Behavior and its ‘isms

As little kids, we find the world to be a generally incomprehensible and often hostile place. So we make quick and comfortable affiliation with other kids who are equally clueless and fearful, and form clubs, gangs, and Cub Scout packs. We meet in tree houses or playgrounds, and beat up on or malign anybody who seems different (and thus threatening), like grownups, girls, and the kids who live on the other side of the tracks.

As compared to being totally ignorant or totally informed, a little knowledge can be a dangerous thing, and we can trace the social consequences of information with our growing maturity. Thus, as infants, no social knowledge makes you needy, but as kids a little knowledge makes us precocious self-centered snots. However, when our social knowledge is ‘complete’, we know better than to trumpet our specialized knowledge on how to drive cars, shop for groceries, and put on our pants (one leg at a time usually).

When knowledge is universal and easily accessible, and its authors are obscure, forgotten, or dead, then we forget about the controversy that once surrounded it, and simply use it, as if it was as mundane as a wheel or a fork. That is, when special knowledge becomes ordinary, then we forget about all the contentiousness about who thought it first, the ideas it replaced, whose feelings got hurt, or why it was unique to begin with. Thus, we don’t know and don’t care about why our ancestors got bent out of shape when confronted with the flat vs. round earth controversy, evil spirits as the cause of disease, or why Noah left behind all those dinosaurs.

Ultimately, the mystery of knowledge surrenders to the mastery of knowledge, and we achieve mastery through various schooling or through the school of hard knocks. Yet because there is so much to know, and we have scant time and capability to know it all, we rely upon experts to dispense and utilize this knowledge for us. This is an economical way of going about our business, and the business it engenders is accordingly, economics. Thus the privilege of knowledge, and the tokens or currencies that denote the exchange rates of knowledge enable us encourage those folks who do mysterious things, like calculating income taxes, fixing auto transmissions, and throwing footballs well.

Knowledge is power, but specialized knowledge is where the money is. So to keep the power, and more importantly, the money that goes along with it, the incentive is there to keep one’s wisdom to oneself, and ration it out to those who are willing to pay the price. So like medieval guild members (or kids in a clubhouse in a tree), we get certified, specialized, and form interest groups or ‘schools’ of thought that have their own special languages and buzz words, and are lacking only super secret decoder rings. Like a Rumpelstilskin spinning gold out of linguistic straw, one can talk about oblong rotating spheroids (i.e. a wheel) or four pronged mastication utensils (i.e. a fork), charge folks again and again for reinventing something they pretty much know about already. Luckily, the reason why knife and fork consultants do not exist is that we can easily explain and use knives and forks. More specifically, the technical details of knifes and forks yield to the simple instructions that describe their use, since simple uses are all that we require.

Ultimately, complexity of explanation depends upon the accuracy demanded by the questions one asks, and it is here where the experts creep back in. Simple questions and simple answers are the province of common sense, which is free to all. However, it is often complex notions that give birth to simple truisms, and when we want our answer to be precisely true, then we rely on a certified master of detail. Thus to know when an action is precisely legal, whether we are precisely healthy, or how to precisely land a man on the moon, then we consult properly certified and registered experts in law, medicine, or physics. Normally, we use only one type of law, engage in one type of medicine, and use one set of uniform mathematical principles to do physics because our knowledge of them is complete or near complete. A lawyer does not choose between English and Napoleonic law, a doctor between faith healing and biological models of disease, or a physicist between the physics of Aristotle and Galileo because experts have settled upon a common sense of principles that drive these disciplines. However, when knowledge is incomplete and unintegrated, then science becomes beholden to the particular school of thought with the greatest claim to precision.

