Biomedical subjects

Deborah L Harrington

Publications and source records attributed to Deborah L Harrington.

7 recordsLinked to original sources

PubMed2006

Vector-based spatial-temporal minimum L1-norm solution for MEG.

Minimum L1-norm solutions have been used by many investigators to analyze MEG responses because they provide high spatial resolution images. However, conventional minimum L1-norm approaches suffer from instability in spatial construction, and poor smoothness of the reconstructed source time-courses. Activity commonly "jumps" from one grid point to (usually) the neighboring grid points. Equivalently, the time-course of one specific grid point can show substantial "spiky-looking" discontinuity. In the present study, we present a new vector-based spatial-temporal analysis using a L1-minimum-norm (VESTAL). This approach is based on a principle of MEG physics: the magnetic waveforms in sensor-space are linear functions of the source time-courses in the imaging-space. Our computer simulations showed that VESTAL provides good reconstruction of the source amplitude and orientation, with high stability and resolution in both the spatial and temporal domains. "Spiky-looking" discontinuity was not observed in the source time-courses. Importantly, the simulations also showed that VESTAL can resolve sources that are 100% correlated. We then examined the performance of VESTAL in the analysis of human median-nerve MEG responses. The results demonstrated that this method easily distinguishes sources very spatially close to each other, including individual primary somatosensory areas (BA 1, 2, 3b), primary motor area (BA 4), and other regions in the somatosensory system (e.g., BA 5, 7, SII, SMA, and temporal-parietal junction) with high temporal stability and resolution. VESTAL's potential for obtaining information on source extent was also examined.

Adult↗

PubMed2005

A parietal-frontal network studied by somatosensory oddball MEG responses, and its cross-modal consistency.

Previous studies using functional magnetic resonance imaging (fMRI) and event-related potentials (ERPs) of the brain have found that a distributed parietal-frontal neuronal network is activated in normals during both auditory and visual oddball tasks. The common cortical regions in this network are inferior parietal lobule (IPL)/supramarginal gyrus (SMG), anterior cingulate cortex (ACC), and dorsolateral prefrontal cortex (DLPFC). It is not clear whether the same network is activated by oddball tasks during somatosensory stimulation. The present study addressed this question by testing healthy adults as they performed a novel median-nerve oddball paradigm while undergoing magnetoencephalography (MEG). An automated multiple dipole analysis technique, the Multi-Start Spatio-Temporal (MSST) algorithm, localized multiple neuronal generators, and identified their time-courses. IPL/SMG, ACC, and DLPFC were reliably localized in the MEG median-nerve oddball responses, with IPL/SMG activation significantly preceding ACC and DLPFC activation. Thus, the same parietal-frontal neuronal network that shows activation during auditory and visual oddball tests is activated in a median-nerve oddball paradigm. Regions uniquely related to somatosensory oddball responses (e.g., primary and secondary somatosensory, dorsal premotor, primary motor, and supplementary motor areas) were also localized. Since the parietal-frontal network supports attentional allocation during performance of the task, this study may provide a novel method, as well as normative baseline data, for examining attention-related deficits in the somatosensory system of patients with neurological or psychiatric disorders.

Adult↗

PubMed2005

Distinct neural systems underlie learning visuomotor and spatial representations of motor skills.

Motor skill learning depends upon acquiring knowledge about multiple features of sequential behaviors, including their visuomotor and spatial properties. To investigate the neural systems that distinguish these representations, we carried out functional magnetic resonance imaging (fMRI) as healthy adults learned to type sequences on a novel keyboard. On the initial training day, learning-related changes in brain activation were found in distributed cortical regions, only a subset of which correlated with improvements in movement time (MT), suggesting their preeminence in controlling movements online. Subjects received extended training on the sequences during the ensuing week, after which they returned to the scanner for another imaging session. Relative to performance at the end of the first training day, continued plasticity was most striking in the inferior parietal cortex and new areas of plasticity were uncovered in the caudate and cerebellum. Plasticity in these regions correlated with reaction time (RT), suggesting their role in planning sequences before movement onset. Two transfer conditions probed for "what" subjects learned. The probe for visuomotor learning produced increased activation in visual analysis (left inferior visual cortex) and advance planning (left caudate) systems. The probe for spatial learning produced increased activation in visuomotor-transformation (left dorsal visual pathway) and retrieval (left precuneus) systems. Increased activity in all of these regions correlated with increased RT, but not MT, indicating that both transfer conditions interfered with the neural representation of plans for the sequences, but not processes that controlled their implementation. These findings demonstrated that neuroanatomically dissociable systems support the acquisition of visuomotor and spatial representations of actions.

Adolescent↗

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↗

PubMed2004

Neural systems supporting timing and chronometric counting: an FMRI study.

At least two strategies are available to humans for estimating multisecond intervals. One depends on an interval timing system that is common to many species. The other is the language-based strategy of chronometric counting. These two strategies are easily distinguished by the psychophysical properties of their behavioral correlates: counting supports substantially more precise estimates than are possible using the more general interval timing system. The present study investigates the neural systems that underlie the execution of these different strategies. Eighteen adults reproduced a 16-s interval either by internally timing or covertly counting the duration. Comparison of counting and timing to a resting baseline suggested that these strategies engage some nonoverlapping neural systems. Counting, but not timing, strongly activated Broca's area, primary motor cortex in the mouth region, and right cerebellum, all of which are associated with internal speech. Counting also activated parts of the medial premotor circuit, including the putamen, supplementary motor area (SMA) proper, and cingulate motor area (CMA), that have been associated with reproducing isochronous and syncopated rhythms of elements lasting hundreds of milliseconds. During timing, only a portion of this circuit, the SMA proper and CMA, was engaged. Both timing and counting interfered with semantic processing during the resting state, evidenced by task-related decreases in the left inferior and middle frontal gyri, right superior frontal gyrus, left angular gyrus, and bilateral posterior cingulate cortex. This study suggests that counting activates a corticostriatal network associated with millisecond, rhythmic timing. In contrast, timing long durations without the benefit of linguistic strategies for subdividing counts reduces activity in this circuitry.

Adult↗