Discriminability of intracranial stimuli: the role of anatomical connectedness

Selected Principles of Pankseppian Affective Neuroscience

In the early nineties of the twentieth century Jaak Panksepp coined the term "Affective Neuroscience" (AN) today being accepted as a unique research area in cross-species brain science. By means of (i) electrical stimulation, (ii) pharmacological challenges, and (iii) brain lesions of vertebrate brains (mostly mammalian), Panksepp carved out seven primary emotional systems called SEEKING, CARE, PLAY, and LUST on the positive side, whereas FEAR, SADNESS, and ANGER belong to the negative affects. Abundant research into human clinical applications has supported the hypothesis that imbalances in these ancient primary emotional systems are strongly linked to psychiatric disorders such as depression. The present paper gives a concise overview of Panksepp's main ideas. It gives an historical overview of the development of Panksepp's AN thinking. It touches not only areas of neuroscience, but also shows how AN has been applied to other research fields such as personality psychology. Finally, the present work gives a brief overview of the main ideas of AN.

Neurologizing the Psychology of Affects: How Appraisal-Based Constructivism and Basic Emotion Theory Can Coexist

Abundant neurobehavioral data, not discussed by Lisa Feldman Barrett (2006) , support the existence of a variety of core emotional operating systems in ancient subneocortical regions of the brain ( Panksepp, 1998a , 2005a ). Such brain systems are the primary-process ancestral birthrights of all mammals. There may be as many genetically and neurochemically coded subcortical affect systems in emotionally rich medial regions of the brain as there are “natural” emotional action systems in the brain. When emotional primes are aroused directly, as with local electrical or chemical stimulation, the affective changes sustain conditioned place preferences and place aversions, which are the premier secondary-process indices of affective states in animals. Humans are not immune to such brain manipulations; they typically exhibit strong emotional feelings. Human emotion researchers should not ignore these systems and simply look at the complex and highly variable culturally molded manifestations of emotions in humans if they wish to determine what kinds of “natural” emotional processes exist within all mammalian brain. Basic emotion science has generated workable epistemological strategies for under-standing the primal sources of human emotional feelings by detailed study of emotional circuits in our fellow animals.

Cross-Species Neuroaffective Parsing of Primal Emotional Desires and Aversions in Mammals

The primal motivational systems of all mammals are constituted of the evolved affective brain networks that gauge key survival issues. However, since progress in functional neuroscience has historically lagged behind conceptual developments in psychological science, motivational processes have traditionally been anchored to behavioral rather than neural and affective issues. Attempts to retrofit neuroaffective issues onto established psychological-conceptual structures are problematic, especially when fundamental evidence for primal affective circuits, and their neural nature, comes largely from animal research. This article provides a synopsis of our growing understanding of primary-process emotional systems of mammalian brains and minds, which provides a new empirically based infrastructure for higher levels of human theorizing.

What is Basic about Basic Emotions? Lasting Lessons from Affective Neuroscience

A cross-species affective neuroscience strategy for understanding the primary-process (basic) emotions is defended. The need for analyzing the brain and mind in terms of evolutionary stratification of functions into at least primary (instinctual), secondary (learned), and tertiary (thought-related) processes is advanced. When viewed in this context, the contentious battles between basic-emotion theorists and dimensional-constructivist approaches can be seen to be largely nonsubstantial differences among investigators working at different levels of analysis.

Cross-species affective neuroscience decoding of the primal affective experiences of humans and related animals

BACKGROUND

The issue of whether other animals have internally felt experiences has vexed animal behavioral science since its inception. Although most investigators remain agnostic on such contentious issues, there is now abundant experimental evidence indicating that all mammals have negatively and positively-valenced emotional networks concentrated in homologous brain regions that mediate affective experiences when animals are emotionally aroused. That is what the neuroscientific evidence indicates.

