Towards a scientific concept of free will as a biological trait: spontaneous actions and decision-making in invertebrates

Active causation and the origin of meaning

Purpose and meaning are necessary concepts for understanding mind and culture, but appear to be absent from the physical world and are not part of the explanatory framework of the natural sciences. Understanding how meaning (in the broad sense of the term) could arise from a physical world has proven to be a tough problem. The basic scheme of Darwinian evolution produces adaptations that only represent apparent ("as if") goals and meaning. Here I use evolutionary models to show that a slight, evolvable extension of the basic scheme is sufficient to produce genuine goals. The extension, targeted modulation of mutation rate, is known to be generally present in biological cells and gives rise to two phenomena that are absent from the non-living world: intrinsic meaning and the ability to initiate goal-directed chains of causation (active causation). The extended scheme accomplishes this by utilizing randomness modulated by a feedback loop that is itself regulated by evolutionary pressure. The mechanism can be extended to behavioural variability as well and thus shows how freedom of behaviour is possible. A further extension to communication suggests that the active exchange of intrinsic meaning between organisms may be the origin of consciousness, which in combination with active causation can provide a physical basis for the phenomenon of free will.

Universality in ant behaviour

Prediction for social systems is a major challenge. Universality at the social level has inspired a unified theory for urban living but individual variation makes predicting relationships within societies difficult. Here, we show that in ant societies individual average speed is higher when event duration is longer. Expressed as a single scaling function, this relationship is universal because for any event duration an ant, on average, moves at the corresponding average speed except for a short acceleration and deceleration at the beginning and end. This establishes cause and effect within a social system and may inform engineering and control of artificial ones.

A Chance for Attributable Agency

Can we sensibly attribute some of the happenings in our world to the agency of some of the things around us? We do this all the time, but there are conceptual challenges purporting to show that attributable agency, and specifically one of its most important subspecies, human free agency, is incoherent. We address these challenges in a novel way: rather than merely rebutting specific arguments, we discuss a concrete model that we claim positively illustrates attributable agency in an indeterministic setting. The model, recently introduced by one of the authors in the context of artificial intelligence, shows that an agent with a sufficiently complex memory organization can employ indeterministic happenings in a meaningful way. We claim that these considerations successfully counter arguments against the coherence of libertarian (indeterminism-based) free will.

Memory beyond expression

The idea that memories are not invariable after the consolidation process has led to new perspectives about several mnemonic processes. In this framework, we review our studies on the modulation of memory expression during reconsolidation. We propose that during both memory consolidation and reconsolidation, neuromodulators can determine the probability of the memory trace to guide behavior, i.e. they can either increase or decrease its behavioral expressibility without affecting the potential of persistent memories to be activated and become labile. Our hypothesis is based on the findings that positive modulation of memory expression during reconsolidation occurs even if memories are behaviorally unexpressed. This review discusses the original approach taken in the studies of the crab Neohelice (Chasmagnathus) granulata, which was then successfully applied to test the hypothesis in rodent fear memory. Data presented offers a new way of thinking about both weak trainings and experimental amnesia: memory retrieval can be dissociated from memory expression. Furthermore, the strategy presented here allowed us to show in human declarative memory that the periods in which long-term memory can be activated and become labile during reconsolidation exceeds the periods in which that memory is expressed, providing direct evidence that conscious access to memory is not needed for reconsolidation. Specific controls based on the constraints of reminders to trigger reconsolidation allow us to distinguish between obliterated and unexpressed but activated long-term memories after amnesic treatments, weak trainings and forgetting. In the hypothesis discussed, memory expressibility--the outcome of experience-dependent changes in the potential to behave--is considered as a flexible and modulable attribute of long-term memories. Expression seems to be just one of the possible fates of re-activated memories.

Excitation and inhibition in recurrent networks mediate collision avoidance in Xenopus tadpoles

Information processing in the vertebrate brain is thought to be mediated through distributed neural networks, but it is still unclear how sensory stimuli are encoded and detected by these networks, and what role synaptic inhibition plays in this process. Here we used a collision avoidance behavior in Xenopus tadpoles as a model for stimulus discrimination and recognition. We showed that the visual system of the tadpole is selective for behaviorally relevant looming stimuli, and that the detection of these stimuli first occurs in the optic tectum. By comparing visually guided behavior, optic nerve recordings, excitatory and inhibitory synaptic currents, and the spike output of tectal neurons, we showed that collision detection in the tadpole relies on the emergent properties of distributed recurrent networks within the tectum. We found that synaptic inhibition was temporally correlated with excitation, and did not actively sculpt stimulus selectivity, but rather it regulated the amount of integration between direct inputs from the retina and recurrent inputs from the tectum. Both pharmacological suppression and enhancement of synaptic inhibition disrupted emergent selectivity for looming stimuli. Taken together these findings suggested that, by regulating the amount of network activity, inhibition plays a critical role in maintaining selective sensitivity to behaviorally-relevant visual stimuli.

