Basic timekeeping deficit in the Beat-based form of congenital Amusia pauline tranchant 1,2 ✉ & isabelle peretz 1,2 Humans have the capacity to match movements' timing with the beat of music. Yet some individuals show marked difficulties. The causes of these difficulties remain to be determined. Here, we investigate to what extend a beat synchronization deficit can be traced to basic timekeeping abilities. Eight beatimpaired individuals who were unable to successfully synchronize to the beat of music were compared to matched controls in their ability to tap a self-paced regular beat, to tap to a metronome spanning a large range of tempi (225-1709 ms inter-tone onsets), and to maintain the tempi after the sounds had ceased. Whether paced by a metronome or not, beat-impaired individuals showed poorer regularity (higher variability) in tapping, with an inability to synchronize at a fast tempo (225 ms between beats) or to sustain tapping at slow tempi (above 1 sec). Yet, they showed evidence of predictive and flexible processing. We suggest that the beat impairment is due to imprecise internal timekeeping mechanism. When dancing or listening to music, we typically perceive a "beat" or an underlying metronome-like periodicity. We are extremely precise at synchronizing our movements to this auditory beat, without much awareness and without explicit tutoring. Yet, a few individuals have marked difficulties with synchronizing simple movements, such as bouncing their body, clapping their hands, or tapping their finger, with the musical beat 1-4. This deficit has been described as "beat-deafness" and to date has been diagnosed using musical stimuli. Here, we examine the possibility that the musical deficit arises from an anomaly in the basic timekeeping mechanisms underlying humans' exquisite ability to synchronize with external rhythms. Musical deficits can result from abnormal tuning of the auditory system. The most common form concerns the processing of musical pitch which has been ascribed to a faulty mechanism for detecting fine-grained pitch variations 5. Music requires the processing of much smaller pitch intervals than speech, which uses coarser pitch variations, at least in non-tonal languages. Indeed, the amusic individuals who suffer from a fine-grained pitch deficit report normal understanding of speech and prosody in everyday life. What characterizes them behaviourally is a difficulty with detecting mistuning in singing, including their own, recognizing a familiar tune without the aid of the lyrics, discriminating melodies varying in pitch, and maintaining melodies in short-term memory 6. It has been associated with abnormal connectivity between the auditory cortex and inferior frontal cortex, mostly in the right cerebral hemisphere 7. This pitch disorder is hereditary 8 , and molecular analyses are in progress to identify the responsible genes. In sum, research on the pitch-based form of amusia has uncovered links between acoustical pitch, music, brain networks, and genes. Likewise, impairments in musical bea...