| 1. |
- Ackerley, Rochelle, 1980, et al.
(författare)
-
Differential effects of radiant and mechanically applied thermal stimuli on human C-tactile afferent firing patterns.
- 2018
-
Ingår i: Journal of neurophysiology. - : American Physiological Society. - 1522-1598 .- 0022-3077. ; 120:4, s. 1885-1892
-
Tidskriftsartikel (refereegranskat)abstract
- C-tactile (CT) afferents respond to gentle tactile stimulation, but only a handful of studies in humans and animals have investigated whether their firing is modified by temperature. We describe the effects of radiant thermal stimuli, and of stationary and very slowly moving mechanothermal stimuli, on CT afferent responses. We find that CT afferents are primarily mechanoreceptors, as they fired little during radiant thermal stimuli, but they exhibited different patterns of firing during combined mechano-cool stimulation compared with warming. CTs fired optimally to gentle, very slowly moving, or stationary mechanothermal stimuli delivered at neutral temperature (~32°C, normal skin temperature), but they responded with fewer spikes (median 67% decrease) and at significantly lower rates (47% decrease) during warm (~42°C) tactile stimuli. During cool tactile stimuli (~18°C), their mean instantaneous firing frequency significantly decreased by 35%, but they often fired a barrage of afterdischarge spikes at a low frequency (~5 Hz) that outlasted the mechanical stimulus. These effects were observed under a variety of stimulus conditions, including during stationary and slowly moving touch (0.1 cm/s), and we complemented these tactile approaches using a combined electrical-thermal stimulation experiment where we found a suppression of spiking during warming. Overall, CT afferents are exquisitely sensitive to tactile events, and we show that their firing is modulated with touch temperatures above and below neutral skin temperature. Warm touch consistently decreased their propensity to fire, whereas cool touch produced lower firing rates but afterdischarge spiking. NEW & NOTEWORTHY C-tactile (CT) afferents are thought to underpin pleasant touch, and previous work has shown that they respond optimally to a slow caress delivered at typical (neutral) skin temperature. Here, we show that, although CTs are primarily mechanoreceptive afferents, they are modified by temperature: warm touch decreases their firing, whereas cool touch produces lower firing rates but long-lasting spiking, frequently seen as afterdischarges. This has implications for the encoding of affective sensory events in human skin.
|
|
| 2. |
- Björnsdotter, Malin, et al.
(författare)
-
Somatotopic organization of gentle touch processing in the posterior insular cortex.
- 2009
-
Ingår i: The Journal of neuroscience : the official journal of the Society for Neuroscience. - Washington, DC, United States : Society for Neuroscience. - 1529-2401 .- 0270-6474. ; 29:29, s. 9314-20
-
Tidskriftsartikel (refereegranskat)abstract
- A network of thin (C and A delta) afferents relays various signals related to the physiological condition of the body, including sensations of gentle touch, pain, and temperature changes. Such afferents project to the insular cortex, where a somatotopic organization of responses to noxious and cooling stimuli was recently observed. To explore the possibility of a corresponding body-map topography in relation to gentle touch mediated through C tactile (CT) fibers, we applied soft brush stimuli to the right forearm and thigh of a patient (GL) lacking A beta afferents, and six healthy subjects during functional magnetic resonance imaging (fMRI). For improved fMRI analysis, we used a highly sensitive multivariate voxel clustering approach. A somatotopic organization of the left (contralateral) posterior insular cortex was consistently demonstrated in all subjects, including GL, with forearm projecting anterior to thigh stimulation. Also, despite denying any sense of touch in daily life, GL correctly localized 97% of the stimuli to the forearm or thigh in a forced-choice paradigm. The consistency in activation patterns across GL and the healthy subjects suggests that the identified organization reflects the central projection of CT fibers. Moreover, substantial similarities of the presently observed insular activation with that described for noxious and cooling stimuli solidify the hypothesized sensory-affective role of the CT system in the maintenance of physical well-being as part of a thin-afferent homeostatic network.
|
|
| 3. |
|
|
| 4. |
- Jones, K E, et al.
(författare)
-
Directional tuning of human forearm muscle afferents during voluntary wrist movements.