The contentious squawking between rival schools of thought peppers our intellectual history, as knowledge, in its beckoning incompleteness, is championed by different schools of thought that aim to show us the way. Of course, in an incomplete world, the seemingly proper way to determine and use knowledge often crowds out other ways that are less productive, or just get in the way. Like little children in an exclusive clubhouse, there is little or no place for deductive/inductive, subjective/objective, value laden/value free, or other differing methods of knowing on the same intellectual page. Thus philosophy, and its step child psychology is populated be a raft of ‘isms, particular and parochial ways of looking at the world that have individual claims of completeness, rightness, and unerring precision.

These idiosyncratic ways of looking at the world can reflect the general ways we determine facts (deduction vs. induction), the perspectives (microscopic/macroscopic) that we employ to view facts, the ways we interpret facts (subjective vs. objective), the time frames that facts take place (past, present, future), the rules whereby one may use facts (moral, amoral), and the methods (between vs. within group experimental design) and methodological tools (microscopes, Skinner boxes, projective tests) that one chooses to use to ascertain facts. The permutations of these intellectual foci and the degree that one embraces each of them determine one’s school of thought, or the intellectual clubhouse where one and his or her likeminded peers may secret themselves and their semi-secret wisdom, content in the knowledge that they have the key to the ways of the world. In a fractious intellectual climate where knowledge about the mind is boundlessly (and redundantly) rendered by numberless data languages, methods, and points of view, the social sciences have seen a multiplication of the ‘isms that have fractured language into more incommensurate tongues since human language after the fall of Babel.

So, what is the cure for this plague of 'ism's that is drowning psychology in a sea of redundant and often useless jargon? Whether our ailment is logorrhea or diarrhea, the best remedy to useless thinking is to simply follow the model that our doctor uses. This medical model comes to quick and sound conclusions by its simple recognition that the human condition is best understood through a respect for all ideas, and a recognition that ideas, when viewed in concert, have a way of sorting each other out. This leaves us with the refreshing clarity of bare facts, simple theories, and effective procedures. But as we will also note, the medical model in its early development was also infected with a predilection for 'isms.

Nowadays, when we talk of awfully complex human bodies, there are precious few 'isms that dictate how we think of them. For biology, and its practical applications in medicine, all perspectives on body and soul are in harmony. And so we universally admit that people hurt, and that they have physiologies and genetic codes, and that health and infirmity, suffering and wellness reflect on matters both mechanical and spiritual. And so we can move from subjective to objective, molar to molecular, depending upon the questions we ask. Thus we know all the mechanics of our bodies and all of its rules, and still have room to believe in consciousness, good and evil, supreme beings, and life after death.

Before the 17^th century, 'doctors' were uneducated or self-educated priests, barber surgeons, or quacks. Medical science at the time 'knew' how our bodies worked, since without a venue to microscopic causes, macroscopic events were the only reality available or even conceivable. So the nature and workings of the human body, the causes of health and the remedies for its misfortunes and malfunctions were a matter of ascertaining which large scale cause, from spirit forces to bodily fluids to atmospheric vapors that was responsible. But, in the meanwhile people got sick and died, ate and drank the wrong things, and dropped like flies.

Before the advent of microscopic models that provided the genetic and biochemical codes for the molecular processes underlying our biological existence, the mediational events that lay between different actions (drinking too much beer) and reactions (getting sick), were macroscopic and metaphorical. That is, they used common concepts (wind, vapors, fluids) as proxies for the actual events. The human body was not so much a black box as a Pandora’s box, that was filled (we were assured) with numberless creatures, phantasms and forces. The metaphorical representations of human health and infirmity could easily account for every aspect the human condition, and their predictive power was a matter of adjusting them post hoc to meet every eventuality. Thus, if you died of the plague, it’s just that you didn’t sacrifice enough chickens to placate the Gods, or perhaps didn’t drink enough chicken soup. However, when medical science finally developed the tools that enabled the determination of the actual biological sources of disease, and as importantly the development of easy metaphors that could describe those sources, then the notion of evil spirits, noxious humours, and mysterious forces died a quick death. Because they could not translate down to the most elemental level of human reality, mediational forces that translated input (causes of disease) into output (disease symptoms) were finally reduced to those metaphorical descriptions (I hurt) that could reliably map downwards to simply describe realistic elemental causes (I have an ear infection).

