Biomedical subjects

R C Miall

Publications and source records attributed to R C Miall.

At least 19 recordsLinked to original sources

PubMed2006

Evidence for stronger visuo-motor than visuo-proprioceptive conflict during mirror drawing performed by a deafferented subject and control subjects.

It has been proposed that mirror drawing is difficult because of the conflict between visual and proprioceptive signals from the arm. However, even without proprioception, there should be difficulties in planning movements to visual targets observed in a mirror, as the mirror-reversed spatial information must be translated into appropriate hand actions. Mirror drawing tasks suggest these planning conflicts are likely to be most obvious at corners, when encountering sharp changes in direction. We have therefore tested the speed of mirror drawing in a chronically deafferented man and in a control group of normal subjects, and hypothesized that increases in template complexity (number of corners) would result in reduced drawing speeds in all subjects. Indeed, all subjects, including the deafferented man, showed movement durations that increased linearly as the complexity of the drawings increased. However, the deafferented man was significantly faster than the control subjects at tracing curved templates. We suggest that the major difficulty in mirror tracking is in the visuo-motor planning of actions based on mirror-reversed visual information, and is not a conflict between visual and proprioceptive signals about arm motion.

Adult↗

PubMed2006

Concurrent adaptation to opposing visual displacements during an alternating movement.

It has been suggested that, during tasks in which subjects are exposed to a visual rotation of cursor feedback, alternating bimanual adaptation to opposing rotations is as rapid as unimanual adaptation to a single rotation (Bock et al. in Exp Brain Res 162:513-519, 2005). However, that experiment did not test strict alternation of the limbs but short alternate blocks of trials. We have therefore tested adaptation under alternate left/right hand movement with opposing rotations. It was clear that the left and right hand, within the alternating conditions, learnt to adapt to the opposing displacements at a similar rate suggesting that two adaptive states were formed concurrently. We suggest that the separate limbs are used as contextual cues to switch between the relevant adaptive states. However, we found that during online correction the alternating conditions had a significantly slower rate of adaptation in comparison to the unimanual conditions. Control conditions indicate that the results are not directly due the alternation between limbs or to the constant switching of vision between the two eyes. The negative interference may originate from the requirement to dissociate the visual information of these two alternating displacements to allow online control of the two arms.

Adaptation, Physiological↗

PubMed2006

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.

Adult↗

PubMed2006

Adaptation to visual feedback delays in manual tracking: evidence against the Smith Predictor model of human visually guided action.

We report adaptation to delayed visual feedback during a manual tracking task, testing the nature of the adapted responses with frequency analysis. Two groups of seven subjects tracked unpredictable targets using a handheld joystick, alternating between pursuit and compensatory display trials. The test group then practised for 1 h per day with a visual feedback delay of 300 ms; the control group practice under normal undelayed conditions. Introduction of the visual feedback delay significantly disrupted tracking performance, with an increase in errors and a reduction in frequency of corrective movements. Subjects showed clear evidence of adaptation during the 5 day experiment, decreasing tracking error and decreasing the mean power of intermittent corrections. However, there was no evidence of a return towards the initial high frequency intermittent tracking. We suggest that the adaptation observed in this study reflects the modification of predictive feedforward actions, but that these data do not support control based on Smith Prediction.

Adaptation, Physiological↗

PubMed2005

Two waves of a long-lasting aftereffect of prism adaptation measured over 7 days.

Prism adaptation is a useful paradigm to study the integration and reorganization of various sensory modalities involved in sensory-motor tasks. By prolonging the prismatic aftereffect and well-timed observation, we aimed to dissociate the components and mechanisms involved in human prism adaptation by their differential decay and development time courses. Here, we show that a single session of prism adaptation training, combining small increments of prism strength below the subjects' awareness threshold, during a pointing task with a free walk session with total prism exposure duration of 75 min, generated a surprisingly long-lasting aftereffect. The aftereffect was measured by the magnitude of the proprioceptive shift (assessed by straight-ahead pointing in the dark) for 7 days. An aftereffect was observed, which lasted for more than 6 days, by a single prism adaptation session. The aftereffect did not decay gradually. Unlike previous descriptions, the aftereffect showed two separate time-courses of decay and increase. After a significant initial decay within 6 h, the aftereffect increased again from 1 day up to 3 days. The novel decay and delayed development profile of this adaptation aftereffect suggests two separate underlying neural mechanisms with different time scales. Our experimental paradigms promise to reveal directly the temporal characteristics of early versus late long-term neural plasticity in complex human adaptive behavior.