- 2001
-
Ingår i: The Journal of physiology. - 0022-3751. ; 536:Pt 2, s. 635-47
-
Tidskriftsartikel (refereegranskat)abstract
- 1. Single unit activity was recorded with the microneurography technique from sixteen spindle afferents and one Golgi tendon organ afferent originating from the forearm extensor muscles. Impulse rates were studied while subjects performed unobstructed aiming movements at the wrist in eight different directions 45 deg apart. In addition, similar imposed movements were performed while the subject was instructed to remain relaxed. Movement amplitudes were about 5 deg and the speed 10-30 deg x s(-1). Joint movements were translated to movements of a cursor on a monitor to provide visual feedback. 2. Individual spindle afferents modulated their activity over a number of targets, i.e. were broadly tuned, during these aiming movements. The preferred direction for a spindle afferent was the same during both passive and active movements, indicating that the fusimotor effects associated with active contractions had little or no effect on the direction of tuning. 3. The direction of tuning of individual spindle afferents could be predicted from the biomechanically inferred length changes of the parent muscle. Thus spindle afferents responded as stretch receptors, i.e. impulse rates increased with lengthening and decreased with shortening, in active as well as passive movements. 4. Spindles from muscles, which continuously counteracted gravity exhibited a stretch response and directional tuning during the phase of movement alone whereas their position sensitivity was poor. In contrast, spindle afferents from the muscles that had no or minimal antigravity role were directionally tuned during both the dynamic and the static phase of the aiming task and their position sensitivity was substantially higher. 5. In spite of the limited data base from three extensor muscles it could be demonstrated that wrist joint position was remarkably well encoded in the ensemble muscle spindle data. In some cases the ensemble muscle spindle data encoded the instantaneous trajectory of movement as well.
|
|
| 5. |
- Jones, K E, et al.
(författare)
-
Proprioceptive feedback is reduced during adaptation to a visuomotor transformation: preliminary findings.
- 2001
-
Ingår i: Neuroreport. - 0959-4965. ; 12:18, s. 4029-33
-
Tidskriftsartikel (refereegranskat)abstract
- Adapting movements in relation to visual feedback is a ubiquitous characteristic of sensorimotor control and involves the integration of multiple sources of sensory information. We recorded sensory feedback from muscle spindle afferents during visuomotor adaptation while subjects performed an aiming task to investigate whether the activity of the muscle spindles was modulated by the fusimotor system under these learning conditions. None of the muscle spindles showed an increase in activity, rather in 83% of the trials the firing rates were decreased. These preliminary results suggest that the CNS reduces the sensory signals arising from muscle spindles perhaps as a means of resolving the conflict between visual and proprioceptive feedback during the task.
|
|
| 6. |
- Kakuda, Naoyuki, et al.
(författare)
-
Is human muscle spindle afference dependent on perceived size of error in visual tracking?
- 1997
-
Ingår i: Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale. - 0014-4819. ; 114:2, s. 246-54
-
Tidskriftsartikel (refereegranskat)abstract
- Impulses of 16 muscle spindle afferents from finger extensor muscles were recorded from the radial nerve along with electromyographic (EMG) activity and kinematics of joint movement. Twelve units were classified as Ia and 4 as II spindle afferents. Subjects were requested to perform precision movements at a single metacarpophalangeal joint in an indirect visual tracking task. Similar movements were executed under two different conditions, i.e. with high and low error gain. The purpose was to explore whether different precision demands were associated with different spindle firing rates. With high error gain, a small but significantly higher impulse rate was found in pooled data from Ia afferents during lengthening movements but not during shortening movements, nor with II afferents. EMG was also significantly higher with high error gain in recordings with Ia afferents. When the effect of EMG was factored out, using partial correlation analysis, the significant difference in Ia firing rate vanished. The findings suggest that fusimotor drive as well as skeletomotor activity were both marginally higher when the precision demand was higher, whereas no indication of independent fusimotor adjustments was found. These results are discussed with respect to data from behaving animals and the role of fusimotor independence in various limb muscles proposed.
|
|
| 7. |
- McGlone, Francis, et al.
(författare)
-
Discriminative touch and emotional touch.
