Cognition and Emotion: Perspectives of a Closing Gap
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Cogn Comput (2010) 2:78–85 DOI 10.1007/s12559-010-9034-7 Cognition and Emotion: Perspectives of a Closing Gap Claudius Gros Published online: 16 March 2010 Ó Springer Science+Business Media, LLC 2010 Abstract The primary tasks of a cognitive system are to life has fascinated philosophers from the beginning of times survive and to maximize a life-long utility function, like the and is subject to libraries of literature. Quite often it is number of offsprings. A direct computational maximization assumed in this context that the emotional groundings of of life-long utility is however not possible in complex human behavior are somehow a leftover heritage from our environments, especially in the context, of real-world time more ‘animal-like’ predecessors and that ‘rational behavior’ constraints. The central role of emotions is to serve as an is more appropriate for humans and ‘superior’ to affective intermediate layer in the space of policies available to conducts. agents and animals, leading to a large dimensional reduc- This popular appraisal of emotions is however utterly tion of complexity. We review our current understanding of wrong, since emotional control has functional purposes the functional role of emotions, stressing the role of the which are indispensable for full fledged cognitive systems neuromodulators mediating emotions for the diffusive and which cannot be substituted by cognitive information homeostatic control system of the brain. We discuss a recent processing. We review here our current understanding of the proposal, that emotional diffusive control is characterized, human emotional control system, from the functional point in contrast to neutral diffusive control, by interaction of view, including considerations from dynamical systems effects, viz by interferences between emotional arousal and theory. The emphasis will be on general properties, being of reward signaling. Several proposals for the realization of possible relevance not only for the understanding of the brain synthetic emotions are discussed in this context, together but also for eventual human-level artificial intelligences. with key open issues regarding the interplay between The emotional control system is, from the evolutionary emotional motivational drives and diffusive control. perspective, a specialization of homeostatic control. Myriads of auto-regulative processes are maintaining our Keywords Diffusive emotional control Á bodily functions at every moment, and we are conscious of Synthetic emotions Á Cognitive system theory Á only a small subset having an emotional context. The Motivational problem question then arises which traits are characteristic for automatic and which for emotional homeostatic processes. In this context, we discuss a recent proposal suggesting that Introduction emotional processes have a genetically determined pre- ferred level of activation and are characterized by inter- The apparent dichotomy between the progression of human action effects within the homeostatic control system, cognitive achievements during the last millenia and the whereas neural control processes are void of any geneti- pervasiveness of affective behavioral patterns in everyday cally preferred levels of activation. Functional Emotions C. Gros (&) Institute of Theoretical Physics, J.W. Goethe University Frankfurt, 60054 Frankfurt/Main, Germany We are around nowadays only because our ancestors e-mail: [email protected] managed to survive and to produce offsprings, the basic 123 Cogn Comput (2010) 2:78–85 79 prerequisites for evolutionary fitness. Daily survival can be interactions but clearly do not correspond to true ‘synthetic regarded as a homeostatic process for keeping the basic emotions’, which need to be related to behavioral control bodily parameters, via interaction with the environment, in [16–18], the focus of the present review. their proper range. Being a product of evolutionary selec- tion processes, the emotional constituents of our self must Homeostasis and Diffusive Control necessarily contribute to survivability [1].1 One can therefore classify the overall functionality of our emotional An essential aspect of the living condition is homeostasis, control system as homeostatic [2, 3].2 the active regulation of biological relevant parameters, like The perspective of this short review is the functional the blood-sugar level or the heart beating frequency. role of emotions. Instead of the plain expression ‘‘emo- Homeostatic regulation is also necessary for the internal tions’’ we will be using mainly the terminology ‘‘emotional parameters of individual neurons, like membrane conduc- control system’’, which reflects more precisely the func- tivities or firing thresholds, as well as for networks of tional role of emotions as part of the homeostatic control neurons [19]. The availability of the neurotransmitter glu- system of the brain. Emotions are part of the web of tamate and GABA, to give an example, has to be regulated physical and biochemical processes occurring which, as a through a homeostatic cycle involving the astrocytes [20]. whole is denoted ‘‘cognitive system’’ [4]. The cognitive Complex dynamical systems, like the neural net in the system has the task to keep its support unit (the body) alive, brain, need to retain their overall dynamical properties in a as well as its wetware (the brain). A cognitive system is suitable range, they need to adjust their working point [4]. what has been called ‘organismic’ in the framework of The occurrence of epileptic seizures is an example of what enactive artificial intelligences [5, 6]. The term cognitive can happen when homeostasis breaks down. In addition to system places then emphasis on the dynamical system the homeostatic regulation, necessary to retain operation- perspective; the physical brain tissue is not identical with ability, neural circuits in the brain also need to allow for human consciousness and affection, but the collection of transient modulatory adaption [21]. This second type of interacting neural, physical and chemical dynamical pro- regulation allows the neural circuits to work in several cesses occurring at every moment of time. different regimes, increasing e.g. the relative importance of afferent input [21] or the relative importance of inter-neural Natural and Synthetic Emotions competition [22]. Homeostasis is fundamentally diffusive in nature. The An extensive literature is devoted to the question of the need to regulate the concentration of a given ion or of a introperspective content of emotions as they are experi- certain neurotransmitter is normally performed non-locally. enced, see [7]. The spectrum of emotional experiences is We are interested here, with regard to the functional role of vast, ranging from plain fear conditioning [8] and romantic emotional control, in the diffusive control of the properties love [9], to the complexity of social interactions [10, 11]. of neural circuits by neuromodulators like dopamine or Emotional expressions play a paramount role in social serotonin. interactions [12] and are studied increasingly in the context of human–robot interactions [13]. These important issues are not the subject of this review, they are however closely Neurobiology of Emotional and Diffusive Control related to the core questions regarding the defining func- tional characteristics of emotional processes. We will now discuss a few selected aspects of the neuro- It is clearly possible to build humanoid robots showing biology of emotions relevant for understanding the func- facial expressions, which an anthropomizing observer tionality of emotional control. Our aim is however not to would interpret as emotional [14, 15]. Emotional expres- provide an extensive review of the neurobiological foun- sions by socializing robots may be helpful for human–robot dations of emotions, for comprehensive reviews on the subject see [8, 23, 24]. 1 Subject to evolutionary pressure are all traits which influence The neurobiological foundations of emotions are Darwinian fitness. An emotional arousal typically leads to behavioral neuromodulators like dopamine, serotonin and the ophids consequences and behavior is a primary toehold for evolutionary selection. This evolutionary perspective sometimes contrasts with our [25]. These neuromodulators are emitted by specialized daily experiences, as certain human emotions are routinely viewed to neurons originating in quite localized subcortical struc- be more a handicap, instead of being beneficial, when living in tures, like the raphe nucleus and the substantia nigra, modern societies. ascending to cortical areas, in particular to the prefrontal 2 One may actually wonder, against the background of the fact that cortex, as well as to sub-cortical areas like the amygdala our emotional suit contributes in important ways to our Darwinian fitness, why then are emotions portrayed often as irrational and and the hippocampus, to mention a few exemplary target counterproductive in everyday life. areas. Emotional experiences, involving complex recurrent 123 80 Cogn Comput (2010) 2:78–85 interactions with cognitive processing [26, 27], are not output identical with neuromodulator concentrations, but there is probably no fragile or robust emotional experience without the concurrent release of some combination of neural network neuromodulators. A neuromodulator, like dopamine, is released synapti- modulatory cally. A dopaminergic neuron fires, like any other neuron, and the depolarization pulse travelling along its axon cognitive