memories on multiple timescales: the importance of heterogeneity and memory transfer
DESCRIPTION
Memories on multiple timescales: the importance of heterogeneity and memory transfer. Stefano Fusi. MANY SYNAPSES = MANY MEMORIES. Idealized synapses (~ N ). Bounded synapses (~log N ). ( N ). Amit, Fusi (1992,1994), Brunel, Carusi, Fusi (1998), Fusi (2001). time. time. time. time. - PowerPoint PPT PresentationTRANSCRIPT
Memories on multiple timescales: the importance of heterogeneity and memory transfer
Stefano Fusi
Idealized synapses (~N)
Bounded synapses (~log N)
MANY SYNAPSES = MANY MEMORIES
Amit, Fusi (1992,1994), Brunel, Carusi, Fusi (1998), Fusi (2001)
(N)
time time
timetime
Slow learning
Heterogeneity
FAST SLOW
N = Number of synapses (1010)
qs = Smallest rate (slowest timescale) = 10-3
…
m groups
FAST SLOW
q1 qm-1q2 qm=qs
qk=(qs)k/m
N/m N/m N/m N/m
m=10
Homogenous q=q
s
Hom
ogenous q=q
1
Heterogeneous
m=50
qs√N
√Nlog(1/qs)
qs√Nqs√N
√m
Memory transfer
FAST SLOW
m=10
m=50
m=100
√Nlog(1/qs)
qs√N
√N√m
1/qsm/qs
FAST SLOW
The cascade model
1/ ~Signal Noise t N
Fusi, Drew, Abbott, Neuron (2005)StrongWeak
……
~Memory lifetime N
METAPLASTICITY
PLASTICITY
1/n
2n-1
n=number of levels in the cascadeInitial signal/noise
Sign
al/N
oise
Power law range
Important ingredients
• Multiple timescales• Efficient forms of interactions to transfer
memories
Alex Roxin
Larry AbbottPatrick Drew
Collaborators
q=0.1
q=0.01
q=0.001
q=0.1
q=0.01
q=0.001
q=0.1
q=0.8
Bounded synapses RANGE=1
Bounded synapses RANGE=10, balanced
Bounded synapses, any RANGE, imbalanced
Unrealistic unbounded synapses (~
N)
Unrealistic unbounded synapses (~
N)
Bounded synapses RANGE=10, balanced
Bounded synapses, any RANGE, imbalancedSoft bounds synapses RANGE=10
Homogeneousq=0.1
Homogeneousq=0.6
Heterogeneous
q=0.1
q=0.8