Biomedical subjects

W Richard Staines

Publications and source records attributed to W Richard Staines.

13 recordsLinked to original sources

PubMed2006

Unexplained neurologic symptoms: an fMRI study of sensory conversion disorder.

We investigated three subjects with unexplained sensory loss meeting criteria for conversion disorder using brain fMRI during unilateral and bilateral vibrotactile stimulation. In each subject, stimulation of the affected limb did not produce activation of the contralateral primary somatosensory (S1) region, whereas bilateral limb stimulation did. These findings implicate selective alterations in primary sensorimotor cortex activity in conversion disorder, and may also reconcile the discordant results of previous studies.

Adult↗

PubMed2006

Predictability of the target stimulus for sensory-guided movement modulates early somatosensory cortical potentials.

OBJECTIVE: To investigate the role of sensory modulation in the control of sensory-guided behaviour. Specifically, we hypothesized that early somatosensory evoked potentials (SEPs) would be facilitated during performance of continuous sensory-guided movement requiring sustained attention. METHODS: Median nerve SEPs were elicited via electrical stimulation and recorded from scalp electrodes while subjects performed tasks requiring continuous sensory-motor transformations. Subjects received a predictable (rhythmic amplitude modulation) or unpredictable (random amplitude modulation) amplitude varying tactile stimulus (frequency constant at 20 Hz) delivered to the tip of the index finger either alone or with the requirement to track it by modulating the isometric grip force produced by the opposite hand. RESULTS: Early SEP (N20-P27) amplitudes were differentially modulated during unpredictable tracking compared to sensory-motor controls. Specifically, N20 amplitudes were attenuated and P27 amplitudes were enhanced during sensory-guided tracking. CONCLUSIONS: Sustained attention to task-relevant sensory stimuli differentially modulates areas within primary somatosensory cortex (S1) during a continuous sensory-motor transformation. SIGNIFICANCE: These data have implications for understanding the role of attention in regulating somatosensory cortices during sensory-motor behaviour.

Adult↗

PubMed2006

Cortical adaptations and motor performance improvements associated with short-term bimanual training.

Bimanual movement can increase activity within the stroke-affected hemisphere and may contribute to recovery in some patients. To understand how bimanual learning may aid recovery post-stroke, the present study used EEG to investigate cortical adaptations associated with short-term bimanual training and the behavioral modulations that transfer to unimanual movement in healthy individuals. Movement-related potentials (MRP) and reaction times (RT) were recorded from 10 healthy subjects during blocks of unimanual visuomotor trials before and after a bimanual training task. We hypothesized that short-term bimanual practice would induce adaptive cortical changes evident in the MRPs to movements involving a single hand. Post-training results showed that: (1) the late MRP amplitude did not change, (2) RT significantly decreased, and (3) there was a trend for the early MRP amplitude to increase. There was a strong relationship between modulation of early MRP amplitude and RT in the unimanual movement blocks before and after training. Specifically, a subgroup showed a significant decrease in RT in conjunction with a significant increase in the early MRP amplitude. Lastly, comparing later to earlier trials within the bimanual training block, task accuracy and early MRP amplitude significantly increased and (2) a positive re-afferent potential significantly decreased. Results suggest that short-term bimanual training is associated with possible transfer effects to a unimanual task reflected in changes of MRP components and RT. Furthermore, results from the bimanual training trial itself indicate that short-term bimanual training can change the level of motor preparation and sensory feedback in all subjects.

Adult↗

PubMed2005

Physiotherapy coupled with dextroamphetamine for rehabilitation after hemiparetic stroke: a randomized, double-blind, placebo-controlled trial.

