Learning impairments in Fmr1−/− mice on an audio-visual temporal pattern discrimination task

Estimating time and making predictions is integral to our experience of the world. Given the importance of timing to most behaviors, disruptions in temporal processing and timed performance are reported in a number of neuropsychiatric disorders such as Schizophrenia, Autism Spectrum Disorder (ASD), Fragile X Syndrome (FXS), and Attention-deficit Hyperactivity Disorder (ADHD). Symptoms that implicitly include disruption in timing are atypical turn-taking during social interactions, unusual verbal intonations, poor reading, speech and language skills, inattention, delays in learning, and difficulties making predictions. Currently, there are no viable treatments for these symptoms, the reason being the underlying neural dysfunction that contributes to timing deficits in neuropsychiatric disorders is unknown. To address this unknown, we have designed a novel Temporal Pattern Sensory Discrimination Task (TPSD) for awake-behaving mice. Stimuli consist of paired audiovisual stimuli that differ in duration. Compared to Wild-Type (WT) mice, Fmr1^-/- mice, a well-established mouse model of FXS, showed significant impairment in learning the TPSD task, as evidenced by reduced discriminability indices and atypical licking patterns. Often sensory information is multimodal and, indeed, studies show that learning in humans and rodents improves with multimodal stimuli than with unimodal stimuli. To test how the multimodal nature of stimuli impacted performance of Fmr1^-/- mice, following training on the audiovisual stimuli, we tested mice on audio-only or visual-only stimuli. While WT mice showed significant disruption in performance when tested on unimodal stimuli, Fmr1^-/- mice displayed equivalent performance on visual-only stimuli when compared to the multimodal task. Our novel task captures timing difficulties and multisensory integration issues in Fmr1^-/- mice and provides an assay to examine the associated neural dysfunction.