Prefrontal involvement in "temporal bridging" and timing movement

Adaptive reconfiguration of fractal small-world human brain functional networks

Brain function depends on adaptive self-organization of large-scale neural assemblies, but little is known about quantitative network parameters governing these processes in humans. Here, we describe the topology and synchronizability of frequency-specific brain functional networks using wavelet decomposition of magnetoencephalographic time series, followed by construction and analysis of undirected graphs. Magnetoencephalographic data were acquired from 22 subjects, half of whom performed a finger-tapping task, whereas the other half were studied at rest. We found that brain functional networks were characterized by small-world properties at all six wavelet scales considered, corresponding approximately to classical delta (low and high), , alpha, beta, and gamma frequency bands. Global topological parameters (path length, clustering) were conserved across scales, most consistently in the frequency range 2-37 Hz, implying a scale-invariant or fractal small-world organization. Dynamical analysis showed that networks were located close to the threshold of order/disorder transition in all frequency bands. The highest-frequency gamma network had greater synchronizability, greater clustering of connections, and shorter path length than networks in the scaling regime of (lower) frequencies. Behavioral state did not strongly influence global topology or synchronizability; however, motor task performance was associated with emergence of long-range connections in both beta and gamma networks. Long-range connectivity, e.g., between frontal and parietal cortex, at high frequencies during a motor task may facilitate sensorimotor binding. Human brain functional networks demonstrate a fractal small-world architecture that supports critical dynamics and task-related spatial reconfiguration while preserving global topological parameters.

The substantia nigra pars compacta and temporal processing

The basal ganglia and cerebellum are considered to play a role in timing, although their differential roles in timing remain unclear. It has been proposed that the timing of short milliseconds-range intervals involves the cerebellum, whereas longer seconds-range intervals engage the basal ganglia (Ivry, 1996). We tested this hypothesis using positron emission tomography to measure regional cerebral blood flow in eight right-handed males during estimation and reproduction of long and short intervals. Subjects performed three tasks: (1) reproduction of a short 500 ms interval, (2) reproduction of a long 2 s interval, and (3) a control simple reaction time (RT) task. We compared the two time reproduction tasks with the control RT task to investigate activity associated with temporal processing once additional cognitive, motor, or sensory processing was controlled. We found foci in the left substantia nigra and the left lateral premotor cortex to be significantly more activated in the time reproduction tasks than the control RT task. The left caudate nucleus and right cerebellum were more active in the short relative to the long interval, whereas greater activation of the right putamen and right cerebellum occurred in the long rather than the short interval. These results suggest that the basal ganglia and the cerebellum are engaged by reproduction of both long and short intervals but play different roles. The fundamental role of the substantia nigra in temporal processing is discussed in relation to previous animal lesion studies and evidence for the modulating influence of dopamine on temporal processing.

Time perception: manipulation of task difficulty dissociates clock functions from other cognitive demands

Previous studies suggest the involvement in timing functions of a surprisingly extensive network of human brain regions. But it is likely that while some of these regions play a fundamental role in timing, others are activated by associated task demands such as memory and decision-making. In two experiments, time perception (duration discrimination) was studied under two conditions of task difficulty and neural activation was compared using fMRI. Brain activation during duration discrimination was contrasted with activation evoked in a control condition (colour discrimination) that used identical stimuli. In the first experiment, the control task was slightly easier than the time task. Multiple brain areas were activated, in line with previous studies. These included the prefrontal cortex, cerebellum, inferior parietal lobule and striatum. In the second experiment, the control task was made more difficult than the time task. Much of the differential time-related activity seen in the first experiment disappeared and in some regions (inferior parietal cortex, pre-SMA and parts of prefrontal cortex) it reversed in polarity. This suggests that such activity is not specifically concerned with timing functions, but reflects the relative cognitive demands of the two tasks. However, three areas of time-related activation survived the task-difficulty manipulation: (i) a small region at the confluence of the inferior frontal gyrus and the anterior insula, bilaterally, (ii) a small portion of the left supramarginal gyrus and (iii) the putamen. We argue that the extent of the timing "network" has been significantly over-estimated in the past and that only these three relatively small regions can safely be regarded as being directly concerned with duration judgements.

Effect of task difficulty on the functional anatomy of temporal processing

Temporal processing underlies many aspects of human perception, performance and cognition. The present study used fMRI to examine the functional neuroanatomy of a temporal discrimination task and to address two questions highlighted by previous studies: (1) the effect of task difficulty on neuronal activation and (2) the involvement of the dorsolateral prefrontal cortex (DLPFC) in timing. Twenty healthy subjects were scanned while either judging whether the second in a pair of tones was shorter or longer in duration than the standard tone or simply responding to the presentation of two identical tones as a control condition. Two levels of difficulty were studied. Activation during the less difficult condition was observed only in the cerebellum and superior temporal gyrus. As difficulty increased, additional activation of the supplementary motor area, insula/operculum, DLPFC, thalamus and striatum was observed. These results suggest the cerebellum plays a critical role in timing, particularly in gross temporal discrimination. These results also suggest that recruitment of frontal and striatal regions during timing tasks is load-dependent. Additionally, robust activation of the dorsolateral prefrontal cortex under conditions of minimal working memory involvement supports the specific involvement of this region in temporal processing rather than a more general involvement in working memory.

Parameterization of movement execution in children with developmental coordination disorder

The Rhythmic Movement Test (RMT) evaluates temporal and amplitude parameterization and fluency of movement execution in a series of rhythmic arm movements under different sensory conditions. The RMT was used in combination with a jumping and a drawing task, to evaluate 36 children with Developmental Coordination Disorder (DCD) and a matched control group. RMT errors in space and in time were significantly larger for children with DCD. Omission of sensory information decreased the accuracy of movement parameterization in children with DCD more than in the control group, suggesting that children with DCD have more problems in building up an internal representation of the movement. Errors in time correlated significantly with the jumping and drawing task, while errors in space did not. Deficits of temporal movement parameterization might be one of the underlying causes of poor motor performance in some children with DCD.

