The effects of posteroventral pallidotomy on the preparation and execution of voluntary hand and arm movements in Parkinson's disease.
(1/389)
We studied the effect of posteroventral pallidotomy on movement preparation and execution in 27 parkinsonian patients using various motor tasks. Patients were evaluated after overnight withdrawal of medication before and 3 months after unilateral pallidotomy. Surgery had no effect on initiation time in unwarned simple and choice reaction time tasks, whereas movement time measured during the same tasks was improved for the contralesional hand. Movement times also improved for isometric and isotonic ballistic movements. In contrast, repetitive, distal and fine movements measured in finger-tapping and pegboard tasks were not improved after pallidotomy. Preparatory processes were investigated using both behavioural and electrophysiological measures. A precued choice reaction time task suggested an enhancement of motor preparation for the contralesional hand. Similarly, movement-related cortical potentials showed an increase in the slope of the late component (NS2) when the patients performed joystick movements with the contralesional hand. However, no significant change was found for the early component (NS1) or when the patient moved the ipsilesional hand. The amplitude of the long-latency stretch reflex of the contralesional hand decreased after surgery. In summary, the data suggest that pallidotomy improved mainly the later stages of movement preparation and the execution of proximal movements with the contralesional limb. These results provide detailed quantitative data on the impact of posteroventral pallidotomy on previously described measures of upper limb akinesia in Parkinson's disease. (+info)
Impairment of willed actions and use of advance information for movement preparation in schizophrenia.
(2/389)
OBJECTIVES: To assess willed actions in patients with schizophrenia using reaction time (RT) tasks that differ in the degree to which they involve volitionally controlled versus stimulus driven responses. METHODS: Ten patients diagnosed with schizophrenia and 13 normal controls of comparable age were tested. Subjects performed a visual simple RT (SRT), an uncued four choice reaction time (CRT), and a fully cued four choice RT task. A stimulus 1(S1)-stimulus 2(S2) paradigm was used. The warning signal/precue (S1) preceded the imperative stimulus (S2) by either 0 (no warning signal or precue) 200, 800, 1600, or 3200 ms. RESULTS: The patients with schizophrenia had significantly slower RTs and movement times than normal subjects across all RT tasks. The unwarned SRT trials were significantly faster than the uncued CRT trials for both groups. For both groups, fully cued CRTs were significantly faster than the uncued CRTs. However, the S1-S2 interval had a differential effect on CRTs in the two groups. For the normal subjects fully cued CRTs and SRTs were equivalent when S1-S2 intervals were 800 ms or longer. A similar pattern of effects was not seen in the patients with schizophrenia, for whom the fully cued CRT were unexpectedly equivalent to SRT for the 200 ms interval and expectedly for the 1600 ms S1-S2 interval, but not the 3200 or 800 ms intervals. CONCLUSIONS: Patients with schizophrenia were able to use advance information inherent in SRT or provided by the precue in fully cued CRT to speed up RT relative to uncued CRT. However, in the latter task, in which the volitional demands of preprogramming are higher since a different response has to be prepared on each trial, patients showed some unusual and inconsistent interval effects suggesting instability of attentional set. It is possible that future studies using RT tasks with higher volitional demands in patients with predominance of negative signs may disclose greater deficits in willed action in schizophrenia. (+info)
Voluntary movement after pallidotomy in severe Parkinson's disease.
(3/389)
The mechanisms of improvement in parkinsonian bradykinesia after posteroventral pallidotomy were investigated in 17 patients undergoing unilateral pallidotomy for severe Parkinson's disease. Clinical ratings of 'off' period bradykinesia demonstrated a maximal improvement of 22% 3 months postoperatively. Kinematic assessments of rapid repetitive finger and sequential arm movements were performed after overnight withdrawal of antiparkinsonian medications. There was a bilateral reduction in the inter-onset latency of a two-stage sequential arm movement and a contralateral increase in speed of arm movement after pallidotomy. There was no significant improvement postoperatively in the rhythm, amplitude or speed of repetitive finger movements. The results confirm the clinical impression that pallidotomy improves bradykinesia. This was more evident for complex limb movements, which used attentional strategies and external (visual and auditory) cues, than for repetitive fingertapping movements, which were largely internally generated. Since ablation of the pallidum can only reduce inhibitory pallidal outflow, it is unlikely to restore the normal pallidal influence on thalamocortical motor circuits. Therefore, any improvement in bradykinesia after pallidotomy must be related to mechanisms other than restoration of pallidothalamocortical connectivity. Based on the above observations, we suggest that some of the changes in motor control may be explained by the greater efficacy of external cues in facilitating movement after withdrawal of the abnormal pallidal discharge. (+info)
Cognitive motor control in human pre-supplementary motor area studied by subdural recording of discrimination/selection-related potentials.
