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I H Jenkins

Publications and source records attributed to I H Jenkins.

15 recordsLinked to original sources
PubMed1998

Cerebral control of unimanual and bimanual movements: an H2(15)O PET study.

We measured regional cerebral blood flow (rCBF) during unimanual and bimanual movements using H2(15)O PET. Six healthy volunteers performed unimanual, bimanual-symmetric and bimanual-asymmetric ballistic finger movements. The study was designed to minimize anticipation and preparation of movements. Data were analysed using SPM. Unpredictably paced unimanual movements resulted in significant activation of contralateral primary motor-somatosensory cortex (M1-S1) and mesial frontal cortex (p < 0.001). Performance of symmetric bimanual movements resulted in bilateral activation, but no additional activation of mesial frontal cortex was shown. Comparison of asymmetric with symmetric bimanual movements revealed additional recruitment of mesial frontal cortex (p< 0.001). We suggest that rostral mesial frontal cortex facilitates asymmetric non-mirrored bimanual finger movements.

Aged↗
PubMed1997

The effect of movement frequency on cerebral activation: a positron emission tomography study.

Knowledge of the effect of performance frequency on activation of motor areas in positron emission tomography (PET) studies is crucial to the interpretation of experiments in which performance is a variable. We studied this effect in six normal right-handed volunteers using H2(15)O PET to measure regional cerebral blood flow (rCBF). Subjects were scanned at rest and while executing joystick movements with the right hand in freely chosen directions at different frequencies. Significant frequency dependent increases in rCBF were demonstrated in contralateral sensorimotor cortex, lateral premotor cortex bilaterally, posterior supplementary motor area (SMA), and ipsilateral cerebellar hemisphere and vermis. The striatum and the right dorsal prefrontal cortex were also activated by joystick movement compared with rest, but the magnitude of activation found in these areas was independent of the frequency of movement. The results suggest that primary motor cortex, posterior SMA, lateral premotor cortex and cerebellum are involved in determining the basic parameters of movement. Frequency dependent activation in these areas suggests phasic activity related to movement. In contrast, activation of the dorsal prefrontal cortex and the striatum is not frequency dependent. This may reflect continuous rather than phasic activity in these areas during the task and suggests their role is not simply related to movement execution but higher level during this free selection joystick task.

Adult↗
PubMed1996

The sensory guidance of movement: a comparison of the cerebellum and basal ganglia.

We used positron emission tomography (PET) to compare the contribution of the cerebellum and basal ganglia to the sensory guidance of movement. In one condition the subjects used a computer mouse to draw a series of lines on a computer screen (DRAW). In the second condition the same lines were presented to the subjects, and they had to track the lines with a mouse pointer on the screen (COPY). In a third condition the subjects were again presented with the same lines, and they simply followed movements of the pointer with their eyes (EYES). In the fourth condition, the subjects fixated a central point, ignoring the sequence of presented lines (FIX). The pons and cerebellum were activated more during visually guided tracking than in freely generated drawing (COPY vs DRAW). The basal ganglia were activated equally in both DRAW and COPY. The prefrontal and inferior temporal cortex were activated more when subjects drew lines freely (DRAW) than when they copied them (COPY). We conclude that the cerebellum is specialized for using sensory information to correct movements, but that the basal ganglia are involved both in movements that are self-generated and in movements that are guided by external cues.

Adult↗
PubMed1996

Tremor associated with benign IgM paraproteinaemic neuropathy.

The clinical and neurophysiological features of six patients with action tremor of the upper limbs associated with IgM paraproteinaemic neuropathy are described. Symptomatic tremor was confined to the upper limbs and was broadly symmetrical. The frequency of associated rhythmic muscle activity ranged from 2.8 to 5.5 Hz in abductor pollicis brevis and from 3.7 to 5.5 Hz in the forearm flexor muscles. Magnetic brain stimulation, somatosensory evoked potentials (SEPs) and stretch reflex studies did not provide evidence for delayed conduction within central pathways. There was marked slowing of the maximum motor conduction velocities in peripheral nerves. Forearm stretch reflexes were present but their latencies were prolonged. Somatosensory evoked potentials were obtained in the majority of patients, but were delayed. Wrist tremor could be modulated by mechanical perturbations or median nerve electrical shocks. Simple voluntary wrist movements were of normal duration and peak velocity, but the kinematic profile was asymmetric. Each movement was associated with a triphasic EMG pattern in agonist-antagonist-agonist muscles but the durations of the bursts were prolonged and the onset of the second agonist was delayed. These results support the hypothesis that distorted, mistimed peripheral inputs reach a central processor (probably the cerebellum) which although intact is misled into producing tremor in certain parts of the body.

