Neural underpinnings of temporal processing: a review of focal lesion, pharmacological, and functional imaging research

Discrimination of temporal information at the cerebellum: functional magnetic resonance imaging of nonverbal auditory memory

Until recently, the cerebellum was held to play its chief role in motor control. By contrast, Keele and Ivry (1990) proposed that it may subserve time estimation within the perceptual domain as well. In accordance with this suggestion, speech perception requiring minute differentiation of time intervals was found compromised by cerebellar pathology a subsequent functional magnetic resonance imaging (fMRI) study found hemodynamic activation of the right neocerebellum under these conditions. In the current fMRI investigation a non-speech task involving duration storage and comparison yielded significant hemodynamic responses within the lateral Crus I area of the right cerebellar hemisphere. Concomitantly, a left prefrontal cluster was observed. The present fMRI study employed single-shot double-echo echo-planar imaging (EPI) to reduce image distortion and acquisition time with whole-brain coverage (TE = 28 and 66 ms, TR = 5 s, 28 slices, TA = 2.8 s). Twelve healthy subjects performed two tasks: identifying pauses between tones as "short" or "long" (30-130 ms) and deciding which of two successive pauses was longer. The activation pattern in the discrimination task was analogous to that seen during speech perception and verbal working memory (WM) tasks. We suggest that the storage of precise temporal structures relies on a cerebellar-prefrontal loop. This network allows for temporal organization of verbal sequences and phoneme encoding based on durational operations in a linguistic context.

Early processing stages are modulated when auditory stimuli are presented at an attended moment in time: an event-related potential study

The present study investigated with event-related potentials whether attending to a moment in time modulates the processing of auditory stimuli at a similar early, perceptual level as attending to a location in space. The participants listened to short (600 ms) and long (1,200 ms) intervals marked by white noise bursts. The task was to attend in alternating runs either to the short or to the long intervals and to respond to rare offset markers that differed in intensity from the frequent standard offset markers. Prior to the to-be-attended moment, a slow negative potential developed over the frontal scalp. Stimuli presented at the attended compared to the unattended moments in time elicited an enhanced N1 and an enhanced posteriorly distributed positivity (300-370 ms). The results show that attention can be flexibly controlled in time and that not only late but also early perceptual processing stages are modulated by attending to a moment in time.

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.

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.

Neural Basis of Rhythmic Timing Networks in the Human Brain

The study of rhythmicity provides insights into the understanding of temporal coding of music and temporal information processing in the human brain. Auditory rhythms rapidly entrain motor responses into stable steady synchronization states below and above conscious perception thresholds. Studying the neural dynamics of entrainment by measuring brain wave responses (MEG) we found nonlinear scaling of M100 amplitudes generated in primary auditory cortex relative to changes in the period of the rhythmic interval during subliminal and supraliminal tempo modulations. In recent brain imaging studies we have described the neural networks involved in motor synchronization to auditory rhythm. Activated regions include primary sensorimotor and cingulate areas, bilateral opercular premotor areas, bilateral SII, ventral prefrontal cortex, and, subcortically, anterior insula, putamen, and thalamus. Within the cerebellum, vermal regions and anterior hemispheres ipsilateral to the movement became significantly activated. Tracking temporal modulations additionally activated predominantly right prefrontal, anterior cingulate, and intraparietal regions as well as posterior cerebellar hemispheres. Furthermore, strong evidence exists for the substantial benefits of rhythmic stimuli in rehabilitation training with motor disorders.

The CNV peak: An index of decision making and temporal memory

A slow brain potential change, the contingent negative variation (CNV), was recorded in a temporal generalization schedule. The task was to judge the duration of a signal (1.250 to 3.125 s) as being equal or not to that of a 2-s target that had been previously memorized. Two signal modalities, visual and tactile, were contrasted in distinct trial blocks, in order to explore possible localization differences. Significant results were found at CPz, irrespective of signal modality. The CNV that developed during signal presentation peaked around 2 s and then declined when the current signal was longer than the 2-s target, instead of peaking at signal extinction as was the case for shorter signals. Thus, for signals longer than the target, the CNV peak and the following slope change provide a memory trace of the encoded target duration, leading to decision making.

Relationships between time estimation, memory, attention, and processing speed in patients with severe traumatic brain injury

The present experiment was aimed at investigating the effects of memory and attention deficits and of information processing slowing on time estimation in patients with severe traumatic brain injury (TBI). Patients with TBI and normal control subjects reproduced and produced durations (5, 14, 38s) in both a control counting condition and in a concurrent reading condition. They also performed finger-tapping tasks at a free rate and at a 1s rate. Both groups were assessed on processing speed using a reaction-time task, and on memory and attention using a battery of neuropsychological tests. The results showed that time estimation was not less accurate in patients with TBI than in control subjects on the reproduction task or on the production task performed either in the control counting condition or in the concurrent reading condition. Conversely, duration judgments were more variable in patients with TBI than in control subjects on both tasks in both conditions. The results also showed that TBI patients exhibited slower reaction-times, and poorer working and episodic memory scores than control subjects. Most importantly, the variability index in the duration reproduction task was related to both working memory scores and processing speed measures, whereas the variability index in the duration production task was only related with the processing speed measures. The temporal performance pattern in TBI patients does not appear to reflect specific deficits in timing, but rather overall problems in attention, working memory, and processing speed mechanisms.