Intermittent control models of human standing: similarities and differences

Two architectures of intermittent control are compared and contrasted in the context of the single inverted pendulum model often used for describing standing in humans. The architectures are similar insofar as they use periods of open-loop control punctuated by switching events when crossing a switching surface to keep the system state trajectories close to trajectories leading to equilibrium. The architectures differ in two significant ways. Firstly, in one case, the open-loop control trajectory is generated by a system-matched hold, and in the other case, the open-loop control signal is zero. Secondly, prediction is used in one case but not the other. The former difference is examined in this paper. The zero control alternative leads to periodic oscillations associated with limit cycles; whereas the system-matched control alternative gives trajectories (including homoclinic orbits) which contain the equilibrium point and do not have oscillatory behaviour. Despite this difference in behaviour, it is further shown that behaviour can appear similar when either the system is perturbed by additive noise or the system-matched trajectory generation is perturbed. The purpose of the research is to come to a common approach for understanding the theoretical properties of the two alternatives with the twin aims of choosing which provides the best explanation of current experimental data (which may not, by itself, distinguish between the two alternatives) and suggesting future experiments to distinguish between the two alternatives.

Mechanistic analysis of the search behaviour of Caenorhabditis elegans

A central question in movement research is how animals use information and movement to promote encounter success. Current random search theory identifies reorientation patterns as key to the compromise between optimizing encounters for both nearby and faraway targets, but how the balance between intrinsic motor programmes and previous environmental experience determines the occurrence of these reorientation behaviours remains unknown. We used high-resolution tracking and imaging data to describe the complete motor behaviour of Caenorhabditis elegans when placed in a novel environment (one in which food is absent). Movement in C. elegans is structured around different reorientation behaviours, and we measured how these contributed to changing search strategies as worms became familiar with their new environment. This behavioural transition shows that different reorientation behaviours are governed by two processes: (i) an environmentally informed 'extrinsic' strategy that is influenced by recent experience and that controls for area-restricted search behaviour, and (ii) a time-independent, 'intrinsic' strategy that reduces spatial oversampling and improves random encounter success. Our results show how movement strategies arise from a balance between intrinsic and extrinsic mechanisms, that search behaviour in C. elegans is initially determined by expectations developed from previous environmental experiences, and which reorientation behaviours are modified as information is acquired from new environments.

Predictability as a personality trait: consistent differences in intraindividual behavioral variation

Although animal behavior is generally repeatable, most behavioral variation apparently occurs within rather than across individuals. With the exception of very recent interest in individual behavioral plasticity (consistent differences in responsiveness), this within-individual variation has been largely ignored despite its importance in the study of proximate and ultimate questions about behavior. Here, we repeatedly scored the undisturbed activity of 30 adult male mosquitofish across multiple observation bouts spanning 132 days ([Formula: see text] observations per fish). We found that the behavior of some individuals was consistently more predictable in a given context than others. Repeatability for this "intraindividual variation" (IIV; [Formula: see text]) was evident after accounting for individual differences in activity trends across days, and activity responses due to fine-scale temperature variation (i.e., individual plasticity in response to both variables). To our knowledge, this is the first evidence that predictability of behavior is a repeatable characteristic of individual animals. We suggest that IIV represents an important axis of consistent behavioral variation that has previously not been formally considered. Finally, individual differences in predictability may similarly exist for labile morphological and physiological traits but have seemingly not been studied.

Genotypic differences in behavioural entropy: unpredictable genotypes are composed of unpredictable individuals