PRINCIPAL FINDINGS

The relevant lines of evidence are as follows: 1) It is easy to elicit powerful unconditioned emotional responses using localized electrical stimulation of the brain (ESB); these effects are concentrated in ancient subcortical brain regions. Seven types of emotional arousals have been described; using a special capitalized nomenclature for such primary process emotional systems, they are SEEKING, RAGE, FEAR, LUST, CARE, PANIC/GRIEF and PLAY. 2) These brain circuits are situated in homologous subcortical brain regions in all vertebrates tested. Thus, if one activates FEAR arousal circuits in rats, cats or primates, all exhibit similar fear responses. 3) All primary-process emotional-instinctual urges, even ones as complex as social PLAY, remain intact after radical neo-decortication early in life; thus, the neocortex is not essential for the generation of primary-process emotionality. 4) Using diverse measures, one can demonstrate that animals like and dislike ESB of brain regions that evoke unconditioned instinctual emotional behaviors: Such ESBs can serve as 'rewards' and 'punishments' in diverse approach and escape/avoidance learning tasks. 5) Comparable ESB of human brains yield comparable affective experiences. Thus, robust evidence indicates that raw primary-process (i.e., instinctual, unconditioned) emotional behaviors and feelings emanate from homologous brain functions in all mammals (see Appendix S1), which are regulated by higher brain regions. Such findings suggest nested-hierarchies of BrainMind affective processing, with primal emotional functions being foundational for secondary-process learning and memory mechanisms, which interface with tertiary-process cognitive-thoughtful functions of the BrainMind.

Affective consciousness: Core emotional feelings in animals and humans

The position advanced in this paper is that the bedrock of emotional feelings is contained within the evolved emotional action apparatus of mammalian brains. This dual-aspect monism approach to brain-mind functions, which asserts that emotional feelings may reflect the neurodynamics of brain systems that generate instinctual emotional behaviors, saves us from various conceptual conundrums. In coarse form, primary process affective consciousness seems to be fundamentally an unconditional "gift of nature" rather than an acquired skill, even though those systems facilitate skill acquisition via various felt reinforcements. Affective consciousness, being a comparatively intrinsic function of the brain, shared homologously by all mammalian species, should be the easiest variant of consciousness to study in animals. This is not to deny that some secondary processes (e.g., awareness of feelings in the generation of behavioral choices) cannot be evaluated in animals with sufficiently clever behavioral learning procedures, as with place-preference procedures and the analysis of changes in learned behaviors after one has induced re-valuation of incentives. Rather, the claim is that a direct neuroscientific study of primary process emotional/affective states is best achieved through the study of the intrinsic ("instinctual"), albeit experientially refined, emotional action tendencies of other animals. In this view, core emotional feelings may reflect the neurodynamic attractor landscapes of a variety of extended trans-diencephalic, limbic emotional action systems-including SEEKING, FEAR, RAGE, LUST, CARE, PANIC, and PLAY. Through a study of these brain systems, the neural infrastructure of human and animal affective consciousness may be revealed. Emotional feelings are instantiated in large-scale neurodynamics that can be most effectively monitored via the ethological analysis of emotional action tendencies and the accompanying brain neurochemical/electrical changes. The intrinsic coherence of such emotional responses is demonstrated by the fact that they can be provoked by electrical and chemical stimulation of specific brain zones-effects that are affectively laden. For substantive progress in this emerging research arena, animal brain researchers need to discuss affective brain functions more openly. Secondary awareness processes, because of their more conditional, contextually situated nature, are more difficult to understand in any neuroscientific detail. In other words, the information-processing brain functions, critical for cognitive consciousness, are harder to study in other animals than the more homologous emotional/motivational affective state functions of the brain.

On the ability of rats to discriminate between microstimulations of the olfactory bulb in different locations

An investigation was made into the ability of rats to discriminate between electrical stimulations applied to the mitral cell layer of the olfactory bulb in different locations. Water-deprived rats implanted with permanent electrodes were trained to use single- or multi-site microstimulations as discriminative stimuli for selecting a palatable solution without tasting it in a two-choice test. Spontaneous reactions of the animals to stimulation with sinusoidal currents higher than 3 microA per electrode resembled sensory arousal. All rats were found to discriminate between the effects of concurrent microstimulations applied to bulbar sites separated by 500 micron. Changing the current intensity in the range 4-20 microA had no detectable effect on the discrimination. Discrimination was still possible, with a few exceptions, when electrodes were separated by 250 micron and even when they were closely adjacent. Spatial resolution of discrimination seemed not to vary in different regions along the rostrocaudal axis of the bulb. The discrimination of patterns of simultaneous stimulation at several sites was also investigated. Different multi-site patterns were easily distinguished, even when their respective components were closely adjacent or when some components occupied the same area. The findings are discussed with reference to the concept of spatial coding of odours in the olfactory bulb.

