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

Neuronal activity related to elapsed time in prefrontal cortex

We studied prefrontal cortex activity during a saccade task. On each trial, one of three delay periods elapsed between the onset of a visual stimulus and its offset, which triggered a saccade. After stimulus offset, many neurons showed phasic increases in activity that depended on the duration of the preceding delay period. This delay-dependent activity varied only weakly with reaction time and instead appeared to reflect a more general aspect of elapsed time.

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.

Sensorimotor synchronization: A review of the tapping literature

Sensorimotor synchronization (SMS), the rhythmic coordination of perception and action, occurs in many contexts, but most conspicuously in music performance and dance. In the laboratory, it is most often studied in the form of finger tapping to a sequence of auditory stimuli. This review summarizes theories and empirical findings obtained with the tapping task. Its eight sections deal with the role of intention, rate limits, the negative mean asynchrony, variability, models of error correction, perturbation studies, neural correlates of SMS, and SMS in musical contexts. The central theoretical issue is considered to be how best to characterize the perceptual information and the internal processes that enable people to achieve and maintain SMS. Recent research suggests that SMS is controlled jointly by two error correction processes (phase correction and period correction) that differ in their degrees of cognitive control and may be associated with different brain circuits. They exemplify the general distinction between subconscious mechanisms of action regulation and conscious processes involved in perceptual judgment and action planning.

The neural basis of temporal auditory discrimination

When two identical stimuli, such as a pair of clicks, are presented with a sufficiently long time-interval between them they are readily perceived as two separate events. However, as they are presented progressively closer together, there comes a point when the two separate stimuli are perceived as one. This phenomenon applies not only to hearing but also to other sensory modalities. Damage to the basal ganglia disturbs this type of temporal discrimination irrespective of sensory modality, suggesting a multimodal process is involved. Our aim was to study the neural substrate of auditory temporal discrimination in healthy subjects and to compare it with structures previously associated with analogous tactile temporal discrimination. During fMRI scanning, paired-clicks separated by variable inter-stimulus intervals (1-50 ms) were delivered binaurally, with different intensities delivered to each ear, yielding a lateralised auditory percept. Subjects were required (a) to report whether they heard one or two stimuli (TD: temporal discrimination); or (b) to report whether the stimuli were located on the right or left side of the head mid-line (SD: spatial discrimination); or (c) simply to detect the presence of an auditory stimulus (control task). Our results showed that both types of auditory discrimination (TD and SD) compared to simple detection activated a network of brain areas including regions of prefrontal cortex and basal ganglia. Critically, two clusters in pre-SMA and the anterior cingulate cortex were specifically activated by TD. Furthermore, these clusters overlap with regions activated for similar judgments in the tactile modality suggesting that they fulfill a multimodal function in the temporal processing of sensory events.

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.

Overloading temporal memory

This study tested the hypothesis that memory is a major source of variance in temporal processing. Participants categorized intervals as short or long. The number of base durations and interval types mixed within blocks of trials varied from 1 session to another. Results revealed that mixing 2 base durations within blocks increased categorization errors, but mixing 2 marker types did not. Results are attributed to the involvement of more than 1 memory representation, which is argued to show the critical role of memory in temporal processing. Because mixing modalities has no such effect, it was argued that modalities share a common representation in memory. Finally, there was no difference in the perceived duration of auditory and visually marked intervals, which is inconsistent with most reports on this effect.

Neural network involved in time perception: an fMRI study comparing long and short interval estimation

In this study, long ( approximately 1,300 ms) and short duration ( approximately 450 ms) estimation trials in an event-related functional MRI (fMRI) study were contrasted in order to reveal the regions within a time estimation network yielding increased activation with the increase of the duration to be estimated. In accordance with numerous imaging studies, our results showed that the presupplementary motor area (preSMA), the anterior cingulate, the prefrontal and parietal cortices, and the basal ganglia were involved in the estimation trials whatever the duration to be estimated. Moreover, only a subset of the regions within this distributed cortical and subcortical network yielded increased activation with increasing time, namely, the preSMA, the anterior cingulate cortex, the right inferior frontal gyrus (homolog to Broca's area), the bilateral premotor cortex, and the right caudate nucleus. This suggests that these regions are directly involved in duration estimation. We propose that the caudate-preSMA circuit, the anterior cingulate, and the premotor-inferior frontal regions may support a clock mechanism, decision and response-related processes, and active maintenance of temporal information, respectively.

