Spatial discrimination learning of electrocutaneous stimuli.

The present study investigates whether the spatial discrimination of somatosensory stimuli can be improved with training when sets of 1, 2, 3, or 4 simultaneously stimulated electrodes (so called patterns) have to be discriminated. Healthy human subjects were trained over a period of 5 days to discriminate 23 different somatosensory stimulus patterns. Somatosensory stimulation was based on electrical stimuli applied through an array of eight electrodes attached with a cuff to the skin of the left upper arm. Daily sessions consisted of a pretest, a training phase, and a posttest. Pre- and posttests revealed subject's discrimination ability. Performance of a treatment group receiving sensory real training was compared to performance of a control group receiving sham training. Results revealed (1) improvements of discrimination ability in both groups, and (2) a significantly greater discrimination performance throughout the training period in the treatment group as compared to the control group. The present study demonstrates that discrimination of electrocutaneous stimuli can be improved through training. Results illustrate that electrocutaneous stimuli are a possible and easy-to-apply tool for biofeedback settings.

Naturopathic reflex therapies for the treatment of chronic back and neck pain - Part 1: Neurobiological foundations.

Evidence from recent RCT's has shown that naturopathic reflex therapies such as massage, Gua Sha massage, cupping, wet packs, or rhythmic embrocation etc. are helpful in reducing symptoms of chronic pain. These bodily oriented therapies are likely able to influence chronic pain not only through brain mechanisms such as expectation or the feeling of well-being, but also through mechanisms at the level of the peripheral nociceptor and the spinal cord. However, the neurobiological basis of these effects has rarely been investigated even though the accumulating knowledge of the pathophysiology of chronic pain syndromes allows for developing specific hypotheses. This essay discusses specific reflex therapies (cupping, Gua Sha massage, classical massage, and rhythmic embrocation) and their possible mechanisms of action via ascending pathways to the brain.

Naturopathic reflex therapies for the treatment of chronic pain - Part 2: Quantitative sensory testing as a translational tool.

Naturopathic reflex therapies such as massage, Gua Sha massage, cupping, wet packs etc. are likely able to influence chronic pain at different levels of the nociceptive system. Since naturopathic reflex therapies have been shown to reduce symptoms of chronic pain and often utilize intense manipulation of the environment of the nociceptor (e.g. Gua Sha massage or cupping), it can be hypothesized that they unfold part of their effect at the level of the peripheral nociceptor and the spinal cord. However, these hypotheses have to date not been tested systematically. Standardized sensory testing, e.g., as performed by 'quantitative sensory testing' (QST), a comprehensive battery of tests for clinical trials, may offer additional information about the mechanisms of naturopathic reflex therapies since it provides a measure for the mechanisms of nociceptive pain on all levels of the pain processing system. This method paper describes the potential role of QST in research on the neurobiological mechanisms of naturopathic reflex therapies.

Laser heat stimulation of tiny skin areas adds valuable information to quantitative sensory testing in postherpetic neuralgia.

Patients suffering from postherpetic neuralgia often complain about hypo- or hypersensation in the affected dermatome. The loss of thermal sensitivity has been demonstrated by quantitative sensory testing as being associated with small-fiber (Aδ- and C-fiber) deafferentation. We aimed to compare laser stimulation (radiant heat) to thermode stimulation (contact heat) with regard to their sensitivity and specificity to detect thermal sensory deficits related to small-fiber dysfunction in postherpetic neuralgia. We contrasted detection rate of laser stimuli with 5 thermal parameters (thresholds of cold/warm detection, cold/heat pain, and sensory limen) of quantitative sensory testing. Sixteen patients diagnosed with unilateral postherpetic neuralgia and 16 age- and gender-matched healthy control subjects were tested. Quantitative sensory testing and laser stimulation of tiny skin areas were performed in the neuralgia-affected skin and in the contralateral homologue of the neuralgia-free body side. Across the 5 thermal parameters of thermode stimulation, only one parameter (warm detection threshold) revealed sensory abnormalities (thermal hypoesthesia to warm stimuli) in the neuralgia-affected skin area of patients but not in the contralateral area, as compared to the control group. In contrast, patients perceived significantly less laser stimuli both in the affected skin and in the contralateral skin compared to controls. Overall, laser stimulation proved more sensitive and specific in detecting thermal sensory abnormalities in the neuralgia-affected skin, as well as in the control skin, than any single thermal parameter of thermode stimulation. Thus, laser stimulation of tiny skin areas might be a useful diagnostic tool for small-fiber dysfunction.

Spatial discrimination learning of electrocutaneous stimuli is influenced by the type of stimulation.

Although spatial discrimination of electrocutaneous stimuli can be improved by training, we do not know whether the improvement of spatial discrimination varies as a function of the type of stimulus presentation. In the present study, two groups of healthy human volunteers were trained over a period of 5 days to discriminate 23 patterns of one, two, three, or four simultaneously stimulated electrodes on the upper arm. In group one, two or three simultaneously stimulated electrodes were applied at different skin areas with an anchor electrode. This type of stimulation was hypothesised to facilitate discrimination performance by providing a cue about stimulus patterns applied. In group two, two or three simultaneously stimulated electrodes were applied at different skin areas with electrodes arranged as adjacent electrodes like a zoned field. Double and triple stimulus patterns presented with an anchor electrode were discriminated significantly better than double and triple patterns presented as zoned fields. This improvement in stimulus discrimination resulted primarily from a better discrimination of double stimulation patterns. However, there was a clear influence of spatial distance between simultaneously activated electrodes on the results. Thus, both spatial distances between stimulated electrodes and, to a minor extent, the anchor stimulation per se influenced this result. Furthermore, results revealed an overall significant improvement of stimulus discrimination in both groups and an improvement varying as a function of the number of stimulated electrodes. Overall, results indicate that the improvement of spatial discrimination of electrocutaneous stimuli varies as a function of the type of stimulus presentation.

Brain activation upon selective stimulation of cutaneous C- and Adelta-fibers.

Thermal and nociceptive cutaneous stimuli activate the brain via two types of nerve fibers, slightly myelinated Adelta-fibers with moderate conduction velocity and unmyelinated C-fibers with slow conduction velocity. Differences in central processing upon selective stimulation of these two fiber types in healthy human subjects still remain poorly understood. By means of event-related functional magnetic resonance imaging the present study investigated brain activation in response to stimulation of Adelta- and C-fibers in healthy subjects. We used the stimulation of tiny skin areas to perform a selective stimulation upon cutaneous C-fibers. Besides similar activation in several brain areas in response to both kinds of stimulation, we observed pronounced brain activation to selective C-fiber stimulation as compared to Adelta-fiber stimulation in the right frontal operculum and anterior insula. Based on a putative function of these structures we suggest that the C-fiber system might be engaged in homeostatic and interoceptive functions in a manner other than the Adelta-fiber system, producing a signal of greater emotional salience.