A right hemispheric prefrontal system for cognitive time measurement

Despite a growing body of neuroimaging data, little consensus has been reached regarding the neural correlates of temporal processing in humans. This paper presents a reanalysis of two previously published neuroimaging experiments, which used two different cognitive timing tasks and examined both sub- and supra-second intervals. By processing these data in an identical manner, this reanalysis allows valid comparison and contrasting across studies. Conjunction of these studies using inclusive masking reveals shared activity in right hemispheric dorsolateral and ventrolateral prefrontal cortex and anterior insula, supporting a general-purpose system for cognitive time measurement in the right hemispheric prefrontal cortex. Consideration of the patterns of activity in each dataset with respect to the others, and taking task characteristics into account, provides insight into the possible role of dorsolateral prefrontal cortex in working memory and of posterior parietal cortex and anterior cingulate in attentional processing during cognitive time measurement tasks.

The supplementary motor area in motor and perceptual time processing: fMRI studies

The neural bases of timing mechanisms in the second-to-minute range are currently investigated using multidisciplinary approaches. This paper documents the involvement of the supplementary motor area (SMA) in the encoding of target durations by reporting convergent fMRI data from motor and perceptual timing tasks. Event-related fMRI was used in two temporal procedures, involving (1) the production of an accurate interval as compared to an accurate force, and (2) a dual-task of time and colour discrimination with parametric manipulation of the level of attention attributed to each parameter. The first study revealed greater activation of the SMA proper in skilful control of time compared to force. The second showed that increasing attentional allocation to time increased activity in a cortico-striatal network including the pre-SMA (in contrast with the occipital cortex for increasing attention to colour). Further, the SMA proper was sensitive to the attentional modulation cued prior to the time processing period. Taken together, these data and related literature suggest that the SMA plays a key role in time processing as part of the striato-cortical pathway previously identified by animal studies, human neuropsychology and neuroimaging.

Timing of covert articulation: An fMRI study

Timing is an important constituent of speech and language. Different brain regions have been associated with time management functions such as time estimation and motor timing. This study aims to identify the less well known neural networks associated with timing of internally paced covert articulation. Functional MRI was performed on subjects who either spontaneously, or in response to a visual cue, covertly generated words every 2 s. Results show the involvement of anterior cingulate gyrus, right dorsolateral and inferior frontal and right inferior parietal cortices in a putatively modality independent circuit associated with timing of covert speech. Modality specific activation in the right temporal cortex may have reflected the involvement of this region in auditory-verbal processing.

What makes us tick? Functional and neural mechanisms of interval timing

Time is a fundamental dimension of life. It is crucial for decisions about quantity, speed of movement and rate of return, as well as for motor control in walking, speech, playing or appreciating music, and participating in sports. Traditionally, the way in which time is perceived, represented and estimated has been explained using a pacemaker-accumulator model that is not only straightforward, but also surprisingly powerful in explaining behavioural and biological data. However, recent advances have challenged this traditional view. It is now proposed that the brain represents time in a distributed manner and tells the time by detecting the coincidental activation of different neural populations.

Keeping time: effects of focal frontal lesions

This study examined the performance of 32 normal subjects and 39 patients with focal lesions of the frontal lobes on two simple timing tasks-responding in time with a tone that regularly repeated at a rate of once every 1.5s, and then maintaining the same regular response rhythm without any external stimulus. The hypothesis was that lesions to the right prefrontal cortex would disrupt timing performance. The two main findings were (1) an abnormally high variability in the timing performance (both self-timed and tone-timed) of patients with lesions to the right lateral frontal lobe, particularly involving Brodmann area 45 and subjacent regions of the basal ganglia; (2) an increase in the variability of timing performance as the task continued in patients with lesions to the superior medial regions of the frontal lobe. These findings indicate that the right lateral frontal lobe is crucially involved in the ongoing control of timed behavior, either because of its role in generating time intervals or in monitoring the passage of these intervals. In contrast, the superior medial regions of the frontal lobe are necessary to maintain consistent timing performance over prolonged periods of time.

Cumulative blood oxygenation-level-dependent signal changes support the ‘time accumulator’ hypothesis

We studied time-related changes in the blood oxygenation-level-dependent signal during a time reproduction task. Nine healthy study participants retained and reproduced stimuli of varying durations in the multi-second range. During the encoding phase of the task, activity in the left dorsolateral prefrontal cortex inversely correlated with the interval duration, while an adjacent region in the dorsolateral prefrontal cortex showed positive correlation with duration in the reproduction phase. Cumulative signal increase during the reproduction phase, as found in the primary motor and supplementary motor areas, may also reflect the time-sensitive behavior. Signal accumulation in the right caudate nucleus is in agreement with presumed role of basal ganglia in time perception. These results support the 'time accumulator' hypothesis.

Functional MRI reveals the existence of modality and coordination-dependent timing networks

Growing evidence suggests that interval timing in humans is supported by distributed brain networks. Recently, we demonstrated that the specific network recruited for the performance of rhythmic timing is not static but is influenced by the coordination pattern employed during interval acquisition. Here we expand on this previous work to investigate the role of stimulus modality and coordination pattern in determining the brain areas recruited for performance of a self-paced rhythmic timing task. Subjects were paced with either a visual or an auditory metronome in either a synchronized (on the beat) or syncopated (off the beat) coordination pattern. The pacing stimulus was then removed and subjects continued to move based on the required interval. When compared with networks recruited for auditory pacing and continuation, the visual-specific activity was observed in the classic dorsal visual stream that included bilateral MT/V5, bilateral superior parietal lobe, and right ventral premotor cortex. Activity in these regions was present not only during pacing, when visual information is used to guide motor behavior, but also during continuation, when visual information specifying the temporal interval was no longer present. These results suggest a role for modality-specific areas in processing and representing temporal information. The cognitive demands imposed by syncopated coordination resulted in increased activity in a broad network that included supplementary motor area, lateral pre-motor cortex, bilateral insula, and cerebellum. This coordination-dependent activity persisted during the subsequent continuation period, when stimuli were removed and no coordination constraints were imposed. Taken together, the present results provide additional evidence that time and timing are served by a context-dependent distributed network rooted in basic sensorimotor processes.

Time estimation and performance on reproduction tasks in subtypes of children with attention deficit hyperactivity disorder

This study compared Hispanic children (ages 7 to 11) with combined type (CT, n=33) and inattentive type (IT, n=21) attention deficit hyperactivity disorder (ADHD) and a control group (n=25) on time-estimation and time-reproduction tasks. The ADHD groups showed larger errors in time reproduction but not in time estimation than the control group, and the groups did not differ from each other on their performance on this task. Individual differences could not be accounted for by oppositional-defiance ratings and low math or reading scores. Although various measures of executive functioning did not make significant unique contributions to time estimation performance, those of interference control and nonverbal working memory did so to the time-reproduction task. Findings suggest that ADHD is associated with a specific impairment in the capacity to reproduce rather than estimate time durations and that this may be related to the children's deficits in inhibition and working memory.

