It is concerning this article: The Effects of a Co-Application of Menthol and Capsaicin on Nociceptive Behaviors of the Rat on the Operant Orofacial Pain Assessment Device (Anderson et al., 2014)
The L/F ratio is the number of licks an animal makes while it's face is in contact with the peltier probe - a higher number suggest the temperature is not aversive.
Using the L/F ratio rather than total licks during the trial allows you to distinguish behavioural differences in number of contacts e.g. one rat may make numerous contacts with a low lick rate, or few contacts but a high lick rate.
Great question !
Rosie's answer is very accurate and has important implications for understanding findings of co-stimuli of different MOA at different temperatures. They selected rats who would lick (rewarding behavior) 2000 times over the 17 minute time for non-aversive facial stimuli . If few contact stimuli are perceived as aversive then the the L/F ratio would go down, but operant conditioning at lower temperatures may have the rat seek out more contacts (even though aversive with lower L/F ratios) so that the total number of licks increases at the lower temperature in their misguided attempt to consume anticipated rewards that are clearly not forthcoming.
Humans can be very similar if you think this thru! Hope this helps !!!
The study you refer to thus found that different effects of temperature were observed for Lick/Face, licking behavior, and contact behavior at baseline on the OPAD. The non-neutral temperature conditions caused rats to alter their behavior from many licks per facial contact to few licks per facial contact at both 21°C and 45°C. This demonstrates that they perceive pain during these conditions. Nociception decreases the Lick/Face value on operant orofacial assays and analgesia can increase it . However, the 45°C condition had a greater impact on the rats' reward consumption behavior than 21°C. Licking was equally high between the 33°C and 21°C temperatures. So even though the rats' have a nociceptive and/or aversive response at 21°C, they continue to consume reward. A combination of increased number of contacts and a low Lick/Face ratio allows them to consume more reward at 21°C.