Neuropsychology of timing and time perception

Interval timing in the range of milliseconds to minutes is affected in a variety of neurological and psychiatric populations involving disruption of the frontal cortex, hippocampus, basal ganglia, and cerebellum. Our understanding of these distortions in timing and time perception are aided by the analysis of the sources of variance attributable to clock, memory, decision, and motor-control processes. The conclusion is that the representation of time depends on the integration of multiple neural systems that can be fruitfully studied in selected patient populations.

Emergence of rhythm during motor learning

Complex motor skill often consists of a fixed sequence of movements. Recent studies show that a stereotyped temporal pattern or rhythm emerges as we learn to perform a motor sequence. This is because the sequence is reorganized during learning as serial chunks of movements in both a sequence-specific and subject-specific manner. On the basis of human imaging studies we propose that the formation of chunk patterns is controlled by the cerebellum, its posterior and anterior lobes contributing, respectively, to the temporal patterns before and after chunk formation. The motor rhythm can assist the motor networks in the cerebral cortex to control automatic movements within chunks and the cognitive networks to control non-automatic movements between chunks, respectively. In this way, organized motor skill can be performed automatically and flexibly.

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.

The cardiac cycle time effect revisited: temporal dynamics of the central-vagal modulation of heart rate in human reaction time tasks

Lacey and Lacey (1974) suggested that during reaction time tasks higher brain centers dynamically adjust efferent vagal nerve pulses to the sino-atrial node of the heart, inducing phase-dependent heart rate changes. Since then, animal and human neuro-physiological results have provided evidence for this hypothesis. Higher subcortical and cortical brain centers may have reciprocal interactive pathways relating to autonomic control comparable to those at the level of peripheral autonomic changes and brain stem reflexes. In humans such central effects may be observed in the short latency vagal control of heart rate that has been studied mostly in reaction time (RT) tasks. RT task parameters modulate vagal pulses to the cardiac sino-atrial node (SAN), which in turn exerts a phase-dependent change in the ongoing cardiac interbeat interval. Simulations of human RT task effects in an animal model of heart rate change support this hypothesis. The current study examined evidence for vagal control of three human phasic heart rate responses in RT tasks. The evidence indicates that the initiation of an RT response triggers a reflexive shift from vagal activation to vagal inhibition. This shift is cardiac cycle phase dependent. Graded anticipatory cardiac deceleration during the warning interval of an RT task varies with task relevance and time uncertainty. This response may be part of a control process engaged in time keeping. Hence, temporal variables mediate the central-autonomic-vagal modulation of heart rate.

Temporal perception in velo-cardio-facial syndrome

Temporal perception abilities refer to timing mechanisms used in daily life, such as the ability to reproduce and judge time, previously associated with the basal ganglia and the cerebellum, respectively. In individuals affected by velo-cardio-facial (VCFS), both the basal ganglia and the cerebellum have been shown to be particularly vulnerable to abnormal brain development, though related temporal perception abilities have yet to be investigated. In this study, our goal was to characterize time perception and reproduction abilities in individuals with VCFS. Compared to controls, we hypothesized that individuals with VCFS would be less accurate and show more variability when reproducing a fixed-interval series of auditory beeps; furthermore, we predicted that they would show a higher perceptive acuity threshold when discriminating between subtle time differences. Forty-two subjects with VCFS and 35 matched controls participated in temporal perception evaluations. In the reproduction of time finger-tapping task, subjects were asked to press a button in cadence with a series of fixed interval beeps, and then to hold the same tempo when the beeps stopped. Overall, the VCFS group showed less accuracy and more variability in reproduction ability when compared to controls. In the second experiment, subjects were tested on auditory and visual time perception tasks. Subjects were presented with a fixed interval stimulus and a stimulus of varying duration, and were asked to determine the longer of the two. The VCFS group required a greater discrepancy between tones to accurately discriminate the two stimuli. The results point to an alteration in temporal perception associated with VCFS. Implications of altered temporal perception abilities and their relationship to the VCFS phenotype are discussed.

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.

