Biomedical Engineering Reference
In-Depth Information
Figure 7
. (
A
) Basic plan of a simple non-adaptive functional feedback model (37). The stimulus function is a
linear, ramp-shaped passive movement of the paw around the wrist joint. Different types of ideal linear recep-
tors encode at a first (1) level of computation the position G(
t
), the velocity
d
G/
dt
, and the acceleration
d
2
G/
dt
2
of the movement, either directly (left column) or reciprocally (middle column). At the second (2) multiplicative
level of computation the product of low-threshold (LTH) signals transmitting G(
t
) and LTH-signals transmit-
ting
d
G
/dt
form
ON
U or
ON
V patterns, depending on the positive or negative velocity. Analogously, high-
threshold (HTH) signals form corresponding
OFF
patterns. At the third (3) additive level, different
ON
U and
OFF
V patterns are summed. Conceivable synaptic connections are shown in the right column. (
B
) Physiologi-
cal responses (histograms of extracellularly recorded spikes of a cerebellar granule cell in counts per bin,
middle row) and results from the computer simulation of the model (bottom row) to different stimulus func-
tions (top row). Stimulus function in the first column: linear ramp-shaped function, starting from a low holding
position of -10(, proceeding with a constant velocity of 40(/s to a high holding position of 10(, with 0( as the
horizontal plane. Second column: ramp of identical amplitude but of quadratic increase and decrease of the
position. Sinusoidal movement function of constant amplitude with logarithmically increasing and decreasing
frequency (third column) and that of damped oscillation at a constant frequency (fourth column). Modified
with permission from (36).
patterns obtained during extracellular recordings from cerebellar elements. For
the computer simulation of the model, acceleration signals were included as well
as amplitude limiters and dead time elements. The responses of such a model are
