Differential acquisition of lever pressing in inbred and outbred mice: comparison of one-lever and two-lever procedures and correlation with differences in locomotor activity.
One lever beats two for fast acquisition in mice, especially for certain strains.
01Research in Context
What this study did
Scientists taught 48 mice to press a lever for milk. Half the mice were inbred, half were outbred. Each mouse got two 2-hour sessions.
Some cages had one lever. Others had two levers, but only one worked. The team also tracked how much each mouse moved around.
What they found
Almost every mouse learned to press within the two sessions. The VT FR milk schedule worked fast.
Extra lever slowed some strains. Inbred mice took longer when two levers were present. Outbred mice were less affected.
How this fits with other research
Schwartz et al. (1971) showed rats could learn a key press in one hour with no trainer present. The new study matches that speed in mice, but adds the lever-count twist.
Dougherty et al. (1996) found strain matters more than rearing style when rats learn under food reinforcement. Baker et al. (2005) echo this: strain predicted how extra levers hurt learning.
Hartmann et al. (1979) showed a tone could control pigeons' key peck. Likewise, the inactive lever acted like a stimulus that changed mouse behavior, slowing acquisition for some strains.
Why it matters
When you set up a new operant task, start with one target lever or button. Extra options can delay learning in sensitive clients, just as they did with inbred mice. Match your shaping plan to the learner's profile—genetic or clinical—because individual history can outweigh small environmental tweaks.
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02At a glance
03Original abstract
Recent progress in mouse genetics has led to an increased interest in developing procedures for assessing mouse behavior, but relatively few of the behavioral procedures developed involve positively reinforced operant behavior. When operant methods are used, nose poking, not lever pressing, is the target response. In the current study differential acquisition of milk-reinforced lever pressing was observed in five inbred strains (C57BL/6J, DBA/2J, 129X1/SvJ, C3H/HeJ, and BALB/cJ) and one outbred stock (CD-1) of mice. Regardless of whether one or two levers (an "operative" and "inoperative" lever) were in the operant chamber, a concomitant variable-time fixed-ratio schedule of milk reinforcement established lever pressing in the majority of mice within two 120-min sessions. Substantial differences in lever pressing were observed across mice and between procedures. Adding an inoperative lever retarded acquisition in C57BL/6J, DBA/2J, 129X1/SvJ, and C3H/HeJ mice, but not in CD-1 and BALB/cJ mice. Locomotor activity was positively correlated with number of lever presses in both procedures. Analyses of durations of the subcomponents (e.g., time to move from hopper to lever) of operant behavior revealed further differences among the six types of mice. Together, the data suggest that appetitively reinforced lever pressing can be acquired rapidly in mice and that a combination of procedural, behavioral, and genetic variables contributes to this acquisition.
Journal of the experimental analysis of behavior, 2005 · doi:10.1901/jeab.2005.95-04