Abnormal gating of somatosensory inputs in essential tremor.
OBJECTIVE
To study whether sensorimotor cortical areas are involved in Essential Tremor (ET) generation.


BACKGROUND
It has been suggested that sensorimotor cortical areas can play a role in ET generation. Therefore, we studied median nerve somatosensory evoked potentials (SEPs) in 10 patients with definite ET.


METHODS
To distinguish SEP changes due to hand movements from those specifically related to central mechanisms of tremor, SEPs were recorded at rest, during postural tremor and during active and passive movement of the hand. Moreover, we recorded SEPs from 5 volunteers who mimicked hand tremor. The traces were further submitted to dipolar source analysis.


RESULTS
Mimicked tremor in controls as well as active and passive hand movements in ET patients caused a marked attenuation of all scalp SEP components. These SEP changes can be explained by the interference between movement and somatosensory input ('gating' phenomenon). By contrast, SEPs during postural tremor in ET patients showed a reduction of N20, P22, N24 and P24 cortical SEP components, whereas the fronto-central N30 wave remained unaffected.


CONCLUSIONS
Our findings suggest that in ET patients the physiological interference between movement and somatosensory input to the cortex is not effective on the N30 response. This finding thus indicates that a dysfunction of the cortical generator of the N30 response may play a role in the pathogenesis of ET.
Restuccia
Domenico
D
Department of Neurology, Catholic University, Policlinico A. Gemelli, L.go A. Gemelli 8, 00168, Rome, Italy. drestuccia@rm.unicatt.it
Valeriani
Massimiliano
M
Barba
Carmen
C
Le Pera
Domenica
D
Bentivoglio
Annarita
A
Albanese
Alberto
A
Rubino
Marco
M
Tonali
Pietro
P
D000328:Adult; D000368:Aged; D004569:Electroencephalography; D020329:Essential Tremor / Q000503:physiopathology*; D005073:Evoked Potentials, Somatosensory; D005260:Female; D006801:Humans; D015640:Ion Channel Gating; D008297:Male; D008475:Median Nerve / Q000503:physiopathology; D008875:Middle Aged; D011187:Posture; D012146:Rest; D013003:Somatosensory Cortex / Q000503:physiopathology*; D014836:Volition