This study describes the psychometric similarities and differences in motor timing performance between 20 human subjects and three rhesus monkeys during two timing production tasks. These tasks involved tapping on a push-button to produce the same set of intervals (range of 450 to 1,000 ms), but they differed in the number of intervals produced (single vs. multiple) and the modality of the stimuli (auditory vs. visual) used to define the time intervals. The data showed that for both primate species, variability increased as a function of the length of the produced target interval across tasks, a result in accordance with the scalar property. Interestingly, the temporal performance of rhesus monkeys was equivalent to that of human subjects during both the production of single intervals and the tapping synchronization to a metronome. Overall, however, human subjects were more accurate than monkeys and showed less timing variability. This was especially true during the self-pacing phase of the multiple interval production task, a behavior that may be related to complex temporal cognition, such as speech and music execution. In addition, the wellknown human bias toward auditory as opposed to visual cues for the accurate execution of time intervals was not evident in rhesus monkeys. These findings validate the rhesus monkey as an appropriate model for the study of the neural basis of time production, but also suggest that the exquisite temporal abilities of humans, which peak in speech and music performance, are not all shared with macaques.

Merchant H, Zarco W, Prado L. Do we have a common mechanism for measuring time in the hundreds of millisecond range? Evidence from multiple-interval timing tasks. J Neurophysiol 99: 939 -949, 2008. First published December 19, 2007 doi:10.1152/jn.01225.2007. In the present study we examined the performance variability of a group of 13 subjects in eight different tasks that involved the processing of temporal intervals in the subsecond range. These tasks differed in their sensorimotor processing (S; perception vs. production), the modality of the stimuli used to define the intervals (M; auditory vs. visual), and the number of intervals (N; one or four). Different analytical techniques were used to determine the existence of a central or distributed timing mechanism across tasks. The results showed a linear increase in performance variability as a function of the interval duration in all tasks. However, this compliance of the scalar property of interval timing was accompanied by a strong effect of S, N, and M and the interaction between these variables on the subjects' temporal accuracy. Thus the performance variability was larger not only in perceptual tasks than that in motor-timing tasks, but also using visual rather than auditory stimuli, and decreased as a function of the number of intervals. These results suggest the existence of a partially overlapping distributed mechanism underlying the ability to quantify time in different contexts. I N T R O D U C T I O NOrganisms have developed different mechanisms to quantify time over a wide range of durations, from microseconds to daily circadian rhythms. It has been suggested that in the middle of these extremes there is a timing mechanism devoted to the hundreds of millisecond scale (Harrington and Haaland 1999;Hazeltine et al. 1997), which is the range of durations used in the present study. Interval timing in this range is a prerequisite in several behaviors, including the perception and production of speech, music, and dance, as well as the performance of sports and estimation of the time that remains before the occurrence of an important event, such as estimating time to contact (Merchant and Georgopoulos 2006). Different sources of information support the hypothesis of a common timing mechanism in hundreds of milliseconds. First, several psychological studies have shown that the temporal performance follows the scalar property, which defines a linear relationship between the variability of temporal performance and interval duration, in conformity with Weber's law (Matell and Meck 2000). Thus Weber's law is given as SD(T) ϭ kT, where k is a constant corresponding to the Weber fraction. In this sense, the coefficients of variation (/) or the Weber fractions show similar values in a variety of tasks and species, suggesting a dedicated temporal mechanism in this time range (Gibbon et al. 1997). For example, in a human discrimination task of time intervals, Getty (1975) described a constant Weber fraction for intervals between 200 and 2,000 ms. Now, another conce...