Aged↗
PubMed1995

The functional anatomy of remembered saccades: a PET study.

Studies of patients with damage to the dorsolateral prefrontal cortex (DLPFC) and the basal ganglia have shown that these areas are involved in the control of remembered saccades. However, although positron emission tomography (PET) studies of remembered saccades have demonstrated extensive cortical and subcortical activation, they have failed to detect any significant increase in regional cerebral blood flow (rCBF) in these areas. This study was designed to see if these areas could be activated. Eight right-handed male volunteers were studied using H2(15)O PET. Comparison of the rCBF in the remembered saccade task to a rest control state revealed significant activation in both the DLPFC and the basal ganglia, and also the frontal eye fields, the supplementary motor area, the posterior parietal lobe, the cingulate cortex, the striate cortex, the extrastriate cortex and the superior temporal lobe. These findings confirm that remembered saccades are controlled by an extensive cortical and subcortical network, which includes the DLPFC and the basal ganglia.

Adult↗
PubMed1995

A positron emission tomography study of cerebral activation associated with essential and writing tremor.

OBJECTIVE: To compare the abnormal patterns of cerebral activation associated with essential and writing tremors. DESIGN: Positron emission tomography using oxygen 15-labeled water was utilized to determine regional cerebral blood flow. Positron emission tomography images that were taken of the brain in individual patients were coregistered with magnetic resonance images of the same brain to ascertain accurate localization of cerebral activation in single patients. Patients with essential tremor underwent scanning at rest, during involuntary postural tremor, and during passive wrist oscillation. Normal control subjects underwent scanning at rest and during voluntary and passive wrist oscillation. Patients with writing tremor underwent scanning while they were holding a pen to paper with consequent involuntary tremor and again while they were holding a pen in the same supinated arm without tremor. SETTING: Research hospital. PATIENTS OR OTHER PARTICIPANTS: Seven patients with essential tremor, six patients with writing tremor, and six matched control subjects. INTERVENTIONS: None. MAIN OUTCOME MEASURES: Regional cerebral blood flow. RESULTS: Essential tremor was associated with abnormal bilateral cerebellar, red nuclear, and thalamic activation. Writing tremor was also associated with abnormal bilateral cerebellar activation. Voluntary wrist oscillation in control subjects caused only ipsilateral cerebellar activation. These findings were evident in single patients, when positron emission tomography images were coregistered with magnetic resonance images and on group analysis of the pooled positron emission tomography data after transformation into stereotaxic space. CONCLUSION: These results indicate that both essential and writing tremors are associated with abnormal bilateral overactivity of cerebellar connections.

Adult↗
PubMed1995

Self-initiated versus externally triggered movements. I. An investigation using measurement of regional cerebral blood flow with PET and movement-related potentials in normal and Parkinson's disease subjects.

We investigated the functional anatomy of self-initiated and externally triggered movements. Six patients with Parkinson's disease off medication and six age-matched normals were assessed. All subjects had regional cerebral blood flow (rCBF) measurement with PET and recording of movement-related cortical potentials (MRPs) from frontal (F), fronto-central (FC), central (C) and parietal (P) sites to obtain measures of the Bereitschaftspotential (BP). The tasks were (i) self-initiated extension of the right index finger on average once every 3 s, (ii) externally triggered finger extension with the rate yoked to the self-initiated task, and (iii) rest condition with tones presented at a rate yoked with the self-initiated task. For the self-initiated movements, the amplitude of the early and peak BP were lower in Parkinson's disease relative to normals. For the externally triggered movements, the patients and the normals did not differ on any of the measures of cortical negativity prior to movement. For both groups, the late and peak BP components, but not the early component, had a lower amplitude in the externally triggered than the self-initiated movements. In normals, the left primary sensorimotor cortex, the supplementary motor area bilaterally, anterior cingulate, the lateral premotor cortex bilaterally, the insular cortex bilaterally, the left thalamus and the left putamen, parietal area 40 bilaterally and the right dorsolateral prefrontal cortex (DLPFC) were significantly activated during the self-initiated movements relative to rest. For the normals, greater activation of the right DLPFC during the self-initiated movements was the only area that significantly differentiated them from the externally triggered movements. When Parkinson's disease patients and normals were compared for the self-initiated movements relative to rest, normals showed greater activation of the supplementary motor area and anterior cingulate, left putamen, left insular cortex, right DLPFC and right parietal area 40. When the groups were compared for the externally triggered movements relative to rest, the global pattern of blood flow and rCBF change in the two groups did not differ, confirming the absence of group differences in BPs for the externally triggered movements. During the self-initiated movements, the lower amplitude of the early BP in patients with Parkinson's disease as well as the underactivation of the supplementary motor area relative to normals support the premises that (i) the supplementary motor area contributes to the early BP, and (ii) the deficit is self-initiated movements in Parkinson's disease is due to supplementary motor area underactivation. The DLPFC is activated in situations requiring non-routine decision making as in the self-initiated movements.

