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Brain Arousal and Information Theory (Pfaff, 2006)
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Arousal is fundamental to all cognition. It is intuitively obvious, absolutely necessary, but what exactly is it? In Brain Arousal and Information Theory, Donald Pfaff presents a daring perspective on this long-standing puzzle. Pfaff argues that, beneath our mental functions and emotional dispositions, a primitive neuronal system governs arousal. Employing the simple but powerful framework of information theory, Pfaff revolutionizes our understanding of arousal systems in the brain.
 
Starting with a review of the neuroanatomical, neurophysiological, and neurochemical components of arousal, Pfaff asks us to look at the gene networks and neural pathways underlying the brain's arousal systems much as a design engineer would contemplate information systems. This allows Pfaff to postulate that there is a bilaterally symmetric, bipolar system universal among mammals that readies the animal or the human being to respond to stimuli, initiate voluntary locomotion, and react to emotional challenges. Applying his hypothesis to heightened states of arousal--sex and fear--Pfaff shows us how his theory opens new scientific approaches to understanding the structure of brain arousal.
 
A major synthesis of disparate data by a preeminent neuroscientist, Brain Arousal and Information Theory challenges current thinking about cognition and behavior. Whether you subscribe to Pfaff's theory or not, this book will stimulate debate about the nature of arousal itself.
 

CNS - Central Nervous System
 
p.1 The arousal system thus emerging in the human brain drives all of our behavioral responses to stimuli in a manner best understood through the mathematics of information theory.
 
p.2 Because arousal is fundamental to all cognition and temperament, its explanation is a holy grail of neuroscience.
 
p.2 arousal explains the initiation and persistence of motivated behaviors in a wide variety of species, not just mammals... Arousal, fueling drive mechanisms, potentiates behavior, while specific motives and incentives explain why an animal does one thing rather than another.
 
p.3 Arousal "moves the animal toward readiness for action from a state of inactivity." ...In this book... I lay bare many of the mechanisms for CNS arousal and add a quantitative, mathematical approach... Arousal provides the fundamental force that makes animals and humans active and responsive so they will perform instinctive behaviors or learned behaviors directed toward goal objects.
 
p.4 I theorize that explaining arousal will permit us to understand the states of behavior that lie beneath large numbers of specific response mechanisms.
 
p.5 "Generalized arousal" is higher in an animal or human being who is: (S) more alert to sensory stimuli of all sorts, and (M) more motorically active, and (E) more reactive emotionally.
 
This is a concrete definition of the most fundamental force in the nervous system... The primitive arousal responses I discuss comprise the very first, most elementary responses to any sensory stimulus, preparatory for ever behavioral response that follows.
 
p.6 It may seem mind-boggling that such an arcane and important function as arousal can have such a straightforward working definition. Do not be surprised. Complex behaviors need not have complex explanations.
 
p.7-8 A = F(KgAg + Ks1As1 + Ks2As2 + Ks3As3... + KsnAsn) where A = arousal, as a function (F) of generalized arousal (Ag) and specific forms of arousal (As). The plus sign is not meant to imply simple linearity, but rather to indicate that A is an increasing function of the variables Ag and As(1 to n)
 
p.8 Surprisingly, the overall conclusion that generalized arousal accounted for about one-third of our data held true despite different populations of mice, different investigators, different experimental manipulations and details of response measures, and different configurations of particular factor analysis solutions involving four to six factors for each experiment.
 
p.13 Because CNS arousal depends on surprise and unpredictability, its appropriate quantification (surprisingly!) depends on the mathematics of information. [JLJ - Claude Shannon's work on this subject is then described]
 
p.19-20 I base my theoretical approach on the idea that, for a lower animal or human to be aroused, there must be some change in the environment. If there is change, there must be some uncertainty about the state of the environment.
 
p.21 All of the stimulus characteristics listed in Table 1.2 share an opposition to monotonous, regular, predictable situations that kill arousal. All produce and sustain aroused responses. I propose that reconceiving this large family of responses - in terms of their information content - will enhance the analysis of their mechanisms
 
p.23 information theory applications can provide sensitive, quantitative, and detailed diagnostic profiles of a variety of fatigue states... The ability of informatic calculations during well-chosen test protocols to reveal unexpected differences or similarities in CNS function and behavior will add dimensions to our diagnoses of fatigue states... and thus guide therapies.
 