Frontal-striatal circuitry activated by human peak-interval timing in the supra-seconds range

Functional magnetic resonance imaging (fMRI) was used to measure the location and intensity of brain activations when participants time an 11-s signal duration. The experiment evaluated six healthy adult male participants who performed the peak-interval timing procedure in variants of stimulus modality (auditory or visual) and condition (foreground or background: i.e., whether the presence or absence of the stimulus is the signal to be timed). The complete experimental design called for each signal variant to be used across four behavioral tasks presented in the following order: control, timing+motor, timing, and motor. In the control task, participants passively experienced the stimuli. The timing+motor and timing tasks were preceded by five fixed-time training trials in which participants learned the 11-s signal they would subsequently reproduce. In the timing+motor task, participants made two motor responses centered around their subjective estimate of the criterion time. For the timing task, participants were instructed to time internally without making a motor response. The motor task had participants make two cued responses that were not determined by the participant's sense of the passage of time. Neuroimaging data from the timing+motor and timing tasks showed activation of the frontal cortex, striatum and thalamus--none of which was apparent in the control or motor tasks. These results, combined with other peak-interval procedure data from drug and lesion studies in animals as well as behavioral results in human patient populations with striatal damage, support the involvement of frontal-striatal circuitry in human interval timing.

Visually cued motor synchronization: modulation of fMRI activation patterns by baseline condition

A well-known issue in functional neuroimaging studies, regarding motor synchronization, is to design suitable control tasks able to discriminate between the brain structures involved in primary time-keeper functions and those related to other processes such as attentional effort. The aim of this work was to investigate how the predictability of stimulus onsets in the baseline condition modulates the activity in brain structures related to processes involved in time-keeper functions during the performance of a visually cued motor synchronization task (VM). The rational behind this choice derives from the notion that using different stimulus predictability can vary the subject's attention and the consequently neural activity. For this purpose, baseline levels of BOLD activity were obtained from 12 subjects during a conventional-baseline condition: maintained fixation of the visual rhythmic stimuli presented in the VM task, and a random-baseline condition: maintained fixation of visual stimuli occurring randomly. fMRI analysis demonstrated that while brain areas with a documented role in basic time processing are detected independent of the baseline condition (right cerebellum, bilateral putamen, left thalamus, left superior temporal gyrus, left sensorimotor cortex, left dorsal premotor cortex and supplementary motor area), the ventral premotor cortex, caudate nucleus, insula and inferior frontal gyrus exhibited a baseline-dependent activation. We conclude that maintained fixation of unpredictable visual stimuli can be employed in order to reduce or eliminate neural activity related to attentional components present in the synchronization task.

fMRI studies of temporal attention: allocating attention within, or towards, time

Attention is distributed in time as well as space. Moreover, attention can be actively directed both within, and towards, time. This review article summarises behavioural and neuroanatomical correlates of temporal aspects of attention. Orienting attention to particular moments in time, or selectively attending to temporal rather than non-temporal stimulus features, improves behavioural measures of performance. These effects are accompanied by specific increases in activity of functionally specialised, and anatomically discrete, brain regions. Left parietal cortex is associated with orienting attention to specific moments in time. Pre-supplementary motor area (SMA) is associated with selectively attending to, and estimating, time. Frontal operculum is associated with all of these processes as well as being activated when attentional resources are limited by time itself. The frontal operculum therefore plays a pivotal role in the multi-faceted interaction between time and attention.

Medial prefrontal cortex and precision of temporal discrimination: a lesion, microinjection, and microdialysis study

In this paper, we examined the role of the medial prefrontal cortex in temporal discrimination in three experiments using rats. Experiment 1 attempted to dissociate the roles of the medial precentral (PrCm) area from the prelimbic and infralimbic (PL-IL) area in temporal discrimination using fixed-interval (FI) schedule. The gradient of response rate distribution became more moderate by a lesion of the PrCm, but not by a lesion of the PL-IL. In experiment 2, the efflux of acetylcholine (ACh) in the PrCm area during temporal discrimination tasks was compared to that during non-temporal discrimination tasks. ACh efflux was not different between these two tasks. In experiment 3, microinjection of the anticholinergic drug scopolamine (10 microg) into the PrCm area made the gradient of response rate distribution moderate. These findings suggest that reduced activity of the ACh system within the PrCm area impairs the precision of temporal discrimination, even though enhancement of this system is not indispensable for performing temporal discrimination.

Event-related potentials in the frontal lobe during performance of a visual duration discrimination task

An event-related potential (ERP) study was conducted to elucidate the role of the prefrontal cortex (PFC) in time estimation. Subjects discriminated between three pairs of visual stimuli lasting from 100 ms and 2 seconds by determining whether the second stimulus was longer or briefer than the first. Event-related potentials were recorded in frontal and prefrontal regions after offset of the second stimulus (S2). The results indicated that the accuracy of the performances depended on stimulus duration and presentation order. In the brief-long order, the number of successful responses was higher as a function of stimulus duration. A time-related late positive component (LPCt) was revealed at prefrontal and frontal electrodes whose latency and amplitude differed depending on stimulus duration and order. The amplitude of this positive wave was higher when performance levels increased in the brief-long but not the reverse order. These results indicate that the LPCt may reflect successful decision-making or retrieval during time estimation as a result of neuronal activity in the PFC.

Time predictability modulates pre-supplementary motor area neuronal activity

Two monkeys were trained in a delayed sequential motor task in which the time interval between events and the delay duration were either fixed or variable. Single-unit neuronal activity was recorded in the pre-supplementary motor area (pre-SMA). During the delay, we observed a gradual increase in activity (build-up pattern) in the fixed but not in the variable condition. In the former but not in the latter, the monkey had the opportunity to estimate time duration. Consequently, the build-up pattern observed in the pre-SMA might represent the neuronal substrate of a time accumulator system proposed by previous authors on the basis of functional imaging data. Such a system could play a critical role in the working memory of temporal information.

