Rudolf Töpper

Cortical activation patterns during complex motor tasks in piano players and control subjects. A functional magnetic resonance imaging study

We performed functional magnetic resonance imaging (MRI) in professional piano players and control subjects during an overtrained complex finger movement task using a blood oxygenation level dependent echo-planar gradient echo sequence. Activation clusters were seen in primary motor cortex, supplementary motor area, premotor cortex and superior parietal lobule. We found significant differences in the extent of cerebral activation between both groups with piano players having a smaller number of activated voxels. We conclude that, due to long-term motor practice a different cortical activation pattern can be visualized in piano players. For the same movements lesser neurons need to be recruited. The different volume of the activated ortical areas might therefore reflect the different effort necessary for motor performance in both groups.

Facilitation of picture naming by focal transcranial magnetic stimulation of Wernicke’s area

Abstract On the basis of an evolutionary concept of language it was postulated that activation of the motor systems for arm movements, which are phylogenetically older, should facilitate language processes. In aphasic subjects picture naming can be improved by a concomitant movement of the dominant arm. In the present study it was investigated whether a similar facilitation can be observed in normal subjects by studying the effects of transcranial magnetic stimulation (TMS) on picture naming latencies. Suprathreshold focal TMS was applied to the left motor cortex for proximal arm muscles in right-handed subjects. The effects were compared with TMS of Wernicke’s area. While TMS of the motor cortex and the non-dominant temporal lobe had no facilitatory effects, TMS of Wernicke’s area decreased picture naming latencies significantly when TMS preceded picture presentation by 500 or 1000 ms. The observed effects depended on the intensity of the stimulus used. While clearly present with intensities of 35% and 55% of maximum output the facilitation disappeared with higher stimulation intensities. It is concluded that focal magnetic stimulation is able to facilitate lexical processes due to a general preactivation of language-related neuronal networks when delivered over Wernicke’s area.

Localization of the motor hand area using transcranial magnetic stimulation and functional magnetic resonance imaging

OBJECTIVE The anatomical location of the motor area of the hand may be revealed using functional magnetic resonance imaging (fMRI). The motor cortex representation of the intrinsic hand muscles consists of a knob-like structure. This is omega- or epsilon-shaped in the axial plane and hook-shaped in the sagittal plane. As this knob lies on the surface of the brain, it can be stimulated non-invasively by transcranial magnetic stimulation (TMS). It was the aim of our study to identify the hand knob using fMRI and to reveal if the anatomical hand knob corresponds to the hand area of the motor cortex, as identified by TMS, by means of a frameless MRI-based neuronavigation system. METHODS Suprathreshold transcranial magnetic stimuli were applied over a grid on the left side of the scalp of 4 healthy volunteers. The motor evoked potentials (MEPs) were recorded from the contralateral small hand muscles, and the centers of gravity (CoG) of the MEPs were calculated. The exact anatomical localization of each point on the grid was determined using a frameless MRI-based neuronavigation system. In each subject, the hand area of the motor cortex was visualized using fMRI during sensorimotor activation achieved by clenching the right hand. RESULTS In all 4 subjects, the activated precentral site in the fMRI and the CoG of the MEP of all investigated muscles lay within the predicted anatomical area, the so-called hand knob. This knob had the form of an omega in two subjects and an epsilon in the other two subjects. CONCLUSIONS TMS is a reliable method for mapping the motor cortex. The CoG calculated from the motor output maps may be used as an accurate estimation of the location of the represented muscle in the motor cortex.

Motor cortex hand area and speech: implications for the development of language

Recently a growing body of evidence has suggested that a functional link exists between the hand motor area of the language dominant hemisphere and the regions subserving language processing. We examined the excitability of the hand motor area and the leg motor area during reading aloud and during non-verbal oral movements using transcranial magnetic stimulation (TMS). During reading aloud, but not before or afterwards, excitability was increased in the hand motor area of the dominant hemisphere. This reading effect was found to be independent of the duration of speech. No such effect could be found in the contralateral hemisphere. The excitability of the leg area of the motor cortex remained unchanged during reading aloud. The excitability during non-verbal oral movements was slightly increased in both hemispheres. Our results are consistent with previous findings and may indicate a specific functional connection between the hand motor area and the cortical language network.

Clinical significance of intracranial developmental venous anomalies

OBJECTIVES Venous angiomas, or developmental venous anomalies (DVAs), represent the most often occurring cerebral vascular malformation. The clinical significance of a DVA is, however, at present unclear. METHODS A retrospective analysis was carried out on two series of consecutive cranial MRIs performed between January 1990 and August 1996 in a university department of neuroradiology and in a large radiological private practice. The medical records of all patients in whom a DVA was diagnosed were screened to identify the specific complaint which necessitated the imaging procedure. RESULTS A total of 67 patients with DVA could be identified. In 12 patients an associated cavernoma was found. The main reason for performing the MRI was the evaluation of seizures or of headaches. In all patients with DVA in whom an intracerebral haemorrhage was diagnosed an associated cavernoma was present at the site of the haemorrhage. None of the 67 patients showed an association between the complaints that led to the MRI and the location of the DVA. CONCLUSIONS DVAs do not seem to be associated with a specific clinical presentation. In a significant percentage of cases, however, coexisting cavernomas are found which have a defined bleeding potential and should be treated independently of the DVA. This study supports the hypothesis that DVAs are a congenital abnormality of venous drainage without clinical significance.

