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

The representation of time for motor learning

We have identified factors that control precise motor timing by studying learning in smooth pursuit eye movements. Monkeys tracked a target that moved horizontally for a fixed time interval before changing direction through the addition of a vertical component of motion. After repeated presentations of the same target trajectory, infrequent probe trials of purely horizontal target motion evoked a vertical eye movement around the time when the change in target direction would have occurred. The pursuit system timed the vertical eye movement by keeping track of the duration of horizontal target motion and by measuring the distance the target traveled before changing direction, but not by learning the position in space where the target changed direction. We conclude that high temporal precision in motor output relies on multiple signals whose contributions to timing vary according to task requirements.

Timing functions of the supplementary motor area: an event-related fMRI study

Two previous studies in which we recorded slow brain potential shifts over the scalp revealed performance-dependent effects that sustained one prominent model of timing mechanisms. These effects seemed to be derived from the supplementary motor area (SMA). Event-related functional magnetic resonance imagery (fMRI) was used to check this hypothesis. Brain activations were contrasted in Time production and (control) Force production tasks involving left-hand responding. These tasks, presented in mixed order, were designed to be of equivalent difficulty and involve comparable levels of attention. Several brain areas were activated in both tasks relative to baseline: the SMA, the putamen, and the lateral cerebellum. Contrasts between tasks gave clear-cut differences. Activations specific to the Time task were found in the SMA proper and the left primary motor cortex. The Force task activated the right sensorimotor cortex and the left cerebellum, and, bilaterally, the infero-parietal cortex and the insula. The main result, i.e. prominent activation of the SMA proper in relation to temporal production, corroborates our previous studies based on slow cortical potentials. The data are referred to current evidence suggesting that timing processes are subtended by a striato-thalamo-cortical pathway including the SMA.

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.

Intentional and Unintentional Contributions to Nonspecific Preparation: Electrophysiological Evidence

The authors hypothesized that there are distinct intentional and unintentional influences on nonspecific preparation for a future event. In 2 experiments, participants responded to an imperative stimulus (S-sub-2) that was presented equiprobably either 400 ms or 1,200 ms after the offset of a warning stimulus (S-sub-1). During the S-sub-1-S-sub-2 interval, the authors measured the contingent negative variation (CNV), an event-related brain potential reflecting nonspecific preparation. S-sub-1 provided either no information or reliable information about the duration of the impending S-sub-1-S-sub-2 interval, thereby allowing an intentional influence on the state of preparation. The effect of S-sub-1 information on the CNV was approximately additive to the effect of the S-sub-1-S-sub-2 interval that was used on the preceding trial. This supports the view that the preceding S-sub-1-S-sub-2 interval contributes unintentionally to the state of nonspecific preparation guided by a process of trace conditioning.

Behavioural aspects of cerebellar function in adults with Asperger syndrome

Aside from social deficits, Asperger and autistic individuals also exhibit motor control abnormalities such as impaired gait, balance, manual dexterity and grip. One brain area that has consistently been reported on autopsy and imaging studies to be abnormal in such individuals is the cerebellum. As the cerebellum controls sensorimotor coordination and lesions here typically cause hypotonia, dysmetria and dyscoordination, we performed a series of quantitative tests aimed at investigating cerebellar function in Asperger individuals. Tests examining visually guided movement (rapid pointing), speeded complex movement (finger tapping, rapid hand turning), muscle tone (catching dropped weight), prediction, coordination and timing (balance, grip force and interval timing) were conducted on 12 Asperger subjects and 12 age and IQ matched controls. In comparison to control subjects, Asperger subject's demonstrated: (i) decreased pointing accuracy and rate, (ii) increased postural instability, and (iii) decreased timing accuracy. IQ was found to co-vary with some parameters of each of these tasks and no further impairments were found on the remaining tests. We suggest that these specific deficits reflect impairment in the ability to integrate sensory input with appropriate motor commands and are consistent with cerebellar dysfunction in Asperger syndrome.

Memory for time intervals is impaired in left hemi-Parkinson patients

The basal ganglia have been proposed as one of the neural correlates of timekeeping functions. Both encoding and memory retrieval components for time perception are impaired in Parkinson's disease (PD). The aim of our study was to investigate in hemi-Parkinsonian patients the existence of a specific alteration in memory for time depending on the affected side, to better understand the contribution of the left or right basal ganglia circuits in different components of time perception. Right and left hemi-PD patients performed a time reproduction task in which they were required to reproduce in the same session short (5 s) and long (15 s) time intervals, in off- and on-therapy condition. While the right hemi-PD patients overestimated the shorter interval, only the left hemi-PD group showed the memory migration effect, overestimating the shorter and underestimating the longer time intervals. These results argue for a critical involvement of the right basal ganglia in memory retrieval for time intervals, in the range of seconds.

