Effects of Differing Response‐force Requirements on Food‐maintained Responding in C57bl/6j Mice

Abstract

The effect of force requirements on response effort was examined using inbred C57BL/6J mice trained to press a disk with their snout. Lateral peak forces greater than 2 g were defined as responses (i.e., all responses above the measurement threshold). Different, higher force requirements were used to define criterion responses (a subclass of all responses) that exceeded the requirement and produced a reinforcer. The reinforcer was sweetened, condensed milk, delivered upon response termination. All mice were exposed to two ascending series of criterion force requirements (2, 4, 8, 16, and 32 g). Increasing the force requirement initially decreased criterion response rates, but criterion response rates recovered with continued exposure, except at the 32-g requirement. Response rates for all measured responses initially increased with increasing force requirements, but then decreased with continued exposure. The second exposure series produced more stable response rate changes than the first series. The time-integral of force (area under the force-time curve for individual responses, which is proportional to energy expenditure for each response) increased with the increase in the force requirement. The C57BL/6J inbred strain generated average force output similar to CD-1 outbred stock mice trained on the same force requirements. C57BL/6J inbred strain mice differed from CD-1 mice in initial response rates (for all responses above threshold) and had lower response rates at the 16 and 32 g requirements resulting in lower total force output. These data show for both mice types that increased force requirements resulted in increased overall responding (all measured responses), which contradicts a punishment interpretation of criterion response decrements. C57BL\6 inbred mice showed individual differences comparable to the outbred CD-1 stock. C57BL/6 mice did not maintain responding as well at the higher force requirements, which may be due to their small body size and weight, compared to the larger and heavier CD-1 mice.

The Isolation of Motivational, Motoric, and Schedule Effects on Operant Performance: A Modeling Approach

“…Interestingly, no effect of workload on overall response rate was detected. This result is inconsistent with many reports indicating an inverse relationship between force requirements and response rate (Adair & Wright, 1976; Alling & Poling, 1995; Bradshaw, Szabadi & Ruddle, 1983; Chung, 1965; Posadas‐Sanchez, 2005), although support for this relationship is not unequivocal (Collier & Jennings, 1969; Elsmore & Brownstein, 1968; Stanley & Aamodt, 1954; Zarcone, Chen & Fowler, 2007, 2009). Nonetheless, overall response rate is a crude measure of performance: By collapsing all the IRTs into the denominator, response rates neglect the information contained in the distribution of IRTs.…”

Aversive functions of response effort: Fact or artifact?

“…Responses counted at one point in a study are not counted at other points, and apparent rate decreases observed when force requirements are increased are likely because a portion of the original response class goes unmeasured. When the subcriterion responses are measured by defining a constant threshold, a consistent response definition is maintained, and we typically observed rate increases following increased force requirements, replicating the results of others (Mintz et al, ; Zarcone et al, , ). Our data underscore the importance of measuring subcriterion responses when force criteria are changed (Notterman & Mintz, ; Walker, Faustman, Fowler, & Kazar, ; Zarcone et al, ).…”

“…Zarcone et al () went on to conclude that apparent punishment effects observed under increased force requirements may be due to the definitional changes in the operant that arise when levers are used to define force criteria. Zarcone, Chen, and Fowler () replicated their prior study with a different mouse strain, C57Bl/6 J, and found again that increased force requirements increase operant behavior.…”

“…The work by Mintz et al (1965) and Zarcone et al (, ) indicates that increased force requirements may lead to increases in overall responding, an outcome at odds with an interpretation of effort as aversive. Zarcone et al (), moreover, speculated that increased response rates were perhaps due to the induced intermittency of reinforcers when the force was increased because the functional response:reinforcer ratio changed unpredictably with additional subcriterion responses.…”

The translational utility of behavioral economics: The experimental analysis of consumption and choice.

“…As any grocer will tell you, changing the unit price of a reinforcer may be accomplished by either increasing the cost of obtaining the reinforcer or decreasing the benefits of the reinforcer (e.g., selling an ounce less dried pasta at the same price). In the laboratory, cost is typically quantified by the number of responses the subject must emit per reinforcer, but it could also be quantified as effort expended per reinforcer (e.g., time integral of force; Zarcone, Chen, & Fowler, 2009), time to a reinforcer (e.g., Tsunematsu, 2000), or a commodity loss after each response (e.g., a responsecost contingency), to name just a few cost dimensions. For humans, the cost component may also be specified as the amount of money paid per reinforcer (money being a medium by which past labor is exchanged for present goods and services).…”