p.23 Information theory is an essential component of systems biology. In particular, for this book, it offers us a theoretical entry to the mathematics of arousal.
 
p.25 I have introduced a system that is universal, natural, and permanent. It underlies the first responses to all stimuli and therefore influences everything that happens thereafter. This system is exciting to study because its phenomena... are important for all aspects of human mental and emotional life.
 
p.41-42 (1) If information passage into the forebrain is to be maximized, a lack of correlation, an unpredictability of peak activity among the ascending systems, according to information theory, is required; and (2) it is very good for the health of arousal systems that the separate ascending systems not be correlated. That is precisely what is needed for stable performance... the lack of correlations among the systems exemplifies precisely what is needed for high-information, biologically adaptive performance.
 
p.66 The power of uncertainty, unpredictability, and change to control the sizes of responses to sensory stimuli by neurons is illustrated dramatically by the phenomenon of habituation. Habituation refers to the universal observation that steady repetition of the same stimulus causes a steady reduction of response.
 
p.96 Once you have achieved a high state of arousal, perhaps for an emergency, how do you turn it off?
 
p.128 can we envision the mathematics of arousal? Yes.
 
p.129 [Diagram] BBURP theory: A bilaterally symmetric, bipolar (bidirectional, ascending and descending) universal (among vertebrates) response potentiating system. This abstract, theoretical diagram is restricted to the major features of arousal systems that have been conserved throughout vertebrate phylogeny. [JLJ - okay, looks like we just design one of these BBURP things into our game-playing machine and we are done. On to the next problem. Oh wait. This BBURP thing is complicated.]
 
p.129-130 Especially when confronted with dangerous circumstances, we must move into a state of high alertness and respond rapidly and adaptively. How? To answer this question theoretically, I suggest that positive feedback steps are required in arousal systems to achieve rapid transitions from soporific to alert states and to mount very fast and accurate responses.
 
p.131-132 I hypothesize that arousal mechanisms behave like a pendulum. They regain equilibrium by a dynamic in which, the farther they are from baseline state, the greater the force to return to baseline state.
 
p.133 One of the major themes in control systems engineering has to do with limitations and bounds within which input and output variables are allowed to swing... These are hardest to figure out in multiple-input/multiple-output devices for which the relations are resonances among interior loops may not be anticipated. What are we optimizing...? ...In homeostatic systems even rapid, large-amplitude changes must allow critical parameters to return to baseline. This becomes a serious problem when feedback control systems are improperly designed and thus allow wild oscillations of their outputs.
 
p.136 I have claimed repeatedly that arousal is heightened by surprise, by change. The natural electrical engineering analogy is to a capacitor in an electronic circuit. A capacitor will not pass current when the circuit is in steady state. Only a sudden increase in voltage applied to the circuit will result in the capacitor allowing a peak of current to flow, which will then return exponentially to zero. Its mathematical expression is the first-order differential of voltage as a function of time, dv/dt.
 
p.138 The greater the number of possibilities is, the less we know about their arrangement at time t.
 
p.143 This book addresses the most elementary question of CNS state: What determines the ability of an animal or person to mount any response to any stimulus, or to initiate voluntary motor activity, or to express an emotion? That is, I have reformulated the classic arousal problem.
 
p.144 Arousal is the function that supports all cognitive abilities and all emotional expression. Cognition and emotion come together in arousal, which is why understanding this function constitutes a holy grail in neurobiology.
 
p.144 Arousal neurobiology is the neuroscience of change, uncertainty, unpredictability, and surprise - that is, of information science.
 
p.144-145 Nerve cells actually encode probabilities and uncertainties, with the result that they can guide behavior in unpredictable circumstances. CNS arousal itself absolutely depends on change, uncertainty, unpredictability, and surprise... declining information content leads to declining CNS arousal. Thus, arousal theory and information theory were made for each other.

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