A psychology without ‘ism’s is inevitable, since at present simple and workable models of the brain are being rapidly developed that are grounded in actual observations of the brain ‘in action’, hence eliminating the need to have some privileged psychological viewpoint. Since psychologists as a whole (and this includes humanist, social, and behavioristic psychologists in particular) are coming rather tardily to the rather common sense notion that to understand the workings of a mind, one must first understand how biologically minds work, it will be interesting to see how the fur will fly as logic (and an informed public who will be less inclined to put up with nonsense) compels psychologists to finally make sense.

We are only in the initial stages of a second cognitive revolution (see my ‘Crank science in a cranky age’ section on my site for more on this), and one must still endeavor to make a formal case out of thinking straight. As the uncomfortable possessor of an ‘ism myself (try ‘radical behaviorist’ on for size!), my alter ego has recently made the case that this ‘ism, and the entire concept of ‘behaviorism’ should be retired. The following article, which is appearing in the February, 2002 edition of the Journal Behavior and Social Issues (at behavior.org), attempts to cleanse me of this affiliation. (Well actually, I am rather comfortable with the title ‘ironic behaviorist’, but that’s another story.)

Hayes, Steven C. (2001) The greatest dangers facing behavior analysis today, The Behavior Analyst Today vol2(2), pp. 61-63

A hallmark virtue of behaviorism and behavior analysis is its adherence to a thoroughgoing empiricism with a commitment to discovering the lawfulness of behavior and the development of procedures for its prediction and control. Ultimately, the aspects of behavior that can become a subject matter for a behavioristic examination are dependent upon the capability of the tools available that can measure those aspects. Thus, respondent and operant behaviors become grist for a behavioristic analysis only because we have the devices (e.g. Skinner box, cumulative record, Pavlov's gastric fistula) available to measure and control for these responses. Unfortunately, if schools of thought become defined through the unique methodology they employ rather than the empirical principles they espouse, then these schools of thought become ultimately built on artificial principles. In the case of behaviorism, the dogmatic reliance on methodological at the expense of empirical principles not only constrains behaviorism, but as I must agree with the aforementioned quotation, may ultimately kill it.

The fact that respondent and operant conditioning have only recently been analyzed using uniform methodological principles (Donahoe and Palmer, 1993) underscores the fact that different procedures can be wrongly imputed to underscore subject matters that are incommensurable. However, the methodological divisions that can separate practitioners into different camps is presently repeating itself once again, and with results that are of key importance to the future of behaviorism.

Presently, the rapid development of new and powerful experimental tools (MRI, in vivo micro-dialysis, neuronal modeling, etc.) that can map neural processes has demonstrated that neuromodulator production (Barrett and Hoffman, 1991), micro-cellular processes (Stein et al. 1993), and many other neural events can now be mapped to environmental contingencies. These findings are no less behavioristic than Pavlov's measure of gastric secretions, yet because the experimental methods and devices are so different from those customarily employed by behavior analysts, the tools themselves have defined a subject matter, namely neuro-psychology, that seems quite different from behaviorism, even though the former is in principle behavioristic.

A major emerging concept in cognitive neuro-psychology that is being examined through the use of operant principles is the concept of embodiment, a notion that has received scant attention from behavior analysts. Embodiment, which is now held as a first principle by the major voices in neuro-psychology today (e.g. Antonio Damasio (1994), Jaak Panksepp (1999)) in effect holds that behavior is not only instantiated by environmental contingencies, but is continuously guided by somatic events (e.g. muscle tension, neuromodulator production, hormonal responses, etc.) that are instigated by and mediate the effectiveness of those contingencies. Embodiment is different from the more general concept of emotion because unlike the latter, it possesses 'theoretical coherence'. In other words, embodied events represent measurable somatic responses that vary in time and across other independent measures (e.g. response contingencies) that can be altered and replicated.

