On building a bridge between brain and behavior.

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 event-related 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 

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 of 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.