Intra-genotypic variability (IGV) occurs when individuals with the same genotype, raised in the same environment and then tested under the same conditions, express different trait values. Game theoretical and bet-hedging models have suggested two ways that a single genotype might generate variable behaviour when behavioural variation is discrete rather than continuous: behavioural polyphenism (a genotype produces different types of individuals, each of which consistently expresses a different type of behaviour) or stochastic variability (a genotype produces one type of individual who randomly expresses different types of behaviour over time). We first demonstrated significant differences across 14 natural genotypes of male Drosophila melanogaster in the variability (as measured by entropy) of their microhabitat choice, in an experiment in which each fly was allowed free access to four different types of habitat. We then tested four hypotheses about ways that within-individual variability might contribute to differences across genotypes in the variability of microhabitat choice. There was no empirical support for three hypotheses (behavioural polymorphism, consistent choice, or time-based choice), nor could our results be attributed to genotypic differences in activity levels. The stochastic variability hypothesis accurately predicted the slope and the intercept of the relationship across genotypes between entropy at the individual level and entropy at the genotype level. However, our initial version of the stochastic model slightly but significantly overestimated the values of individual entropy for each genotype, pointing to specific assumptions of this model that might need to be adjusted in future studies of the IGV of microhabitat choice. This is among a handful of recent studies to document genotypic differences in behavioural IGV, and the first to explore ways that genotypic differences in within-individual variability might contribute to differences among genotypes in the predictability of their behaviour.

Plastic proteans: reduced predictability in the face of predation risk in hermit crabs

Variation in behaviour occurs at multiple levels, including between individuals (personality) and between situations (plasticity). Behaviour also varies within individuals, and intra-individual variation (IIV) in behaviour describes within-individual residual variance in behaviour that remains after the effects of obvious external and internal influences on behaviour have been accounted for. IIV thus describes how predictable an individual's behaviour is. Differences in predictability, between individuals and between situations, might be biologically significant. For example, behaving unpredictably under predation threat might reduce the chance of capture. Here, we investigated the duration of startle responses in hermit crabs, in the presence and absence of a predator cue. Individuals differed in startle response duration (personality) and while individuals also varied in their sensitivity to risk, mean response time was greater in the presence of a predator (plasticity). Moreover, IIV was greater in the presence of a predator, providing some of the first evidence that the facultative injection of unpredictability into behaviour might represent a strategy for dealing with risk.

Information driven self-organization of complex robotic behaviors

Information theory is a powerful tool to express principles to drive autonomous systems because it is domain invariant and allows for an intuitive interpretation. This paper studies the use of the predictive information (PI), also called excess entropy or effective measure complexity, of the sensorimotor process as a driving force to generate behavior. We study nonlinear and nonstationary systems and introduce the time-local predicting information (TiPI) which allows us to derive exact results together with explicit update rules for the parameters of the controller in the dynamical systems framework. In this way the information principle, formulated at the level of behavior, is translated to the dynamics of the synapses. We underpin our results with a number of case studies with high-dimensional robotic systems. We show the spontaneous cooperativity in a complex physical system with decentralized control. Moreover, a jointly controlled humanoid robot develops a high behavioral variety depending on its physics and the environment it is dynamically embedded into. The behavior can be decomposed into a succession of low-dimensional modes that increasingly explore the behavior space. This is a promising way to avoid the curse of dimensionality which hinders learning systems to scale well.

Predictable or not? Individuals' risk decisions do not necessarily predict their next ones

This research examines the extent to which people may be free to make choices by testing their consistency in choosing risk options. In two experiments, participants were instructed to make the "same" type of risk decisions repeatedly. Experiment 1 showed that when the information for decision is positively framed in terms of gain, the participant's choice in a particular decision could not be predicted by his or her choice in another decision (R(2)s<.02). Experiment 2 showed a statistically significant predictability when the information is negatively framed in terms of loss, although the predictability was still very low (R(2)s<.07). These findings indicate the existence of a large room of variations in which a person may freely choose.

The psychology of volition

Volition can be studied from two perspectives. From the third-person view, volitional behaviour is internally generated, rather than being determined by the immediate environmental context, and is therefore, to some extent, unpredictable. Such behaviour is not unique to humans, since it is seen in many other species including invertebrates. From the first-person view, our experience of volitional behaviour includes a vivid sense of agency. We feel that, through our intentions, we can cause things to happen and we can choose between different actions. Our experience of agency is not direct. It depends on sub-personal inferences derived from prior expectations and sensations associated with movement. As a result, our experiences and intuitions about volition can be unreliable and uncertain. Nevertheless, our experience of agency is not a mere epiphenomenon. Anticipation of the regret we might feel after making the wrong choice can alter behaviour. Furthermore, the strong sense of responsibility, associated with agency, has a critical role in creating social cohesion and group benefits. We can only study the experience of agency in humans who can describe their experiences. The discussion of the experience of volition, that introspection and communication make possible, can change our experience of volitional actions. As a result, agency, regret and responsibility are cultural phenomena that are unique to humans.