Interval timing and the encoding of signal duration by ensembles of cortical and striatal neurons

This study investigated the firing patterns of striatal and cortical neurons in rats in a temporal generalization task. Striatal and cortical ensembles were recorded in rats trained to lever press at 2 possible criterion durations (10 s or 40 s from tone onset). Twenty-two percent of striatal and 15% of cortical cells had temporally specific modulations in their firing rate, firing at a significantly different rate around 10 s compared with 40 s. On 80% of trials, a post hoc analysis of the trial-by-trial consistency of the firing rates of an ensemble of neurons predicted whether a spike train came from a time window around 10 s versus around 40 s. Results suggest that striatal and cortical neurons encode specific durations in their firing rate and thereby serve as components of a neural circuit used to represent duration.

Hemispheric asymmetries in the perception of rapid (timbral) and slow (nontimbral) amplitude fluctuations of complex tones

Hemispheric asymmetries for processing rapid (timbral) and slow (nontimbral) amplitude fluctuations of complex tones were investigated in 32 right-handed nonmusicians. Two monaural matching-to-sample tests with contralateral white noise and attention directed to 1 ear were used, 1 with tones presenting slow fluctuations of amplitude and 1 with tones presenting rapid fluctuations of amplitude perceived as different timbres. Stimuli were generated by altering the amplitude envelope of a steady state complex tone. Dependent variables were reaction time and accuracy. The results suggest an important role for the right hemisphere in the perception of temporal variations of intensity of sounds both when these variations are rapid and perceived as timbral qualities and when they are slow and perceived as changes of loudness.

Neural networks for the coordination of the hands in time

Without practice, bimanual movements can typically be performed either in phase or in antiphase. Complex temporal coordination, e.g., during movements at different frequencies with a noninteger ratio (polyrhythms), requires training. Here, we investigate the organization of the neural control systems for in-phase, antiphase, and polyrhythmic coordination using functional magnetic resonance imaging (fMRI). Brisk rhythmic tapping with the index fingers was used as a model behavior. We demonstrate different patterns of brain activity during in-phase and antiphase coordination. In-phase coordination was characterized by activation of the right anterior cerebellum and cingulate motor area (CMA). Antiphase coordination was accompanied by extensive fronto-parieto-temporal activations, including the supplementary motor area (SMA), the preSMA, and the bilateral inferior parietal gyri, premotor cortex, and superior temporal gyri. When contrasting polyrhythmic tapping with in-phase tapping, activity was seen in the same set of brain regions, and in the posterior cerebellum and the CMA. Antiphase and polyrhythmic coordination may thus to a large extent use common neural control circuitry. In a separate experiment, we analyzed the neural control of the rhythmic structure and the serial order of finger movements during polyrhythmic tapping. Polyrhythmic tapping was compared with an isochronous coordination pattern that retained the same serial order of finger movements as the polyrhythm. This experiment showed that the preSMA and the bilateral superior temporal gyri may be crucial for the rhythmic control of polyrhythmic tapping, while the cerebellum, the CMA, and the premotor cortices presumably are more involved in the ordinal control of the sequence of finger movements.

Processes involved in tempo perception: a CNV analysis

The purpose of this research was to study the mechanisms underlying tempo perception, by looking at their electrophysiological brain correlates. The subjects' task consisted of comparing the tempos of two isochronous tone sequences made up of either three (condition 13) or six (condition 16) 600-ms intervals. Contingent negative variation (CNV), known to be linked to the judgment of a single interval, kept increasing in amplitude for three intervals during tempo encoding, thereby providing evidence of the occurrence of CNVs also for several intervals in succession. This CNV increase could reflect the use of interval-based processes in the building of the interval memory trace. During the comparison phase, a CNV decrease was observed in condition 16, suggesting that subjects did not build a new memory trace, but used beat-based processes to check whether the beats of the new tempo occurred at the times they anticipated.

