Invited commentary.
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Cognition Disorders↗
Biomedical subjects
Lara A Boyd
Publications and source records attributed to Lara A Boyd.
Does the representation of time depend on the cerebellum? Effect of cerebellar stroke.
Behaviours that appear to depend on processing temporal information are frequently disrupted after cerebellar damage. The present study examined the role of the cerebellum in explicit timing and its relationship to other psychological processes. We hypothesized that if the cerebellum regulates timekeeping operations then cerebellar damage should disrupt the perception and the reproduction of intervals, since both are thought to be supported by a common timekeeper mechanism. Twenty-one patients with cerebellar damage from stroke and 30 normal controls performed time perception and time reproduction tasks. In the time reproduction task, timing variability was decomposed into a central timing component (clock variability) and a motor component (motor implementation variability). We found impairments only in time reproduction (increased clock variability) in patients with medial and lateral damage involving the middle- to superior-cerebellar lobules. To explore potential reasons for the temporal processing deficits, time reproduction and perception performance were correlated with independent measures of attention, working memory, sensory discrimination and processing speed. Poorer working memory correlated with increased variability in the 'clock' component of time reproduction. In contrast, processing speed correlated best with time perception. The results did not support a role for the cerebellum in timekeeping operations. Rather, deficits in timing movements may be related to a disruption in acquiring sensory and cognitive information relevant to the task, coupled with an additional impairment in the motor-output system.
Aged↗
Neural representation of interval encoding and decision making.
Our perception of time depends on multiple psychological processes that allow us to anticipate events. In this study, we used event-related functional magnetic resonance imaging (fMRI) to differentiate neural systems involved in formulating representations of time from processes associated with making decisions about their duration. A time perception task consisting of two randomly presented standard intervals was used to ensure that intervals were encoded on each trial and to enhance memory requirements. During the encoding phase of a trial, activation was observed in the right caudate nucleus, right inferior parietal cortex and left cerebellum. Activation in these regions correlated with timing sensitivity (coefficient of variation). In contrast, encoding-related activity in the right parahippocampus and hippocampus correlated with the bisection point and right precuneus activation was associated with a measure of memory distortion. Decision processes were studied by examining brain activation during the decision phase of a trial that was associated with the difficulty of interval discriminations. Activation in the right parahippocampus was greater for easier than harder discriminations. In contrast, activation was greater for harder than easier discriminations in systems involved in working memory (left middle-frontal and parietal cortex) and auditory rehearsal (left inferior-frontal and superior-temporal cortex). Activity in the auditory rehearsal network correlated with memory distortion. Our results support the independence of systems that mediate interval encoding and decision processes. The results also suggest that distortions in memory for time may be due to strategic processing in cortical systems involved in either encoding or rehearsal.
Acoustic Stimulation↗
Cerebellar stroke impairs temporal but not spatial accuracy during implicit motor learning.
OBJECTIVE: Numerous studies have demonstrated cerebellar activity during implicit motor learning, but few have addressed its specific role. The purpose of this study was to determine if specific components (spatial or temporal) of an implicit motor-tracking task were affected by cerebellar stroke. METHODS: The authors studied the performance of individuals with unilateral cerebellar stroke (n = 7)and a control group (n = 10) across 3 acquisition days and at a delayed retention test as they practiced a unimanual tracking task with the contralesional upper extremity. RESULTS: After cerebellar stroke, participants demonstrated reduced tracking errors for repeating sequences compared to random sequences; however, decomposition of tracking performance into temporal and spatial components revealed persistent deficits in tracking time lag despite improved spatial accuracy. A lesion analysis showed that the dentate nucleus was the only common region affected by all cerebellar strokes. CONCLUSIONS: During implicit motor learning, the cerebellum appears to participate in the formation of predictive strategies for the timing of motor responses, rather than for the accuracy of motor execution. Because deficits were found in the contralesional upper extremity, the authors suggest that this function is not lateralized to 1 hemisphere; cerebellar output may affect the formation of an internal model for timing movements in both upper extremities.
Adult↗
Impact of explicit information on implicit motor-sequence learning following middle cerebral artery stroke.
BACKGROUND AND PURPOSE: Recovery of motor skills following stroke is supported, in part, by the implicit memory system. However, attempts to guide learning commonly use explicit instructions concerning "how to" perform a movement task. The purpose of this work was to systematically investigate the impact of explicit information (EI) on implicit motor-sequence learning using the ipsilesional arm in people with damage in the middle cerebral artery (MCA) distribution. SUBJECTS AND METHODS: Ten people with unilateral stroke in the MCA distribution affecting the sensorimotor cortical areas and 10 people with no known pathology or impairment (control participants) were randomly divided into 2 groups. One group was provided with EI and one group was not (EI and No-EI groups, respectively) as the participants practiced an implicit motor-sequencing task over 3 days, with a retention test on day 4. RESULTS: A 3-way interaction demonstrated that, across days of practice, EI had opposite effects on implicit motor-sequence performance for the 2 groups. Post hoc tests confirmed that EI facilitated the performance of the control participants in the EI group but interfered with the performance of the participants with stroke in the EI group. This interference effect persisted, and was evident during the retention test in the participants with stroke in the EI group. DISCUSSION AND CONCLUSION: Explicit information was detrimental for implicit motor-sequence learning following MCA stroke. Rehabilitation outcomes may benefit from consideration of stroke location when determining the degree to which EI can augment implicit motor skill learning.
Analysis of Variance↗
Providing explicit information disrupts implicit motor learning after basal ganglia stroke.
Despite their purported neuroanatomic and functional isolation, empirical evidence suggests that sometimes conscious explicit processes can influence implicit motor skill learning. Our goal was to determine if the provision of explicit information affected implicit motor-sequence learning after damage to the basal ganglia. Individuals with stroke affecting the basal ganglia (BG) and healthy controls (HC) practiced a continuous implicit motor-sequencing task; half were provided with explicit information (EI) and half were not (No-EI). The focus of brain damage for both BG groups was in the putamen. All of the EI participants were at least explicitly aware of the repeating sequence. Across three days of practice, explicit information had a differential effect on the groups. Explicit information disrupted acquisition performance in participants with basal ganglia stroke but not healthy controls. By retention (day 4), a dissociation was apparent--explicit information hindered implicit learning in participants with basal ganglia lesions but aided healthy controls. It appears that after basal ganglia stroke explicit information is less helpful in the development of the motor plan than is discovering a motor solution using the implicit system alone. This may be due to the increased demand placed on working memory by explicit information. Thus, basal ganglia integrity may be a crucial factor in determining the efficacy of explicit information for implicit motor-sequence learning.
Adult↗