Philipp Stude

Movement preparation in self-initiated versus externally triggered movements: an event-related fMRI-study

In the present study, we used fMRI to investigate whether event-related preparatory processes of self-initiated and externally triggered movements differ. Twenty subjects were examined with 1000 T2*-weighted images in two consecutive sessions. During the first session subjects performed self-initiated abductions of the right index finger. For the second session subjects were instructed to perform the movements in response to visual cues. Number and timing of movements were matched between conditions. For statistical inference on multisubject level, random effects analyses were performed. Significantly enhanced activity during self-initiated compared to externally triggered movements was found within the left SMA, the left pre- and sensorimotor cortex, the right putamen, the left anterior cingulate gyrus, and the left inferior parietal lobe. The significantly increased activity during self-initiated in comparison to externally triggered movements might represent differential demands of the two conditions on the neuronal motor net during movement preparation, reflecting utilization of precise knowledge when to move in self-initiated movements. Our results emphasize a possible role of the primary motor cortex for movement preparation as observed in electrophysiological studies, but do not support a specific involvement of the dorsolateral prefrontal cortex as suggested by former block design studies.

Balo's concentric sclerosis

1. Medical student, Faculty of Health, Medicine and Life Sciences, Maastricht University, Maastricht, The Netherlands, 2. Department of Radiology, St. Elizabeth Hospital, Tilburg, The Netherlands, 3. Department of Neurology, Maxima Medisch Centrum Veldhoven, Veldhoven, The Netherlands Background: A 46-year-old woman was admitted with right-sided weakness, vertigo and nausea. Clinical examination revealed ataxia of the right limbs, diplopia and a counter-clockwise rotatory nystagmus. MRI of the brain was performed.Abstract. We report a case of Balos concentric sclerosis with peculiar MRI findings. Unlike previously published cases all concentric rings in our case showed marked enhancement, supporting the view of synchronous active demyelination in the lesion. Follow-up MRI disclosed a change of the lesions into a confluent pattern more resembling a typical large MS plaque. There were no oligoclonal bands or intrathecal Ig-G synthesis. The hypothesis concerning the pathophysiology of the lesions typical and peculiar morphological appearance and its relationship to multiple sclerosis are briefly discussed.

Kinesthesia is impaired in focal dystonia.

Parkinsons disease (PD) and focal dystonia (FD) are both predominantly characterized by motor symptoms. Also, recent research has shown that sensory processing is impaired in both movement disorders. FD is characterized by involuntary movements and abnormal limb postures; thus, abnormal kinesthesia could be involved in the pathogenesis. We examined passive index finger movements in patients with FD (n = 12) and PD (n = 11) and in age‐matched healthy controls (n = 13). Compared to healthy controls, patients with PD and FD were significantly impaired in the correct detection of the movement direction. The perceptual thresholds for 75% correct responses of movement direction were 0.21 degrees for FD and 0.28 degrees for PD patients compared to 0.13 degrees in control subjects. Subjects with PD and FD were also significantly impaired when they had to judge consecutive amplitudes. Results of the present study point to impaired kinesthesia in FD. Defective sensory processing could be involved in the pathophysiology of the disease and may influence dystonic contractions.

Visual Cortex Excitability in Migraine Evaluated by Single and Paired Magnetic Stimuli

Objective.—To determine the excitability of the visual cortex by phosphene thresholds (PT) in patients with migraine using transcranial magnetic stimulation (TMS) with single‐ and paired‐pulses.

Impaired movement-related potentials in acute frontal traumatic brain injury.

OBJECTIVEnFocal brain lesions due to traumatic brain injury (TBI) do not only lead to functional deficits in the lesion area, but also disturb the structurally intact neuronal network connected to the lesion site. Therefore we hypothesized dysfunctions of the cortical motor network after frontal TBI. The movement related potential (MRP) is an EEG component related to voluntary movement consisting of the Bereitschaftspotential (BP), the negative slope (NS), and the motor potential (MP). The aim of our study was to demonstrate alterations in the movement related cortical network in the acute stage after TBI by comparing our patients MRPs to those of a healthy control group.nnnMETHODSnEEGs of 22 patients with magnetic resonance imaging defined contusions of the prefrontal cortex were recorded within 8 weeks after TBI. We further recruited a healthy control group. The paradigm consisted of self-paced abductions of the right index finger.nnnRESULTSnCompared to healthy controls, the BP in the patient group was significantly reduced and its onset delayed. Moreover, an enhanced contribution of the postrolandic hemisphere ipsilateral to the movement and a reduced contribution of the left frontal cortex, ipsilateral to the lesion in the majority of the patients, were observed during motor execution (MP).nnnCONCLUSIONSnAnatomical connections between the prefrontal cortex and the supplementary motor area (SMA) are known to exist. We suggest that prefrontal lesions lead to reduced neuronal input into the SMA. This deficit in the preparatory motor network may cause the reduced BPs in our patients. Moreover, an increased need for attentional resources might explain the enhanced motor potentials during movement execution. In conclusion, we demonstrated altered MRPs in the acute stage after frontal TBI, which are a consequence of disturbed neuronal networks involved in the preparation and execution of voluntary movements.

Comparison of Intravenous Valproate With Intravenous Lysine‐Acetylsalicylic Acid in Acute Migraine Attacks

Objective.—The study compared efficacy and tolerability of intravenous valproate (iVPA) with intravenous lysine‐acetylsalicylic acid (iLAS) in acute migraine attacks.

Antinociceptive reflex alteration in acute posttraumatic headache following whiplash injury.

