Optimizing with synapses

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Optimizing with synapses
Sebastian Seung Howard Hughes Medical
Institute and Brain Cog. Sci. Dept., MIT
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Practice makes perfect

• Birdsong learned from male tutor
• Stored template
• Zebra finch up to 100,000 iterations
• Known anatomy and physiology

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Hahnloser, Kozhevnikov, Fee (2002)
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Supervisory signals in the brain

• Global broadcast of reward signal
• E.g. dopaminergic system

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Neural basis of learning
Global signal (Reward, motor error, etc.)
Local signals (Voltage, calcium, etc.)
Synaptic plasticity
The interaction between global and local signals
is largely uncharacterized.
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Noise injection hypothesis

• HVC vs. LMAN
• lesion
• neural activity

HVC
RA
LMAN
motor neurons
Doya and Sejnowski
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Trial and error learning

• Generation of variability
• Reinforcement of favorable variations

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Synaptic learning rule
regular synapses
reward
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noise synapses
regular
noise
reward
Fiete and Seung
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Optimization in biology

• Evolution
• Search in genotype space
• Random genetic variation
• Learning
• Search in synapse space?
• Unreliable synapses
• Noise injection

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Stochastic gradient learning

• Systems-level models of learning
• Birdsong
• Oculomotor system
• Synaptic plasticity in vitro
• Microisland cultures
• Training neural circuits in vitro
• Silicon stimulation
• Pattern culture
• Intrinsic imaging by interferometry

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Reward-driven plasticity in vitro
Jen Wang Naveen Agnihotri
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Patterned culture by inkjet printing
Sawyer Fuller and Neville Sanjana
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In vitro models of learning

• Goal study how synaptic plasticity affects the
  dynamics of neural circuits
• Technical challenge electrical and chemical
  control of neurons
• Conceptual challenge training neural circuits