Perceived duration of expected and unexpected stimuli

Three experiments assessed whether perceived stimulus duration depends on whether participants process an expected or an unexpected visual stimulus. Participants compared the duration of a constant standard stimulus with a variable comparison stimulus. Changes in expectancy were induced by presenting one type of comparison more frequently than another type. Experiment 1 used standard durations of 100 and 400 ms, and Experiments 2 and 3 durations of 400 and 800 ms. Stimulus frequency did not affect perceived duration in Experiment 1. In Experiments 2 and 3, however, frequent comparisons were perceived as shorter than infrequent ones, and discrimination performance was better for infrequent comparisons. Overall, this study supports the notion that infrequent stimuli increase the speed of an internal pacemaker.

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.

The right dorsolateral prefrontal cortex is essential in time reproduction: an investigation with repetitive transcranial magnetic stimulation

This study used repetitive transcranial magnetic stimulation (rTMS) to investigate the roles of the right dorsolateral prefrontal cortex (DLPFC) and supplementary motor area (SMA) in short (500 ms) and long (2 s) interval timing. The results were compared with rTMS over the leg area of motor cortex, an area not thought to be involved with time estimation. rTMS was delivered during one of two phases of a time reproduction task: at the onset of the Estimation Phase (presentation of the interval to be timed) and at the onset of the Reproduction Phase (subjects' reproduction of the timed interval). There was a significant main effect of Site (SMA vs. right DLPFC vs. leg motor area) due to the fact that rTMS over the right DLPFC caused subjects to underestimate time intervals compared with rTMS over the leg motor area. There was also a significant three-way interaction between Site, Duration and Phase (Estimation Phase vs. Reproduction Phase) that post hoc analyses showed was due to underestimation of long intervals when rTMS was given over the right DLPFC at the start of the Reproduction Phase. There was no effect of rTMS over the right DLPFC or SMA in the short interval task. This is consistent with previous studies showing that the right DLPFC is important in estimating time intervals in the seconds-range. In addition, we suggest that the selectivity of the rTMS effect for the Reproduction Phase indicates that the right DLPFC plays a particular role in memory processes.

Effects of time-order, interstimulus interval, and feedback in duration discrimination of noise bursts in the 50- and 1000-ms ranges

Participants compared durations of paired white-noise bursts, with interstimulus interval (ISI) 100, 300, 900, or 2700 ms, presented in the order standard (St)-comparison (Co) or Co-St. St was 50 or 1000 ms, and 75% difference thresholds for "longer" and "shorter" judgments were estimated. In Experiment 1 feedback was given; in Experiment 2, with ISIs 900 and 2700 ms, there was no feedback. For St=1000 ms, the just noticeable difference (JND) in noise duration was generally smaller with the order St-Co than with Co-St; for St=50 ms, the JND relation was the opposite. JNDs increased with shorter ISIs. Time-order errors were positive for St=50 ms and negative for St=1000 ms, and approached zero for longer ISIs. Using Hellström's sensation-weighting (SW) model, the ratio of the stimulus weights for the first and second burst was estimated; this ratio was generally >1 for St=50 ms and <1 for St=1000 ms. JNDs were smaller with feedback than without; the greatest reduction was found for St=1000 ms and an ISI of 2700 ms with the order Co-St, possibly because feedback increased participants' attention to the first stimulus. These results demonstrate the sensitivity of discrimination measures for long as well as brief durations to the factors of ISI, presentation order, and feedback. They also suggest different modes of stimulus processing for short and long durations.

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.

Dynamics of brain activity in motor and frontal cortical areas during music listening: a magnetoencephalographic study

There are formidable problems in studying how 'real' music engages the brain over wide ranges of temporal scales extending from milliseconds to a lifetime. In this work, we recorded the magnetoencephalographic signal while subjects listened to music as it unfolded over long periods of time (seconds), and we developed and applied methods to correlate the time course of the regional brain activations with the dynamic aspects of the musical sound. We showed that frontal areas generally respond with slow time constants to the music, reflecting their more integrative mode; motor-related areas showed transient-mode responses to fine temporal scale structures of the sound. The study combined novel analysis techniques designed to capture and quantify fine temporal sequencing from the authentic musical piece (characterized by a clearly defined rhythm and melodic structure) with the extraction of relevant features from the dynamics of the regional brain activations. The results demonstrated that activity in motor-related structures, specifically in lateral premotor areas, supplementary motor areas, and somatomotor areas, correlated with measures of rhythmicity derived from the music. These correlations showed distinct laterality depending on how the musical performance deviated from the strict tempo of the music score, that is, depending on the musical expression.

Event-Related Potentials as Indices of Time Processing: A Review

Abstract This review examines ERP data that document the mechanisms and neural bases of time processing in the millisecond-to-minute range. Several types of ERP attest to the existence of timing capacities. Among them, one component of the Contingent Negative Variation (CNV) provides an on-line index of timing. CNV data strengthen the temporal accumulator concept, designed to subtend duration encoding. This conclusion is based on four main results: The positive relationship between temporal estimates and CNV amplitude is an index of the accumulation mechanism; the CNV peak is an index of time-based decision making; the CNV relates to temporal encoding, whereas temporal long-term memory may be linked to shifts of positive polarity; learning effects on CNV amplitude depend on topographic features, thus revealing functional differences among brain regions with respect to timing.

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.