COMPUTATIONAL STUDIES
ON RAPIDLY-ADAPTING
MECHANORECEPTIVE FIBERS
Burak GÜÇLÜ, PhD
Syracuse University
A
firing-rate-based
population response
model
for
monkey
rapidly-adapting (RA)
mechanoreceptive
fibers
was used to find the
probability
of
tactile stimulus
detection
in the
population .
It is shown that several
rapidly-adapting (RA)
mechanoreceptive
fibers
are required for the
tactile stimulus
detection
However, this
firing-rate-based
population response
model
does not include the
rate
variance
and
cannot directly predict
psychophysical
thresholds.
Therefore, a
time-dependent
model
was established.
The
responses
of
cat RA
fibers
were modeled using a
Markov
process
and
Laplace
Distribution
of
action-potential
phases
with respect to the
stimulus.
The
population
model
based on the
Markov
process
was used to obtain the
40-Hz
thresholds
of the
Non-Pacinian I (NP I)
psychophysical
channel
as a function of the
stimulus-contactor
location.
Different receptive-field
distributions
and
rate-based decision
criteria
were also studied.
Predictions
of the
population
model
are close to the
human psychophysical
results.
*
The
experiments
show that the
NP I
thresholds
remain approximately constant
across the
terminal
phalanx
of the
finger,
suggesting that the
receptive-field
distribution
may be
uniform
as opposed to the
findings
in the
literature.
Thus,
this is in contradiction
with the increase of the
innervation
density
towards the
distal
end
of the
phalanx
which would be expected to
produce
lower
thresholds.
*
It was also found that the
mechanical
impedance
of the
skin
varies across the
fingertip.
Therefore,
it is concluded that the
mechanical attenuation
function
used in the
model
should be modified in such a way
that the
effects
of the
innervation
density
and
skin
mechanics
cancel out.