Abstract: Although there is increasing agreement that the cerebellum plays an important role in motor learning, the basic substance of what constitutes motor learning has been difficult to define. Unless motor learning is somehow radically different from other forms of learning, it must involve relatively simple stimulus-stimulus and stimulus-response associations. All forms of learning, including purely sensory associations and cognitive learning as well as motor learning, effect changes in behavior. However, a singular characteristic of motor learning is that it adjusts joint and limb mechanics by altering the neural input to muscles through practice and mental rehearsal. The hypothesis proposed here is that the cerebellum plays an important role in motor learning by forming and storing associated muscle activation patterns for the time-varying control of limb mechanics. By modulating the cocontraction of agonist-antagonist muscles through adjustments in the timing and amplitude of muscle activity, the viscoelastic properties of joints can be appropriately regulated throughout movement and adapted for transitions between postures and movements. Optimal control of joint viscoelastic properties cannot be achieved by online corrections initiated by reflex feedback because of the delays and consequent instabilities incurred. Instead, strategies for optimizing muscle activation patterns or synergies must be learned from the temporal association of proprioceptive stimuli signaling muscle lengths and forces and the rates of changes in these parameters, with reinforcement occurring when the movement achieves its objective. Such strategies would involve varying degrees of cocontraction or reciprocal inhibition of agonist-antagonist muscles that ultimately contribute to joint and limb stiffness.

In this study I propose an account of the biological and psychological bases of moral agency. I am motivated to do so by a commitment common to many philosophers: the search for what Wilfrid Sellars aptly called the synoptic vision, the attempt to see things as a whole: “The aim of philosophy, abstractly formulated, is to understand how things in the broadest possible sense of the term hang together in the broadest possible sense of the term” (Sellars 1963, p. 1). In order to achieve a synoptic vision of the whole, Sellars aimed to articulate the connections between what he termed the manifest and scientific images of human persons. A guiding principle for my investigation is the new scientific naturalistic turn in philosophy, the attempt to bring to bear the best theories and findings of the sciences in the solution of philosophical problems.

The use of the sciences has immeasurably enhanced philosophical attempts to understand such phenomena as time, space, matter, motion, change, causality, and life. Today, philosophy of mind and epistemology are both feeling the positive effects of inputs from biology and the cognitive sciences. Scientifically informed philosophical investigations have, I contend, advanced the quest for a synoptic vision of things. However, I do not believe that a synoptic vision of human beings can be achieved without a similar endeavor in ethics or moral philosophy.

WHAT DOES AN EVOLUTIONARILY BASED CAPACITY LOOK LIKE?

Granting the scientific plausibility of the claim that evolutionarily based moral capacities exist, what can we learn about them and their acquisition by studying their development? Consider two approaches to understanding the nature of these moral capacities as adaptive proximate mechanisms, one straightforward and the other indirect. On the straightforward approach, the identification of different fitness-enhancing patterns of moral behavior, for instance, patterns of parental care for offspring, kin altruism, and reciprocal or group altruism, leads to an inference to a disposition for such behaviors, namely — to use the preceding examples — dispositions to care for offspring, kin altruism, reciprocal altruism, and group altruism. These four dispositions would constitute the totality of our moral agency or a significant part of it and, as evolutionarily based moral capacities, would be the adaptations for which there has been selection. But, of course, things cannot be that simple; even Wilson and Alexander implicitly recognize that. Any one of these simple dispositions, at least in higher organisms and certainly in humans, either must be associated with other proximate mechanisms that are cognitive and motivational in nature or must themselves be complex dispositions with cognitive and motivational components. A bare dispositional account of the nature of the proximate mechanisms that constitute our evolutionarily based moral capacities, if there are such, is unsatisfactory.

MORAL AGENCY AND THE BEHAVIORIST CONNECTION

B. F. Skinner (1971) tells us that the science of operant behavior is the science of values. Using this simple and elegant proposal, we may have a way to link sociobiologically based theories about values with a theory of learning to form an integrated biologically and psychologically based theory of moral agency. The basic reinforcers on which all operant learning builds can be considered from the sociobiological point of view to be evolutionarily based. On the foundation of these basic reinforcers, we can then learn new and complex behaviors that enable us to achieve our goals in complex and changing environments. Can the behaviorist connection provide the necessary supplement to a sociobiological account of moral agency, making it an adequate account of our moral agency? In this chapter, I lay out the major points of Skinner's behaviorist account of moral agency. My goal is to understand and assess Skinner's claim that the science of operant behavior is the science of values and to determine to what extent our moral agency can be accounted for in terms of evolutionarily and operantly based moral capacities. Before we examine the details of Skinner's account of moral agency, let's sketch out some of the distinctive features of both behaviorism and Skinner's own brand of behaviorism.

