Behavioral variability in SHR and WKY rats as a function of rearing environment and reinforcement contingency.
Genetics and the payoff rule steer variability; the childhood room décor does not.
01Research in Context
What this study did
Scientists raised two kinds of rats in two kinds of cages. Some cages had toys and friends. Others were bare and lonely.
Later the rats worked for sugar water. A computer paid them only if their lever presses formed a new pattern each minute. Other rats got sugar no matter how they pressed. The team counted how unpredictable each rat stayed.
What they found
SHR rats, the hyperactive strain, kept pressing in wild, jumpy ways no matter where they grew up or what the rule was.
WKY rats, the calm strain, quickly matched the rule. When the rule said "be different," they became more varied. When sugar was free, they settled into steady rhythms. Cage toys or bare walls changed none of this.
How this fits with other research
Baker et al. (2005) saw the same strain split in lever training. Extra levers slowed some mice but not others. Together the papers show genes set the speed limit; the task just reveals it.
Schwartz et al. (1971) shaped a brand-new key press in one hour with no trainer in the room. H et al. now show a machine can also sculpt how variable that press is. Both prove smart programming can replace hand shaping.
Brown et al. (1968) found pigeons pecked just because light predicted food, even without a contingency. H et al. show the opposite: when the contingency demanded variety, only certain rats changed. The two studies sit side-by-side, reminding us that both Pavlovian pairings and operant rules can drive the same muscle, depending on what you program.
Why it matters
You can stop blaming the cage. Enrichment is nice, but the payoff rule matters more. If a child with ADHD shows rigid play, tweak the reinforcement for new moves, not just the toy shelf. Start by reinforcing any novel response; once variability rises you can shape it toward useful forms.
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02At a glance
03Original abstract
The spontaneously hypertensive rat (SHR) may model aspects of human attention deficit hyperactivity disorder (ADHD). For example, just as responses by children with ADHD tend to be variable, so too SHRs often respond more variably than do Wistar-Kyoto (WKY) control rats. The present study asked whether behavioral variability in the SHR strain is influenced by rearing environment, a question related to hypotheses concerning the etiology of human ADHD. Some rats from each strain were reared in an enriched environment (housed socially), and others were reared in an impoverished environment (housed in isolation). Four groups--enriched SHR, impoverished SHR, enriched WKY, and impoverished WKY--were studied under two reinforcement contingencies, one in which reinforcement was independent of response variability and the other in which reinforcement depended upon high variability. The main finding was that rearing environment did not influence response variability (enriched and impoverished subjects responded similarly throughout). However, rearing environment affected body weight (enriched subjects weighted more than impoverished subjects) and response rate (impoverished subjects generally responded faster than enriched subjects). In addition, SHRs tended to respond variably throughout the experiment, whereas WKYs were more sensitive to the variability contingencies. Thus, behavioral variability was affected by genetic strain and by reinforcement contingency but not by the environment in which the subjects were reared.
Journal of the experimental analysis of behavior, 1996 · doi:10.1901/jeab.1996.65-129