Embodiment should be particularly of importance to behaviorism for the simple reason that embodiment is now at the root of contemporary bio-behavioral definitions of reinforcement. Current discrepancy models of reward hold that reinforcement is coextensive with the production of the neuromodulator dopamine that fixes attention, assigns appetitive value to perceptual events, and increases synaptic or neural efficiency. The concept of embodiment as reflected in the activity of dopamine neurons represents a particular challenge to the canonical behavioristic representation of a reinforcer as a discrete event that controls or motivates behavior as the consequence of a fixed response contingency. Rather, neuroscientific theories of reinforcement assign reinforcement to the prediction error that derives from an individual's moment-to-moment perception of prevailing response contingencies. That is, reinforcement is a continuous and variable and not an intermittent and fixed event, and is relative to prediction error perceived at any moment in time. This view, which is presently the dominant interpretation of learning in neuroscience proposes (Hollerman and Schultz, 1998) that : "Learning depends on the extent to which behavioral outcomes are different than predicted, being governed by the discrepancy of 'error' between outcome and prediction. Outcomes that affect learning in this way are termed 'reinforcers.'..."Learning proceeds when outcomes occur that are not fully predicted, then slows down as outcomes become increasingly predicted and ends when outcomes are fully predicted."(p.304) Furthermore, "the magnitude of dopamine responses to reward reflect the degree of reward predictability during individual learning episodes...".(p.304) Although a dopaminergic based discrepancy theory was first ventured by Donahoe's unified reinforcement principle (Donahoe and Palmer, 1993), the fact that dopamine production co-varies with the magnitude and timing of prediction error, and does not just mark prediction error impacts not just the quality of reinforcement, but also the attendant quality of subjective experience. In other words, the phenomenology of happiness, or its subjective feeling, can now be rooted to actual physiological processes that can be simply conceived. These facts can be simply illustrated through three examples that appeal to common experience.

Take a simple piecework task, such as pulling a lever many times a minute to stamp out buttons on an assembly line. The reward for performing this task, namely a salary, is wholly predictable in its timing and its amount. However, if the timing of the reward as well as its size radically varied over time, then although the average weekly salary would remain the same, the worker could be rewarded substantially, marginally, or not at all upon the after each lever pull. The latter example, which makes the button machine into a slot machine, will result in the otherwise tired and bored worker becoming suddenly animated, interested, excited, and ironically, indifferent to the reasonable expectation that he or she may likely have a net loss at the end of the week. The manipulation of prediction error alone therefore transforms an onerous 'extrinsically' motivated task into a highly desirable 'intrinsically' motivated task.

As another example, consider a non-rote task that requires an individual to figure out a puzzle or other problem. The solution for novel problem solving task also involves unpredictable prediction errors, when progress towards solving the problem occurs intermittently and surprisingly as different options are considered. If the prediction errors are positive, rapid, and high, then we have a lot of dopamine produced and a corresponding enjoyable, flowing, peak, or otherwise pleasurable experience. Similar activities that involve high, rapid, and positive prediction error are creative, sporting, gaming, or other tasks.

As a final example, let us consider the exemplar of all positively motivated individuals: Shakespeare. If the fanciful movie 'Shakespeare in Love' is to be believed, Shakespeare's genius was spurred by a confluence of motivators, including girlfriends, competitors, fellow actors and investors, not to mention the approval of the crowd, the Queen, and posterity. It was indeed a volatile matrix of uncertainty that excited the imagination and the pen, giving us a play, 'Romeo and Juliet', a sublime mixture of pratfalls and poetry that appealed to crowd and Queen alike. But what indeed motivated Shakespeare, uncertainty or contingency? Simple, remove the uncertainty (but not the contingency) and the edifice collapses, and Shakespeare then knows all the right moves, and would likely become bored to tears. He would be no more inspired than a baseball player who knows the final score beforehand, or a gambler who knows the impending face of each card. Shakespeare in Love would become Shakespeare in Hell, a presumption that has at least literary precedent.