Impact and sources of neuronal variability in the fly's motion vision pathway

Nervous systems encode information about dynamically changing sensory input by changes in neuronal activity. Neuronal activity changes, however, also arise from noise sources within and outside the nervous system or from changes of the animal's behavioral state. The resulting variability of neuronal responses in representing sensory stimuli limits the reliability with which animals can respond to stimuli and may thus even affect the chances for survival in certain situations. Relevant sources of noise arising at different stages along the motion vision pathway have been investigated from the sensory input to the initiation of behavioral reactions. Here, we concentrate on the reliability of processing visual motion information in flies. Flies rely on visual motion information to guide their locomotion. They are among the best established model systems for the processing of visual motion information allowing us to bridge the gap between behavioral performance and underlying neuronal computations. It has been possible to directly assess the consequences of noise at major stages of the fly's visual motion processing system on the reliability of neuronal signals. Responses of motion sensitive neurons and their variability have been related to optomotor movements as indicators for the overall performance of visual motion computation. We address whether and how noise already inherent in the stimulus, e.g. photon noise for the visual system, influences later processing stages and to what extent variability at the output level of the sensory system limits behavioral performance. Recent advances in circuit analysis and the progress in monitoring neuronal activity in behaving animals should now be applied to understand how the animal meets the requirements of fast and reliable manoeuvres in naturalistic situations.

Does the brain “initiate” freely willed processes? A philosophy of science critique of Libet-type experiments and their interpretation

In the extensive, recent debates on free will, the pioneering experiments by Benjamin Libet continue to play a significant role. It is often claimed that these experiments demonstrate the illusory nature of freely willed actions. In this article, we provide a detailed analysis and evaluation of Libet’s experiments from a philosophy of science perspective. Our analysis focuses on Libet’s central notion of the “initiation” of freely willed processes by the brain. We examine four interpretations of the notion of initiation: in terms of a cause, a necessary condition, a correlation, and a regular succession. We argue that none of these four interpretations can be supported by the design and results of Libet’s experiments. In addition, we analyze two recent Libet-type experiments. Our general conclusion is that neither Libet’s original experiments nor later Libet-type experiments can justify the claim that allegedly freely willed processes are in fact initiated by the brain.

Functional organization and adaptability of a decision-making network in aplysia

Whereas major insights into the neuronal basis of adaptive behavior have been gained from the study of automatic behaviors, including reflexive and rhythmic motor acts, the neural substrates for goal-directed behaviors in which decision-making about action selection and initiation are crucial, remain poorly understood. However, the mollusk Aplysia is proving to be increasingly relevant to redressing this issue. The functional properties of the central circuits that govern this animal’s goal-directed feeding behavior and particularly the neural processes underlying the selection and initiation of specific feeding actions are becoming understood. In addition to relying on the intrinsic operation of central networks, goal-directed behaviors depend on external sensory inputs that through associative learning are able to shape decision-making strategies. Here, we will review recent findings on the functional design of the central network that generates Aplysia’s feeding-related movements and the sensory-derived plasticity that through learning can modify the selection and initiation of appropriate action. The animal’s feeding behavior and the implications of decision-making will be briefly described. The functional design of the underlying buccal network will then be used to illustrate how cellular diversity and the coordination of neuronal burst activity provide substrates for decision-making. The contribution of specific synaptic and neuronal membrane properties within the buccal circuit will also be discussed in terms of their role in motor pattern selection and initiation. The ability of learning to “rigidify” these synaptic and cellular properties so as to regularize network operation and lead to the expression of stereotyped rhythmic behavior will then be described. Finally, these aspects will be drawn into a conceptual framework of how Aplysia’s goal-directed circuitry compares to the central pattern generating networks for invertebrate rhythmic behaviors.

Visually guided decision making in foraging honeybees

Honeybees can easily be trained to perform different types of discrimination tasks under controlled laboratory conditions. This review describes a range of experiments carried out with free-flying forager honeybees under such conditions. The research done over the past 30 or so years suggests that cognitive abilities (learning and perception) in insects are more intricate and flexible than was originally imagined. It has become apparent that honeybees are capable of a variety of visually guided tasks, involving decision making under challenging situations: this includes simultaneously making use of different sensory modalities, such as vision and olfaction, and learning to use abstract concepts such as “sameness” and “difference.” Many studies have shown that decision making in foraging honeybees is highly flexible. The trained animals learn how to solve a task, and do so with a high accuracy, but when they are presented with a new variation of the task, they apply the learnt rules from the earlier setup to the new situation, and solve the new task as well. Honeybees therefore not only feature a rich behavioral repertoire to choose from, but also make decisions most apt to the current situation. The experiments in this review give an insight into the environmental cues and cognitive resources that are probably highly significant for a forager bee that must continually make decisions regarding patches of resources to be exploited.