BACKGROUND AND PURPOSE: Hemiparesis is the commonest disabling deficit caused by stroke. In animals, dextroamphetamine (AMPH) paired with training enhances motor recovery, but its clinical efficacy is uncertain. METHODS: In a randomized, double-blind, placebo-controlled trial, 71 stroke patients were stratified by hemiparesis severity and randomly assigned to 10 sessions of physiotherapy coupled with either 10 mg AMPH or placebo. Study treatments were administered by 1 physiotherapist, beginning 5 to 10 days after stroke and continuing twice per week for 5 weeks. Outcomes were assessed by 1 physiotherapist at baseline, after each treatment session, at 6 weeks, and at 3 months. The primary outcome was motor recovery (impairment level) on the Fugl-Meyer (FM) scale. Secondary outcomes assessed mobility, ambulation, arm/hand function, and independence in activities of daily living. RESULTS: Baseline hemiparesis was severe overall (mean FM score 27.7+/-20.0). Motor scores improved during treatment in both groups (mean change, baseline to 3 months 29.5+/-16.6). Repeated-measures ANOVA revealed no significant differences in recovery between the treatment groups for the entire cohort (n=67) or for subgroups with a severe hemiparesis (n=43), moderate hemiparesis (n=24), or cortically based stroke (n=26). In the moderate subgroup, there was a significant drug x time interaction for upper extremity motor recovery (F=5.14; P<0.001), although there was a significant baseline imbalance in motor scores in this subgroup. CONCLUSIONS: In stroke patients with a severe motor deficit, 10 mg AMPH coupled with physiotherapy twice per week for 5 weeks in the early poststroke period provided no additional benefit in motor or functional recovery compared with physiotherapy alone. Patients with moderate severity hemiparesis deserve further investigation. Increased intensity and longer duration drug/therapy dosing regimens should be explored, targeting the upper and lower limbs separately.

Aged↗

PubMed2004

The effect of a concurrent cognitive task on cortical potentials evoked by unpredictable balance perturbations.

BACKGROUND: Although previous studies suggest that postural control requires attention and other cognitive resources, the central mechanisms responsible for this relationship remain unclear. To address this issue, we examined the effects of altered attention on cortical activity and postural responses following mechanical perturbations to upright stance. We hypothesized that cortical activity would be attenuated but not delayed when mechanical perturbations were applied during a concurrent performance of a cognitive task (i.e. when attention was directed away from the perturbation). We also hypothesized that these cortical changes would be accompanied by alterations in the postural response, as evidenced by increases in the magnitude of anteroposterior (AP) centre of pressure (COP) peak displacements and tibialis anterior (TA) muscle activity. Healthy young adults (n = 7) were instructed to continuously track (cognitive task) or not track (control task) a randomly moving visual target using a hand-held joystick. During each of these conditions, unpredictable translations of a moving floor evoked cortical and postural responses. Scalp-recorded cortical activity, COP, and TA electromyographic (EMG) measures were collected. RESULTS: Results revealed a significant decrease in the magnitude of early cortical activity (the N1 response, the first negative peak after perturbation onset) during the tracking task compared to the control condition. More pronounced AP COP peak displacements and EMG magnitudes were also observed for the tracking task and were possibly related to changes in the N1 response. CONCLUSION: Based on previous notions that the N1 response represents sensory processing of the balance disturbance, we suggest that the attenuation of the N1 response is an important central mechanism that may provide insight into the relationship between attention and postural control.

Adult↗

PubMed2004

Activation in SI and SII: the influence of vibrotactile amplitude during passive and task-relevant stimulation.

Using functional magnetic resonance imaging (fMRI), responses in human somatosensory cortex were quantified in response to changes in the amplitude of peripheral stimulation during (1) passive vibration and (2) an attention-demanding tactile tracking task whereby changes in vibration amplitude were used to guide motor behaviour. Functional MRI was conducted using a scanner operating at 1.5 T, and vibration was delivered to the volar surface of the right index finger with a custom-built magnetomechanical device. Results showed that primary somatosensory cortex (SI) reliably reflects changes in vibration amplitude applied to the finger during passive vibration and also in the presence of a task that modulates the activity in SI. Secondary somatosensory cortex did not reveal any clear relationship with vibration amplitude but was more often activated during the attention demanding tracking task compared with passive vibration. The present study supports an increasing stimulus-response relationship between vibrotactile stimuli and activity in SI that persists during attentive, active states.

Adult↗

PubMed2004

Optimizing the experimental design for ankle dorsiflexion fMRI.

