OZAKI Makoto Tokyo Women's Medical University, Medicine, Professor, 医学部, 教授 (30160849)
MITSUHASHI Norio Tokyo Women's Medical University, Medicine, Professor, 医学部, 教授 (20008585)
赤嶋 夕子 東京女子医科大学, 医学部, 助手 (50318143)
酒向 正春 東京女子医科大学, 医学部, 助手 (40304604)
|Budget Amount *help
¥3,400,000 (Direct Cost: ¥3,400,000)
Fiscal Year 2006: ¥500,000 (Direct Cost: ¥500,000)
Fiscal Year 2005: ¥1,000,000 (Direct Cost: ¥1,000,000)
Fiscal Year 2004: ¥1,900,000 (Direct Cost: ¥1,900,000)
The cerebral substrates for the anesthetic-induced analgesia and unconsciousness remains an unanswered question despite the well-defined pharmacological actions at the molecular level. To answer the question from the viewpoint of cognitive neuroscience, we studied anesthetic-induced attenuation of pain and conscious perception in the human brain using functional magnetic resonance imaging (fMRI).
First, we observed the pain-related cerebral activation and its association with psychophysical evaluation of pain. We used an electrical stimulator of the peripheral nerves (Neurometer), which allegedly activated Aβ, Aδ, or C nerve fibers selectively by 2000, 250, or 5Hz sine-wave pulses. Thirteen healthy adult volunteers received pain stimulus at the left volar forearm. The 250 and 5Hz stimuli induced sharper and more unpleasant pain at lesser current, by under one-fourth, than the 2000Hz stimulus, which might validate nociceptive specificity of the former stimuli.
Second, we applied an electr
ical pain stimulus at a pain rating score (VAS) of 5 or 7 out of 10 to another group of volunteers and observed pain-related brain activities using fMRI. The least current of 5Hz required for pain induction was chosen for its high selectivity for nociceptive activation to guard against the electricity-induced artifact. Three subjects underwent a whole-brain fMRI experiment with a block-design pain-stimulus paradigm, and another one underwent the same experiment under moderate and deep sedation by titrated, target-controlled infusion of propofol. We used a computer-controlled syringe pump (Graseby) for propofol infution, and 1.5-Tesla MRI scanner (Vision, Siemens). General linear model was used to analyze the functional images (BrainVoyager QX).
Pain at VAS=3 activated the right secondary somatosensory, right prefrontal cortices, and right inferior parietal lobule; pain at VAS=5 further activated the bilateral prefrontal cortices, bilateral inferior parietal lobules, and bilateral supplementary motor areas. On the other hand, propofol-infusion experiments were contaminated by significant background noise up to 2.8% of the signal amplitude, which could have come from a fluid-infusion line and a syringe pump device. We plan to trace and eliminate the origin of such noise to improve the fidelity of pharmacological fMRI experiments. Less