Experimental brush-evoked allodynia activates posterior parietal cortex.
OBJECTIVE
To study the brain activation pattern of coexisting experimental ongoing pain and brush-evoked allodynia (pain evoked by innocuous brush) with the use of PET.


BACKGROUND
Neuropathic pain usually has two essential phenomena: ongoing pain and brush-evoked allodynia, which coexist and may influence each other. Capsaicin induces both ongoing pain and brush-evoked allodynia.


METHODS
Eight healthy right-handed volunteers participated in eight H2(15)O PET scans with two blocks of four randomized conditions: 1) rest, 2) brush, 3) capsaicin pain, and 4) capsaicin pain + brush (brush-evoked allodynia). Capsaicin was injected intradermally on the nondominant forearm and the subjects rated pain intensity and unpleasantness on 100-mm visual analogue scales.


RESULTS
Pain intensity and unpleasantness were significantly higher during brush-evoked allodynia (74 +/- 4 and 67 +/- 4 mm) compared with capsaicin pain alone (60 +/- 4 and 51 +/- 5 mm). Brush-evoked allodynia, but not capsaicin pain alone, increased blood flow significantly in the contralateral right sensory association cortex Brodmann area (BA) 5/7, and in bilateral prefrontal cortex BA 9/10/47 and insula. No significant activity was seen in thalamus or primary somatosensory cortex (SI). Direct comparison between capsaicin pain and brush-evoked allodynia revealed significant increase in contralateral BA 5/7 only.


CONCLUSIONS
The specific activation of contralateral BA 5/7 indicates that this brain region is important to the processing of brush-evoked allodynia. The involvement of BA 5/7 in brush-evoked allodynia is claimed to reflect multisensory input to this region, its role in conscious pain perception, and its neuroplastic properties.
Witting
N
N
Department of Neurology, Aarhus University Hospital, Denmark. nanna@akhphd.au.dk
Kupers
R C
RC
Svensson
P
P
Arendt-Nielsen
L
L
Gjedde
A
A
Jensen
T S
TS
D000328:Adult; D001921:Brain / Q000098:blood supply* / Q000000981:diagnostic imaging; D001931:Brain Mapping; D002211:Capsaicin; D004292:Dominance, Cerebral / Q000502:physiology; D005260:Female; D006801:Humans; D008297:Male; D009437:Neuralgia / Q000000981:diagnostic imaging / Q000503:physiopathology*; D010147:Pain Measurement; D017288:Pain Threshold / Q000502:physiology*; D010812:Physical Stimulation; D012016:Reference Values; D012039:Regional Blood Flow / Q000502:physiology; D014055:Tomography, Emission-Computed
D002211:Capsaicin