China
Africa
Explore chapters and articles related to this topic
ENTRIES A–Z
Published in Philip Winn, Dictionary of Biological Psychology, 2003
One of the DORSAL COLUMN NUCLEI OF THE MEDULLA OBLONGATA (the GRACILE NUCLEUS is the other) which receives sensory fibres from the DORSAL FUNICULUS of the SPINAL CORD carrying sensations of fine, discriminative TOUCH and vibration.
Evidence for the Presence of a Visceral Pain Pathway in the Dorsal Column of the Spinal Cord
Published in Mark J Rowe, Yoshiaki Iwamura, Somatosensory Processing: From Single Neuron to Brain Imaging, 2001
William D. Willis, Elie D. Al-Chaer, Michael J. Quast, Karin N. Westlund
From these experiments in which it was shown that the responses of neurons in the VPL nucleus to noxious colorectal distention depended largely on signals transmitted through the dorsal column, it seemed likely that this information would have been relayed through the gracile nucleus. To check that this was indeed the case, a study was done in which the responses of neurons in the VPL nucleus of rats to noxious colorectal distention were recorded before and after small lesions were placed in the gracile nucleus (Al-Chaer et al., 1997). The lesions were made either by passing an electric current through a metal electrode inserted into the gracile nucleus or by microinjection of kainic acid into the nucleus. Even though the lesions were incomplete, destroying only a part of the gracile nucleus, the responses of VPL neurons to distentions of 80 mmHg were reduced on average by 66% following electrolytic lesions and by 51% after chemical lesions. The same lesions reduced the responses to brushing the skin by 84% and 81%, but did not affect the responses to pinching the skin. Presumably, more extensive lesions of the gracile nucleus would have reduced the responses of VPL neurons to noxious colorectal distention somewhat more. However, the maximum reduction expected, based on the results following dorsal column lesions (Fig. 4.5) would have been by 80%.
Burst and high frequency stimulation: underlying mechanism of action
Published in Expert Review of Medical Devices, 2018
Shaheen Ahmed, Thomas Yearwood, Dirk De Ridder, Sven Vanneste
On a systemic level, changes in source-localized electroencephalography were analyzed to elucidate the relationships between different frequency bands in tonic and burst stimulation [25]. Significantly more alpha activity was seen in burst stimulation as opposed to tonic stimulation in the dorsal anterior cingulate cortex, the dorsolateral prefrontal cortex, the primary somatosensory cortex, and the posterior cingulate cortex. These findings suggest that burst stimulation has a profound effect on medial, lateral, and descending pathways, whereas tonic stimulation influences the lateral pain pathways [34]. The question remains, however, how burst SCS reaches the brain without – according to animal research – altering the firing rate of the gracile nucleus. The gracile nucleus processes proprioceptive information from the dorsal column such as touch, pressure, and vibration [35]. One hypothesis is that burst SCS modulates the medial pain pathway directly via C-fiber activation, ending in lamina1 connections to the medial thalamic nuclei and anterior cingulate cortex. Another existing question is regarding the mechanism by which burst stimulation suppresses pain. One possible answer to this question is that burst stimulation disrupts synchronous firing of the high-threshold C-fibers related to pain perception [36–38]. This could be caused by reducing synchrony or generating inhibitory postsynaptic potentials which are maximal at 500-Hz bursts [39]. Another possibility is that burst SCS exerts its pain-improving effects by activating the antinociceptive low-threshold tactile C-fibers.