The histological simplicity and organization of the cerebellar cortex have fascinated neuroscientists for more than 150 years. These structural features made it possible for early anatomists to establish the basic connectivity among the different cellular elements of the cerebellum; and the same features facilitated the physiological work of J. Eccles, M. Ito, R. Llinas, and others in the 1960s that established the polarity and other aspects of the synaptic connections. The cerebellum thus became the first central nervous system structure in a vertebrate for which a wiring diagram could be drawn showing the morphology of the different elements, their connectivity, and their physiological interactions. This knowledge generated a great deal of excitement in the late 1960s and convinced many neuroscientists that a fundamental understanding of a major central nervous system structure was near at hand. It seemed that only a few years' work would be necessary to establish “what the cerebellum does and how it does it,” in the phrase of the time. The excitement and promise were reflected in the title of the 1967 book by J. Eccles, M. Ito, and J. Szentagothai that summarized the anatomical and physiological findings, The Cerebellum as a Neuronal Machine. The circuitry of the cerebellum and its promise still fascinate many neuroscientists, but a good functional understanding continues to elude us.

Fascination with the cerebellum was heightened by the addition of a second theme to that of circuitry in our conceptual approach to cerebellar function.

FROM EPISTEMOLOGY TO METAPHYSICS

In the previous chapter, I was pursuing epistemological issues, in particular, an integrationist model for the justification of moral beliefs. One of my major claims was that justification should be understood in terms of reliable mechanisms that enable the acquisition of approximately true moral beliefs. We can take it for granted that if we hang around with epistemology for very long, her companion metaphysics will show up. In fact, issues of truth are ones that often bring metaphysics around. So it will behoove us, for a number of reasons, to turn now to the metaphysical issues that have been lurking around our epistemological discussions.

Although none of the classical views on truth we have examined thus far are necessarily antithetical to a realist view, the correspondence view is the one that seems to fit best with a realist position, that is, roughly, the view that true beliefs correspond with a reality that is independent of the ways that we might conceive of it in our thinking or theorizing and independent of the ways in which we might desire or wish it to be. Although one might rightly suppose that integrationists have a certain affinity for both scientific realism and moral realism, it is easy to see that that combination is not the only one available to an integrationist.

In this chapter and the next, I examine the question of whether humans possess an evolutionarily based moral agency. Assuming that humans are moral agents, I seek to establish that there are biologically based reasons for postulating that humans possess evolutionarily based moral tendencies and capacities as part of a base level of moral agency. In these two chapters, I lay out the grounds for the theoretical plausibility of the claim that humans possess such capacities and tendencies. In Chapter 4, I argue for the existence of one such capacity, the capacity for empathetic distress. Even if these arguments are convincing, their limitations should be obvious. One biologically based moral capacity doth not a base level of moral agency make! However, I think that it is plausible that there are other base-level, evolutionarily founded moral capacities; for instance, for parental care. To develop a reasonable case for the existence of some or all of these moral capacities would be a daunting task. My hope is that I will make a reasonably good case for one such capacity and that, in so doing, I will illustrate the plausibility and the potential fruitfulness of my approach and model.

To establish the theoretical plausibility of evolutionarily based moral capacities I discuss evolutionary theory, since it provides the fundamental basis for biological altruism (Section 2.1), and then present some of the results of sociobiology, because it serves as the proximate theoretical source for an account of biological altruism (Section 2.2).

Abstract: This article reviews models of the cerebellum and motor learning, from the landmark papers by Marr and Albus through those of the present time. The unique architecture of the cerebellar cortex is ideally suited for pattern recognition, but how is pattern recognition incorporated into motor control and learning systems? The present analysis begins with a discussion of exactly what the cerebellar cortex needs to regulate through its anatomically defined projections to premotor networks. Next, we examine various models showing how the microcircuitry in the cerebellar cortex could be used to achieve its regulatory functions. Having thus defined what it is that Purkinje cells in the cerebellar cortex must learn, we then evaluate theories of motor learning. We examine current models of synaptic plasticity, credit assignment, and the generation of training information, indicating how they could function cooperatively to guide the processes of motor learning.

Introduction

Lesion studies carried out in the nineteenth century demonstrated that the cerebellum is important for coordinating movements (Florens 1824). Mechanistic models of the cerebellum, however, awaited an analysis of its histology (Braitenberg & Atwood 1958) and combined analyses of its histology and electrophysiology (Albus 1971; Marr 1969). The clear orthogonal relationships between parallel and climbing fibers and the dendritic trees of Purkinje cells (PCs) convinced Braitenberg that the cerebellum functions as a timing organ.

