Search results for "touch"
showing 10 items of 168 documents
Object-Guided Spatial Selection in Touch Without Concurrent Changes in the Perceived Location of the Hands
2012
In an endogenous cueing paradigm with central visual cues, observers made speeded responses to tactile targets at the hands, which were either close together or far apart, and holding either two separate objects or one common object between them. When the hands were far apart, the response time costs associated with attending to the wrong hand were reduced when attention had to be shifted along one object jointly held by both hands compared to when it was shifted over the same distance but across separate objects. Similar reductions in attentional costs were observed when the hands were placed closer together, suggesting that processing at one hand is less prioritized over that at another …
Interoceptive and multimodal functions of the operculo-insular cortex: tactile, nociceptive and vestibular representations.
2013
The operculo-insular cortex has been termed the 'homeostatic control center' or 'general magnitude estimator' of the human mind. In this study, somatosensory, nociceptive and caloric vestibular stimuli were applied to reveal, whether there are mainly common, or possibly specific regions activated by one modality alone and whether lateralization effects, time pattern differences or influences of the aversive nature of the stimuli could be observed. Activation of the dorsal posterior insula was caused by all stimuli alike thus terming this area multimodal. Early phases of the noxious heat and caloric vestibular stimulation led to responses in the anterior insula. Using conjunction analyses we…
Secondary hyperalgesia and perceptual wind-up following intradermal injection of capsaicin in humans.
1998
Wind-up and secondary hyperalgesia both are related to central sensitization, but whereas the former is explained by homosynaptic facilitation, the latter is due to heterosynaptic facilitation. To investigate possible interactions between both types of facilitation, we tested for alterations of perceptual wind-up in the secondary hyperalgesic skin zone adjacent to a capsaicin injection with light touch (by a cotton wisp) and punctate stimuli (calibrated von Frey hairs and pin pricks). Temporal summation of pain sensation (perceptual wind-up) was only observed with a clearly noxious stimulus (pin prick) presented at a repetition frequency of 0.6 s(-1), but not 0.2 s(-1). Pain ratings to trai…
Illusion of Pain: Pre-existing Knowledge Determines Brain Activation of ‘Imagined Allodynia’
2007
Abstract Allodynia means that innocuous tactile stimulation is felt as pain. Accordingly, cerebral activations during allodynia or touch should markedly differ. The aim of this study was to investigate whether the imagination of allodynia affects brain processing of touch in healthy subjects. Seventeen healthy subjects divided into 2 subgroups were investigated: The first group (n = 7) was familiar with allodynia, based on previous pain studies, whereas the second group (n = 10) had never knowingly experienced allodynia. Using functional magnetic resonance imaging, 2 experimental conditions were investigated. In one condition the subjects were simply touched at their left hand, whereas duri…
Neurogenic hyperalgesia versus painful hypoalgesia: two distinct mechanisms of neuropathic pain
2002
Patients with sensory disturbances of painful and non-painful character show distinct changes in touch and/or pain sensitivity. The patterns of sensory changes were compared to those of human surrogate models of neuropathic pain to assess the underlying mechanisms. We investigated 30 consecutive in-patients with dysaesthesia of various origins (peripheral, spinal, and brainstem lesions) and 15 healthy subjects. Tactile thresholds were determined with calibrated von Frey hairs (1.1mm). Thresholds and stimulus-response functions for pricking pain were determined with a series of calibrated punctate mechanical stimulators (0.2mm). Allodynia was tested by light stroking with a brush, Q-tip, and…
The role of heterosynaptic facilitation in long-term potentiation (LTP) of human pain sensation
2008
Long-term potentiation (LTP) of nociceptive synaptic transmission induced by high-frequency electrical stimulation (HFS) predominantly modulates natural somatosensory perceptions mediated by Adelta- and Abeta-fibers in humans at the site of conditioning stimulation. The relative contribution of homo- and heterosynaptic mechanisms underlying those perceptual changes remained unclear. We therefore compared changes of the somatosensory profile between a conditioned skin site (homotopic zone) and an area adjacent to conditioning HFS (heterotopic zone). HFS of the ventral forearm in 24 healthy subjects (mean pain 41/100) led to an abrupt increase of pain to single electrical test stimuli (pain a…
Activation of the cortical pain network by soft tactile stimulation after injection of sumatriptan.
2006
The anti-migraine drug sumatriptan often induces unpleasant somatosensory side effects, including a dislike of being touched. With a double-blind cross-over design, we studied the effects of sumatriptan and saline on perception (visual analogue scale) and cortical processing (functional magnetic resonance imaging) of tactile stimulation in healthy subjects. Soft brush stroking on the calf (n = 6) was less pleasant (p < 0.04) and evoked less activation of posterior insular cortex in the sumatriptan compared to the saline condition. Soft brushing activated pain processing regions (anterior insular, lateral orbitofrontal, and anterior cingulate cortices, and medial thalamus) only in the sumatr…
Spatial discrimination thresholds for pain and touch in human hairy skin
2001
The traditional concept that pain is poorly localized has been challenged by recent studies, where subjects were able to point to the stimulated spot on the skin with an accuracy of 10-20 mm. Pointing movements themselves, however, have errors of about 15 mm. To determine the limits of sensory performance of the nociceptive system independent of motor performance, point localization of heat pain (540 mJ punctate laser stimuli, 5 mm diameter), mechanical pain (256 mN punctate probe, 200 microm diameter), and touch (16 mN von Frey probe, 1.1 mm diameter) were tested in a two-alternative forced-choice paradigm in 12 healthy subjects. Stimuli were applied in randomized order to two parallel lin…
Numbness in clinical and experimental pain – A cross-sectional study exploring the mechanisms of reduced tactile function
2008
Pain patients often report distinct numbness of the painful skin although no structural peripheral or central nerve lesion is obvious. In this cross-sectional study we assessed the reduction of tactile function and studied underlying mechanisms in patients with chronic pain and in healthy participants exposed to phasic and tonic experimental nociceptive stimulation. Mechanical detection (MDT) and pain thresholds (MPT) were assessed in the painful area and the non-painful contralateral side in 10 patients with unilateral musculoskeletal pain. Additionally, 10 healthy participants were exposed to nociceptive stimulation applied to the volar forearms (capsaicin; electrical stimulation, twice e…
Cutaneous Painful Laser Stimuli Evoke Responses Recorded Directly From Primary Somatosensory Cortex in Awake Humans
2004
Negative and positive laser evoked potential (LEP) peaks (N2*, P2**) were simultaneously recorded from the primary somatosensory (SI), parasylvian, and medial frontal (MF: anterior cingulate and supplementary motor area) cortical surfaces through subdural electrodes implanted for the surgical treatment of intractable epilepsy. Distribution of the LEP N2*and P2**peaks was estimated to be in cortical areas (SI, parasylvian, and MF) identified by anatomic criteria, by their response to innocuous vibratory stimulation of a finger (v-SEP), and to electrical stimulation of the median nerve (e-SEP). The maximum of the LEP N2*peak was located on the CS, medial (dorsal) to the finger motor area, as …