- 2007
-
Ingår i: Canadian journal of experimental psychology = Revue canadienne de psychologie expérimentale. - : American Psychological Association (APA). - 1196-1961 .- 1878-7290. ; 61:3, s. 173-83
-
Forskningsöversikt (refereegranskat)abstract
- Somatic sensation comprises four main modalities, each relaying tactile, thermal, painful, or pruritic (itch) information to the central nervous system. These input channels can be further classified as subserving a sensory function of spatial and temporal localization, discrimination, and provision of essential information for controlling and guiding exploratory tactile behaviours, and an affective function that is widely recognized as providing the afferent neural input driving the subjective experience of pain, but not so widely recognized as also providing the subjective experience of affiliative or emotional somatic pleasure of touch. The discriminative properties of tactile sensation are mediated by a class of fast-conducting myelinated peripheral nerve fibres--A-beta fibres--whereas the rewarding, emotional properties of touch are hypothesized to be mediated by a class of unmyelinated peripheral nerve fibres--CT afferents (C tactile)--that have biophysical, electrophysiological, neurobiological, and anatomical properties that drive the temporally delayed emotional somatic system. CT afferents have not been found in the glabrous skin of the hand in spite of numerous electrophysiological explorations of this area. Hence, it seems reasonable to conclude that they are lacking in the glabrous skin. A full understanding of the behavioural and affective consequences of the differential innervation of CT afferents awaits a fuller understanding of their function.
|
|
| 8. |
- Olausson, Håkan, 1965, et al.
(författare)
-
Functional role of unmyelinated tactile afferents in human hairy skin: sympathetic response and perceptual localization.
- 2008
-
Ingår i: Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale. - : Springer Science and Business Media LLC. - 1432-1106. ; 184:1, s. 135-40
-
Tidskriftsartikel (refereegranskat)abstract
- In addition to A-beta fibres the human hairy skin has unmyelinated (C) fibres responsive to light touch. Previous functional magnetic resonance imaging (fMRI) studies in a subject with a neuronopathy who specifically lacks A-beta afferents indicated that tactile C afferents (CT) activate insular cortex, whereas no response was seen in somatosensory areas 1 and 2. Psychophysical tests suggested that CT afferents give rise to an inconsistent perception of weak and pleasant touch. By examining two neuronopathy subjects as well as control subjects we have now demonstrated that CT stimulation can elicit a sympathetic skin response. Further, the neuronopathy subjects' ability to localize stimuli which activate CT afferents was very poor but above chance level. The findings support the interpretation that the CT system is well suited to underpin affective rather than discriminative functions of tactile sensations.
|
|
| 9. |
- Olausson, Håkan, 1965, et al.
(författare)
-
The neurophysiology of unmyelinated tactile afferents.
- 2010
-
Ingår i: Neuroscience and biobehavioral reviews. - : Elsevier BV. - 1873-7528 .- 0149-7634. ; 34:2, s. 185-91
-
Forskningsöversikt (refereegranskat)abstract
- CT (C tactile) afferents are a distinct type of unmyelinated, low-threshold mechanoreceptive units existing in the hairy but not glabrous skin of humans and other mammals. Evidence from patients lacking myelinated tactile afferents indicates that signaling in these fibers activate the insular cortex. Since this system is poor in encoding discriminative aspects of touch, but well-suited to encoding slow, gentle touch, CT fibers in hairy skin may be part of a system for processing pleasant and socially relevant aspects of touch. CT fiber activation may also have a role in pain inhibition. This review outlines the growing evidence for unique properties and pathways of CT afferents.
|
|
| 10. |
- Olausson, Håkan, 1965, et al.
(författare)
-
Unmyelinated tactile afferents have opposite effects on insular and somatosensory cortical processing.
- 2008
-
Ingår i: Neuroscience letters. - : Elsevier BV. - 0304-3940. ; 436:2, s. 128-32
-
Tidskriftsartikel (refereegranskat)abstract
- A previous functional magnetic resonance imaging (fMRI) study of an A-beta deafferented subject (GL) showed that stimulation of tactile C afferents (CT) activates insular cortex whereas no activation was seen in somatosensory cortices. Psychophysical studies suggested that CT afferents contribute to affective but not to discriminative aspects of tactile stimulation. We have now examined cortical processing following CT stimulation in a second similarly deafferented subject (IW), as well as revisited the data from GL. The results in IW showed similar activation of posterior insular cortex following CT stimulation as in GL and so strengthen the view that CT afferents underpin emotional aspects of touch. In addition, CT stimulation evoked significant fMRI deactivation in somatosensory cortex in both subjects supporting the notion that CT is not a system for discriminative touch.
|
|
