Diazepam effects on the cerebral responses to tonic pain: a SPET study

Rationale: Pain is a complex phenomenon with a strong affective-emotional c omponent in addition to a sensory-discriminative one. This causes the activ ation of multiple brain areas, which process different aspects of pain simu ltaneously. Objectives: We investigated the effects of diazepam (DZ) on a w ell-known pattern of brain regions activated by cold, tonic pain stimuli. M ethods: Quantitative cerebral blood flow (CBF) was assessed by single photo n emission tomography (SPET) and the Xe-133 inhalatory method, at rest and during tonic pain activation in eight normal, right-handed, male volunteers . The cold pressor test (CPT) was performed by immersion of the left hand i n cold water twice, first during CPT alone, and again 30 min after intraven ous administration of diazepam (CPT+DZ). Results: During CPT we observed a significant CBF increase in the right thalamus, primary sensory-motor corte x (S1/M1), frontal and temporal regions, and in the left temporal region an d anterior cingulate cortex (ACC). During CPT+DZ, the average CBF was signi ficantly lower than during the CPT state (-11%, P<0.05). After normalisatio n, during CPT+DZ we again observed a significant CBF increase in the right thalamus, SIM and frontal regions, and in the left ACC, though not in the t emporal regions. DZ administration first causes a global reduction in CBF, then modifies the pattern of brain activation. Conclusions: During CPT, act ivation of the temporal regions has been interpreted as part of the affecti ve-emotional component of pain response. DZ seems to affect the "pain-relat ed" pattern of activation by abolishing the CBF increase in the temporal re gions, without, however, modifying the pain perception or determining a sed ating effect.