Aged↗
PubMed1994

Red nuclear and cerebellar but no olivary activation associated with essential tremor: a positron emission tomographic study.

There has been debate as to whether essential tremor has a central origin and over the possible role of the inferior olivary nucleus in its genesis. We used positron emission tomography with radioactive water (H2(15)O) to detect abnormal patterns of cerebral activity associated with this condition, at rest, without tremor, and on posture when the tremor was present. At rest, cerebellar blood flow was significantly increased bilaterally in the group with essential tremor (30-40%) but no increased olivary activity was evident. Essential tremor during arm extension was associated with further abnormal increases in bilateral cerebellar and abnormal red nuclear activation. Again, no olivary overactivity was evident. Voluntary wrist oscillation in control subjects caused only ipsilateral cerebellar activation. We conclude that essential tremor is associated with abnormal bilateral overactivity of cerebellar and red nuclear connections but found no evidence of intrinsic overactivity of the inferior olivary nucleus, as evidenced by raised blood flow.

Adult↗
PubMed1994

Cortical control of saccades and fixation in man. A PET study.

To identify cortical regions activated during saccades and visual fixation, regional cerebral blood flow (rCBF) was measured in eight healthy subjects using C15O2 PET during the performance of three tasks: (i) central fixation; (ii) reflexive saccades to random targets; (iii) remembered saccades to locations of recent target appearance. Significant rCBF increases were identified using analysis of covariance and the t statistic (P < 0.001). Compared with central fixation there was activation of striate and extra-striate cortex, posterior parietal cortex (PPC) and frontal eye fields (FEF) during both reflexive and remembered saccades. During remembered saccades there was additional activation of supplementary motor area (SMA), insula, cingulate, thalamus, midbrain, cerebellum and right superior temporal gyrus (Brodmann's area 22). Compared with the individual saccadic tasks, central fixation activated extensive regions of ventromedial (areas 10, 11 and 32) and anterolateral (areas 8, 9, 10, 45 and 46) prefrontal cortex, and foveal visual cortex. We conclude that FEF and PPC are associated with the generation of both reflexive and remembered saccades, with SMA additionally involved during remembered saccades. Sustained voluntary fixation is mediated by prefrontal cortex.

Adult↗
PubMed1994

Motor sequence learning: a study with positron emission tomography.

We have used positron emission tomography to study the functional anatomy of motor sequence learning. Subjects learned sequences of keypresses by trial and error using auditory feedback. They were scanned with eyes closed under three conditions: at rest, while performing a sequence that was practiced before scanning until overlearned, and while learning new sequences at the same rate of performance. Compared with rest, both sequence tasks activated the contralateral sensorimotor cortex to the same extent. Comparing new learning with performance of the prelearned sequence, differences in activation were identified in other areas. (1) Prefrontal cortex was only activated during new sequence learning. (2) Lateral premotor cortex was significantly more activated during new learning, whereas the supplementary motor area was more activated during performance of the prelearned sequence. (3) Activation of parietal association cortex was present during both motor tasks, but was significantly greater during new learning. (4) The putamen was equally activated by both conditions. (5) The cerebellum was activated by both conditions, but the activation was more extensive and greater in degree during new learning. There was an extensive decrease in the activity of prestriate cortex, inferotemporal cortex, and the hippocampus in both active conditions, when compared with rest. These decreases were significantly greater during new learning. We draw three main conclusions. (1) The cerebellum is involved in the process by which motor tasks become automatic, whereas the putamen is equally activated by sequence learning and retrieval, and may play a similar role in both. (2) When subjects learn new sequences of motor actions, prefrontal cortex is activated. This may reflect the need to generate new responses. (3) Reduced activity of areas concerned with visual processing, particularly during new learning, suggests that selective attention may involve depressing the activity of cells in modalities that are not engaged by the task.

Adult↗
PubMed1993

A positron emission tomography study of essential tremor: evidence for overactivity of cerebellar connections.

The origin of essential tremor is unknown. Animal models have suggested that the inferior olivary nucleus may act as a tremor generator. We used positron emission tomography to study changes in regional cerebral blood flow associated with involuntary postural tremor and passive wrist oscillation in patients with essential tremor. Activation due to voluntary wrist oscillation and arm extension without tremor was studied in normal control subjects. The essential tremor group had bilaterally increased cerebellar blood flow at rest (without tremor) compared with the control group. Involuntary postural tremor was associated with further bilateral cerebellar activation, and also contralateral striatal, thalamic, and sensorimotor cortex activation. Voluntary wrist oscillation, maintained arm extension without tremor, and passive wrist oscillation were all associated with significant ipsilateral rather than bilateral cerebellar activation. We conclude that essential tremor is associated with increased bilateral cerebellar activity both at rest and during tremor.