Compared to motor studies of the upper limb, few experiments have sought a relationship between blood oxygen level-dependent (BOLD) functional magnetic resonance imaging (fMRI) sensorimotor signals and the resulting lower limb output. In Experiment 1, using an fMRI simulator system, we determined the optimized experimental protocol based on two design types and four behavioral movement types during ankle dorsiflexion. Experiment 2 involved testing the BOLD sensitivity at 1.5 T during ankle movements. Subjects performed large- and small-amplitude dorsiflexion movement types using an event-related design, with the intent of contrasting spatial and temporal features of the BOLD signal. In both experiments, the subject's behavior was guided by visual biofeedback of their ankle flexion angle, using an MR-compatible fiberoptic tape. From Experiment 1, we found electromyography (EMG) difference voltage ratio of approximately 2:1 for large (40 degrees ) and small (15 degrees ) dorsiflexion, 0.13 mV and 0.07 mV, respectively. In Experimental 2, we found the peak BOLD % signal changes of 1.04% and 0.89%, for large (40 degrees ) and small (15 degrees ) dorsiflexion, respectively. In addition, graded dorsiflexion produced graded BOLD signals in the primary sensorimotor and supplementary motor areas in 10 of 12 healthy young subjects, attesting to the feasibility of lower-limb fMRI at 1.5 T. This study provides insight into the cortical network involved in dorsiflexion using an experimental paradigm that is likely to translate effectively to hemiparetic stroke subjects.

Adult↗

PubMed2004

Brain mechanisms for preparing increasingly complex sensory to motor transformations.

Movements made in response to sensory cues require the brain to transform sensory information into an appropriate motor output. Sensorimotor mappings used in daily life range from direct or "standard" to highly complex. In "nonstandard" sensorimotor tasks, the visual stimulus guiding an action is often not the target of the action. A common example of such a nonstandard mapping is the use of a computer mouse on a horizontal surface to guide an object visible on a vertical monitor. The present study used event-related BOLD fMRI to examine how patterns of brain activity vary as sensorimotor mappings become progressively more complicated. We observed significantly different patterns of cortical activity depending on the level of dissociation between a sensory input and a required motor response. Our results suggest the presence of a functional network generally involved in performing the type of nonstandard sensorimotor tasks examined. This putative network includes regions of the primary motor cortex, medial motor areas, the superior parietal lobule (SPL), and the lateral premotor cortex. The extent of activity in active areas varied depending on the characteristics of the particular sensorimotor mapping used in performing a task. Furthermore, in addition to this putative network, specific task-related areas of activity were observed.

Adult↗

PubMed2003

A platform for combining virtual reality experiments with functional magnetic resonance imaging.

How the brain functions during behavioural tasks conducted in virtual reality (VR) remains largely unresolved. This issue is extremely important both in terms of establishing the benefits of VR through basic science, as well as for future optimization of tasks conducted in VR environments. Here, the authors describe their current work to develop a testing platform for conducting VR experiments that can be probed by functional magnetic resonance imaging (fMRI) to measure brain activity. Examples involving human spatial navigation and data glove operation illustrate the technical feasibility of the approach and introduce thought-provoking observations of brain activation patterns. Future research directions for combined use of VR and fMRI are also discussed.

Brain↗

PubMed2002

The time course of attention shifts following perturbation of upright stance.

Recent work has revealed the specific time course of attention shifts associated with balance control in a seated model using a dual-task paradigm. This work highlighted an initial "automatic" and later "attention-demanding" phase of the evoked balance reaction. The objective of the present study was to determine if comparable influences would be observed for performance of a visuomotor tracking task when responding to perturbations of upright stability. Small-amplitude floor translations were applied in the forward or backward direction to evoke stabilizing postural reactions. Balance reactions were evoked with and without the concurrent performance of a visuomotor tracking task using the right hand. Results showed significant disruptions (pauses) in tracking that invariably occurred after onset of the earliest balance reaction measured in ankle muscles. On average, there was a delay of 345 ms between ankle-muscle activation (average onset 144 ms) and the pause in visuomotor tracking. The concurrent tracking led to modest change in later phases of the balance reaction, as measured by an increase in center-of-pressure excursions, but did not affect the earliest phase of the reaction. These results support the view that compensatory balance reactions, even those evoked by small perturbations, are characterized by an initial "automatic" phase and subsequent control that may be more dependent on cognitive resources.

Adult↗

PubMed2002

Task-relevant modulation of contralateral and ipsilateral primary somatosensory cortex and the role of a prefrontal-cortical sensory gating system.

