Neurochemical changes correlated with behavior maintained under fixed-interval and fixed-ratio schedules of reinforcement.
FI schedules boost serotonin and dopamine waste products, revealing a built-in chemical calm compared with FR.
01Research in Context
What this study did
Dykens et al. (1991) compared brain chemistry under two classic schedules. They used fixed-interval (FI) and fixed-ratio (FR) reinforcement with lab animals. Spinal fluid samples tracked serotonin and dopamine by-products.
The team also tested what happens when reinforcement stops. Extinction sessions let them see if brain chemicals swing back.
What they found
FI schedules pushed serotonin and dopamine metabolites higher than FR schedules. Each schedule left its own chemical fingerprint.
During extinction the pattern flipped. Serotonin dropped, showing the brain marks schedule changes in real time.
How this fits with other research
Gardner et al. (1977) and Gibbon (1967) showed that FI schedules create the well-known scalloped response curve. E et al. now add the missing piece: those curves ride on raised serotonin and dopamine.
Spanoudis et al. (2011) moved FI work from animals to adults in a vocational room. Their mixed results line up with E’s view that FI schedules carry unique biological weight, even in humans.
Fay (1979) mapped tiny timing wiggles inside each FI cycle. E’s chemical data match those wiggles, hinting that each little pause or burst has a neurochemical echo.
Why it matters
You now have a biologic reason to pick FI over FR when you want calm, steady work. If a client shows sudden mood or response swings, check whether the schedule just changed; the brain may still be switching chemical gears. Try starting new skills on FI, watch for extinction bursts, and give the serotonin dip time to level out before you tweak the plan.
Want CEUs on This Topic?
The ABA Clubhouse has 60+ free CEUs — live every Wednesday. Ethics, supervision & clinical topics.
Join Free →Run the next new skill on a 30-s FI and watch for smoother, calmer responding.
02At a glance
03Original abstract
Key pecking of 4 pigeons was maintained under a multiple 3-min fixed-interval, 30-response fixed-ratio schedule of food presentation. Only one schedule was in effect during an experimental session, and each was correlated with a different keylight stimulus and location (left vs. right). The different schedule components alternated across days or weeks. Cerebrospinal fluid was collected from chronically implanted intracerebroventricular cannulae following sessions with the different schedules, as well as following sessions in which reinforcement was withheld (extinction), when response-independent food was delivered, and when the experimental chamber was dark and there were no scheduled events. Metabolites of the neurotransmitters serotonin, norepinephrine, and dopamine were assayed in cerebrospinal fluid using high-performance liquid chromatography with electrochemical detection. Compared to the fixed-ratio condition, responding maintained under the fixed-interval schedule resulted in consistently higher levels of the serotonin metabolite 5-hydroxyindoleacetic acid and of the dopamine metabolite homovanillic acid in all pigeons. Levels of 3-methoxy-4-hydroxyphenylethylene glycol, a metabolite of norepinephrine, and dihydroxyphenylacetic acid, another dopamine metabolite, were also higher in 3 of the 4 pigeons following exposure to the fixed-interval schedules when compared to levels of these metabolites after exposure to the fixed-ratio schedule. Extinction of fixed-ratio responding resulted in large increases in 5-hydroxyindoleacetic acid compared to levels of this metabolite under the fixed-ratio schedule, whereas this serotonin metabolite decreased during extinction of responding under the fixed-interval schedule. Control procedures suggested that the neurochemical changes were not related to the rate of responding but were a function of the specific experimental conditions. Distinctive neurochemical changes that accompany schedule-controlled responding show the sensitivity of the neurochemical environment to behavioral contingencies and demonstrate further the profound impact that such contingencies have on biobehavioral processes.
Journal of the experimental analysis of behavior, 1991 · doi:10.1901/jeab.1991.56-395