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Changes of medium-latency SEP-components following peripheral nerve lesion.

Stendel R, Jahnke U, Straschill M - J Brachial Plex Peripher Nerve Inj (2006)

Bottom Line: Surprisingly 16 of the 29 patients (55.2%) showed a reduction or elimination of N35, P45 and N60.With paired stimulation a suppression of the amplitude of N20, P25 and P45 (p < 0.05; sign test), and a marked increment of N35 (p < 0.05; sign test) and N60 (not significant; sign test) of the second response could be observed.The results of the present investigation do not provide evidence of collateral innervation of peripherally denervated cortical neurons by neurons of adjacent cortical representation areas.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Neurosurgery, Charité-Universitätsmedizin Berlin, Campus Benjamin Franklin, Berlin, Germany. ruediger.stendel@charite.de

ABSTRACT

Background: Animal studies have demonstrated complex cortical reorganization following peripheral nerve lesion. Central projection fields of intact nerves supplying skin areas which border denervated skin, extended into the deafferentiated cortical representation area. As a consequence of nerve lesions and subsequent reorganization an increase of the somatosensory evoked potentials (SEPs) was observed in cats when intact neighbouring nerves were stimulated. An increase of SEP-components of patients with nerve lesions may indicate a similar process of posttraumatic plastic cortical reorganization.

Methods: To test if a similar process of post-traumatic plastic cortical reorganization does occur in humans, the SEP of intact neighbouring hand nerves were recorded in 29 patients with hand nerve lesions. To hypothetically explain the observed changes of SEP-components, SEP recording following paired stimulation of the median nerve was performed in 12 healthy subjects.

Results: Surprisingly 16 of the 29 patients (55.2%) showed a reduction or elimination of N35, P45 and N60. Patients with lesions of two nerves showed more SEP-changes than patients with a single nerve lesion (85.7%; 6/7 nerves; vs. 34.2%; 13/38 nerves; Fisher's exact test, p < 0.05). With paired stimulation a suppression of the amplitude of N20, P25 and P45 (p < 0.05; sign test), and a marked increment of N35 (p < 0.05; sign test) and N60 (not significant; sign test) of the second response could be observed.

Conclusion: The results of the present investigation do not provide evidence of collateral innervation of peripherally denervated cortical neurons by neurons of adjacent cortical representation areas. They rather suggest that secondary components of the excitatory response to nerve stimulation are lost in cortical areas, which surround the denervated region.

No MeSH data available.


Related in: MedlinePlus

Hypothetical explanation for changes of SEP-components. Schematic illustration of SEP-component generation in area 3b with an intact (A, B) and a lesioned (C) neighbouring hand nerve (R = radial nerve afference; M = median nerve afference). 4A The cortical recipients of radial nerve afference generate N20. Thalamo-cortical excitation spreads to the cortical representants of the neighbouring median nerve, which generate N35. 4B Threshold co-activation of the median nerve enhances selectively N35. 4C Inactivity due to nerve lesion makes the cortical representants of the lesioned nerve less excitable. Radial afference fails to co-activate cortical median neurons to generate N35.
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Figure 4: Hypothetical explanation for changes of SEP-components. Schematic illustration of SEP-component generation in area 3b with an intact (A, B) and a lesioned (C) neighbouring hand nerve (R = radial nerve afference; M = median nerve afference). 4A The cortical recipients of radial nerve afference generate N20. Thalamo-cortical excitation spreads to the cortical representants of the neighbouring median nerve, which generate N35. 4B Threshold co-activation of the median nerve enhances selectively N35. 4C Inactivity due to nerve lesion makes the cortical representants of the lesioned nerve less excitable. Radial afference fails to co-activate cortical median neurons to generate N35.

Mentions: To conclude, the cortical neuronal representants of innervation field borders of a sensory nerve seem to be co-innervated by afferents from the neighbouring nerve. The anatomical basis of this co-activation is the spread and overlap of axonal arborizations in the somatosensory cortex [21]. Co-activation may normally produce subliminal secondary depolarization in the middle layer of area 3b (N35), and in the upper layer of area 1 (N60) without spike discharge. Hypothetically, after nerve lesion the collateral innervation from the intact nerve may become unmasked and supraliminal and account for the expansion of the cortical projection area of the intact nerve as observed in the monkey [6] (Figure 4). In the human the influence of collateral innervation onto the cortical recipients of a lesioned nerve seems rather to decrease. The presumed SEP-correlates of co-activation (N35, N60) disappear. There seems to be no shift of the innervation field border of the intact nerve, since allaesthesia was never observed in our sample of 29 patients with hand nerve lesions.


