View/Open - Scholarly Commons Home

Chapter 2 – Literature Review
instead of a single central oscillatory source of tremor in ET participants.
The authors however acknowledged that this possibility has yet to be
fully investigated. The potential influence of peripheral sources in ET was
initially seen in a study by Lee and Stein (1981). The authors assessed
tremor phase resetting after mechanically ‘disturbing’ wrist tremor in 11
ET and 13 PD participants. Tremor pattern and a Normalised Resetting
Index (NRI) with 0 = complete reset, 1 = not reset at all, were measured.
Lee and Stein (1981) found that in ET mechanical perturbation lead to
significant tremor phase resetting (mean NRI = 0.64) however this did
not occur in the PD participants (mean NRI = 0.16). The presence of this
phase resetting coupled with similar tremor amplitudes in the ET and PD
participants was purported by the authors to suggest that ET has a
greater peripheral contribution to its tremor. Lee and Stein (1981)
therefore proposed that pathological tremor is not so much limited to
either central or peripheral sources but rather a contribution of both,
with the differences reflecting different relative contributions of these
components.
Such possible coupling between central and peripheral oscillators was
shown by Elble, Higgins and Hughes (1992) who further examined phase
resetting in 10 ET patients and 10 healthy controls. They found that the
central oscillator responsible for ET can be coupled with the stretch
reflex. Interestingly the reflex was identified to be not abnormally
enhanced, as results were similar between the ET and control group. The
authors suggested that this coupling may have a bearing on tremor
amplitude, and suggested this may explain the inter-individual
differences in tremor observed in ET.
14