Disruptive effects of lateral hypothalamic stimulation on the lick-interrupt cycle in rats

Consummatory licking at a water spout was compared with licking at a dry spout maintained by electrical hypothalamic stimulation in the same rats. Both forms of licking, recorded photoelectrically, were maintained on a fixed ratio 8 schedule. Duration of reinforcement delivery was equated [300 ms]. A computer analysis of the temporal distribution of licks in each 1024 ms period from onset of reinforcement revealed that lateral hypothalamic stimulation decreased the occurrence of licking and disrupted the normally synchronous pattern of this behaviour. An analysis of the effects of delivering lateral hypothalamic stimulation contingent on water-maintained licking revealed that this effect of stimulation was clearly current-dependent. It is proposed that differences in licking rates maintained by water and by electrical hypothalamic stimulation, respectively, are due to response interference in the latter case. This interference effect is also proposed to be a major factor underlying higher reward thresholds for self-stimulation when licking is the operant response.