Cortical and subcortical networks underlying syncopated and synchronized coordination revealed using fMRI. Functional magnetic resonance imaging

Inherent differences in difficulty between on the beat (synchronization) and off the beat (syncopation) coordination modes are well known. Synchronization is typically quite easy and, once begun, may be carried out with little apparent attention demand. Syncopation tends to be difficult, even though it has been described as a simple, phase-shifted version of a synchronized pattern. We hypothesize that syncopation, unlike synchronization, is organized on a cycle-by-cycle basis, thereby imposing much greater preparatory and attentional demands on the central nervous system. To test this hypothesis we used fMRI to measure the BOLD response during syncopation and synchronization to an auditory stimulus. We found that the distribution of cortical and subcortical areas involved in intentionally coordinating movement with an external metronome depends on the timing pattern employed. Both synchronized and syncopated patterns require activation of contralateral sensorimotor and caudal supplementary motor cortices as well as the (primarily ipsilateral) cerebellum. Moving off the beat, however, requires not only additional activation of the cerebellum but also the recruitment of another network comprised of the basal ganglia, dorsolateral premotor, rostral supplementary motor, prefrontal, and temporal association cortices. No areas were found to be more active during synchronization than syncopation. The functional role of the cortical and subcortical regions areas involved in syncopation supports the hypothesis that whereas synchronization requires little preparation and monitoring, syncopated movements are planned and executed individually on each perception-action cycle.

Orienting attention to instants in time

My colleagues and I have investigated whether the temporal framework can be used to guide selective attention, and have applied non-invasive methodology to reveal the brain systems and mechanisms involved. Our findings show that we are able to orient attention selectively to different points in time, enhancing behavioral performance. These effects are mediated by a left-hemisphere dominant parietal-frontal system, which partially overlaps with the networks involved in spatial orienting. The neural system for temporal orienting also includes brain areas associated with motor preparation and anticipation, suggesting that sensorimotor areas with different specializations can contribute to attentional orienting depending on the stimulus attributes guiding selection. The optimization of behavior by temporal orienting involves enhancement of the latency and amplitude of event-related potentials that are associated with motor responses and decisions. The effects are distinct from those during visual spatial attention, indicating that behavioral advantages can be conferred by multiple types of neural mechanisms. Taken together, the findings illustrate the flexibility of attentional functions in the human brain.

Statistical analysis of timing errors

Human rhythmic activities are variable. Cycle-to-cycle fluctuations form the behavioral observable. Traditional analysis focuses on statistical measures such as mean and variance. In this article we show that, by treating the fluctuations as a time series, one can apply techniques such as power spectra and rescaled range analysis to gain insight into the mechanisms underlying the remarkable abilities of humans to perform a variety of rhythmic movements, from maintaining memorized temporal patterns to anticipating and timing their movements to predictable sensory stimuli.

Dissecting the brain's internal clock: how frontal-striatal circuitry keeps time and shifts attention

The ability of organisms to time and coordinate temporal sequences of events and to select particular aspects of their internal and external environments to which they will attend is vital to the organism's ability to adapt to the world around them. Numerous psychological theories have been proposed that describe how organisms might accomplish such stimulus selection and represent discrete temporal events as well as rhythm production. In addition, a large number of studies have demonstrated that damage to the frontostriatal circuitry appears to compromise the ability of organisms to successfully shift attention and behavior to adapt to changing temporal contexts. This suggests that frontostriatal circuitry is involved in the ability to make such shifts and to process temporal intervals. A selective review is accomplished in this article which focuses upon the specific neural mechanisms that may be involved in interval timing and set shifting. It is concluded that prefrontal cortex, substantia nigra pars compacta, pedunculopontine nucleus, and the direct and indirect pathways from the caudate to the thalamus may provide the neuroanatomical and neurophysiological substrates that underlie the organism's ability to shift its attention from one temporal context to another.

Neuropsychology: time out of mind

We have always known that some form of clock is needed to measure time. It now seems that a variety of different neural clocks are involved in determining our temporal perceptions, some specialised for shorter and some for longer durations.

The cerebellum: it's about time! But timing is not everything--new insights into the role of the cerebellum in timing motor and cognitive tasks

Converging evidence from different research studies supports a role for the cerebellum in timing neural processes. The cerebellum is part of a distributed system for motor control. The timing hypothesis provides a specific functional role for the unique contribution of the cerebellum. The timing capabilities of the cerebellum appear to extend beyond motor control into tasks focusing on perceptual processing that require the precise representation of temporal information and sensorimotor learning. Behavioral and modeling studies suggest that the cerebellar timing system is best characterized as providing a near-infinite set of interval-type timers rather than as a single clock with pacemaker or oscillatory properties, but this is controversial. In addition to learning precisely timed motor responses, the cerebellum is involved in on-line processing using feed-forward systems for which sensory input is used prior to movement execution to improve movement accuracy. This would be a mechanism for triggering accurate "time." The cerebellum continues to fascinate scientists, and although survival is possible without the cerebellum, the resultant quality of life is significantly compromised with clumsiness, ataxia, hypotonia, dysarthria, slowing of various cognitive perceptual processes, and impaired fine motor and ocular-motor coordination. The last three decades have seen the development of research that has focused on how the cerebellum functions. Further neurophysiologic research in cerebellar cortical neurotransmission is likely to further our understanding of the cerebellar contribution to timing sensorimotor processes.

