The fine temporal structure of the rat licking pattern: What causes the variabiliy in the interlick intervals and how is it affected by the drinking solution?

Abstract

Licking is a repetitive behavior controlled by a central pattern generator. Even though interlick intervals (ILIs) within bursts of licks are considered fairly regular, the conditions that affect their variability are unknown. We analyzed the licking pattern in rats that licked water, 10% sucrose solution, or 10% ethanol solution, in 90-min recording sessions after 4 h of water deprivation. The histograms of ILIs indicate that licking typically occurred at a preferred ILI of about 130-140 ms with evidence of bimodal or multimodal distributions due to occasional licking failures. We found that the longer the pause between bursts of licks, the shorter was the first ILI of the burst. When bursts of licks were preceded by a pause >4 s, the ILI was the shortest (~110 ms) at the beginning of the burst, and then it increased rapidly in the first few licks and slowly in subsequent licks. Interestingly, the first ILI of a burst of licks was not significantly different when licking any of the 3 solutions, but subsequent licks exhibited a temporal pattern characteristic of each solution. The rapid deceleration in intraburst licking rate was due to an increase from ̃27 ms to ̃56 ms in the tongue-spout contact duration while the intercontact interval was only slightly changed (80-90 ms). Therefore, the contact duration seems to be the major factor that increases the variability in the ILIs and could be another means for the rat to adjust the amount of fluid ingested in each individual lick. © The Authors 2013. Published by Oxford University Press. All rights reserved.