Testing rodents in their home cages has become increasingly popular. Since human intervention, handling, and transport are
minimized, behavior can be recorded undisturbed and continuously. Currently existing home cage systems are too complex if
only relatively simple operant-learning tests are to be carried out in rats. For that purpose, a new low-cost computer-controlled
operant panel was designed, which can be placed inside the home cage. A pilot study was carried out, using an intolerance-to-delay
protocol, classically developed for testing behavioral impulsivity. Male adult rats were tested in their home cages, containing
the operant panel provided with nosepoking holes. Nose poking in one hole resulted in the immediate delivery of one food pellet
(small-soon, SS), whereas nose poking in the other hole delivered five food pellets after a delay (large-late), which was
increased progressively each day (0–150 sec). The two daily sessions, spaced 8 h apart, lasted 1 h each, and the time-out
after food delivery was 90 sec. A clear-cut shift toward preference for SS, which is considered a classical index of cognitive
impulsivity, was shown at the longest delay. It is noteworthy that rats shifted when the delay interval was longer than the
mean intertrial interval—that is, when they experienced more than one delay-equivalent odds against discounting (see Adriani
& Laviola, 2006). The shortened training (2 days) and testing (5 days) phases, as allowed by prolonged and multiple daily
sessions, can be advantageous in testing rodents during selected short phases of development. Current research is focusing
on further validation of this and similar protocols.
Research was performed along the lines of the “ADHD-sythe” young investigator project (to W.A.): “under-40 call” by the Italian
Ministry of Health (assigned), and “ERC-StG” by EU-FP7-Ideas (pending). It was also supported by the bilateral Italy-U.S.
Program on Rare Diseases (7NR1) and by the ERARE-EuroRETT Network (ERAR/6), EU (to G.L.). S.K. was a recipient of an Erasmus
fellowship, within the Lifelong Learning Programme (to L.S.), supporting her stay at the Istituto Superiore di Sanità.
Note—This article is based on a presentation made at Measuring Behavior 2008.