Neural correlates of switching set as measured in fast, event-related functional magnetic resonance imaging

Attentional switching has shown to involve several prefrontal and parietal brain regions. Most cognitive paradigms used to measure cognitive switching such as the Wisconsin Card Sorting Task (WCST) involve additional cognitive processes besides switching, in particular working memory (WM). It is, therefore, questionable whether prefrontal brain regions activated in these conditions, especially dorsolateral prefrontal cortex (DLPFC), are involved in cognitive switching per se, or are related to WM components involved in switching tasks. Functional magnetic resonance imaging (fMRI) was used to examine neural correlates of pure switching using a paradigm purposely designed to minimize WM functions. The switching paradigm required subjects to switch unpredictably between two spatial dimensions, clearly indicated throughout the task before each trial. Fast, event-related fMRI was used to compare neural activation associated with switch trials to that related to repeat trials in 20 healthy, right-handed, adult males. A large cluster of activation was observed in the right hemisphere, extending from inferior prefrontal and pre- and postcentral gyri to superior temporal and inferior parietal cortices. A smaller and more caudal cluster of homologous activation in the left hemisphere was accompanied by activation of left dorsolateral prefrontal cortex (DLPFC). We conclude that left DLPFC activation is involved directly in cognitive switching, in conjunction with parietal and temporal brain regions. Pre- and postcentral gyrus activation may be related to motor components of switching set.

Differential processing of duration changes within short and long sounds in humans

It has been postulated that there exist two different mechanisms of duration processing. Brief durations, shorter than 500 ms, are processed sensorially, whereas longer durations are processed via a cognitive mechanism. We investigated whether electrophysiological evidence for this distinction can be found. In particular, we measured the mismatch negativity (MMN) to auditory duration deviants (40% decrements) in blocks of short (200 ms) and long sounds (1000 ms) in Ignore and in Attend conditions. Our results show a typical MMN for long and short durations in the Attend condition, whereas no MMN was obtained for long durations in the Ignore condition. This interaction between duration and attention seems to reflect a breakdown of the sensorial mechanism of temporal processing at some critical duration of about 1 s when sounds are ignored.

Left inferior parietal cortex integrates time and space during collision judgments

Left inferior parietal lobe lesions can cause perturbation of the space-time plans underlying skilled actions. But does the perceptual integration of spatiotemporal information use the same neural substrate or is the role of the left inferior parietal cortex restricted to visuomotor transformations? We use fMRI and a collision judgment paradigm to examine whether the left inferior parietal cortex integrates temporal and spatial variables in situations in which no complex action and no visuomotor transformation is required. We used a perceptual task in which healthy subjects indicated by simple button presses whether two moving objects (of the same or different size) would or would not collide with each other. This task of interest was contrasted with a control task that employed the same stimuli and identical motor responses but in which the size of the two moving objects had to be compared. To assess putative differential eye-movement effects both tasks were performed with and without central fixation. Analysis of the fMRI data (employing a random-effects model and SPM99) showed that collision judgments (relative to size judgments) provoked a significant increase in neural activity in the left inferior parietal cortex (supramarginal gyrus) only. These results show that left inferior parietal cortex is involved in the integration of perceptual spatiotemporal information and thus provide a neural correlate for the use of space-time plans (whose perturbation can lead to apraxia as originally hypothesized by Liepmann). Furthermore, the data suggest that the left supramarginal gyrus combines temporal and spatial variables more widely than previously supposed.

A right hemispheric frontocerebellar network for time discrimination of several hundreds of milliseconds

Debate still surrounds the nature of the role of the dorsolateral prefrontal gyrus (DLPFC) in time perception. This region is frequently associated with working memory and is thus implicated as a so-called "accumulator" within a hypothesized internal clock model. However, we hypothesized that this region may have a more primary role in time perception. To test this hypothesis we used functional magnetic resonance imaging (fMRI) to examine the neural correlates of relatively pure time perception with a temporal discrimination task where intervals of 1 s had to be discriminated from those of 1.3, 1.4, and 1.5 s. Time perception in this particular time domain within the "perceived present" has not previously been investigated using fMRI. By using relatively short time periods to be discriminated and also contrasting activation with an order judgment task, we aimed to minimize the confounding aspects of sustained attention and working memory. In a group of 20 healthy right-handed adult males, neural activation associated with time discrimination was found in a predominantly right hemispheric network of right dorsolateral and inferior prefrontal cortices, right supplementary motor area, and left cerebellum. We conclude that right DLPFC, rather than having a purely working memory function, might be more centrally involved in time perception than previously thought.

Brain activation patterns during measurement of sub- and supra-second intervals

The possibility that different neural systems are used to measure temporal durations at the sub-second and several second ranges has been supported by pharmacological manipulation, psychophysics, and neural network modelling. Here, we add to this literature by using fMRI to isolate differences between the brain networks which measure 0.6 and 3s in a temporal discrimination task with visual discrimination for control. We observe activity in bilateral insula and dorsolateral prefrontal cortex, and in right hemispheric pre-supplementary motor area, frontal pole, and inferior parietal cortex during measurement of both intervals, suggesting that these regions constitute a system used in temporal discrimination at both ranges. The frontal operculum, left cerebellar hemisphere and middle and superior temporal gyri, all show significantly greater activity during measurement of the shorter interval, supporting the hypotheses that the motor system is preferentially involved in the measurement of sub-second intervals, and that auditory imagery is preferentially used during measurement of the same. Only a few voxels, falling in the left posterior cingulate and inferior parietal lobe, are more active in the 3s condition. Overall, this study shows that although many brain regions are used for the measurement of both sub- and supra-second temporal durations, there are also differences in activation patterns, suggesting that distinct components are used for the two durations.

Right inferior prefrontal cortex mediates response inhibition while mesial prefrontal cortex is responsible for error detection

Inhibitory control and error detection are among the highest evolved human self-monitoring functions. Attempts in functional neuroimaging to effectively isolate inhibitory motor control from other cognitive functions have met with limited success. Different brain regions in inferior, mesial, and dorsolateral prefrontal cortices and parietal and temporal lobes have been related to inhibitory control in go/no-go and stop tasks. The widespread activation reflects the fact that the designs used so far have comeasured additional noninhibitory cognitive functions such as selective attention, response competition, decision making, target detection, and inhibition failure. Here we use rapid, mixed trial, event-related functional magnetic resonance imaging to correlate brain activation with an extremely difficult situation of inhibitory control in a challenging stop task that controls for noninhibitory functions. The difficulty of the stop task, requiring withholding of a triggered motor response, was assured by an algorithm that adjusted the task individually so that each subject only succeeded on half of all stop trials, failing on the other half. This design allowed to elegantly separate brain activation related to successful motor response inhibition and to inhibition failure or error detection. Brain activation correlating with successful inhibitory control in 20 healthy volunteers could be isolated in right inferior prefrontal cortex. Failure to inhibit was associated with activation in mesial frontopolar and bilateral inferior parietal cortices, presumably reflecting an attention network for error detection.