&NA; Brainstem‐mediated antinociceptive inhibitory reflexes of the temporalis muscle were investigated in 82 patients (47 F, 35 M, mean age 28.3 years, SD 9.4) with acute posttraumatic headache (PH) following whiplash injury but without neurological deficits, bone injury of the cervical spine or a combined direct head trauma on average 5 days after the acceleration trauma. Latencies and durations of the early and late exteroceptive suppression (ES1 and ES2) and the interposed EMG burst (IE) of the EMG of the voluntarily contracted right temporalis muscle evoked by ipsilateral stimulation of the second and third branches of the trigeminal nerve were analyzed and compared to a cohort of 82 normal subjects (43 F, 39 M, mean age 27.7 years, SD 7.1). Highly significant reflex alterations were found in patients with PH with a shortening of ES2 duration with delayed onset and premature ending as the primary parameter of this study, a moderate prolongation of ES1 and IE duration and a delayed onset of IE. The latency of ES1 was not significantly changed. These findings indicate that acute PH in whiplash injury is accompanied by abnormal antinociceptive brainstem reflexes. We conclude that the abnormality of the trigeminal inhibitory temporalis reflex is based on a transient dysfunction of the brainstem‐mediated reflex circuit mainly of the late polysynaptic pathways. The reflex abnormalities are considered as a neurophysiological correlate of the posttraumatic (cervico)‐cephalic pain syndrome. They point to an altered central pain control in acute PH due to whiplash injury.

Sparse imaging and continuous event-related fMRI in the visual domain: A systematic comparison

Continuous image acquisition as used in most functional magnetic resonance imaging (fMRI) designs may conflict with specific experimental settings due to attendant, noisy gradient switching. In sparse fMRI, single images are recorded with a delay that allows the registration of the predicted peak of an evoked hemodynamic response (HDR). The aim of this study was to assess validity and sensitivity of single‐trial sparse imaging within the visual domain. Thirteen subjects were scanned twice. Either continuous or sparse image acquisition was applied while participants viewed single trains of flashlights. Sparse fMRI results were compared to continuous event‐related fMRI results on single‐ and multisubject level regarding spatial extent, overlap, and intensity of activation. In continuously recorded data, the variability of the HDR peak latency was examined because this measure determined the timing of sparse image acquisition. In sparse fMRI, the sensitivity was analyzed considering different numbers of averaged trials. Sparse imaging detected the core activity revealed using continuous fMRI. The intensity of signal changes detected by continuous or sparse fMRI was comparable. The HDR peak latency was stable across sessions, but intersubject and regional variability might have affected the power of sparse fMRI. In sparse imaging, adding trials resulted in extension of activation and improvement in statistical power. The comparison with established continuous fMRI confirms the validity of sparse imaging. Conventional event‐related data acquisition and analysis provided more comprehensive results. However, only sparse fMRI offers the opportunity to apply stimuli and record further biosignals free of scanner‐related artifacts during intervals without image acquisition. Hum. Brain Mapping 24:130–143, 2005.

Reorganization of Motor Execution Rather Than Preparation in Poststroke Hemiparesis

Background and Purpose— The aim of the present study was to examine movement-related potentials (MRPs) in patients in the “chronic” stage after cortical stroke with recovered hemiparesis compared with healthy control subjects. Methods— Right index finger MRPs were derived from 12 patients ≥1 year after infarction in the territory of the left middle cerebral artery as well as from 12 control subjects. MRP components were compared between groups. Results— In the patient group, the component directly preceding movement onset (negative slope [NS]) was significantly reduced over the lesioned hemisphere contralateral to the movement. Furthermore, increased motor potentials (MPs) were observed over the contralesional hemisphere during movement execution. No changes in the early MRP (Bereitschaftspotential) reflecting movement preparation were found. Conclusions— Because the NS is supposed to be generated by the primary motor cortex, the decreased component over the lesioned hemisphere is interpreted to represent impaired contralateral M1 functioning in stroke patients. Contralesional activity has been reported as a probable sign of brain plasticity by functional imaging studies. Our results broaden these findings, giving new insights into the temporal course of movement-related brain activity in recovered cortical stroke patients. The data point to a functional reorganization of motor execution rather than preparation in poststroke hemiparesis.

Recovery of movement-related potentials in the temporal course after prefrontal traumatic brain injury: a follow-up study

OBJECTIVEnThe movement-related potential (MRP) is an EEG measure related to self-initiated movements, consisting of the Bereitschaftspotential (BP), the negative slope, and the motor potential. Since in a former study the BP was reduced in acute prefrontal traumatic brain injury (TBI) patients, the present study examined the MRPs course in follow-up examinations.nnnMETHODSnRight index finger MRPs of 22 patients with contusions of the prefrontal cortex were recorded 12, 26, and 52 weeks after TBI and compared to controls.nnnRESULTSnWithin the patient group, a significant increase of the BP in the temporal course after TBI was observed. MRPs 12 and 26 weeks after TBI did not differ significantly from the control group. One year after TBI, significantly enhanced BPs were found.nnnCONCLUSIONSnIn the temporal course after prefrontal TBI, a recovery of the initially reduced BP was observed. The enhanced BP areas 1 year after TBI might represent the need for increased cognitive resources during movement preparation, supporting a recovered, but less effective neuronal network.nnnSIGNIFICANCEnThe present study represents the first longitudinal follow-up study of MRPs after prefrontal brain lesion. The observed changes reflect the plastic capacity of the brain, reorganizing the neuronal network function.