Facilitation of picture naming after repetitive transcranial magnetic stimulation

Objective: To investigate the effect of repetitive transcranial magnetic stimulation (rTMS) on picture naming. Background: Previous studies have shown that rTMS disrupts ongoing speech processes when delivered over frontal or parietal areas of the dominant hemisphere. Methods: In 15 healthy right-handed male individuals, rTMS trains of 20 Hz with a duration of 2 seconds and an intensity of 55% of maximum stimulator output were delivered either to Wernicke’s area, to the right-hemisphere homologue of Wernicke’s area, to Broca’s area, or to the primary visual cortex. Twenty black-and-white line drawings, which the individuals had to name as quickly as possible, were shown immediately after the completion of rTMS and again 2 minutes later. Results: Immediately after the end of a train over Wernicke’s area a shortening of naming latency was observed compared with naming without rTMS (p < 0.001). No significant effects on picture naming were observed 2 minutes later or at any time after stimulation of the right-hemisphere homologues of Wernicke’s area, Broca’s area, or the visual cortex. Conclusion: Repetitive transcranial magnetic stimulation over Wernicke’s area leads to a brief facilitation of picture naming by shortening linguistic processing time.

Pathophysiology of chorea and bradykinesia in Huntington's disease

This article reviews the neurophysiological abnormalities described in Huntingtons disease. Among the typical features of choreic movements are variable and random patterns of electromyographic (EMG) activity, including cocontraction of agonist and antagonist muscles. Studies of premotor potentials show that choreic movements are not preceded by a Bereitschaftspotential, therefore demonstrating that choreic movement is involuntary. Early cortical median‐nerve somatosensory‐evoked potentials have reduced amplitudes and the reduction correlates with reduced glucose consumption in the caudate nucleus. Long‐latency stretch reflexes evoked in the small hand muscles are depressed. These findings may reflect failed thalamocortical relay of sensory information. In Huntingtons disease, the R2 response of the blink reflex has prolonged latencies, diminished amplitudes, and greater habituation than normal. These abnormalities correlate with the severity of chorea in the face. Patients with Huntingtons disease perform simple voluntary movements more slowly than normal subjects and with an abnormal triphasic EMG pattern. Bradykinesia is also present during their performance of simultaneous and sequential movements. Eye movements show abnormalities similar to those seen in arm movements. In Huntingtons disease, arm movement execution is associated with reduced PET activation of cortical frontal areas. Studies using transcranial magnetic stimulation show that patients with Huntingtons disease have normal corticospinal conduction but some patients have a prolonged cortical silent period. Bradykinesia results from degeneration of the basal ganglia output to the supplementary motor areas concerned with the initiation and maintenance of sequential movements. The coexisting hyperkinetic and hypokinetic movement disorders in patients with Huntingtons disease probably reflect the involvement of direct and indirect pathways in the basal ganglia–thalamus–cortical motor circuit.

Modulation of the neuronal circuitry subserving working memory in healthy human subjects by repetitive transcranial magnetic stimulation

We studied the effect of repetitive transcranial magnetic stimulation (rTMS) on changes in regional cerebral blood flow (rCBF) as revealed by positron emission tomography (PET) while subjects performed a 2-back verbal working memory (WM) task. rTMS to the right or left dorsolateral prefrontal cortex (DLPFC), but not to the midline frontal cortex, significantly worsened performance in the WM task while inducing significant reductions in rCBF at the stimulation site and in distant brain regions. These results for the first time demonstrate the ability of rTMS to produce temporary functional lesions in elements of a neuronal network thus changing its distributed activations and resulting in behavioral consequences.

Effects of long-term practice and task complexity in musicians and nonmusicians performing simple and complex motor tasks: Implications for cortical motor organization

Motor practice induces plastic changes within the cortical motor system. Whereas rapidly evolving changes of cortical motor representations were the subject of a number of recent studies, effects of long‐term practice on the motor system are so far poorly understood. In the present study pianists and nonmusicians were investigated using functional magnetic resonance imaging. Both groups performed simple and complex movement sequences on a keyboard with the right hand, the tasks requiring different levels of ordinal complexity. The aim of this study was to characterize motor representations related to sequence complexity and to long‐term motor practice. In nonmusicians, complex motor sequences showed higher fMRI activations of the presupplementary motor area (pre‐SMA) and the rostral part of the dorsal premotor cortex (PMd) compared to simple motor sequences, whereas musicians showed no differential activations. These results may reflect the higher level of visuomotor integration required in the complex task in nonmusicians, whereas in musicians this rostral premotor network was employed during both tasks. Comparison of subject groups revealed increased activation of a more caudal premotor network in nonmusicians comprising the caudal part of the PMd and the supplementary motor area. This supports recent results suggesting a specialization within PMd. Furthermore, we conclude that plasticity due to long‐term practice mainly occurs in caudal motor areas directly related to motor execution. The slowly evolving changes in M1 during motor skill learning may extend to adjacent areas, leading to more effective motor representations in pianists. Hum Brain Mapp, 2005.

Visual and motor cortex excitability: a transcranial magnetic stimulation study

OBJECTIVES Phosphene thresholds (PTs) to transcranial magnetic stimulation over the occipital cortex and motor thresholds (MTs) have been used increasingly as measures of the excitability of the visual and motor cortex. MT has been utilized as a guide to the excitability of other, non-motor cortical areas such as dorsolateral prefrontal cortex. The aims of this study were to compare the PTs to MTs; to assess their stability across sessions; and to investigate their relation to MTs. METHODS PTs and MTs were determined using focal transcranial magnetic stimulation over the visual and motor cortex. RESULTS PTs were shown to be significantly higher than MTs. Both PTs and MTs were stable across sessions. No correlation between PTs and MTs could be established. CONCLUSIONS Phosphene threshold is a stable parameter of the visual cortex excitability. MTs were not related to the excitability of non-motor cortical areas.