Reducing self-control by weakening belief in free will

Believing in free will may arise from a biological need for control. People induced to disbelieve in free will show impulsive and antisocial tendencies, suggesting a reduction of the willingness to exert self-control. We investigated whether undermining free will affects two aspects of self-control: intentional inhibition and perceived self-control. We exposed participants either to anti-free will or to neutral messages. The two groups (no-free will and control) then performed a task that required self-control to inhibit a prepotent response. No-free will participants showed less intentional inhibitions than controls, suggesting a reduction of self-control. We assessed perceived self-control by asking participants whether the response resulted from a deliberate intention or from an impulsive reaction. Perceived self-control was lower in the no-free will group than in control group. Our findings show that undermining free will can degrade self-control and provide insights into how disbelieving in free will leads to antisocial tendencies.

Normativity, agency, and life

There is an immense philosophical literature dealing with the notions of normativity and agency, as well as a sizeable and rapidly growing scientific literature on the topic of autonomous agents. However, there has been very little cross-fertilization between these two literatures. As a result, the philosophical literature tends to assume a somewhat outdated mechanistic image of living things, resulting in a quasi-dualistic picture in which only human beings, or the higher animals, can be normative agents properly speaking. From this perspective, the project of 'naturalizing normativity' becomes almost a contradiction in terms. At the same time, the scientific literature tends to misuse 'normativity,' 'agency,' and related terms, assuming that it is meaningful to ascribe these concepts to 'autonomous agents' conceived of as physical systems whose behavior is to be explained in terms of ordinary physical law. From this perspective, the true depth of the difficulty involved in understanding what makes living systems distinctive qua physical systems becomes occluded. In this essay, I begin the attempt to remedy this situation. After some preliminary discussion of terminology and situating of my project within the contemporary philosophical landscape, I make a distinction between two different aspects of the project of naturalizing normativity: (1) the 'Scope Problem,' which consists in saying how widely in nature our concept of normative agency may properly be applied; and (2) the 'Ground Problem,' which consists in rationalizing the phenomenon of normative agency in terms of the rest of our knowledge of nature. Then, in the remainder of this paper, I argue that the Scope Problem ought to be resolved in favor of attributing normative agency, in the proper sense of those words, to living things as such. The Ground Problem will be discussed in a companion paper at a later time.

Attentional switching in humans and flies: rivalry in large and miniature brains

Human perception, and consequently behavior, is driven by attention dynamics. In the special case of rivalry, where attention alternates between competing percepts, such dynamics can be measured and their determinants investigated. A recent study in the fruit fly, Drosophila melanogaster, now shows that the origins of attentional rivalry may be quite ancient. Furthermore, individual variation exists in the rate of attentional rivalry in both humans and flies, and in humans this is under substantial genetic influence. In the pathophysiological realm, slowing of rivalry rate is associated with the heritable psychiatric condition, bipolar disorder. Fly rivalry may therefore prove a powerful model to examine genetic and molecular influences on rivalry rate, and may even shed light on human cognitive and behavioral dysfunction.

Top-down contingent feature-specific orienting with and without awareness of the visual input

In the present article, the role of endogenous feature-specific orienting for conscious and unconscious vision is reviewed. We start with an overview of orienting. We proceed with a review of masking research, and the definition of the criteria of experimental protocols that demonstrate endogenous and exogenous orienting, respectively. Against this background of criteria, we assess studies of unconscious orienting and come to the conclusion that so far studies of unconscious orienting demonstrated endogenous feature-specific orienting. The review closes with a discussion of the role of unconscious orienting in action control.

Information processing in miniature brains

Since a comprehensive understanding of brain function and evolution in vertebrates is often hobbled by the sheer size of the nervous system, as well as ethical concerns, major research efforts have been made to understand the neural circuitry underpinning behaviour and cognition in invertebrates, and its costs and benefits under natural conditions. This special feature of Proceedings of the Royal Society B contains an idiosyncratic range of current research perspectives on neural underpinnings and adaptive benefits (and costs) of such diverse phenomena as spatial memory, colour vision, attention, spontaneous behaviour initiation, memory dynamics, relational rule learning and sleep, in a range of animals from marine invertebrates with exquisitely simple nervous systems to social insects forming societies with many thousands of individuals working together as a 'superorganism'. This introduction provides context and history to tie the various approaches together, and concludes that there is an urgent need to understand the full neuron-to-neuron circuitry underlying various forms of information processing-not just to explore brain function comprehensively, but also to understand how (and how easily) cognitive capacities might evolve in the face of pertinent selection pressures. In the invertebrates, reaching these goals is becoming increasingly realistic.