Motor timing deficits in community and clinical boys with hyperactive behavior: the effect of methylphenidate on motor timing

In a previous paper we showed that community children with hyperactive behavior were more inconsistent than controls in the temporal organization of their motor output. In this study we investigated: (1) various aspects of motor timing processes in 13 clinically diagnosed boys with attention deficit hyperactivity disorder (ADHD) who were compared to 11 community boys with hyperactive behavior and to a control group and (2) the effect of methylphenidate on the motor timing processes in the clinical group with ADHD in a double blind, cross-over, medication-placebo design, including 4 weeks of medication. The clinical group with ADHD, like the community group with hyperactivity, showed greater variability in sensorimotor synchronization and in sensorimotor anticipation relative to controls. The clinical group was also impaired in time perception, which was spared in the community group with hyperactivity. The persistent, but not the acute dose, of methylphenidate reduced the variability of sensorimotor synchronization and anticipation, but had no effect on time perception. This study shows that motor timing functions are impaired in both clinical and community children with hyperactivity. It is the first study to show the effectiveness of persistent administration of methylphenidate on deficits in motor timing in ADHD children and extends the use of methylphenidate from the domain of attentional and inhibitory functions to the domain of executive motor timing.

Cerebral correlates of explicit sequence learning

Using positron emission tomography (PET) and regional cerebral blood flow (rCBF) measurements, we investigated the cerebral correlates of consciousness in a sequence learning task through a novel application of the Process Dissociation Procedure, a behavioral paradigm that makes it possible to separately assess conscious and unconscious contributions to performance. Results show that the metabolic response in the anterior cingulate/mesial prefrontal cortex (ACC/MPFC) is exclusively and specifically correlated with the explicit component of performance during recollection of a learned sequence. This suggests a significant role for the ACC/MPFC in the explicit processing of sequential material.

Distinct systems for automatic and cognitively controlled time measurement: evidence from neuroimaging

A recent review of neuroimaging data on time measurement argued that the brain activity seen in association with timing is not influenced by specific characteristics of the task performed. In contrast, we argue that careful analysis of this literature provides evidence for separate neural timing systems associated with opposing task characteristics. The 'automatic' system draws mainly upon motor circuits and the 'cognitively controlled' system depends upon prefrontal and parietal regions.

ADHD outside the laboratory: boys' executive function performance on tasks in videogame play and on a visit to the zoo

One current theory of attention-deficit/hyperactivity disorder (ADHD) proposes that a primary deficit in behavioral inhibition gives rise to secondary deficits in 4 executive functions and motor control. To date, empirical support for this model is based primarily on laboratory-based cognitive methods. This study assessed behavioral inhibition and executive functioning in children with ADHD in 2 real-life contexts: videogames (motor-skill target game, cognitively demanding adventure game) and an outing at the zoo (route tasks). Participants were a community sample of 57 boys diagnosed with ADHD (20 inattentive, 37 combined type) and 57 normally developing control boys, matched individually for age and nonverbal IQ. Operationally defined measures of behavioral inhibition and specific executive functions were derived from these activities and assessed under contrasting conditions of low or high working memory and distractor loads. There were no group differences in basic motor skills on the target game, nor in terms of the ability to inhibit a prepotent or ongoing response in the adventure videogame. However, boys with ADHD exhibited more self-talk, more effortful response preparation, and completed fewer challenges in the latter videogame. Also, they manifested inhibition deficits in terms of interference control during the route task at the zoo and took longer to complete the tasks. Typically, these differences were greatest under conditions of high working memory and distractor loads. Findings from this study suggest that cognitive difficulties in ADHD may be context dependent and that ADHD is associated with deficits in some but not all aspects of behavioral inhibition.

Infant timekeeping: attention and temporal estimation in 4-month-olds

Four-month-old infants were exposed to sequences in which a 2-s light stimulus alternated with dark interstimulus periods whose length was manipulated to be 3 or 5 s. A predictable on-off pattern occurred for eight trials, but the light stimulus was omitted on the ninth trial. Infants showed heart rate responses on the omission trial that were closely synchronized with the expected recurrence of the stimulus. In addition, these heart rate patterns were observed predominantly in infants who had previously shown high levels of sustained attention in pretests with visual stimuli. These findings indicate remarkable precision in infants' estimation of time intervals, and suggest that the link between time estimation and attentional processes is present in early infancy.

Transitions between dynamical states of differing stability in the human brain

What mechanisms underlie the flexible formation, adaptation, synchronization, and dissolution of large-scale neural assemblies from the 10(10) densely interconnected, continuously active neurons of the human brain? Nonlinear dynamics provides a unifying perspective on self-organization. It shows that the emergence of patterns in open, nonequilibrium systems is governed by their stability in response to small disturbances and predicts macroscopic transitions between patterns of differing stability. Here, we directly demonstrate that such transitions can be elicited in the human brain by interference at the neural level. As a probe, we used a classic motor coordination paradigm exhibiting well described movement states of differing stability. Functional neuroimaging identified premotor (PMA) and supplementary motor (SMA) cortices as having neural activity linked to the degree of behavioral instability. These regions then were transiently disturbed with graded transcranial magnetic stimulation, which caused sustained and macroscopic behavioral transitions from the less stable out-of-phase to the stable in-phase movement, whereas the stable pattern could not be affected. Moreover, the strength of the disturbance needed (a measure of neural stability) was linked to the degree of behavioral stability, demonstrating the applicability of nonlinear system theory as a powerful predictor of the dynamical repertoire of the human brain.

Modulation of activity in temporal cortex during generation of inner speech

Monitoring one's thoughts (in the verbal modality) is thought to be critically dependent on the interaction between areas that generate and perceive inner speech in the frontal and temporal cortex, respectively. We used functional magnetic resonance imaging (fMRI) to examine the relationship between activity in these areas while the rate of inner speech generation was varied experimentally. The faster rate was associated with activation in the left inferior frontal gyrus, the right pre- and postcentral gyri and both superior temporal gyri. Thus, temporal cortical activation was associated with increasing the rate of covert articulation, in the absence of external auditory input, suggesting that there is effective fronto-temporal connectivity. Furthermore, this may provide support for the existence of feed forward models, which suggest that activity in regions responsible for verbal perception is modulated by activity in areas that generate inner speech.