Discriminating between reward and performance: a critical review of intracranial self-stimulation methodology

Despite numerous pharmacological investigations of intracranial self-stimulation (ICSS), the substrates of this behavior have yet to be completely understood. In view of the likelihood that inadequate methodology has hindered the quest for these substrates, the present review was undertaken. Criteria for ICSS methodology should include not only the ability to discriminate reward from gross performance deficit, but also adequate capacity (ability to generate experimental data at a reasonable rate). For numerous reasons, bar-pressing on a continuous reinforcement schedule fails the first criterion despite its ease and rapidity. The use of partial reinforcement schedules may alleviate some of these shortcomings. Analysis of drug-induced response decrement patterns can discriminate gross motoric incapacity from other variables, although the question of subtle response maintenance deficits remains to be answered. Measurements of response rates using alternative operants do not differentiate reward and performance adequately. More promising, "rate-free" measures using locomotion as an operant include the two-platform method of Valenstein and the "locus of rise" method. Comparison of drug effects on ICSS with those on alternate tasks are fraught with pitfalls including the problems of assuring equivalent rates and patterns of responding. The use of differential electrode placements is ideally suited for neurochemically well-characterized drugs, particularly if "double dissociations" can be established during studies of multiple placements. Presentation of different current intensities or frequencies permits the compilation of rate-intensity functions, and drug-induced shifts in these functions have considerable analytical power. Self-regulation of current intensity constitutes a powerful tool that has yet to realize its full potential in the pharmacological study of ICSS. Extensive studies involving self-regulation of stimulation duration ("shuttlebox" studies) suggest that this method may be highly versatile despite several practical difficulties. It is concluded that at least six of these methods appear to do a reasonable job of excluding gross performance deficit. However, the possible influences of other factors, such as subtle response maintenance deficit, incentive or arousal, remain to be resolved in view of the multifactorial nature of ICSS. Multiple tests for ICSS drug or lesion studies are advocated whenever feasible, as no single test appears capable of resolving all theoretical complexities.

Parametric effects in the discrimination of intracranial stimulation: some methodological and analytical issues

Rats were implanted with electrodes in the medial forebrain bundle at the level of the lateral hypothalamus. Electrical stimulation was established as a conditioned stimulus for responding in a modified two-way active shock avoidance procedure. Stimulus generalization experiments were conducted to determine the effects of pulse frequency, current intensity, pulse duration, and of train duration. It was found that the discriminative stimulus properties of the electrical stimulation co-varied in an orderly manner with variations in each of the parameters. The generalization data sets of frequency, intensity, and train duration could be fitted by linear functions in log-linear coordinates; the effects of pulse duration generated a biphasic gradient. An analysis in terms of charge revealed that train duration had the lowest slope, whereas frequency and intensity generated equally steep functions. The most striking differences occurred among conditions which were similar in terms of current intensity, pulse duration and number of pulses, but which differed in the temporal patterning of pulses. Some methodological and analytical aspects of discrimination and generalization with intracranial stimulation are discussed.

Perceptual cues of reinforcing brain stimulations in the postero-lateral area of the hypothalamus

In order to study the perception of intracranial reward in the rat, a rewarding hypothalamic brain stimulation served as conditioned stimulus (CS) in an avoidance paradigm. The rate of self-stimulations behavior was used to estimate the strength of intracranial reward and reinforcement. Tests of stimulus generalization were performed by modifying the electrical parameters of the CS so as to form a set of substitute stimuli (SS). Results show that the discrimination gradient depends mainly on the rewarding value of the intracranial stimulation. A Stevensian power function relates the percentage of avoidance responses to the intensity of the self-stimulation behavior, which in turn was estimated by such methods as continuous reinforcement frequency, fixed ratio schedules, weight, choice, self-regulation and cost methods. Moreover, the latency of the avoidance responses is related directly to the magnitude of the self-stimulation elicited by the same brain stimulations. On grounds of this data, we assume that the internal decisional process could discriminate well between the different brain stimuli on the basis of the rewarding value produced. Differences observed between methods evaluating the magnitude of reinforcement induced by the rewarding electrical brain stimuli are thus mainly due to differences in motor performances required by each method to obtain the electrical reward.

Conditioned aversion to brain-stimulation reward: effects of electrode placement and prior experience

A conditioned aversion to rewarding amygdaloid brain-stimulation was established by injecting rats with toxic doses of 0.15 M LiCl immediately after an initial self-stimulation session. The aversion had extinguished by the third self-stimulation session, 96 h after conditioning. This effect cannot be attributed to general depressant effects of LiCl on self-stimulation as treatment with LiCl 24 h before the second self-stimulation session was ineffective. Furthermore, this conditioned aversion was locus specific as LiCl injections immediately after the first test session had no disruptive effects on self-stimulation in the substantia nigra. The parallels between conditioned aversion to rewarding brain-stimulation in the amygdala and late aversion were strengthened by the fact that the novelty of brain-stimulation reward was an important factor in the conditioning effect. These data have important implications for understanding the sensory properties of brain-stimulation reward.