Figure 1.
Cortical-basal ganglia-thalamo-cortical loop including the Tremor Ameliorating Targets (TAT): STN and thalamus.
Figure 2.
DBS antidromic blockade is less effective for axons with greater diameter.
Interaction is shown between orthodromic beta spikes and an antidromic DBS pulse train in axons of different diameters. Beta somatic spikes at 29Hz are shown in blue traveling orthodromically (downward), while antidromic spikes due to high frequency DBS at 103Hz are shown in red. Velocities, distances, and pulse frequencies are in the physiologically and clinically appropriate ranges for the relevant pathways. The differing diameters result in differing conduction velocities (top to bottom: 9 m/s, 25.5 m/s, and 66.8 m/s) which results in a higher proportion of spikes clearing the axon without interference in larger-diameter axons.
Figure 3.
Transmission probability of a random orthodromic spike as a function of axonal delay, at different antidromic blocking frequencies.
Computations here were based on equation (2). If we negglet the refractory period, the blockade is complete when the axonal delay exceeds one-half of the interval between antidromic spikes.
Figure 4.
Distribution of axonal delays (in terms of Probability Density Function), as modulated by DBS.
Higher frequency DBS dramatically shortens the distribution of delays.
Figure 5.
Distribution of axonal delays, as modulated by DBS, with gain adaptation operating to preserve the area under the curve.
Figure 6.
A simple biomechanical model of a hand.
Figure 7.
Closed-loop control is used to regulate wrist angle at the horizontal position with control gains selected to reproduce the mean measured amplitude and frequency [2].
Panel (a) shows how the frequency of the oscillation increases and the amplitude decreases when reducing the delay. Panels (b)–(c) show different PD tremor at different conditions: (b) no DBS, (c) a non-optimal DBS, and (d) optimal DBS. (Normal physiological tremor usually ranges between 6–15Hz [36].)
Figure 8.
The delay distribution is calculated by assuming a mode of 2[30].