The effect of spatial and temporal information on saccades and neural activity in oculomotor structures

It has been argued that saccade generation is supported by two systems, a'where' system that decides the direction and extent of an impending saccade, and a 'when' system that is involved in the timing of the release of fixation. We evaluated the contributions of these systems to saccade latencies, and used functional MRI to identify the neural substrates of these systems. We found that advance knowledge of the direction and the timing of an impending target movement had both overlapping and discrete effects on saccade latencies and on neural activation. Knowledge of either factor decreased regular saccade latencies. However, knowledge of target direction increased the number of predictive and express saccades while knowledge of target timing did not. The brain activation data showed that advance knowledge of the direction or the timing of the target movement activated primarily overlapping structures. The precentral gyrus, in the region of the frontal eye fields, was more active in conditions in which some aspect of the target movement was predictable than in saccade control and fixation conditions. In the basal ganglia, activation discriminated between advance knowledge of target timing and target direction. The lenticular nuclei were more active when only target timing was known in advance, while the caudate was more active when only target direction was known in advance. These data suggest that the neural structures supporting the 'where' and 'when' systems are highly overlapping, although there is some dissociation sub-cortically. Knowledge of target timing and target direction converge in precentral gyrus, a region where there is strong evidence of context-dependent modulation of neural activity.

Changes in the human brain during rhythm learning

Subjects were scanned with PET while they learned a complex arbitrary rhythm, paced by visual cues. In the comparison condition, the intervals were varied randomly. The behavioral results showed that the subjects decreased their response time with training, thus becoming more accurate in responding to the pacing cues at the appropriate time. There were learning-related increases in the posterior lateral cerebellum (lobule HVIIa), intraparietal and medial parietal cortex, presupplementary motor area (pre-SMA), and lateral premotor cortex. Learning-related decreases were found in the prestriate and inferior temporal cortex, suggesting that with practice the subjects increasingly came to depend on internal rather than external cues to time their responses. There were no learning-related increases in the basal ganglia. It is suggested that it is the neocortical-cerebellar loop that is involved in the timing and coordination of responses.

The evolution of brain activation during temporal processing

Timing is crucial to many aspects of human performance. To better understand its neural underpinnings, we used event-related fMRI to examine the time course of activation associated with different components of a time perception task. We distinguished systems associated with encoding time intervals from those related to comparing intervals and implementing a response. Activation in the basal ganglia occurred early, and was uniquely associated with encoding time intervals, whereas cerebellar activation unfolded late, suggesting an involvement in processes other than explicit timing. Early cortical activation associated with encoding of time intervals was observed in the right inferior parietal cortex and bilateral premotor cortex, implicating these systems in attention and temporary maintenance of intervals. Late activation in the right dorsolateral prefrontal cortex emerged during comparison of time intervals. Our results illustrate a dynamic network of cortical-subcortical activation associated with different components of temporal information processing.

Multisecond oscillations in the subthalamic nucleus: effects of apomorphine and dopamine cell lesion

Clinical and preclinical data indicate that the subthalamic nucleus (STN) plays a critical role in mediating the hyper- and hypoactive behavioral states associated with increases and decreases in dopamine receptor stimulation in the basal ganglia. The present study investigates effects of dopamine receptor stimulation on slow multisecond oscillations in firing rates in STN neurons. Extracellular, single-unit recordings were performed in locally anesthetized and immobilized rats which were either intact or had received unilateral 6-OHDA lesions of the medial forebrain bundle. The majority (64%) of spike trains recorded from STN neurons exhibited periodic oscillations in firing rate within the range of 2-60 sec, with an average period of 24 sec. The distribution of these baseline periodicities was not altered by unilateral 6-OHDA lesion, but periods were significantly shortened by systemic administration of the D1/D2 agonist apomorphine. This effect was observed in a greater proportion of neurons recorded from 6-OHDA-lesioned rats as compared to intact rats, was notably diminished in rats systemically anesthetized with chloral hydrate, and did not correlate with drug-induced changes in firing rate. These oscillations are similar to slow periodicities in firing rate recently reported in other basal ganglia nuclei. The possibility that these periodic oscillations in firing rate play a significant role in basal ganglia function was supported by the observation that the time of onset of apomorphine induced alterations in amplitude and periodicity of slow oscillations in STN spike trains is coincident with the onset of behavioral effects of this drug in 6-OHDA-lesioned animals. Synapse 38:38-50, 2000. Published 2000 Wiley-Liss, Inc.