chris eliasmith centre for theoretical neuroscience · current opinion in neurobiology, 25:1-6. ......
TRANSCRIPT
Recent advances in large-scale, integrated neural modeling
Chris EliasmithCentre for Theoretical Neuroscience
University of Waterloo
Have
ACT-R
HBP
Want
neuralmodels
cognitivemodels
neuro-cognitive models
What is the right level?• Are LIF neurons biologically realistic enough/needed at
all?
• How many compartments/ion channels, etc. is the right number?
• How much biological detail do we need?
• Without context, these questions miss the point
• What computational resources are available?
• What is the purpose of the model?
Eliasmith and Trujillo (2013). The use and abuse of large-scale brain models. Current Opinion in Neurobiology, 25:1-6.
Some friction• "...tremendous historic milestone" Modha
• "...a hoax and a PR stunt" - Markram
• "It is highly unethical of Mohda to mislead the public in making people believe they have actually simulated a cat's brain. Absolutely shocking." - Markram
Mohda’s slide
The deeper problem
Complexity without functionMarkram, H., et al. (2015). Reconstruction and Simulation of Neocortical Microcircuitry. Cell, 163(2), 456–492
Our brain model
• Spaun (Semantic Pointer Architecture Unified Network)
• Simulated in Nengo
• 2.5 million neurons
• 8 different tasks
• Including basic perceptual tasks...
Eliasmith et al., Nov. 2012, Science.
And more cognitive tasks...
With no changes to Spaun between tasks...
(8 tasks include: recognition, copy drawing, reinforcement learning, counting, serial working memory, question answering, RVC, RPM)
V1 tuning
Working memory
1 2 3 4 5 6 70
0.1
Item Position
Accu
racy
a) b)
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0.6
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0.9
1
4 items5 items6 items
1 2 3 4 5 6 70
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Item Position
Accu
racy
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4 items5 items6 items
Data Model
Bandit TaskDelay Approach Reward Return
Time (seconds)
Neu
ron
num
ber
Tria
l num
ber
Freq
uenc
y (s
pike
s/s)
How is it like a brain?
How does it work?
The Semantic Pointer Architecture (SPA)
• Specific functional claims:
• Working memory
• Action selection (BG)
• Motor/perception hierarchies
• Communication protocol:
• Semantic Pointers
• Compressed ‘addresses’ to deep semantic info
Eliasmith (2013), Oxford
Semantic Pointers• E.g. The pointer would be the activity of the top
level of a standard hierarchical visual model for object recognition
• This pointer can then support ‘symbol’ manipulation
• It can also be used toreactivate a full visual representation
Serre et al., 2007 PNAS
• Compress: (spiking DBN)
• Map: (non-sparse -> sparse)
• Compress:
• Recurrence:
• Decompress:
• Map:
• Decompress:
Perception Cognition Action
Neural Engineering
The Neural Engineering Framework (NEF)
• Three principles
• General
• Unified
• Quantitative
• Nengo: A ‘neural compiler’
Eliasmith & Anderson (2003) MIT Press
NEF connection weights
Binding & Memory
“It’s not a brain model” - Henry Markram (Science News, 183(1):13, 2013)
Sounds like a challenge!• Bahl et al., (2012, J. Neuro
Method)
• parameters found by reduction from Stuart & Spruston (1998)
• soma (1 segment); basal dendrite (1 segment); apical dendrite (5 segments)
• 10 different ion channels
Right level of detail?• Depends on your question:
• Effects of channel blockers?
• Large network dynamics?
• Nengo
• Mixed detail models (conductance, point, rate, no neurons; all at once)
• Put computational resources where you need them
• Fast large-scale design and test
Extensions to Spaun• Hierarchical RL (Rasmussen & Eliasmith,
2014)
• Human-scale conceptual representation (Crawford & Eliasmith, 2013)
• Adaptive motor control (DeWolf et al., forthcoming)
• Language parsing, command following (Stewart et al., 2014)
SPA Unifies• Perception
• Statistical categorization, SPs
• Cognition
• Working with structure, SPs
• Action
• Brain/body dynamics, SPs & control
Still a long way to go...
…but I think the NEF, SPA, and Nengo combination can help…
Further information
Research, Papers: http://compneuro.uwaterloo.ca
Tutorials, Spaun videos: http://www.nengo.ca