(4/389)
To clarify the functional role of human pre-supplementary motor area (pre-SMA) in 'cognitive' motor control as compared with other non-primary motor cortices (SMA-proper and lateral premotor areas) and prefrontal area, we recorded epicortical field potentials by using subdural electrodes in five epileptic patients during presurgical evaluation, whose pre-SMA, SMA-proper, prefrontal and lateral premotor areas were defined by electric cortical stimulation and recent anatomical orientations according to the bicommissural plane and callosal grid system. An S1-Go/NoGo choice and delayed reaction task (S1-choice paradigm) and a warned choice Go/NoGo reaction task (S2-choice paradigm) with inter-stimulus intervals of 2 s were employed. The results showed (i) transient potentials with onset and peak latencies of about 200 and 600 ms, respectively, after S1 in the S1-choice paradigm mainly at pre-SMA and to a lesser degree at the prefrontal and lateral premotor areas, but not in the S2-choice paradigm. At SMA-proper, a similar but much smaller potential was seen after S1 in both S1- and S2-choice paradigms and (ii) slow sustained potentials between S1 and S2 in both S1- and S2-choice paradigms in all of the non-primary motor areas investigated (pre-SMA, SMA-proper and lateral premotor areas) and prefrontal area. It is concluded that pre-SMA plays a more important role in cognitive motor control which involves sensory discrimination and decision making or motor selection for the action after stimuli, whereas SMA-proper is one of the main generators of Bereitschaftspotential preceding self-paced, voluntary movements. In the more general anticipation of and attention to the forthcoming stimuli, non-primary motor cortices including pre-SMA, SMA-proper and lateral premotor area, and the prefrontal area are commonly involved. (+info)
Cortical activation during human volitional swallowing: an event-related fMRI study.
(5/389)
Functional magnetic resonance imaging (fMRI) provides a safe, noninvasive method for studying task-related cortical neuronal activity. Because the cerebral cortex is strongly implicated in the control of human swallowing, we sought to identify its functional neuroanatomy using fMRI. In 10 healthy volunteers, a swallow event-related paradigm was performed by injecting 5 ml water bolus into the oral cavity every 30 s. Whole brain functional magnetic susceptibility -weighted spiral imaging data were simultaneously acquired over 600 s on a 1.5-T magnetic resonance scanner, utilizing the blood oxygenation level-dependent technique, and correlation maps were generated using both >99% percentile rank and spatial extent thresholding. We observed areas of increased signal change consistently in caudal sensorimotor cortex, anterior insula, premotor cortex, frontal operculum, anterior cingulate and prefrontal cortex, anterolateral and posterior parietal cortex, and precuneus and superiomedial temporal cortex. Less consistent activations were also seen in posterior cingulate cortex and putamen and caudate nuclei. Activations were bilateral, but almost every region, particularly the premotor, insular, and frontal opercular cortices, displayed lateralization to one or the other hemisphere. Swallow-related cortical activity is multidimensional, recruiting brain areas implicated in processing motor, sensory, and attention/affective aspects of the task. (+info)
"Task-oriented" exercise improves hamstring strength and spastic reflexes in chronic stroke patients.
