Post on 21-Jan-2016
description
Homeostasis and Receptive Field Plasticity
• RF plasticity with the CaDP model
• Synaptic scaling
• Metaplasticity
• RF plasticity with CaDP + Metaplasticity
Input structure:
0 50 100
uncorrelatedcorrelated
rate
Assume: CaDP model as in previous class
0)( )]([)]([ iiii WCaCa
dt
dW
1.
2.
3.
How is this done?
Model Consequences at system level:
Input structure:
0 50 100
uncorrelatedcorrelated
rate
10 Hz
0
0.2
0.4
0.6
0.8
1
final
weight
synaptic
20 40 60 80Input Neuron
1000
0.2
0.4
0.6
0.8
1
20 40 60 80Input Neuron
100
12 Hz
0
0.2
0.4
0.6
0.8
1
20 40 60 80Input Neuron
100
8 Hz
The system is not robust
Review of Homeostatic mechanisms
1. Synaptic scaling
Review by Turrigiano and Nelson 2000
Synaptic scaling is a description of a phenomena, not a mechanism
Possible Mechanism:
Metaplasticity: The experience dependent change in the functional form of synaptic plasticity.
There are many examples, we will concentrate on one type of metaplasticity.
Kirkwood et al 1996
Possible molecular basis for this change in threshold:
1. Change in NMDAR composition (Quinlan et al 1999, Philpot et. al 2001) or number (Watt et. al. 2004) produced by dark rearing.
2. Activity dependent change in Ih previous lecture by Dan Johnston.
Metaplasticity: activity dependent change in synaptic plasticity
NMDAR
membrane
intracellular
extracellular
Voltage-deptransition rates
u
k
VVk
m ggrest
)(
tim
tmm
ggg
gkgkVkdt
dg
final weights
Correlated channel
uncorrelated channel
0 20 40Input (Hz)
40
0.05
Effects of metaplasticity with poisson inputs
100x … 20 x …
Excitatory inhibitory
Different time scales for plasticity and metaplasticity
Plasticity with correlated and uncorrelated group
The spike-triggered presynaptic event density (STPED)
Segregation between correlated and uncorrelated channels is robust.
Segregation with two correlated groups
Selectivity to non-static, non-overlapping square patterns of input rate distribution.
Selectivity to non-static, overlapping Gaussian patterns of input rate distribution.
Summary