Physiological tremor in human subjects with X-linked Kallmann's syndrome and mirror movements

1. Human physiological tremor consists of mechanical-reflex and neurogenic components. The origin of the neurogenic component, classically detected in the frequency range 7-12 Hz, has been much debated. We have studied six su bjects with X-linked Kallmann's syndrome (XKS) and mirror movements. In the se subjects unilateral magnetic brain stimulation results in abnormal bilat eral EMG responses. Furthermore, abnormal sharing of central nervous inputs between the left and right motoneurone pools results in both abnormal moto r unit synchronisation between left and right EMGs and abnormal sharing of long but not short-latency cutaneomuscular reflexes. XKS subjects with mirr or movements thus provide a model for studying the central origin of physio logical tremor. 2. During sustained co-extension of the left and right index fingers, simul taneous finger tremor and extensor indicis (EI) EMGs were recorded and cros s-correlated. The tremor and EMG signals were also subjected to time and fr equency domain analysis. 3. Results of frequency domain analysis between ipsilateral finger tremor a nd EI EMG were similar for both control and XKS subjects. However, in contr ast to the controls, short-term synchronisation of left and right EI motor unit activity and significant coherence between left and right EMG, left an d right tremor, left EMG and right tremor and right EMG and left tremor wer e found in XKS subjects. The frequency range (6-40 Hz) and coherence values between left and right were similar to ipsilateral coherence values of rec tified EMG and tremor. 4. These data provide strong evidence to support the hypothesis that the ne urogenic component of physiological tremor is supraspinal in origin and ran ges from 6 to 40 Hz.