(6/389)
BACKGROUND AND PURPOSE: Despite the belief that after cerebral infarction only limited functional gains are possible beyond the subacute period, we tested the hypothesis that a 12-week program of "task-oriented" treadmill exercise would increase muscle strength and decrease spastic reflexes in chronic hemiparetic patients. METHODS: Fourteen subjects, aged 66+/-3 (mean+/-SEM) years, with residual gait deviations due to remote stroke (>6 months), underwent repeated measures of reflexive and volitional (concentric and eccentric) torque with use of isokinetic dynamometry on the hamstring musculature bilaterally. Torque output was measured at 4 angular velocities (30(o), 60(o), 90(o), and 120(o)/s). RESULTS: After 3 months of 3 times/wk low-intensity aerobic exercise, there were significant main effects (2 legs [P<0.01]x2 times [P<0. 01]x4 angular velocities [P<0.05]) for concentric torque production. Torque/time production in the concentric mode also improved significantly in the paretic (50%, P<0.01) and nonparetic hamstrings (31%, P<0.01). Eccentric torque/time production increased by 21% (P<0.01) and 22% (P<0.01) in the paretic and nonparetic hamstrings, respectively. Passive (reflexive) torque/time generation in the paretic hamstrings decreased by 11% (P<0.027). Reflexive torque/time was unchanged in the nonparetic hamstrings (P=0.45). CONCLUSIONS: These findings provide evidence that progressive treadmill aerobic exercise training improves volitional torque and torque/time generation and reduces reflexive torque/time production in the hemiparetic limb. Strength changes associated with improved functional mobility in chronic hemiparetic stroke survivors after treadmill training will be reported in future articles. (+info)
The neural correlates of 'deaf-hearing' in man: conscious sensory awareness enabled by attentional modulation.
(7/389)
Attentional modulation of normal sensory processing has a two-fold impact on human brain activity: activation of a network of localized brain regions is associated with paying attention, and activation of specific sensory regions is enhanced relative to passive stimulation. The mechanisms underlying attentional modulation of perception in patients with lesions of sensory cortices are less well understood. Here we report a unique patient suffering from extensive bilateral destruction of the auditory cortices (including the primary auditory fields) who demonstrated conscious perception of the onset and offset of sounds only when selectively attending to the auditory modality. This is the first description of such an attentively modulated 'deaf-hearing' phenomenon and its neural correlates, using H(2)(15)O-PET. Increases in cerebral blood flow associated with conscious awareness of sound that was achieved by listening attentively (compared with identical auditory stimulation presented when the patient was inattentive) were found bilaterally in the lateral (pre)frontal cortices, the spared middle temporal cortices and the cerebellar hemispheres. We conclude that conscious awareness of sounds may be achieved in the absence of the primary auditory cortex, and that selective, 'top-down' attention, associated with prefrontal systems, exerts a crucial modulatory effect on auditory perception within the remaining auditory system. (+info)
Modulation of H reflex of pretibial muscles and reciprocal Ia inhibition of soleus muscle during voluntary teeth clenching in humans.
(8/389)
A previous study has demonstrated that the soleus H reflex is facilitated in association with voluntary teeth clenching in proportion with biting force in humans. The present study tried to elucidate the functional significance of this facilitation of the soleus H reflex, by examining 1) whether the facilitation of the H reflex is reciprocal or nonreciprocal between the ankle extensors and flexors and 2) whether the reciprocal Ia inhibition of crural muscles is facilitated or depressed in association with voluntary teeth clenching. The H reflex of the pretibial muscles was evoked by stimulation of the common peroneal nerve in seven healthy subjects with no oral dysfunction. The pretibial H reflex was facilitated in association with voluntary teeth clenching in a force-dependent manner. The facilitation started preceding the onset of electromyographic activity of the masseter muscle. Stimulation of the common peroneal nerve at low intensities subthreshold for evoking the M wave of the pretibial muscles inhibited the soleus H reflex after a short latency corresponding with a disynaptic inhibition, indicating that the reciprocal Ia inhibition was depressed in association with voluntary teeth clenching. Thus, the present study has shown that voluntary teeth clenching evokes a nonreciprocal facilitation of ankle extensor and flexor muscles and attenuated reciprocal Ia inhibition from the pretibial muscles to the soleus muscle. It is concluded that voluntary teeth clenching contributes to improve stability of stance rather than smoothness of movements. (+info)