Evidence for a pure time perception deficit in children with ADHD

BACKGROUND

Deficits have been found previously in children with ADHD on tasks of time reproduction, time production and motor timing, implicating a deficit in temporal processing abilities, which has been interpreted as either secondary or primary to core executive dysfunctions. The aim of this study was to explore further the abilities of hyperactive children in skills of time estimation, using a range of time perception tasks in different temporal domains.

METHOD

Time estimation was tested in a verbal estimation task of 10 seconds. Time reproduction was also acquired for two time intervals of 5 and 12 seconds. A temporal discrimination task aimed to determine the idiosyncratic threshold of minimum time interval (in milliseconds) necessary to distinguish two intervals differing by approximately 300 milliseconds. Twenty-two children diagnosed with ADHD were compared to 22 healthy children, matched for age, handedness and working memory skills.

RESULTS

Children with ADHD were significantly impaired in their time discrimination threshold: on average, time intervals had to be 50 ms longer for the hyperactive children in order to be discriminated when compared with controls. Children with ADHD also responded earlier on a 12-second reproduction task, which however only approached significance after controlling for IQ and short-term memory. No group differences were found for the 5-second time reproduction or verbal time estimation tasks.

CONCLUSIONS

The findings suggest that children with ADHD perform poorly on time reproduction tasks which load heavily on impulsiveness and attentional processes and they also suggest that these children may have a perceptual deficit of time discrimination, which may only be detectable in brief durations which differ by several hundred milliseconds. A temporal perception deficit in the range of milliseconds in ADHD may impact upon other functions such as perceptual language skills and motor timing.

An fMRI study of reduced left prefrontal activation in schizophrenia during normal inhibitory function

Functional magnetic resonance imaging (fMRI) was used to investigate the hypothesis that schizophrenia is associated with a dysfunction of prefrontal brain regions during motor response inhibition. Generic brain activation of six male medicated patients with schizophrenia was compared to that of seven healthy comparison subjects matched for sex, age, and education level while performing 'stop' and 'go-no-go' tasks. No group differences were observed in task performance. Patients, however, showed reduced BOLD signal response in left anterior cingulate during both inhibition tasks and reduced left rostral dorsolateral prefrontal and increased thalamus and putamen BOLD signal response during stop task performance. Despite good task performance, patients with schizophrenia thus showed abnormal neural network patterns of reduced left prefrontal activation and increased subcortical activation when challenged with motor response inhibition.

Neuropsychological analyses of impulsiveness in childhood hyperactivity

BACKGROUND

Neuropsychological analyses of impulsiveness are needed to refine assessment of attention-deficit hyperactivity disorder (ADHD).

AIMS

To investigate specific impairments in hyperactive children in a neuropsychological task battery of impulsiveness, the Maudsley Attention and Response Suppression (MARS) task battery, and to identify the neural substrates.

METHOD

Impulsiveness was assessed using different tasks of inhibitory control and time management (MARS) in 55 children with ADHD, other diagnoses and controls. Functional magnetic resonance images were obtained from adolescents with and without ADHD during three of the tasks.

RESULTS

Children with ADHD, but not psychiatric controls, were impaired on tests of response inhibition, but not of motor timing. Reduced right prefrontal activation was observed in hyperactive adolescents during higher level inhibition and delay management, but not during simple sensorimotor coordination.

CONCLUSIONS

Attention-deficit hyperactivity disorder is characterised by specific deficits in tasks of motor response inhibition, but not motor timing, and by dysfunction of frontostriatal brain regions.

Time perception and reproduction in young adults with attention deficit hyperactivity disorder

Adults with attention deficit hyperactivity disorder (ADHD; n = 104) were compared with a control group (n = 64) on time estimation and reproduction tasks. Results were unaffected by ADHD subtype or gender. The ADHD group provided larger time estimations than the control group, particularly at long intervals. This became nonsignificant after controlling for IQ. The ADHD group made shorter reproductions than did the control group (15- and 60-s intervals) and greater reproduction errors (12-, 45-, 60-s durations). These differences remained after controlling for IQ and comorbid oppositional defiant disorder, depression, and anxiety. Only the level of anxiety contributed to errors (at 12-s duration) beyond the level of ADHD. Results extended findings on time perception in ADHD children to adults and ruled out comorbidity as the basis of the errors.

Neurons in the lateral agranular frontal cortex have divided attention correlates in a simultaneous temporal processing task

The frontal cortex is an important brain area for divided attention. Lesions of the lateral agranular frontal cortex in rats disrupt divided attention in a simultaneous temporal processing task. In the present study, the activity of lateral agranular neurons was examined while rats performed a simultaneous temporal processing procedure. Rats were trained to time two stimuli (a light and a tone), each associated with a different fixed interval. Simple trials, in which a single stimulus was presented, and compound trials, in which both stimuli were presented simultaneously, occurred randomly in a session. Rats were able to divide attention between the two stimuli, as assessed by the pattern of lever presses. Approximately 50% of lateral agranular neurons responded to at least one phase of the task with four response patterns observed. The activity of type 1 cells (60%) was altered to compound, but not simple, stimuli. Type 2 cells (10%) responded to both types of simple stimuli and to compound stimuli. Type 3 cells (27%) had changes in firing rate to one type of simple stimulus and to compound stimuli. Type 4 cells (3%) responded to one type of simple stimulus, but were unresponsive to all other stimuli. The large proportion of type 1 cells supports the hypothesis that the lateral agranular cortex is important in divided attention. Previous studies have suggested that the lateral agranular cortex in rats is equivalent to the primary motor cortex. If so, the results from the present study provide evidence that the lateral agranular cortex may have some cognitive functions, in addition to being part of the motor system.

Functional organization of the lateral premotor cortex: fMRI reveals different regions activated by anticipation of object properties, location and speed

Previous studies have provided evidence that the lateral premotor cortex (PMC) is involved in representations triggered by attended sensory events. However, while the functional specificity of subregions of this large cortical structure has been intensively investigated in the monkey, little is known about functional differences within human lateral premotor areas. In the present study, functional magnetic resonance imaging was used to investigate if attending to object-specific (O), spatial (S), or temporal (T) properties of the same sensory event, i.e. moving objects, involves different premotor areas. We found a frontoparietal 'prehension network' comprising the pre-supplementary motor area (preSMA), the ventral PMC, and the left anterior intraparietal sulcus (aIPS) to be activated independently of the attended stimulus property, but most intensively during object-related attention. Moreover, several areas were exclusively activated according to the attended stimulus property. Particularly, different PMC regions responded to the Object (O) task (left superior ventrolateral PMC), the Spatial (S) task (dorsolateral PMC), and the Timing (T) task (frontal opercular cortex (FOP)). These results indicate that the representation of different stimulus dimensions engage distinct premotor areas and, therefore, that there is a functional specificity of lateral premotor subregions.

