18 Nov 2003 14 3 AR AR207 PS55 02 tex AR207 PS55 02 sgm LaTeX2e 2002 01 18 P1 GCE 10 1146 annurev psych 55 090902 141907 Annu Rev Psychol 2004 55 23 50 doi 10 1146 annurev psych 55 090902 141907 c 2004 by Annual Reviews All rights reserved Copyright First published online as a Review in Advance on October 20 2003 ON BUILDING A BRIDGE BETWEEN BRAIN AND BEHAVIOR Jeffrey D Schall Center for Integrative Cognitive Neuroscience Vanderbilt Vision Research Center Department of Psychology Vanderbilt University Nashville Tennessee 37203 email jeffrey d schall vanderbilt edu Key Words linking proposition linking hypothesis stop signal countermanding response preparation intention eye field reaction time response time saccade Abstract Cognitive neuroscience is motivated by the precept that a discoverable correspondence exists between mental states and brain states This precept seems to be supported by remarkable observations and conclusions derived from eventrelated potentials and functional imaging with humans and neurophysiology with behaving monkeys This review evaluates specific conceptual and technical limits of claims of correspondence between neural events overt behavior and hypothesized covert processes examined using data on the neural control of saccadic eye movements CONTENTS INTRODUCTION Inferring Mechanism from Behavior Inferring Function from Neuronal Properties LINKING PROPOSITIONS Testing Linking Propositions LINKING PROPOSITIONS ABOUT SACCADE PRODUCTION Evidence for Covert Response Preparation Response Preparation and Intention Bridge Locus for Response Preparation Control of Saccade Initiation Relation of Neural Activity to Response Time Relation of Neural Activity to Movement Cancellation Alternative Propositions Mapping GO and STOP onto Neural Processes EVALUATING LINKING PROPOSITIONS FOR THE PRODUCTION OF SACCADES Do Identical Neural States Map onto Identical Saccades Do Identical Saccades Map onto Identical Neural States SUMMARY AND CONCLUSIONS 0066 4308 04 0204 0023 14 00 24 24 25 26 27 29 31 31 32 33 34 37 38 40 40 42 43 23 18 Nov 2003 24 14 3 AR AR207 PS55 02 tex AR207 PS55 02 sgm LaTeX2e 2002 01 18 P1 GCE SCHALL INTRODUCTION Many authors write with conviction that the correspondence of the mental with the neural is so secure that an ultimate theory of mental phenomena will reduce to neural terms e g Churchland 1986 Crick 1994 Others argue that mental states depend on but are not reducible to the physical states of the brain e g Davidson 1970 Fodor 1981 Pylyshyn 1984 Determining whether the mental reduces to or emerges from the neural cannot be accomplished without correctly describing the mapping between the two Inferring Mechanism from Behavior Before the development of methods to monitor brain states during behavior physiological mechanisms could be inferred only from behavioral testing Nevertheless in the nineteenth century investigators began to articulate the correspondence between mental and physical processes For example Mach wrote To every psychical there corresponds a physical and conversely Like psychical processes correspond to like physical unlike to unlike Particulars of the physical correspond to all the particulars of the psychic Boring 1942 Even philosophers who advocate a nonreductionist position acknowledge a mapping between mental and physical processes Although the position I describe denies there are psychophysical laws it is consistent with the view that mental characteristics are in some sense dependent or supervenient on physical characteristics Such supervenience might be taken to mean that there cannot be two events alike in all physical respects but differing in some mental respects or that an object cannot alter in some mental respect without altering in some physical respect Davidson 1970 Such a position can be translated into an effective research strategy according to the proposition that whenever two stimuli cause physically indistinguishable signals to be sent from the sense organs to the brain the sensations produced by these stimuli as reported by the subject in words symbols or actions must also be indistinguishable Brindley 1970 Application of this principle in sensory detection or discrimination experiments permits testing hypotheses about physiological processes Another approach to understanding the mechanisms responsible for behavior has been through mathematically precise models of cognitive processes tested against detailed measurements of performance e g Townsend Ashby 1983 Luce 1986 1995 Unfortunately cognitive psychology abounds with alternative models with mutually exclusive architectures or algorithms many of which are difficult or impossible to distinguish through behavioral testing For example choice behavior can be accounted for by sequential sampling models in which a single accumulator represents the relative evidence for two alternatives e g Ratcliff Rouder 1998 An alternative to a random walk of a single accumulator between alternatives is a race among multiple accumulators representing each alternative e g Bundesen 1990 Logan 2002 In fact models with single or multiple accumulators can account for common sets of data Van Zandt Ratcliff 1995 18 Nov 2003 14 3 AR AR207 PS55 02 tex AR207 PS55 02 sgm LaTeX2e 2002 01 18 P1 GCE BRIDGING BRAIN AND BEHAVIOR 25 Van Zandt et al 2000 highlighting the limitations of arriving at secure inferences about mechanism based only on behavior e g Uttal 1997 The theoretical issue has been articulated most definitely in the theory of finite automata Moore 1956 It has been proven that given any computer with a finite number of inputs outputs and internal states and any experiment that determines the mapping of outputs to inputs there exist other computers that are experimentally distinguishable from the original computer for which the original experiment would have given the same results In other words different architectures and algorithms can produce the same output from a given input Inferring Function from Neuronal Properties The propositions quoted above were regarded initially as axiomatic but the development of diverse means of monitoring neurophysiological processes directly or indirectly during behavior has afforded the unprecedented opportunity to investigate directly how mental processes relate to neural processes Over the past decade numerous publications have carried titles like Neural Correlate of X where X is some cognitive capacity or behavior For example by monitoring