Panksepp & Burgdorf 2000. Panksepp, Jaak; Burgdorf, Jeff (October 2000). "50k-Hz chirping (laughter?) in response to conditioned and unconditioned tickle-induced reward in rats: effects of social housing and genetic variables". Behavioural Brain Research. 115 (1): 25–38. doi:10.1016/s0166-4328(00)00238-2. PMID10996405. S2CID29323849.
Panksepp & Burgdorf 2000. Panksepp, Jaak; Burgdorf, Jeff (October 2000). "50k-Hz chirping (laughter?) in response to conditioned and unconditioned tickle-induced reward in rats: effects of social housing and genetic variables". Behavioural Brain Research. 115 (1): 25–38. doi:10.1016/s0166-4328(00)00238-2. PMID10996405. S2CID29323849.
Panksepp & Burgdorf 2000. Panksepp, Jaak; Burgdorf, Jeff (October 2000). "50k-Hz chirping (laughter?) in response to conditioned and unconditioned tickle-induced reward in rats: effects of social housing and genetic variables". Behavioural Brain Research. 115 (1): 25–38. doi:10.1016/s0166-4328(00)00238-2. PMID10996405. S2CID29323849.
Panksepp 1998. Panksepp, Jaak (1998). Affective neuroscience : the foundations of human and animal emotions. New York: Oxford University Press. ISBN0195096738. OCLC38580282.