Mapping motor inhibition: conjunctive brain activations across different versions of go/no-go and stop tasks

Conjunction analysis methods were used in functional magnetic resonance imaging to investigate brain regions commonly activated in subjects performing different versions of go/no-go and stop tasks, differing in probability of inhibitory signals and/or contrast conditions. Generic brain activation maps highlighted brain regions commonly activated in (a) two different go/no-go task versions, (b) three different stop task versions, and (c) all 5 inhibition task versions. Comparison between the generic activation maps of stop and go/no-go task versions revealed inhibitory mechanisms specific to go/no-go or stop task performance in 15 healthy, right-handed, male adults. In the go/no-go task a motor response had to be selectively executed or inhibited in either 50% or 30% of trials. In the stop task, the motor response to a go-stimulus had to be retracted on either 50 or 30% of trials, indicated by a stop signal, shortly (250 ms) following the go-stimulus. The shared "inhibitory" neurocognitive network by all inhibition tasks comprised mesial, medial, and inferior frontal and parietal cortices. Generic activation of the go/no-go task versions identified bilateral, but more predominantly left hemispheric mesial, medial, and inferior frontal and parietal cortices. Common activation to all stop task versions was in predominantly right hemispheric anterior cingulate, supplementary motor area, inferior prefrontal, and parietal cortices. On direct comparison between generic stop and go/no-go activation maps increased BOLD signal was observed in left hemispheric dorsolateral prefrontal, medial, and parietal cortices during the go/no-go task, presumably reflecting a left frontoparietal specialization for response selection.

Cortical networks recruited for time perception: a monkey positron emission tomography (PET) study

The presence of an "internal clock" in the brain has been assumed to underlie the information processing related to time. This clock plays a critical role in time keeping and time perception, which are closely associated with integrated functions in the brain. To identify the brain areas recruited for time keeping and time perception, we performed positron emission tomography (PET) studies with rhesus monkeys to measure regional cerebral blood flow (rCBF) as an index of neural activity during time discrimination tasks of different durations ranging from 400 to 1500 ms. Changes in rCBF that covaried significantly with the durations of the target being perceived by subjects were found in the dorsolateral prefrontal cortex (DLPFC), the posterior part of the inferior parietal cortex, basal ganglia, and posterior cingulate cortex. Furthermore, a loss of neuronal function in the DLPFC caused by a local application of bicuculline resulted in the selective reduction of performance in time discrimination tasks. The results indicate that a neural network composed of the posterior inferior parietal cortex to the DLPFC plays a crucial role in the temporal monitoring process in time perception.

Prolonged reaction time to a verbal working memory task predicts increased power of posterior parietal cortical activation

We used multislice functional magnetic resonance imaging (fMRI) to investigate the association between behavioral and neurophysiological measures of working memory task performance in 20 right-handed male healthy volunteers. Images were acquired over a 5-min period at 1.5 Tesla. We used a periodic design, alternating 30-s blocks of the "n-back" working memory task with 30-s blocks of a sensorimotor control task to activate verbal working memory systems. The power of functional response to the task was estimated by sinusoidal regression at each voxel. The relationship between power of fMRI response and mean reaction time over all 11 working memory trials was explored by multiple regression, with age and mean reaction time to the control task as covariates, at voxel and regional levels of analysis. All subjects were able to perform the n-back task accurately. A spatially distributed network was activated, including dorsolateral prefrontal cortex, inferior frontal gyrus, lateral premotor cortex, and supplementary motor area (SMA) in the frontal lobes. More posteriorly, there were major foci of activation in parietal and occipitoparietal cortex, precuneus, lingual, and fusiform gyri of the ventral occipital lobe, inferior temporal gyrus, and cerebellum. The power of functional response was positively correlated with reaction time in bilateral posterior parietal cortex (Talairach coordinates in x, y, z (mm) 35, -44, 37 and -32, -56, 42), indicating that subjects who found the task difficult, and responded with a slower reaction time, tended to activate these regions more powerfully. One interpretation of this regionally specific relationship between prolonged reaction time and increased power of posterior parietal activation is consistent with prior studies identifying similar areas of parietal cortex as the site of the phonological storage function in verbal working memory.

Attention deficit/hyperactivity disorder: characteristics, interventions and models

An epidemiological study of Attention Deficit/Hyperactivity Disorder (ADHD) suggests that the prevalence may be two to three times higher than the figure of 3-5% often cited. In addition, the data suggest that both underdiagnosis and overdiagnosis occur frequently. Rodent animal models of ADHD, like the Spontaneously Hypertensive Rat (SHR) and other rat models such as those with chemical and radiation-induced brain lesions and cerebellar stunting, and the Coloboma mouse model exhibit clear similarities with several aspects of the human disorder and should prove useful in studying specific traits. Operant behavioral tasks that model learning, short-term memory and simple discriminations are sensitive to ADHD and methylphenidate has been shown to normalize ADHD performance in a short-term memory task. Recent findings challenge not only the current postulate that response inhibition is a unique deficit in ADHD, but also the concepts of ADHD and its treatment, which presume intact perceptual abilities. Time perception deficits may account, in part, for the excessive variability in motor response times on speeded reaction time tasks, motor control problems and motor clumsiness associated with ADHD. The Multimodality Treatment Study of ADHD (MTA) provided data suggesting that pharmacological interventions that included systematic and frequent follow-up with parents and teachers, with or without psychosocial interventions, are superior to psychosocial interventions or standard community care alone. Additionally, the MTA was one of the first studies to demonstrate benefits of multimodal and pharmacological interventions lasting longer than 1 year. Imaging studies have demonstrated differences in brain areas in children with ADHD: anterior corpus callosum, right anterior white matter, and cerebellar volumes are all decreased in children with ADHD and there is less brain asymmetry in ADHD subjects. Additionally, functional imaging studies, coupled with pharmacological manipulations, suggest decreased blood flow and energy utilization in prefrontal cortex and striatum and the dysregulation of catecholamine systems in persons with ADHD.