In an episode of the classic TV series 'The Twilight Zone', a burglar gets shot and killed, and is met by a jovial fellow who introduces him to a world where he can have anything he wants, from women to power to fame. Unfortunately, everything is totally predictable, from the role of a die to a woman's sigh. He protests that everything has become boring and dull, and requests to be shipped off to hell, where at least he could play chess with the devil. The man laughs, and says to the shocked burglar, "What makes you ever think that you are in heaven?"

In keeping with these findings, dopamine has recently been demonstrated to scale up or down with changes in the probability and importance of expected events (Breiter et al, 2001; Knutson et al. 2001, Berns et al. 2001) and with the frequency of cognitive set shifting between expected events, such as in creative behavior (Fried et al. 2001) and video game playing (Koepp et al. 1998). Elevated dopamine production also occurs or displays 'behavioral momentum' after the conditions or contingencies that elicit it have been altered or withdrawn (Ashby, Isen, and Turken,1999). In particular, because dopamine bestows an appetitive value on behavior, it will alter behavior in ways that cannot be predicted as a function of a consideration of perceptual events alone. That is, response contingencies not only provide a perceptual road map whereby we may categorize value, but also continuously elicit and control somatic responses that confound or skew value. For example, if I do a good deed (e.g. hit a base hit for the Diamondbacks in the ninth inning of game 7 in the World Series), I consider the positive and unpredictable ways my audience will react, and if I do a bad deed (be the guy who threw that same pitch), I will consider the negative albeit unpredictable reactions of the same audience. The prediction error is virtual, not real, and reflects as-if relationships between perceptual events. Yet the pain or pleasure associated with that prediction error is quite real, and serves to modulate or change behavior (e.g. whether you sulk in your dugout or cavort in your clubhouse with champagne). Because dopamine maps to as-if prediction errors, it essentially can influence behavior due to virtual as well as real events. The ability to feel another's pain, which is the root of empathy, does not mean that another's pain is actually modeled, but rather that dopamine production is increased or suppressed due to our consideration of the modeled positive or negative responses of other people. This brings us to a very interesting conclusion. If reinforcers are equivalent to arranging positive and unpredictable prediction error, then happiness if simply finding ways to increase positive prediction error in our daily lives. Yet to increase positive prediction error entails the ability to model other people's responses, and to be effected by knowledge of their pleasure and approval and their disapproval and pain. Thus to be reinforced is to be empathetic, and to increase empathy is ultimately to increase happiness and moral virtue.

Unfortunately, since neuromodulator activity cannot be as easily charted as say a bar press or key peck, indirect and less precise methods must also be used to account for the somatic events elicited by response contingencies. In particular, these methods entail subjective reports of pain and pleasure and how they map to abstract elements of environmental contingencies. However, as behaviorists are amply aware, the use of subjective reporting suffers from a tendency towards unreliability, and at worse an embrace of mentalism. An exemplar of this problem is the work of the psychologist M. Csikszentmihalyi (1990, 1997). After polling thousands of individuals in various circumstances of work and play, Csikszentmihalyi demonstrated a high correlation of self-reports of pleasurable or ecstatic states to elements of response contingencies (a 'demand/skill' match). Unfortunately, Csikszentmihalyi did not ground his observations to neural events, but rather to mentalistic entities such as 'psychic energy', 'undreamed states of consciousness' and the like. The behavioral contingencies that may be reliably inferred from Csikszentmihalyi's work are precisely the same as those that may be mapped to dopamine release, yet the thoroughgoing mentalism that characterizes Csikszentmihalyi's work has rendered it opaque to behavior analysis, and hence the behaviorist community has ignored it.

