Language Acquisition and Use : Learning and Applying Probabilistic Constraints

climb the surface defined by the value function V. 26. A. R. Damasio,Descartes’ Error (Putnam, New York, 1994); A. Bechara, A. R. Damasio, H. Damasio, S. Anderson, Cognition 50, 7 (1994). 27. S. P. Perrett, B. P. Ruiz, M. D. Mauk J. Neurosci. 13, 1708 (1993); J. L. Raymond, S. G. Lisberger, M. D. Mauk Science 272, 1126 (1996). 28. S. Grossberg, Math. Biosci. 15, 253 (1972); R. L. Solomon and J. D. Corbit, Psychol. Rev. 81, 119 (1974); S. Grossberg, ibid. 89, 529 (1982). 29. W. Schultz and R. Romo, J. Neurophysiol. 63, 607 (1990); T. Ljungberg, P. Apicella, W. Schultz, ibid. 67, 145 (1992); J. Mirenowicz and W. Schultz, Nature 379, 449 (1996). 30. W. Schultz, P. Apicella, T. Ljungberg, J. Neurosci. 13, 900 (1993). 31. T. Aosaki et al., ibid. 14, 3969 (1994); A. M. Graybiel Curr. Opin. Neurobiol. 5, 733 (1995); Trends Neurosci. 18, 60 (1995). Recent models of sequence generation in the striatum use fluctuating dopamine input as a scalar error signal [G. S. Berns and T. J. Sejnowski, in Neurobiology of Decision Making, A. Damasio, Ed. (Springer-Verlag, Berlin, 1996), pp. 101–113. 32. T. F. Freund, J. F. Powell, A. D. Smith, Neuroscience 13, 1189 (1984); Y. Smith, B. D. Bennett, J. P. Bolam, A. Parent, A. F. Sadikot, J. Comp. Neurol. 344, 1 (1994). 33. C. Cepeda, N. A. Buchwald, M. S. Levine,Proc. Natl. Acad. Sci. U. S. A. 90, 9576 (1993). 34. J. R. Wickens, A. J. Begg, G. W. Arbuthnott, Neuroscience 70, 1 (1996). 35. P. S. Goldman-Rakic, C. Leranth, M. S. Williams, N. Mons, M. Geffard, Proc. Natl. Acad. Sci. U.S.A. 86, 9015 (1989); T. Sawaguchi and P. S. Goldman-Rakic, Science 251, 947 (1991); G. V. Williams and P. S. Goldman-Rakic, Nature 376, 572 (1995). 36. R. J. Dolan et al., Nature, 378 180 (1995). 37. P. R. Montague, C. D. Gancayco, M. J. Winn, R. B. Marchase, M. J. Friedlander, Science 263, 973 (1994). The mechanistic suggestion requires that local cortical activity (presumably glutamatergic) increases the sensitivity of nearby dopamine terminals to differences from baseline in spike production along their parent axon. This may result from local increases in nitric oxide production. In this manner, baseline dopamine release remains constant in inactive cortical areas while active cortical areas feel strongly the effect of increases and decreases in dopamine delivery due to increases and decreases in spike production along the parent dopamine axon. 38. We thank A. Damasio and T. Sejnowski for comments and criticisms, and C. Person for help in generating figures. The theoretical work received continuing support from the Center for Theoretical Neuroscience at Baylor College of Medicine and the National Institutes of Mental Health (NIMH) (P.R.M.). P.D. was supported by Massachusetts Institute of Technology and the NIH. The primate studies were supported by the Swiss National Science Foundation, the McDonnell-Pew Foundation (Princeton), the Fyssen Foundation (Paris), the Fondation pour la Recherche Midicale (Paris), the United Parkinson Foundation (Chicago), the Roche Research Foundation (Basel), the NIMH (Bethesda), and the British Council.