Abstract: The persistence of many contrasting notions of climbing fiber function after years of investigation testifies that the issue of climbing fiber contributions to cerebellar transactions is still unresolved. The proposed capabilities of the climbing fibers cover an impressive spectrum. For many researchers, the climbing fibers signal errors in motor performance, either in the conventional manner of frequency modulation or as a single announcement of an “unexpected event.” More controversial is the effect of these signals on the simple spike modulation of Purkinje cells. In some hands, they lead to a long-term depression of the strength of parallel fiber synapses, while, in other hands, they lead to a short-lasting enhancement of the responsiveness of Purkinje cells to mossy fiber inputs or contribute to the often-seen reciprocal relation between complex and simple spike modulation. For still other investigators, the climbing fibers serve internal timing functions through their capacity for synchronous and rhythmic firing. The above viewpoints are presented in the spirit of trying to reach some consensus about climbing fiber function. Each point of view is introduced by summarizing first the key observations made by the respective proponents; then the issues of short-lasting enhancement, reciprocity between complex and simple spikes, and synchrony and rhythmicity are addressed in the context of the visual climbing fiber system of the vestibulocerebellum.

Keywords: cerebellum; complex spikes; eye movements; flocculus; inferior olive; mossy fibers; movement; nodulus; posture; Purkinje cells; simple spikes; synchrony.

Abstract: Interest in the role of nitric oxide (NO) in the nervous system began with the demonstration that glutamate receptor activation in cerebellar slices causes the formation of a diffusible messenger with properties similar to those of the endothelium-derived relaxing factor. It is now clear that this is due to the Ca2+/calmodulin-dependent activation of the enzyme NO synthase, which forms NO and citrulline from the amino acid L-arginine. The cerebellum has very high levels of NO synthase, and although it has low levels of guanylyl cyclase, cerebellar cyclic guanosine monophosphate (cGMP) levels are an order of magnitude higher than in other brain regions. A transcellular metabolic pathway is also present in the cerebellar cortex to recycle citrulline back to arginine. The NO formed binds to and activates soluble guanylyl cyclase to elevate cGMP levels in target cells. Studies employing NADPH-diaphorase, a selective histochemical marker for NO synthase, together with immunohistochemistry, in situ hybridization and biochemical studies have indicated that NO production occurs in granule and basket cells in the cerebellar cortex, whereas cGMP formation appears to occur largely in other cells, including Purkinje cells. Given that a long-term depression of AMPA currents can be seen in isolated Purkinje cells, this anatomical localization suggests that NO cannot play an essential role in the induction of this form of synaptic plasticity.

FROM ACQUISITION, ACTION, AND RELEVANCE TO ADEQUACY

I have claimed that a satisfactory account of moral agency must answer questions concerning (1) how moral agency is acquired, (2) how it is put into action, (3) whether the sort of agency that is appealed to is morally relevant, both substantively and functionally, and, finally, (4) whether and how that agency is morally adequate or justified. As an integrationist, I am attempting to develop scientifically based answers to these questions, answers that are both well supported scientifically and account for the phenomenon of moral agency. In particular, I have used the findings of biology and psychology to elaborate an account of how we acquire moral agency and put it to work that adequately describes the phenomenon of moral agency and explains both its acquisition and its execution. Even if I have succeeded in this task, a large and very important question remains about whether and how such scientific findings and theories, that is, scientific facts (indeed, any sort of facts), can help us answer questions about whether our moral beliefs, motivations, and actions are morally justified or justifiable. It is this question that I now undertake to answer. I begin in Section 8.2 by laying out in more detail what is usually thought to be involved in the justification of moral agency.

In Part IV, I presented an integrationist scientific naturalistic account of moral agency. In doing so, I provided support for the critical connection hypothesis and the metaethical connection hypothesis. In the preceding parts, I attempted to make the case for the explanatory connection hypothesis. At this point, then, I contend that a plausible case has been made for three of the four hypotheses that I set out to establish. I now turn to establishing the remaining integrationist hypothesis: the meaningfulness hypothesis.

Questions of meaningfulness are intimately connected with how one views one's life and the living of one's life. The particular challenge that this question poses for an integrationist is to show how a scientific naturalistic account of moral agency can make any meaningful connections with the life of ordinary moral agents. In Section 10.1, I begin to answer that question by making use of the notions of the scientific and manifest image of humans developed by Wilfrid Sellars (1963) and argue, as did Sellars, for a synoptic vision of the two in terms of the notion of the human person. This will return us in Section 10.2 to the reductionist predicament discussed in Chapter 7. Although I offer a tentative resolution of that predicament making use of a synoptic vision of human moral agents as persons, my resolution by no means settles all the issues that the predicament raises; nevertheless, it lends further confirmation to the integrationist's critical connection hypothesis and provides the entry way into an examination of the meaningfulness hypothesis and the integrationist's case for it in Section 10.3.