Dissociating the role of the medial and lateral anterior prefrontal cortex in human planning

The anterior prefrontal cortex is known to subserve higher cognitive functions such as task management and planning. Less is known, however, about the functional specialization of this cortical region in humans. Using functional MRI, we report a double dissociation: the medial anterior prefrontal cortex, in association with the ventral striatum, was engaged preferentially when subjects executed tasks in sequences that were expected, whereas the polar prefrontal cortex, in association with the dorsolateral striatum, was involved preferentially when subjects performed tasks in sequences that were contingent on unpredictable events. These results parallel the functional segregation previously described between the medial and lateral premotor cortex underlying planned and contingent motor control and extend this division to the anterior prefrontal cortex, when task management and planning are required. Thus, our findings support the assumption that common frontal organizational principles underlie motor and higher executive functions in humans.

Limb apraxias: higher-order disorders of sensorimotor integration

Limb apraxia comprises a wide spectrum of higher-order motor disorders that result from acquired brain disease affecting the performance of skilled, learned movements. At present, limb apraxia is primarily classified by the nature of the errors made by the patient and the pathways through which these errors are elicited, based on a two-system model for the organization of action: a conceptual system and a production system. Dysfunction of the former would cause ideational (or conceptual) apraxia, whereas impairment of the latter would induce ideomotor and limb-kinetic apraxia. Currently, it is possible to approach several types of limb apraxia within the framework of our knowledge of the modular organization of the brain. Multiple parallel parietofrontal circuits, devoted to specific sensorimotor transformations, have been described in monkeys: visual and somatosensory transformations for reaching; transformation of information about the location of body parts necessary for the control of movements; somatosensory transformation for posture; visual transformation for grasping; and internal representation of actions. Evidence from anatomical and functional brain imaging studies suggests that the organization of the cortical motor system in humans is based on the same principles. Imitation of postures and movements also seems to be subserved by dedicated neural systems, according to the content of the gesture (meaningful versus meaningless) to be imitated. Damage to these systems would produce different types of ideomotor and limb-kinetic praxic deficits depending on the context in which the movement is performed and the cognitive demands of the action. On the other hand, ideational (or conceptual) apraxia would reflect an inability to select and use objects due to the disruption of normal integration between systems subserving the functional knowledge of actions and those involved in object knowledge.

Neuroimaging in hyperkinetic children and adults: an overview

The application of brain imaging techniques to children with Attention Deficit/Hyperactivity Disorders is reviewed, stressing methodological aspects. Findings are still provisional, but suggest minor structural changes in frontal and candate areas, especially on the right side. Functional studies suggest reduced activation in these and other areas. The techniques do not yet contribute to individual diagnosis.

Functional localization of a "Time Keeper" function separate from attentional resources and task strategy

The functional neuroanatomy of time estimation has not been well-documented. This research investigated the fMRI measured brain response to an explicit, prospective time interval production (TIP) task. The study tested for the presence of brain activity reflecting a primary time keeper function, distinct from the brain systems involved either in conscious strategies to monitor time or attentional resource and other cognitive processes to accomplish the task. In the TIP task participants were given a time interval and asked to indicate when it elapsed. Two control tasks (counting forwards, backwards) were administered, in addition to a dual task format of the TIP task. Whole brain images were collected at 1.5 Tesla. Analyses (n = 6) yielded a statistical parametric map (SPM ¿z¿) reflecting time keeping and not strategy (counting, number manipulation) or attention resource utilization. Additional SPM ¿z¿s involving activation associated with the accuracy and magnitude the of time estimation response are presented. Results revealed lateral cerebellar and inferior temporal lobe activation were associated with primary time keeping. Behavioral data provided evidence that the procedures for the explicit time judgements did not occur automatically and utilized controlled processes. Activation sites associated with accuracy, magnitude, and the dual task provided indications of the other structures involved in time estimation that implemented task components related to controlled processing. The data are consistent with prior proposals that the cerebellum is a repository of codes for time processing, but also implicate temporal lobe structures for this type of time estimation task.

Time perception and motor timing: a common cortical and subcortical basis revealed by fMRI

Though it is well known that humans perceive the temporal features of the environment incessantly, the brain mechanisms underlying temporal processing are relatively unexplored. Functional magnetic resonance imaging was used in this study to identify brain activations during sustained perceptual analysis of auditorally and visually presented temporal patterns (rhythms). Our findings show that the neural network supporting time perception involves the same brain areas that are responsible for the temporal planning and coordination of movements. These results indicate that time perception and motor timing rely on similar cerebral structures.

Functional frontalisation with age: mapping neurodevelopmental trajectories with fMRI

The aim of this study was to investigate whether previously observed hypofrontality in adolescents with attention deficit-hyperactivity disorder (ADHD) during executive functioning [Rubia K, Overmeyer S, Taylor E, Brammer M, Williams S, Simmons A, Andrew C, Bullmore ET. Hypofrontality in attention deficit hyperactivity disorder during higher order motor control: a study using fMRI. Am J Psychiatry 1999;156(6):891-896] could be attributed to delayed maturation of frontal cortex. Brain activation of 17 healthy subjects, 9 adolescents and 8 young adults, during performance of a motor response inhibition task and a motor timing task was measured using functional magnetic resonance imaging (fMRI). The effect of age on brain activation was estimated, using the analysis of variance and regression, at both voxel and regional levels. In the delay task, superior performance in adults was paralleled by a significantly increased power of response in a network comprising prefrontal and parietal cortical regions and putamen. In the stop task, alternative neuronal routes--left hemispheric prefrontal regions in adults and right hemispheric opercular frontal cortex and caudate in adolescents--seem to have been recruited by the two groups for achieving comparable performances. A significant age effect was found for the prefrontal activation in both task, confirming the hypothesis of a dysmaturational pathogenesis for the hypofrontality in ADHD.

Synchronization, anticipation, and consistency in motor timing of children with dimensionally defined attention deficit hyperactivity behaviour

We tested the hypothesis that children with hyperactive behaviour are impaired in the temporal organization of their motor output. The performance of 11 boys, scoring above a cut-off on standard scales of overactivity and inattention, was compared to that of controls in progressively more complex Motor-timing tasks. The tasks administered required self-paced and externally paced Sensorimotor Synchronization and Sensorimotor Anticipation. Deficits at a perceptual level were investigated with a Time-discrimination task. As hypothesized, we found that hyperactive children had no deficits in their perception of time but were impaired in timing their motor output. Hyperactive children were more inconsistent than controls in maintaining a freely chosen tapping rhythm, in synchronizing and in anticipating their motor response to external visual stimulation.