Time perception and delay discounting in the <scp>FMR1</scp> knockout rat
FMR1 rats show loose timing and steep delay discounting, giving us a lab model to screen timing-based interventions for kids with Fragile X or similar delays.
01Research in Context
What this study did
Fox et al. (2025) worked with FMR1 knockout rats. These rats lack the gene that causes Fragile X syndrome in people.
The team ran two tests. First, they asked the rats to tell the difference between short and long tones. Second, they let rats choose between one food pellet now or more pellets later.
What they found
The knockout rats were sloppy timers. They mixed up 2-second and 8-second tones more often than normal rats.
They also acted more impulsive. When the delay grew, they gave up the big reward faster than controls.
How this fits with other research
Hilton et al. (2010) and Haynes et al. (2022) showed that regular rats follow the same hyperbolic discount curve. Fox adds a genetic twist: without FMR1, the curve is steeper.
Droit-Volet et al. (2013) saw similar timing scatter in kids after cerebellar surgery. Both studies link brain changes to clock-like errors.
Amiri et al. (2014) deleted FMR1 only in mouse cortex and saw no behavior change. Fox’s whole-body knockout did show change. The difference warns us that timing and reward circuits sit outside the cortex or need the full-body knock to show up.
Why it matters
You now have a rat model that acts like many clients with developmental delay: poor wait skills and shaky time sense. Use it to pre-test timing or self-control tools before trying them in clinic. Start simple—think visual timers, paced reward schedules, or shorter wait windows—and let the rat data guide dose.
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02At a glance
03Original abstract
There is substantial evidence for timing (time perception) abnormalities related to developmental disabilities, particularly autism spectrum disorder. These findings have been reported in humans and nonhuman preclinical models. Our research objective was to extend that work to a genetic knockout (KO) model of fragile X/developmental disability, the FMR1 KO rat. We also sought to test delay discounting in the model and assess potential relations between timing and choice behavior. Consistent with previous human and nonhuman work, we found reduced timing precision in the FMR1 KO rats. We also discovered significantly increased smaller, sooner reward choice in the FMR1 KO rats. Performance on the timing task appeared to be unrelated to performance on the choice task for both model and control rats. These results add to what has become increasingly clear: timing is disrupted in humans diagnosed with developmental disabilities and in nonhuman models designed to model developmental disabilities. Our findings are consistent with those of previous work and the first to our knowledge to show such effects in the FMR1 KO rat. We discuss the potential clinical implications and future directions surrounding potential "timing interventions" for individuals diagnosed with developmental disabilities.
Journal of the Experimental Analysis of Behavior, 2025 · doi:10.1002/jeab.4227