful stimulus and to examine whether this is likewise reduced in major depression. For this purpose, sympathetic skin response was obtained from 22 patients with major depression and 20 matched controls. To induce sympathetic skin responses, we applied either noxious electrical stimuli (12 and 18mA) or innocuous acoustic stimuli (85dB SPL). Pain intensity was rated using a numeric analogue scale. In contrast to our a priori hypothesis patients showed shorter latencies and higher amplitudes of skin potentials upon noxious stimulation, i.e. a stronger sympathetic response. Intriguingly, the noxious stimuli were still perceived less painful in the patient group. Pain perception weakly correlated with disease severity. From these data, we conclude that despite the diminished pain perception, the autonomic reflex loop following noxious stimulation is not affected in patients with major depressive disorder, and that the increase in sympathetic outflow is not directly related to the perceived pain as in controls, but might rather be attributed to the autonomic dysfunction known for the disease.

What determines pain? The multi-dimensional and, more recently, the anatomical view of pain as derived from brain imaging studies, has attracted many researchers. Melzack and Casey formulated the theory of sensory-discriminative and affective-motivational determinants of pain. However, this paper only loosely linked the cognitive and behavioral consequences of pain to the term “motivational” to indicate the engagement of escape and avoidance behavior during noxious stimulation. Later, Casey and Lorenz revised the concept and included “motivational dominance” as a unique and critical dimension of pain together with “sensory salience” and “affect”. They argued that motivational dominance of pain can be separately identified and measured by interference paradigms. These paradigms are based on the observation that pain and mental tasks compete for attention, the latter intrinsically characterized by its limited resources.