Adaptation, Physiological↗

PubMed2005

Performing hand actions assists the visual discrimination of similar hand postures.

Recent theoretical work has suggested that internal predictive signals are used for motor control and coordination. The predictive signal - proposed to be the output of a forward model - would be a sensory representation of action. Hence, these sensory representations could potentially influence other sensory processes. We report here how performance of hand actions assisted the visual discrimination of target hand postures presented at random times within an on-going series of hand images. Reaction times to discriminate the targets were significantly shorter when the displayed images were both sequential and congruent with the action being performed. Hence, the planning or execution of action appears to allow better prediction of a displayed series of congruent images. In further control experiments, we show that the motor-visual priming effect is unlikely to be due to differential attentional demands and it is specific to a first person perspective display; it is short lasting, being lost if a 500 ms delay is introduced between successive stimulus presentations. The data are interpreted as evidence supporting the hypothesis that forward models in the motor system provide action-specific sensory predictions that are available to cognitive processes.

Adolescent↗

PubMed2005

Functional imaging of changes in cerebellar activity related to learning during a novel eye-hand tracking task.

Coordination between the eyes and the hand is likely to be based on a process of motor learning, so that the interactions between the two systems can be accurately controlled. By using an unusual tracking task we measured the change in brain activation levels, as recorded with 3T functional magnetic resonance imaging (fMRI), between naïve human subjects and the same subjects after a period of extended training. Initially the performance of the two groups was similar. One subject group was then trained in a synchronous, coordinated, eye-hand task; the other group trained with a 304 ms temporal offset between hand and eye tracking movements. After training, different patterns of performance were observed for the groups, and different functional activation profiles. Significant change in the relationship between functional activation levels and eye-hand task conditions was predominantly restricted to visuo-motor areas of the lateral and vermal cerebellum. In an additional test with one of the subject groups, we show that there was increased cerebellar activation after learning, irrespective of change in performance error. These results suggest that two factors contribute to the measured blood oxygen level-dependent (BOLD) signal. One declined with training and may be directly related to performance error. The other increased after training, in the test conditions nearest to the training condition, and may therefore be related to acquisition of experience in the task. The loci of activity changes suggest that improved performance is because of selective modified processing of ocular and manual control signals within the cerebellum. These results support the suggestion that coordination between eye and hand movement is based on an internal model acquired by the cerebellum that provides predictive signals linking the control of the two effectors.

Adult↗

PubMed2004

The effect of rTMS over the cerebellum in normal human volunteers on peg-board movement performance.

Low frequency rTMS over the paramedian part of the right cerebellum was used to test the effects of TMS-induced disruption of the cerebellum on performance of the 10-hole pegboard task. A test group (n = 14) showed significantly increased movement times lasting about 3 min after the 5-min 1 Hz rTMS train, compared to a control group who received no rTMS (n = 14), tested in a parallel group design. The increase was greatest for the hand ipsilateral to the stimulation, but the difference between the two hands was not statistically significant. These results suggest that the rTMS affects cerebellar excitability and cause a short-lasting bilateral change in sensory-motor performance.

Analysis of Variance↗

PubMed2004

Brain activity correlates differentially with increasing temporal complexity of rhythms during initialisation, synchronisation, and continuation phases of paced finger tapping.

