Biomedical subjects

Roland R Lee

Publications and source records attributed to Roland R Lee.

6 recordsLinked to original sources

PubMed2004

Hemispheric asymmetries for kinematic and positional aspects of reaching.

Kinematic analyses of reaching have suggested that the left hemisphere is dominant for controlling the open loop component of the movement, which is more dependent on motor programmes; and the right hemisphere is dominant for controlling the closed loop component, which is more dependent on sensory feedback. This open and closed loop hypothesis of hemispheric asymmetry would also predict that advance planning should be dependent on the left hemisphere, and on-line response modification, which defines closed loop processes, should be dependent on the right hemisphere. Using kinematic analyses of reaching in patients with left or right hemisphere damage (LHD or RHD), we examined the ability: (i) to plan reaching movements in advance by examining changes in reaction time (RT) when response amplitude and visual feedback were cued prior to the response; and (ii) to modify the response during implementation when target location changed at the RT. Performance was compared between the stroke groups, using the ipsilesional arm, and age-matched control groups using their right (RNC) or left (LNC) arm. Aiming movements to a target that moved once or twice, with the second step occurring at the RT, were performed with or without visual feedback of hand position. There were no deficits in advance planning in either stroke group, as evidenced by comparable group changes in RT with changes in amplitude and visual feedback. Response modification deficits were seen for the LHD group in secondary velocity only. In addition, LHD produced slower initial peak velocity with prolongation of the deceleration phase and faster secondary peak velocities, and the RHD group produced deficits in final error only. These differences are more consistent with the dynamic dominance hypothesis, which links left hemisphere specialization to movement trajectory control and right hemisphere specialization to position control, rather than to global deficits in open and closed loop processing.

Aged↗

PubMed2004

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↗

PubMed2004

Temporal dynamics of ipsilateral and contralateral motor activity during voluntary finger movement.

The role of motor activity ipsilateral to movement remains a matter of debate, due in part to discrepancies among studies in the localization of this activity, when observed, and uncertainty about its time course. The present study used magnetoencephalography (MEG) to investigate the spatial localization and temporal dynamics of contralateral and ipsilateral motor activity during the preparation of unilateral finger movements. Eight right-handed normal subjects carried out self-paced finger-lifting movements with either their dominant or nondominant hand during MEG recordings. The Multi-Start Spatial Temporal multi-dipole method was used to analyze MEG responses recorded during the movement preparation and early execution stage (-800 msec to +30 msec) of movement. Three sources were localized consistently, including a source in the contralateral primary motor area (M1) and in the supplementary motor area (SMA). A third source ipsilateral to movement was located significantly anterior, inferior, and lateral to M1, in the premotor area (PMA) (Brodmann area [BA] 6). Peak latency of the SMA and the ipsilateral PMA sources significantly preceded the peak latency of the contralateral M1 source by 60 msec and 52 msec, respectively. Peak dipole strengths of both the SMA and ipsilateral PMA sources were significantly weaker than was the contralateral M1 source, but did not differ from each other. Altogether, the results indicated that the ipsilateral motor activity was associated with premotor function, rather than activity in M1. The time courses of activation in SMA and ipsilateral PMA were consistent with their purported roles in planning movements.

Adult↗

PubMed2004

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↗

PubMed2003

A non-invasive method for observing hippocampal function.

A non-invasive method for observing the functioning of the hippocampus could be invaluable in understanding the role of hippocampal abnormalities in many brain disorders. Transverse patterning, a hippocampal-dependent memory task, was used in an attempt to study the functioning hippocampus. Subjects performed transverse patterning while whole-head MEG data were collected. The MEG data were analyzed using a spatial-temporal multiple-dipole approach. Controls showed right hippocampal activation. Patients with unilateral hippocampal damage showed activation in undamaged hippocampus. MEG during transverse patterning performance is a promising, non-invasive tool for assessing hippocampal function.

Adult↗

PubMed1999

Pain sensitivity alterations as a function of lesion location in the parasylvian cortex.

Six patients with lesions involving parasylvian cerebral cortex were evaluated for their pain thresholds using contact heat (all six) and sharp probes that evoke pin-prick pain (4/6). Without knowledge of the sensory status of the individuals, two of the authors evaluated the MRIs of these patients, and determined to what extent the following cerebral regions were involved in the lesion: anterior insula, posterior insula, retroinsula, and parietal operculum. Each patient's lesion encompassed at least two of these regions. Three individuals demonstrated significant laterality differences in pain sensitivity, with elevated thresholds on the hand contralateral to his/her lesion. The common feature in these cases was the inclusion of the parietal operculum and posterior insula. The three other cases showed no evidence of abnormal pain thresholds. The common feature of these cases was the apparent sparing of the parietal operculum. Thus, this series of cases points to the significance of the parietal operculum, either alone or with adjacent posterior insula, for normal pain thresholds. In comparison, extensive involvement of the anterior insula in two cases was not associated with abnormal pain thresholds. Four of the six patients were also evaluated with a cold pain tolerance test, which presumably involves more affective/motivational aspects of pain than threshold tests. Only two of these patients showed greater tolerance contralaterally versus ipsilaterally, and theirs were the two lesions of the four with involvement of a large part of the insula. This result supports the theory that the insula's involvement in nociceptive processing is related to the affective/motivational aspect of pain.

Adult↗