Temporal information processing is critical for many complex behaviors including speech and music cognition, yet its neural substrate remains elusive. We examined the neurophysiological properties of medial premotor cortex (MPC) of two Rhesus monkeys during the execution of a synchronization-continuation tapping task that includes the basic sensorimotor components of a variety of rhythmic behaviors. We show that time-keeping in the MPC is governed by separate cell populations. One group encoded the time remaining for an action, showing activity whose duration changed as a function of interval duration, reaching a peak at similar magnitudes and times with respect to the movement. The other cell group showed a response that increased in duration or magnitude as a function of the elapsed time from the last movement. Hence, the sensorimotor loops engaged during the task may depend on the cyclic interplay between different neuronal chronometers that quantify the time passed and the remaining time for an action.medial premotor area | timing neurophysiology | supplementary motor area I nterval timing in the milliseconds is a prerequisite for many complex behaviors, such as the perception and production of speech (1), the execution and appreciation of music and dance (2, 3), and the performance of a large variety of sports (4). Time in music comes in a variety of patterns, which include isochronous sequences where temporal intervals are of a single constant duration or, more commonly, sequences containing intervals of many durations. In addition, the ability to capture and interpret the beats in a rhythmic pattern allows people to move and dance in time to music (3). Music and dance, then, are behaviors that depend on intricate loops of perception and action, where temporal processing can be involved during the synchronization of movements with sensory information or during the internal generation of movement sequences (2). In a simplified version of these activities, numerous studies have examined how subjects synchronize taps with pacing isochronous auditory stimuli and then continue tapping at the instructed rate without the advantage of the sensory metronome (5). Thus, the cyclic nature of the synchronizationcontinuation task (SCT) implies that subjects must keep track of the time elapsed since the previous sensorimotor events as well as the time remaining until the next events.Functional imaging studies have shown that the basal ganglia, the medial premotor cortex (MPC, pre-and supplementary motor areas), the prefrontal and posterior parietal cortex, and the cerebellum are the main nodes of a timing network that is engaged during different time production and perception tasks, including the SCT (6, 7). These studies suggest the existence of a partially overlapping distributed system for the temporal information processing in a variety of sensorimotor contexts that reach a complexity peak during musical cognition and speech, but that also include the production and estimation of single intervals (2,8).Neurophysiolog...

Gamma (␥) and beta (␤) oscillations seem to play complementary functions in the cortico-basal ganglia-thalamo-cortical circuit (CBGT) during motor behavior. We investigated the time-varying changes of the putaminal spiking activity and the spectral power of local field potentials (LFPs) during a task where the rhythmic tapping of monkeys was guided by isochronous stimuli separated by a fixed duration (synchronization phase), followed by a period of internally timed movements (continuation phase). We found that the power of both bands and the discharge rate of cells showed an orderly change in magnitude as a function of the duration and/or the serial order of the intervals executed rhythmically. More LFPs were tuned to duration and/or serial order in the ␤-than the ␥-band, although different values of preferred features were represented by single cells and by both bands. Importantly, in the LFPs tuned to serial order, there was a strong bias toward the continuation phase for the ␤-band when aligned to movements, and a bias toward the synchronization phase for the ␥-band when aligned to the stimuli. Our results suggest that ␥-oscillations reflect local computations associated with stimulus processing, whereas ␤-activity involves the entrainment of large putaminal circuits, probably in conjunction with other elements of CBGT, during internally driven rhythmic tapping.

It was recently shown that rhythmic entrainment, long considered a human-specific mechanism, can be demonstrated in a selected group of bird species, and, somewhat surprisingly, not in more closely related species such as nonhuman primates. This observation supports the vocal learning hypothesis that suggests rhythmic entrainment to be a by-product of the vocal learning mechanisms that are shared by several bird and mammal species, including humans, but that are only weakly developed, or missing entirely, in nonhuman primates. To test this hypothesis we measured auditory event-related potentials (ERPs) in two rhesus monkeys (Macaca mulatta), probing a well-documented component in humans, the mismatch negativity (MMN) to study rhythmic expectation. We demonstrate for the first time in rhesus monkeys that, in response to infrequent deviants in pitch that were presented in a continuous sound stream using an oddball paradigm, a comparable ERP component can be detected with negative deflections in early latencies (Experiment 1). Subsequently we tested whether rhesus monkeys can detect gaps (omissions at random positions in the sound stream; Experiment 2) and, using more complex stimuli, also the beat (omissions at the first position of a musical unit, i.e. the ‘downbeat’; Experiment 3). In contrast to what has been shown in human adults and newborns (using identical stimuli and experimental paradigm), the results suggest that rhesus monkeys are not able to detect the beat in music. These findings are in support of the hypothesis that beat induction (the cognitive mechanism that supports the perception of a regular pulse from a varying rhythm) is species-specific and absent in nonhuman primates. In addition, the findings support the auditory timing dissociation hypothesis, with rhesus monkeys being sensitive to rhythmic grouping (detecting the start of a rhythmic group), but not to the induced beat (detecting a regularity from a varying rhythm).