Can We Get There From Here?

The last several decades have been a golden era of many extraordinary experimental and theoretical discoveries in neuroscience and we can expect even more and greater discoveries in the decades ahead. Yet despite these many advances, progress in understanding the overall logic of nervous systems and especially how they produce diverse, precise, and flexible behaviors is still substantially lacking. I discuss from a mainly physics point of view what are some of the difficulties of understanding how nervous systems produce behavior, especially the extremely difficult problem of identifying a physical state that is experimentally measurable and theoretically manageable. This discussion suggests that, just as there are hard limits to what physicists can predict about many physical systems due to the nonlinear dynamics of chaos and what computer scientists can predict about what results a computer will produce from a given program, there are limits that will prevent precise behaviors from being predicted or explained from the necessarily incompletely known physical properties of an animal's nervous system. The future of theoretical neuroscience will not involve precise predictions about behavior but more the calculation of approximate probabilities of different behaviors that are consistent with the hard limits related to measuring and analyzing nervous systems as physical systems.