Activity in parts of the human motor system has been shown to correlate with the complexity of performed motor sequences in terms of the number of limbs moved, number of movements, and number of trajectories. Here, we searched for activity correlating with temporal complexity, in terms of the number of different intervals produced in the sequence, using an overlearned tapping task. Our task was divided into three phases: movement selection and initiation (initiate), synchronisation of finger tapping with an external auditory cue (synchronise), and continued tapping in absence of the auditory pacer (continue). Comparisons between synchronisation and continuation showed a pattern in keeping with prior neuroimaging studies of paced finger tapping. Thus, activation of bilateral SMA and basal ganglia was greater in continuation tapping than in synchronisation tapping. Parametric analysis revealed activity correlating with temporal complexity during initiate in bilateral supplementary and pre-supplementary motor cortex (SMA and preSMA), rostral dorsal premotor cortex (PMC), basal ganglia, and dorsolateral prefrontal cortex (DLPFC), among other areas. During synchronise, correlated activity was observed in bilateral SMA, more caudal dorsal and ventral PMC, right DLPFC and right primary motor cortex. No correlated activity was observed during continue at P<0.01 (corrected, cluster level), though left angular gyrus was active at P<0.05. We suggest that the preSMA and rostral dorsal PMC activities during initiate may be associated with selection of timing parameters, while activation in centromedial prefrontal cortex during both initiate and synchronise may be associated with temporal error monitoring or correction. The absence of activity significantly correlated with temporal complexity during continue suggests that, once an overlearned timed movement sequence has been selected and initiated, there is no further adjustment of the timing control processes related to its continued production in absence of external cues.

Adult↗

PubMed2003

Connecting mirror neurons and forward models.

Two recent developments in motor neuroscience are promising the extension of theoretical concepts from motor control towards cognitive processes, including human social interactions and understanding the intentions of others. The first of these is the discovery of what are now called mirror neurons, which code for both observed and executed actions. The second is the concept of internal models, and in particular recent proposals that forward and inverse models operate in paired modules. These two ideas will be briefly introduced, and a recent suggestion linking between the two processes of mirroring and modelling will be described which may underlie our abilities for imitating actions, for cooperation between two actors, and possibly for communication via gesture and language.

Models, Neurological↗

PubMed2003

Interval timing in mice does not rely upon the circadian pacemaker.

The suprachiasmatic nucleus (SCN) of the hypothalamus is a precise timekeeper that controls and synchronizes the circadian period of countless physiological and behavioural functions and entrains them to the 24 h light/dark cycle. We examined the possibility that it is also indirectly involved in measurement of a briefer interval by observing the effects of lesions targeted at the SCN, and abolishing circadian rhythmicity, upon interval timing behaviour. Fourteen house mice (Mus musculus) were trained to estimate a 10 s interval using a modified peak procedure, and then underwent electrolytic lesions. Six individuals became behaviourally arrhythmic. Peak interval performance was then assessed in 12:12 light/dark conditions and in constant darkness. No significant change in peak characteristics was observed as a consequence of the lesion for either rhythmic or arrhythmic groups. These results show that the accurate measurement of 10 s requires neither a functioning circadian pacemaker nor entrained behavioural rhythmicity.

Animals↗

PubMed2003

System identification applied to a visuomotor task: near-optimal human performance in a noisy changing task.

Sensory-motor integration has frequently been studied using a single-step change in a control variable such as prismatic lens angle and has revealed human visuomotor adaptation to often be partial and inefficient. We propose that the changes occurring in everyday life are better represented as the accumulation of many smaller perturbations contaminated by measurement noise. We have therefore tested human performance to random walk variations in the visual feedback of hand movements during a pointing task. Subjects made discrete targeted pointing movements to a visual target and received terminal feedback via a cursor the position of which was offset from the actual movement endpoint by a random walk element and a random observation element. By applying ideal observer analysis, which for this task compares human performance against that of a Kalman filter, we show that the subjects' performance was highly efficient with Fisher efficiencies reaching 73%. We then used system identification techniques to characterize the control strategy used. A "modified" delta-rule algorithm best modeled the human data, which suggests that they estimated the random walk perturbation of feedback in this task using an exponential weighting of recent errors. The time constant of the exponential weighting of the best-fitting model varied with the rate of random walk drift. Because human efficiency levels were high and did not vary greatly across three levels of observation noise, these results suggest that the algorithm the subjects used exponentially weighted recent errors with a weighting that varied with the level of drift in the task to maintain efficient performance.

Adult↗

PubMed2003

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.

Adult↗

PubMed2003

Instructed delay activity in the human prefrontal cortex is modulated by monetary reward expectation.