Changes of medium-latency SEP-components following peripheral nerve lesion.

Stendel R, Jahnke U, Straschill M - J Brachial Plex Peripher Nerve Inj (2006)

Hypothetical explanation for changes of SEP-components. Schematic illustration of SEP-component generation in area 3b with an intact (A, B) and a lesioned (C) neighbouring hand nerve (R = radial nerve afference; M = median nerve afference). 4A The cortical recipients of radial nerve afference generate N20. Thalamo-cortical excitation spreads to the cortical representants of the neighbouring median nerve, which generate N35. 4B Threshold co-activation of the median nerve enhances selectively N35. 4C Inactivity due to nerve lesion makes the cortical representants of the lesioned nerve less excitable. Radial afference fails to co-activate cortical median neurons to generate N35.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC1636633&req=5

Figure 4: Hypothetical explanation for changes of SEP-components. Schematic illustration of SEP-component generation in area 3b with an intact (A, B) and a lesioned (C) neighbouring hand nerve (R = radial nerve afference; M = median nerve afference). 4A The cortical recipients of radial nerve afference generate N20. Thalamo-cortical excitation spreads to the cortical representants of the neighbouring median nerve, which generate N35. 4B Threshold co-activation of the median nerve enhances selectively N35. 4C Inactivity due to nerve lesion makes the cortical representants of the lesioned nerve less excitable. Radial afference fails to co-activate cortical median neurons to generate N35.
Mentions: To conclude, the cortical neuronal representants of innervation field borders of a sensory nerve seem to be co-innervated by afferents from the neighbouring nerve. The anatomical basis of this co-activation is the spread and overlap of axonal arborizations in the somatosensory cortex [21]. Co-activation may normally produce subliminal secondary depolarization in the middle layer of area 3b (N35), and in the upper layer of area 1 (N60) without spike discharge. Hypothetically, after nerve lesion the collateral innervation from the intact nerve may become unmasked and supraliminal and account for the expansion of the cortical projection area of the intact nerve as observed in the monkey [6] (Figure 4). In the human the influence of collateral innervation onto the cortical recipients of a lesioned nerve seems rather to decrease. The presumed SEP-correlates of co-activation (N35, N60) disappear. There seems to be no shift of the innervation field border of the intact nerve, since allaesthesia was never observed in our sample of 29 patients with hand nerve lesions.

Bottom Line: Surprisingly 16 of the 29 patients (55.2%) showed a reduction or elimination of N35, P45 and N60.With paired stimulation a suppression of the amplitude of N20, P25 and P45 (p < 0.05; sign test), and a marked increment of N35 (p < 0.05; sign test) and N60 (not significant; sign test) of the second response could be observed.The results of the present investigation do not provide evidence of collateral innervation of peripherally denervated cortical neurons by neurons of adjacent cortical representation areas.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Neurosurgery, Charité-Universitätsmedizin Berlin, Campus Benjamin Franklin, Berlin, Germany. ruediger.stendel@charite.de

ABSTRACT

Background: Animal studies have demonstrated complex cortical reorganization following peripheral nerve lesion. Central projection fields of intact nerves supplying skin areas which border denervated skin, extended into the deafferentiated cortical representation area. As a consequence of nerve lesions and subsequent reorganization an increase of the somatosensory evoked potentials (SEPs) was observed in cats when intact neighbouring nerves were stimulated. An increase of SEP-components of patients with nerve lesions may indicate a similar process of posttraumatic plastic cortical reorganization.

Methods: To test if a similar process of post-traumatic plastic cortical reorganization does occur in humans, the SEP of intact neighbouring hand nerves were recorded in 29 patients with hand nerve lesions. To hypothetically explain the observed changes of SEP-components, SEP recording following paired stimulation of the median nerve was performed in 12 healthy subjects.

Results: Surprisingly 16 of the 29 patients (55.2%) showed a reduction or elimination of N35, P45 and N60. Patients with lesions of two nerves showed more SEP-changes than patients with a single nerve lesion (85.7%; 6/7 nerves; vs. 34.2%; 13/38 nerves; Fisher's exact test, p < 0.05). With paired stimulation a suppression of the amplitude of N20, P25 and P45 (p < 0.05; sign test), and a marked increment of N35 (p < 0.05; sign test) and N60 (not significant; sign test) of the second response could be observed.

Conclusion: The results of the present investigation do not provide evidence of collateral innervation of peripherally denervated cortical neurons by neurons of adjacent cortical representation areas. They rather suggest that secondary components of the excitatory response to nerve stimulation are lost in cortical areas, which surround the denervated region.

No MeSH data available.


Related in: MedlinePlus