Electrophysiological studies have shown that task-relevant somatosensory information leads to selective facilitation within the primary somatosensory cortex (SI). The purpose of the present study was (1) to further explore the relationship between the relevancy of stimuli and activation within the contralateral and ipsilateral SI and (2) to provide further insight into the specific sensory gating network responsible for modulating neural activity within SI. Functional MRI of 12 normal subjects was performed with vibrotactile stimuli presented to the pad of the index finger. In experiment 1, the stimulus was presented to either the left or the right hand. Subjects were required to detect transient changes in stimulus frequency. In experiment 2, stimuli were presented to either the right hand alone or both hands simultaneously. Stimuli were applied either (A) passively or (B) when subjects were asked to detect frequency changes that occurred to the right hand only. In experiment 1, task-relevant somatosensory stimulation led not only to enhanced contralateral SI activity, but also to a suppression of activity in the ipsilateral SI. In experiment 2, SI activation was enhanced when stimuli were task-relevant, compared to that observed with passive input. When stimuli were presented simultaneously to both hands, only those that were task-relevant increased SI activation. This was associated with recruitment of a network of cortical regions, including the right prefrontal cortex (Brodmann area 9). We conclude that SI modulation is dependent on task relevancy and that this modulation may be regulated, at least in part, by the prefrontal cortex.

Adult↗

PubMed2002

Frontal-parietal event-related potential changes associated with practising a novel visuomotor task.

Learning novel visuomotor tasks requires precise processing and transformation of incoming sensory information to produce accurate motor responses. The present study characterized neural activity associated with sensorimotor processes during novel visuomotor learning. We hypothesized that the acquisition of a visuomotor skill would be accompanied by experience-dependent modulation of sensorimotor cortical activity. Subjects controlled a cursor on a computer screen with a joystick. With the goal to move the cursor to a cued target after a brief delay, the relationship between joystick and cursor movement was manipulated such that joystick movement controlled cursor velocity, not displacement (rate task). Individual trials in this task were further divided into early (rate1) and late (rate2) blocks. Event-related potentials (ERPs) were averaged to target presentation, the cue for movement, and movement onset. Subjects were more accurate after practice in late rate2 compared to early rate1 blocks. ERPs associated with movement onset were larger in amplitude and occurred earlier over centroparietal sites following practice. In contrast, ERPs to the cue to move were enhanced frontocentrally initially and diminished with practice. The results suggest that practice on a novel visuomotor task is associated with changes in frontoparietal networks involved in motor preparation and sensorimotor integration. Specifically, practice-related enhancement of movement-related ERPs supports experience-dependent alterations in the network subserving motor preparation.

Adolescent↗

PubMed2002

Somatosensory gating and recovery from stroke involving the thalamus.

BACKGROUND AND PURPOSE: In the undamaged brain, sensory input to the cortex is intricately controlled via sensory gating mechanisms. Given the role of corticothalamic pathways in this control, it was hypothesized that in patients recovering from thalamic stroke there would be evidence of disrupted sensory gating and that efficient control of cortical sensory inputs would emerge during recovery. METHODS: Four patients were tested serially after stroke from 1 to 24 weeks after injury. Perceptual thresholds, somatosensory evoked potential amplitudes, and functional MRI activations under specific somatosensory stimulation conditions were measured. RESULTS: All patients demonstrated comparable results, revealing disrupted threshold detection to vibrotactile stimuli in the presence of a concurrent competing, contralateral input. In contrast, threshold detection was comparable between the affected and unaffected sides when there were no competing stimuli. This compromised capacity to inhibit competing sensory inputs was paralleled by a reduction in the measured activation of cortical representation in the stroke-affected hemisphere (functional MRI and somatosensory evoked potential) during bilateral stimulation. After recovery, perceptual detection improvements during bilateral stimulation were paralleled by enhancements of primary somatosensory cortical activation in the stroke-affected hemisphere. CONCLUSIONS: These results provide insight into potential mechanisms that contribute to sensory gating and suggest that the ability to control sensory input through effective gating mechanisms, in addition to primary somatosensory representation, may be important for poststroke sensory recovery.

Aged↗