The pedunculopontine tegmental nucleus and responding for sucrose reward

Pedunculopontine tegmental nucleus (PPTg) lesions in rodents lead to increased sucrose consumption, but the psychological deficit behind this remains uncertain. To understand better the relationship between consumption of, and motivation for, sucrose, the authors trained rats to traverse a runway for 20% or 4% sucrose solution; after 7 days, concentrations were reversed. Control rats consumed more 20% than 4% sucrose solution and promptly altered run times in response to concentration change. PPTg-lesioned rats consumed normal quantities of 4% but more 20% sucrose solution than controls and took longer to alter their runway time following the concentration change. These data suggest that lesions of the PPTg do not alter motivation per se and might be better understood as inducing a response selection deficit.