What is common to brain activity evoked by the perception of visual and auditory filled durations? A study with MEG and EEG co-recordings

EEG and MEG scalp data were simultaneously recorded while human participants were performing a duration discrimination task in visual and auditory modality, separately. Short durations were used ranging from 500 to 900 ms, among which participants had to discriminate a previously memorized 700-ms "standard" duration. Behavioral results show accurate but variable performance within and between participants with expected modality effects: the percentage of responses was greater and the mean response time was shorter for auditory than for visual signals. Sustained electric and magnetic activities were obtained correlatively to duration estimation, but with distinct spatiotemporal properties. Electric CNV-like potentials showed fronto-central negativity in both modalities, whereas magnetic sustained fields were distributed with respect to the modality of the interval to be timed. Time courses of these slow brain activities were found to be dependent on stimulus duration but not on its modality nor on the recording signal (EEG or MEG). Source reconstruction demonstrated that these sustained potentials/fields were generated by superimposed contributions from visual and auditory cortices (sustained sensory responses, SSR) and from prefrontal and parietal regions. By using these two complementary techniques, we thus demonstrated the involvement of frontal and parietal cerebral cortex in human timing.

Neuroimaging of interval timing

Exactly how the brain is able to measure the durations of events lasting from seconds to minutes while maintaining time-scale invariance remains largely a mystery. Neuroimaging studies are only now beginning to unravel the nature of interval timing and reveal whether different timing mechanisms are required for the perception and production of sub- and supra-second intervals that can be defined by different stimulus modalities. We here review the impact that neuroimaging studies have had on the field of timing and time perception and outline the major challenges that remain to be addressed before a physiologically realistic theory of interval timing can be established involving cortico-striatal circuits.

The neural representation of time

This review summarizes recent investigations of temporal processing. We focus on motor and perceptual tasks in which crucial events span hundreds of milliseconds. One key question concerns whether the representation of temporal information is dependent on a specialized system, distributed across a network of neural regions, or computed in a local task-dependent manner. Consistent with the specialized system framework, the cerebellum is associated with various tasks that require precise timing. Computational models of timing mechanisms within the cerebellar cortex are beginning to motivate physiological studies. Emphasis has also been placed on the basal ganglia as a specialized timing system, particularly for longer intervals. We outline an alternative hypothesis in which this structure is associated with decision processes.

Neurobiology of perceptual and motor timing in children with spina bifida in relation to cerebellar volume

The cerebellum is important for perceptual and motor timing in the mature brain, but the timing function of the cerebellum in the immature brain is less well understood. We investigated timing in children with spina bifida meningomyelocele (SB), a neural tube defect that involves cerebellar dysgenesis, and in age-matched controls. Specifically, we studied perceptual timing (judgements of 400 ms duration) and motor timing (isochronous motor tapping); measured cerebellar volumes; and related perceptual and motor timing to each other and to cerebellar volume measurements. Children with SB had impairments in the perception of duration (around 400 ms) but not frequency (around 3000 Hz), showing that their perceptual timing deficit was not a generalized auditory impairment. Children with SB had motor timing deficits on unpaced but not paced isochronous tapping, and their unpaced timing performance was associated with clock variance rather than with motor implementation. Perceptual and motor timing were correlated, suggesting that children with SB have impairments in a central timing mechanism. Children with SB, especially those with upper spinal cord lesions, had significant cerebellar volume reductions in grey and white matter, as well as different regional patterns of grey matter, white matter and CSF. Duration perception was correlated with cerebellar volumes, and the number of valid tapping trials was correlated with cerebellar volumes in the SB group, which data demonstrate structure-function relations between timing and cerebellar volumes.

Functional anatomy of the attentional modulation of time estimation

Attention modulates our subjective perception of time. The less we attend to an event's duration, the shorter it seems to last. Attention to time or color stimulus attributes was modulated parametrically in an event-related functional magnetic resonance imaging study. Linear increases in task performance were accompanied by corresponding increases in brain activity. Increasing attention to time selectively increased activity in a corticostriatal network, including pre-supplementary motor area and right frontal operculum. Increasing attention to color selectively increased activity in area V4. By identifying areas whose activity was specifically modulated by attention to time, we have defined the core neuroanatomical substrates of timing behavior.

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.