Biomedical subjects

Jan Raethjen

Publications and source records attributed to Jan Raethjen.

5 recordsLinked to original sources

PubMed2006

Tremor amplitude is logarithmically related to 4- and 5-point tremor rating scales.

Tremor rating scales (TRSs) are used commonly in the clinical assessment of tremor, but the relationship of a TRS to actual tremor amplitude has never been quantified. Consequently, the resolution of these scales is unknown, and the clinical significance of a 1-point change in TRS is uncertain. We therefore sought to determine the change in tremor amplitude that corresponds to a 1-point change in a typical 5-point TRS. Data from five laboratories were analysed, and 928 patients with various types of hand tremor were studied. Hand tremor was quantified with a graphics tablet in three different labs, an accelerometer in three labs and a mechanical-linkage device in one lab. Tremor in writing, drawing, horizontal posture, rest and finger-nose testing was graded using a variety of TRSs. The relationship between TRS scores and tremor amplitude was computed for each task and laboratory. A logarithmic relationship between a 5-point (0-4) TRS and tremor amplitude (T, measured in centimetres) was found in all five labs, despite widely varying rating scales and transducer methodology. Thus, T2/T1 = 10(alpha(TRS2-TRS1)). The value of alpha ranged from 0.414 to 0.441 for writing, 0.355-0.574 for spiral drawing, 0.441 to 0.488 for rest tremor, 0.266-0.577 for postural tremor and 0.306 for finger-nose testing. For alpha = 0.3, 0.4, 0.5, 0.6 and 0.7, the ratios T2/T1 for a 1-point decrease in TRS are 0.501, 0.398, 0.316, 0.251 and 0.200. Therefore, a 1-point change in TRS represents a substantial change in tremor amplitude. Knowledge of the relationship between TRS and precise measures of tremor is useful in interpreting the clinical significance of changes in TRS produced by disease or therapy.

Adolescent↗

PubMed2006

Time delay and partial coherence analyses to identify cortical connectivities.

Recently it has been demonstrated by Albo that partial coherence analysis is sensitive to signal to noise ratio (SNR) and that it will always identify the signal with the highest SNR among the three signals as the main (driving) influence. We propose to use time delay analysis in parallel to partial coherence analysis to identify the connectivities between the multivariate time series. Both are applied to a theoretical model (used by Albo) to analyse the connections introduced in the model. Time delay analysis identifies the connections correctly. We also apply these analyses to the electroencephalogram (EEG) and electromyogram of essential tremor patients and EEG of normal subjects while bimanually tapping their index fingers. Biologically plausible cortico-muscular and cortico-cortical connections are identified by these methods.

Algorithms↗

PubMed2004

Is the rhythm of physiological tremor involved in cortico-cortical interactions?

The function of low-frequency oscillations as correlates of physiological tremor in supplementary motor area (SMA) and M1 remains unclear. In epicortical recordings from M1 and SMA and surface electromyographic (EMG) recordings in an epileptic patient we found reproducibly significant coherence between all three recording sites in the 6- to 15-Hz band. The partial coherence between SMA and muscle, however, was not significant. There was a constant phase shift between SMA and M1 indicating synchronized activity. We conclude that the cortical correlates of physiological tremor may be involved in linking different cortical motor centers and might therefore play a role in cortical motor planning.

Adult↗

PubMed2002

Monosymptomatic resting tremor and Parkinson's disease: a multitracer positron emission tomographic study.

We sought to elucidate the relationship between monosymptomatic resting tremor (mRT) and Parkinson's disease (PD). We studied eight mRT patients (mean Hoehn and Yahr [H&Y], 1.1 +/- 0.4), eight patients with PD (mean H&Y, 1.5 +/- 0.8), who showed all three classic parkinsonian symptoms, and seven age-matched healthy subjects. Subjects underwent cerebral magnetic resonance imaging (MRI) and multitracer positron emission tomography (PET) with 6-[(18)F]fluoro-L-dopa (F-dopa), [(18)F]fluorodeoxyglucose (FDG), and [(11)C]raclopride (RACLO). PD and mRT patients did not show significant differences in F-dopa-, RACLO-, or FDG-PET scans. In F-dopa- and RACLO-PET, significant differences between the pooled patient data and control subjects were found for the following regions: anterior and posterior putamen ipsilateral and contralateral to the more affected body side, and ipsilateral and contralateral putaminal gradients of the K(i) values. Furthermore, we found a difference for the normalized glucose values of the whole cerebellum between the control group (0.94 +/- 0.06) and PD patients (1.01 +/- 0.04; P < 0.05) but not for the mRT group (0.97 +/- 0.03). Our findings indicate that monosymptomatic resting tremor represents a phenotype of Parkinson's disease, with a nearly identical striatal dopaminergic deficit and postsynaptic D2-receptor upregulation in both patient groups. We suggest that the cerebellar metabolic hyperactivity in PD is closer related to akinesia and rigidity rather than to tremor.

Adult↗

PubMed2001

Corticomuscular coherence in the 6-15 Hz band: is the cortex involved in the generation of physiologic tremor?

Physiologic tremor (PT) consists of a peripheral mechanical oscillation at the limbs' resonance frequency and an independent central component in the 6-15 Hz band. This central component has mainly been attributed to spinal interneuronal systems or subcortical oscillators but more recently also to cortical rhythms. We recorded PT electromyographically and accelerometrically from different parts of the arm in parallel to epicortical recordings from grid electrodes covering the primary sensorimotor areas of the contralateral cortex in six epileptic patients. Previous bipolar electrical stimulation of the cortical electrodes resulted in a somatotopic map of the primary cortex underlying the grid. Spectral and cross-spectral analysis including coherence spectra between epicortical electrodes and EMG and the corresponding phase spectra were performed off-line. We found significant corticomuscular coherence in the 6-15 Hz range in four out of the six patients. This coherence was focal on the cortex and it was distributed somatotopically mainly within the primary motor area. The frequency band of the coherence mostly corresponding to the EMG frequency remained stable with added inertia, while the main accelerometric frequency was clearly reduced following the resonance frequency. The phase spectra between electrocorticogram (ECoG) and EMG showed a clear delay between cortex and muscle in two of the patients, which was compatible with conduction in fast pyramidal pathways. These findings indicate that the 6-15 Hz coherence between cortex and EMG reflects a corticomuscular transmission of the oscillation rather than peripheral feedback to the cortex. We conclude that cortical networks are involved in the generation of physiologic tremor.

Adolescent↗