1. Xiao-Jing Wang Department of Neurobiology Yale University School of Medicine The Concept of a Decision Threshold in Sensory-Motor Processes

2. 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)

3. Hanes and Schall, Science 1996 Frontal eye field neuron Preparation of an action

4. Probabilistic decision-making in a visual motion two-alternative forced choice task

5. Roitman and Shadlen 2002 Reaction Time Task LIP

6. 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?

7. Membrane Time Constant=10-20 ms

8. Lorente de Nó’s reverberatory circuit: attractor network model Levitt et al 1993 Kritzer and Goldman-Rakic 1995 Pucak et al 1996

9. 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 A=Upward motion B=Downward motion A cortical circuit model of decision making Wang, Neuron 2002 Wong and Wang J Neurosci 2006 IAIA IBIB c’=(I A -I B )/(I A +I B )

10. Wang Neuron 2002 Wong & Wang J Neurosci 2006

12. D Munoz and R Wurtz Fixation Target A bursty neuron in superior colliculus Neural substrate of a decision threshold?

13. A Large-Scale Network Model of Decision-Making Cortex Caudate SNr SC Lo and Wang Nature Neurosci (2006)

15. Model Monkey Data

16. Data by J Roitman, J Ditterich and M Shadlen Reaction time decreases with increasing coherence Weber's Law

17. 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

18. 1 s 20 Hz SEFBasal GangliaSensory Thalamus (also PFC, FEF, LIP) Schlag-Rey et al. J. Neurophys. ‘99Tremblay et al. J. Neurophys. ‘98Komura el al. Nature ‘01 Multiple ramping processes in a distributed neural circuit? Hikosaka, Physiol Rev 2000

19. Acknowledgments Nicolas Brunel Chung-Chuan Lo Kong-Fatt Wong The Swartz Foundation