Milestones in clinical neurophysiology

Abstract

Over the last 25 years, clinical neurophysiology has made many advances in the understanding, diagnosis, and even treatment of different movement disorders. Transcranial magnetic stimulation has been the biggest technical advance. Progress in pathophysiology includes improved knowledge about bradykinesia in Parkinson's disease, loss of inhibition and increased plasticity in dystonia, abnormal startle in hyperekplexia, and various features of psychogenic movement disorders that can aid diagnosis. Studies have been done looking at the use of noninvasive brain stimulation for therapy, but effects are generally small.

Figure 1

First public demonstration of transcranial electrical stimulation of the human motor cortex. Seated is P.A. Merton, one of the two developers of the method. He is directing attention to his left hand which would twitch when the stimulus was given. Holding the anode of the stimulator on the scalp is R.H. Adrian. The electrical circuit diagram is on the blackboard, showing the power source (the black box on the table beside Dr. Adrian), a capacitance (visible on the table as a free standing cylinder) and a switch (a Morse key being pressed by the right hand of Dr. Adrian). The audience is a group of 3^rd year preclinical medical students. April, 1980, Cambridge, Physiology Lecture Theatre.

Figure 2

Local field potential (LFP) from the subthalamic nucleus in a patient with Parkinson’s disease. (A) LFP after overnight withdrawal of medication. (B) LFP after subsequent levodopa challenge. (C) Power spectrum LFP after overnight withdrawal of medication (140 s record). (D) Power spectrum LFP after subsequent levodopa challenge (140 s record). Note the peak at around 13 Hz off medication and that at around 70 Hz after levodopa. From Brown and Williams 2005 with permission.

Figure 3

Effect of paired associative stimulation (PAS) on the size of motor evoked potentials (MEPs) of the right APB and FDI muscle in 10 healthy controls (A) and 10 patients with writer’s cramp (B). The bar charts illustrate the mean peak-to-peak amplitude (mV) of MEPs recorded at rest before (open columns) and after (shaded columns) associative stimulation. Each error bar equals SEM. PAS led to an increase in MEP size in patients and controls. However, the facilitatory effect was significantly stronger in patients. Modified from Quartarone et al. 2003 with permission.

Figure 4

Coherence entrainment test using frequency analysis of a dystonic tremor (left side) and a psychogenic tremor (right side). For the dystonic tremor the test is negative, but it is positive for the psychogenic tremor. The left side shows ongoing right hand tremor and simultaneous voluntary tapping movements of the left hand, both measured with accelerometry, without any coherence. The right side shows ongoing right foot shaking and simultaneous right hand voluntary tapping, both measured with EMG, with significant coherence. Modified from McAuley and Rothwell 2004 with permission.