C H A P T E R 52 The Prefrontal Cortex and Executive Brain Functions INTRODUCTION controlled processes as they can provide predictions about the neural mechanisms likely to underlie them What controls your thoughts How do you decide what to pay attention to How do you act appropriately while dining in a restaurant or listening to a lecture How do you plan and execute errands How do you manage to pursue long term goals like obtaining a college degree in the face of the many distractions that can knock you off task In short how does the brain manage to orchestrate the activity of millions of neurons to produce behavior that is willful coordinated and extends over time This is called cognitive control the ability of our thoughts and actions to rise above mere reactions to the immediate environment and be proactive to anticipate possible futures and coordinate and direct thought and action to them It is a hallmark of intelligent behavior Because cognitive control necessarily involves the coordination of many different brain processes it no doubt depends on circuits that extend over much of the cerebral cortex However one cortical region the prefrontal cortex PFC seems to play a central role It is the cortical area that reaches the greatest relative size in the human brain and is thus thought to be the neural instantiation of the mental qualities that we think of as intelligent Accordingly the PFC receives converging information from many brain systems processing external and internal information and it is interconnected with motor system structures needed for voluntary action Here we discuss anatomical neuropsychological and neurophysiological evidence for and theories of the role of the PFC in cognitive control We will begin with a discussion of the characteristics of volitional or Fundamental Neuroscience Third Edition CONTROLLED PROCESSING Behavior varies along a continuum from mindless automatic behaviors to willful and purposeful i e controlled behaviors see Barsalou 1992 Automatic processes are reflexive If a car or a predator is bearing down on us we leap out of the way before we even have had a chance to form the intention to do so our mind seems to catch up afterward Automatic processes thus seem to depend on relatively straightforward hardwired relationships between the brain s input and output systems In neural terms it seems that they depend on well established neural pathways just waiting to be triggered by the right sensory cue That is automatic processes are driven in a bottomup fashion they are determined largely by the nature of the sensory stimuli and whatever reaction they are most strongly wired to These relatively simple hardwired cue response mappings are useful in many situations Because they can simply be fired off by the environment they are quick and can be executed without taxing the limited capacity of our conscious thoughts But a creature that is only at the mercy of its immediate environment is not well equipped to deal with the ambiguity and exploit the opportunity of a complex and dynamic world Sometimes the course of action is not obvious because cues are ambiguous i e they activate more than one possible internal representation or multiple 1199 2008 2003 1999 Elsevier Inc 1200 52 THE PREFRONTAL CORTEX AND EXECUTIVE BRAIN FUNCTIONS behaviors might be triggered and the one that is optimal for a given situation is at a disadvantage relative to better established more automatic alternatives In these situations ambiguity needs to be resolved by our internal states and intentions by knowledge of possible and desired future outcomes goals and what means have been successful at achieving them in the past as well as their relative costs and benefits This information is used to activate the same basic sensory memory and motor processes that are engaged during automatic behaviors Only now they are not triggered by cues from the environment They are orchestrated in a top down fashion by our expectations about goals and the means to achieve them So this mode of behavior is controlled in the sense that we our knowledge and intensions are in charge not the environment A tenet of modern studies of behavior is that this knowledge is obtained by learning mechanisms that detect and store associations between cues internal states and actions that predict goal attainment reward see Dickinson 1980 Insofar as primates are capable of navigating situations that involve diverse arbitrary relationships across a wide range of informational domains it follows that a neural system for cognitive control must have access to information from many brain systems and the ability to encode the goalrelevant relationships between them The cognitive control system must also have the ability to select which sensory memory and motor processes are activated at a given moment Selection is central because of our very limited capacity to engage in controlled behaviors This is evident to anyone who has tried to talk on the phone and answer an e mail at the same time we can think about only a limited number of things at a time This is in contrast to our high capacity for automatic processes Because they can be triggered by the environment any number of them can be fired off at once as long as they do not come into direct conflict with one another It makes sense that brain mechanisms for cognitive control would evolve with this capacity limitation There is the tradeoff between amount of information and depth of analysis focusing processing on a narrow band of information relevant to a current goal allows a much more elaborate analysis of a situation and available options This single mindedness also allows us to stay on track processing information not relevant to a current goal increases the chance for distraction In fact in many views of cognition control and attention are virtual synonyms It follows that a neural system for cognitive control must have the infrastructure and mechanisms for selecting goal relevant and suppressing goal irrelevant processes throughout the cerebral cortex The cognitive control system must also have a way to deal with the gaps in time that are inevitable with goal directed behaviors Information about predicted goals and means must be brought online before the behaviors are executed and maintained until the current task is completed Also because goal directed behaviors typically are extended over time we often must wait for additional information or for a more
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