Xiao-Jing Wang

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The Concept of a Decision Threshold in
Sensory-Motor Processes
Xiao-Jing Wang Department of Neurobiology Yale
University School of Medicine
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Ramp-to-threshold (drift diffusion) Model
Ratcliff (Psychol Rev 1978) Schall (Nature Rev
Neurosci 2001) Mazurek et al (Cereb Cortex
2003) Sigman and Dehaene (PLoS 2005)
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Preparation of an action
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Probabilistic decision-making in a visual motion
two-alternative forced choice task
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Reaction Time Task
LIP
Roitman and Shadlen 2002
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Open Questions

• What is the neural mechanism that produces a long
  integration time for accumulation of evidence in
  favor of one of choice alternatives?
• What is the source of neural stochasticity that
  gives rise to decision variability at the
  behavioral level?
• What is the circuit dynamics underlying
  competition between neural pools representing
  different choice alternatives, or response vs no
  response, or a reflexive vs a voluntary
  response?
• What is the neural substrate of a decision
  threshold?

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A cortical circuit model of decision making
AUpward motion BDownward motion

• 2-population excitatory neurons
  (integrate-and-fire neurons driven by
  Poisson input)
• Slow reverberatory excitation mediated by the
  NMDA receptors at recurrent synapses
• Winner-take-all competition by feedback
  inhibition

Wang, Neuron 2002 Wong and Wang J Neurosci 2006
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Wang Neuron 2002 Wong Wang J Neurosci 2006
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Neural substrate of a decision threshold?
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A Large-Scale Network Model of Decision-Making
Lo and Wang Nature Neurosci (2006)
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Model
Monkey Data
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Reaction time decreases with increasing coherence
Weber's Law
Data by J Roitman, J Ditterich and M Shadlen
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Tentative answers

• What is the neural mechanism that produces a long
  integration time for accumulation of evidence in
  favor of one of choice alternatives?
  Slow
  reverberation mediated by NMDA receptors in a
  recurrent circuit
• What is the source of neural stochasticity that
  gives rise to decision variability at the
  behavioral level?
  
  Fluctuating neural spiking
  activity
• What is the circuit dynamics underlying
  competition between neural pools representing
  different choice alternatives, or response vs no
  response, or a reflexive vs voluntary a response?
  
  
  Winner-take-all attractor dynamics instantiated
  by strong recurrent excitation and feedback
  inhibition
• What is the neural substrate of a decision
  threshold?
  A hard-threshold for the input
  drive to downstream neurons
  

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Multiple ramping processes in a distributed
neural circuit?
Hikosaka, Physiol Rev 2000
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Acknowledgments Nicolas Brunel Chung-Chuan
Lo Kong-Fatt Wong The Swartz Foundation