Mentalism is ubiquitous in our lives, as we couldn't communicate with each other otherwise. Yet we manage to live with the mental homunculi of will, desire, courage, consciousness, and other psychological faculties because we can continuously qualify what we hear, feel and see by a deep knowledge of physical reality (e.g., Einsteinian concepts of time, Darwinian evolution, etc.) But just as a medical doctor must listen to the unreliable patient reports of aches and pains as a way to inform more accurate diagnostic and therapeutic procedures, so too must behaviorists be able to use the imprecision of self reports to inform sound behavioral interventions. Behaviorism has been marginalized by an intolerance of any imprecision in exchange for an incomplete accounting for behavior that has in turn limited the effectiveness of its practical procedures. It has allowed great swaths of its rightful subject matter be co-opted by mentalistic models for behavior (e.g. 'flow states', intrinsic vs. extrinsic motivation, needs for achievement, etc.), and has suffered itself to be commonly relegated to the ash can of science by many popular and academic pundits on psychology whom one might think would know better. This can only change if behaviorists become, well, more behavioristic, and account more thoroughly for the subject matter (namely behavior in all its covert and over manifestations) that they purport to explain. But as I will note with more than a little irony, a true thoroughgoing behaviorism makes the very term behaviorism redundant and useless.

The focus on embodiment, which is so characteristic of modern neuro-psychology, and so reflective of behavioristic principles, has been near totally ignored by contemporary behaviorism. The supreme irony of this statement is that this ignorance runs counter to the inductive principles that were the hallmark of Skinner's perspective on psychological science. As Donahoe and Palmer (1993) note, "the distinction between observed and unobserved events is not a distinction between kinds of events, but between the resolving power of different technologies.".(p.5)...."The view that microbehavioral events are part of a science of behavior was termed radical behaviorism by Skinner. Such unobserved events are admissible so long as they are not accorded characteristics other than those of observed events that have been subjected to experimental analysis."(p.7) Thus, in Donahoe and Palmer's opinion methodological behaviorism must expand to include events that are unobserved at the behavioral level for two reasons: " (A) The distinction between unobserved and observed events is not a fixed line that separates different kinds of events, but a fuzzy boundary that advances as technology progresses. (B) The incorporation of sub behavioral events may improve the precision of the functional relations between events measured at the behavioral level."(p.7)

Behaviorism has long justified itself by a philosophy that exalts prediction and control over theoretical explanation. However, in order to maximize the predictive power of its procedures, it must now consider all aspects of behavior from self-reports to overt behavior to covert and micro-behavioral responses, and thus ironically back into the explanatory models it once ignored. Unfortunately however, if behaviorism is practically defined through a distinctive data language and methodology, the expansion of a methodological behaviorism to encompass subjective and micro-behavioral indices of behavior broadens that language and methodology. It thus dissolves the linguistic and methodological distinctiveness of behaviorism, and identifies it instead with general inductive and empiricist principles. Thus behaviorism dies, but rises again as the culmination of psychological science.

Ultimately, there is only question I will pose. What is behaviorism? Is behaviorism defined by a scientific philosophy, or does it merely reflect the use of a specific type of methodology and the interpretations of the data produced by that method? If it embodies science, then let it embrace science, and integrate itself at long last with those other approaches that see beauty, feel pain, know the molecules that make our behavior and passions, and of course, the overt responses that we know as behavior.

There are three major sources of information on unified reinforcement or discrepancy theory.

The first represents the work of the bio-behaviorists John Donahoe and David Palmer. Their Unified Principle of Reinforcement is the first systematic presentation of a discrepancy theory of reinforcement, and scholarly articles on their work can be found on the web site of the Journal of the Experimental Analysis of Behavior (JEAB).

The most lucid and up to date accounts of discrepancy theory are also found on the web. The Google web directory contains quite a few PDF files on articles by the neuroscientist Wolfram Schultz that are lucid yet rigorously argued. Schultz is presently the major figure in neuroscience who has comprehensively examined the neuro-psychology of reward.

