Analgesia for formalin-induced pain by lateral hypothalamic stimulation

Few studies of analgesia induced by electrical brain stimulation have examined the effects of brain stimulation on responses to tonic pain stimuli. Recent evidence suggests that analgesia for tonic and phasic pain may involve different neural substrates. The present study examined the effects of lateral hypothalamic (LH) stimulation on responses to tonic pain induced by subcutaneous formalin. Our findings demonstrate that LH stimulation produced analgesia for tonic pain and that the effect is primary and not related to stress-induced analgesia. The results are discussed in relation to hypotheses regarding the different neural substrates involved in analgesia for tonic and phasic pain.