| Name: | noise_generator - Device to generate Gaussian white noise current.
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| Description: |
This device can be used to inject a Gaussian "white" noise current into a node.
The current is not really white, but a piecewise constant current with Gaussian
distributed amplitude. The current changes at intervals of dt. dt must be a
multiple of the simulation step size, the default is 1.0ms,
corresponding to a 1kHz cut-off.
Additionally a second sinusodial modulated term can be added to the standard deviation of the noise.
The current generated is given by
I(t) = mean + std * N_j for t_0 + j dt <= t < t_0 + (j-1) dt
where N_j are Gaussian random numbers with unit standard deviation and t_0 is
the device onset time.
If the modulation is added the current is given by
I(t) = mean + sqrt(std^2 + std_mod^2 * sin(omega * t + phase)) * N_j for t_0 + j dt <= t < t_0 + (j-1) dt
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| Parameters: |
The following parameters can be set in the status dictionary:
mean double - mean value of the noise current in pA
std double - standard deviation of noise current in pA
dt double - interval between changes in current in ms, default 1.0ms
std_mod double - modulated standard deviation of noise current in pA
phase double - Phase of sine modulation (0-360 deg)
frequency double - Frequency of sine modulation in Hz
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| Remarks: |
- All targets receive different currents.
- The currents for all targets change at the same points in time.
- The effect of this noise current on a neuron DEPENDS ON DT. Consider
the membrane potential fluctuations evoked when a noise current is
injected into a neuron. The standard deviation of these fluctuations
across an ensemble will increase with dt for a given value of std.
For the leaky integrate-and-fire neuron with time constant tau_m,
membrane potential fluctuations at times t_j+delay are given by
Sigma = std * sqrt( (1-x) / (1+x) ) where x = exp(-dt/tau_m)
for large t_j. In the white noise limit, dt -> 0, one has
Sigma -> std * sqrt(dt / tau).
To obtain comparable results for different values of dt, you must
adapt std.
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| Sends: | CurrentEvent
| SeeAlso: | Device |
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| Author: | Ported to NEST2 API 08/2007 by Jochen Eppler, updated 07/2008 by HEP
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| Source: | /home/abuild/rpmbuild/BUILD/nest-2.4.1/models/noise_generator.h
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