The third major source of information on unified reinforcement theory is found in the 1998 book, ‘Affective Neuroscience’, by Jaak Panksepp. Panksepp is also well represented in the web. His comment (from chapter 8 of his book) is instructive as to the untenability of the concept ‘extrinsic reward’. "From the behaviorist perspective, the incentive properties of a reward were traditionally defined in terms of attributes such as the quality, quantity, and delay of reward rather than in terms of any conception of what the nervous system experiences and undergoes when it is confronted by highly desirable objects. In fact, the high incentive state, from the nervous system perspective, may be the arousal of an emotive process that invigorates search and foraging behaviors. In other words, the unconditional incentive state within the brain may largely consist of the arousal of a psycho-behavioral integrative system (e.g., seeking) of the brain. An increased number of studies measuring DA (dopaminergic) cellular activity, as well as dopamine release in the pathways emanating from the VTA (e.g. a midbrain structure-my note), now indicate that this system is highly tuned to stimuli that predict rewards, rather than to rewards themselves."

References:

Ashby, F. G., Isen, Alice M., and Turken U. (1999). A Neuropsychological Theory of Positive Affect and Its Influence on Cognition, Psychological Review, 106, (3), 529-550

Barrett, J. E. and Hoffman, S. M. (1991) Neurochemical changes correlated with behavior maintained under fixed-interval and fixed-ratio schedules of reinforcement. Journal of the Experimental Analysis of Behavior, 56, 395-405

Berns, G. S., McClure, S. M. , Pagnoni, G., Montague, P. R. (2001) Predictability modulates brain response to reward. Journal of Neuroscience, 21(8): 2793-2798

Breiter, H. C., Aharon, I. Kahneman, D., Anders, Dale, and Shizgal, Peter (2001) Functional Imaging of Neural Responses to Expectancy and Experience of Monetary Gains and Losses, Neuron, 30, 619-639

Csikszentmihalyi, Mihaly (1990). Flow, The Psychology of Optimal Experience. New York: Harper Collins

Csikszentmihalyi, Mihaly (1997). Finding Flow. New York: Basic Books

Damasio, Antonio (1994). Descartes’ Error. Emotion, Reason and the Human Brain. New York: Avon Books

Donahoe, J.W. and D. C. Palmer (1993). Learning and Complex Behavior. Needham Heights, Ma.: Allyn and Bacon

Fried, Itzhak, Wilson, C. L, Morrow, J. W., Cameron, K. A., Behnke, E. D., Ackerson, L. C. and Maidment, N. T. (2001) Increased dopamine release in the human amygdala during performance of cognitive tasks, Nature Neuroscience, 4(2): 201-206

Hollerman, Jeffrey R., and Wolfram Schultz (1998) Dopamine neurons report an error in the temporal prediction of reward during learning, Nature Neuroscience, 1(4) :304-309

Knutson, B., Adams, C. N., Fong, G. W., Hommer, D. (2001) Anticipation of monetary reward selectively recruits nucleus accumbens. Journal of Neuroscience, 21, RC159: 1-5

Koepp, M.J., Gunn, R.N., Lawrence, A.D., Cunningham, V.J. Dagher, A. Jones, T., Brooks, D.J. Bench C. J., Grasby, P.M. (1998). Evidence for striatal dopamine release during a video game. Nature, 393: 266-268

Lakoff, George, and Johnson, Mark (1999). Philosophy in the Flesh: The Embodied Mind and Its Challenge to Western Thought, New York: Basic Books

Panksepp. J. (2000) On preventing another century of misunderstanding: toward a psychoetheology of human experience and a psychoneurology of affect. Neuropsychoanalysis, 1(2), 1-21 (on line supplement at neuro.psa.com/pank.htm)

Panksepp, J. (1998). Affective Neuroscience. New York: Oxford University Press