Goal-directed actions are executed with greater efficiency when the goals of the actions are rewarded and so the reward expectation must influence systems concerned with action-planning and motor control. However, little is known about how this influence is achieved in primates. Here, we demonstrate in human subjects that manual performance is enhanced when the goals of the visually cued actions are monetary rewards. We also used event-related fMRI in the same subjects to localize neural activity related to action preparation and selection that was influenced by the reward. We found three areas with significant interaction between reward and preparation: the prestriate visual cortex, the premotor cortex and the lateral prefrontal cortex. The latter two areas appear to be frontal systems integrating the expectation of rewards with selection and preparation of actions.

Analysis of Variance↗

PubMed2002

The cerebellum and the timing of coordinated eye and hand tracking.

The cerebellum is known to have important functions in motor control, coordination, motor learning, and timing. It may have other "higher" functions as well, up to and including cognitive processing independent of motor behavior. In this article, we will review some of the evidence from functional imaging, lesion studies, electrophysiological recordings, and anatomy which support the theory that the cerebellum provides a "forward model" of the motor system. This forward model would be used for control of movement; it could also underlie a cerebellar role in coordination. In this role, the forward model would generate time-specific signals predicting the motion of each motor effector, essential for predictive control of, for example, eye and hand movements. Data are presented from human eye and hand tracking that support this. Tracking performance is better if eye and hand follow the same spatial trajectory, but better still if the eye leads the hand by about 75 to 100 ms. This suggests that information from the ocular control system feeds into the manual control system to assist its tracking.

Adult↗

PubMed2002

The oscillatory activity in the Parkinsonian subthalamic nucleus investigated using the macro-electrodes for deep brain stimulation.

OBJECTIVES: To investigate the oscillatory activity in the Parkinsonian subthalamic nucleus using the macro-electrodes for deep brain stimulation. METHODS: During bilateral deep brain stimulating electrode implantation, spontaneous and evoked field potentials were recorded from the subthalamic nucleus (STN) in two patients with Parkinson's disease (PD) during spontaneous resting tremor, passive manipulation of the wrist, and following electrical stimulation of the contralateral STN. RESULTS: Frequency analysis of the STN field potentials recorded during spontaneous resting tremor showed significant coherence with electromyographic activity in the contralateral arm, suggesting a close involvement of the STN in the generation of resting tremor in PD. The STN responded to passive movement of the contralateral wrist, but not to ipsilateral movement. High frequency (100 Hz) electrical stimulation of the STN induced tremor (4 Hz) in both forearms, and also oscillation of the contralateral STN (4 Hz). In contrast, low frequency (5 Hz) stimulation induced contralateral arrhythmic involuntary movement (3 Hz), but without altering the contralateral STN activity. CONCLUSIONS: We propose that the functional connection between the STN and arm muscles is mainly contralateral, but cross talk may occur between bilateral STN via a frequency-dependent pathway.

Animals↗

PubMed2001

Increased response to visual feedback of drug-induced dyskinetic movements in advanced Parkinson's disease.

To investigate the response to visual feedback of involuntary movements which have a frequency composition similar to cerebellar tremor but are not caused by cerebellar damage, we have tested six advanced Parkinson's disease (PD) patients with drug-induced dyskinetic movements using visually guided wrist tracking tasks. Tracking performance was assessed under three visual conditions: (1) both guiding target and movement cursor were displayed continuously; (2) the target display was turned off for the second half of each trial; or (3) the cursor display, but not the target, was turned off for the second half of each trial. The response to visual feedback of drug-induced dyskinetic movements at 1-5 Hz in these advanced PD patients were significantly increased than in normal controls. This suggests that increased response to visual feedback might be a common feature of low frequency involuntary movements and not directly caused by cerebellar damages.

Aged↗

PubMed2001

The cerebellum coordinates eye and hand tracking movements.

The cerebellum is thought to help coordinate movement. We tested this using functional magnetic resonance imaging (fMRI) of the human brain during visually guided tracking tasks requiring varying degrees of eye-hand coordination. The cerebellum was more active during independent rather than coordinated eye and hand tracking. However, in three further tasks, we also found parametric increases in cerebellar blood oxygenation signal (BOLD) as eye-hand coordination increased. Thus, the cerebellar BOLD signal has a non-monotonic relationship to tracking performance, with high activity during both coordinated and independent conditions. These data provide the most direct evidence from functional imaging that the cerebellum supports motor coordination. Its activity is consistent with roles in coordinating and learning to coordinate eye and hand movement.

Adult↗