Adult↗
PubMed1993

Functional studies of the human cerebellum with positron emission tomography.

New techniques of functional imaging with PET have resulted in improved understanding of the organisation of the human brain at systems level. Many studies have concentrated on the organisation of the cerebral cortex, while the cerebellum has been subjected to less intensive investigations. In the motor system the contralateral cerebellum is intimately related to the functions of the primary motor cortex. This has been demonstrated in a number of studies involving simple and more complex motor activations. The relationship has also been demonstrated in pathology. The role of the cerebellum in the generation of tremor has been the subject of some considerable study with the demonstration of functional relationships between the olivary nucleus and the cerebellum as well as between the cerebellum, thalamus and motor cortex in essential and parkinsonian tremor. The cerebellum is also involved in motor learning. Parts of the motor system exhibit physiological adaptation during the repeated performance of a simple motor task. The cerebellum, in particular, shows a decrease in regional blood flow with practice of a motor task despite a similar performance. A number of recent reports suggest that the cerebellum is also involved in cognitive functions and particularly language. Functional neuroimaging has not addressed this problem explicitly; however, studies of severely depressed patients with cognitive impairments have shown an unexpected but interesting result in that impaired cognition but not the state of mind is associated with increases in cerebellar activity. The reason for the paucity of systematic investigations of cerebellar function has been the limited field of view, sensitivity and resolution of PET cameras.(ABSTRACT TRUNCATED AT 250 WORDS)

Adaptation, Physiological↗
PubMed1992

Impaired mesial frontal and putamen activation in Parkinson's disease: a positron emission tomography study.

Selection of movement in normal subjects has been shown to involve the premotor, supplementary motor, anterior cingulate, posterior parietal, and dorsolateral prefrontal areas. In Parkinson's disease (PD), the primary pathological change is degeneration of the nigrostriatal dopaminergic projections, and this is associated with difficulty in initiating actions. We wished to investigate the effect of the nigral abnormality in PD on cortical activation during movement. Using C15O2 and positron emission tomography (PET), we studied regional cerebral blood flow in 6 patients with PD and 6 control subjects while they performed motor tasks. Subjects were scanned while at rest, while repeatedly moving a joystick forward, and while freely choosing which of four possible directions to move the joystick. Significant increases in regional cerebral blood flow were determined with covariance analysis. In normal subjects, compared to the rest condition, the free-choice task activated the left primary sensorimotor cortex, left premotor cortex, left putamen, right dorsolateral prefrontal cortex and supplementary motor area, anterior cingulate area, and parietal association areas bilaterally. In the patients with PD, for the free-choice task, compared with the rest condition, there was significant activation in the left sensorimotor and premotor cortices but there was impaired activation of the contralateral putamen, the anterior cingulate, supplementary motor area, and dorsolateral prefrontal cortex. Impaired activation of the medial frontal areas may account for the difficulties PD patients have in initiating movements.

Aged↗
PubMed1992

Impaired activation of the supplementary motor area in Parkinson's disease is reversed when akinesia is treated with apomorphine.

Using positron emission tomography (PET) we previously showed that activation of the putamen, supplementary motor area, and cingulate cortex is impaired in patients with Parkinson's disease (PD) when they are off treatment and perform volitional motor tasks. Evidence suggests that these areas are involved in the generation of internally cued movements in normal subjects. We have now studied the effect of the dopamine agonist apomorphine on cerebral activation when used to treat the akinesia of PD. Regional cerebral blood flow was measured using C15O2 PET in PD patients at rest and when performing paced joystick movements with the right hand in one of four freely chosen directions. All patients used apomorphine regularly, and were studied before treatment, while still "off" but receiving a subcutaneous apomorphine infusion, and when switched "on" with apomorphine. Significant increases in regional cerebral blood flow were determined using statistical parametric mapping. Under resting conditions apomorphine had no effect on focal or global cerebral blood flow. Seven patients with PD performed the motor task adequately in the "off" and "on" states. This group of subjects demonstrated impaired activation of the supplementary motor area and contralateral putamen in the "off" state. Activation of the supplementary motor area significantly improved when the akinesia was reversed with apomorphine. We conclude that the concomitant improvement of supplementary motor area activation and motor function in apomorphine-treated patients with PD provides further evidence for the role of this structure in generating motor programs.

Adult↗