Reductionism and emergence in cognitive neuroscience

Reductionism in Cognitive Neuroscience

Cognitive science is an interdisciplinary field encompassing various aspects of the study of the mind, including perception, reasoning, language, emotion and consciousness. Departing from the strictures of behaviorism, cognitive science permitted experimental psychologists to theorize beyond the limitations of observable behavior and functional relations between stimulus and response, and to posit internal mental representations as legitimate objects for scientific inquiry. With advances in neuroimaging technology, cognitive psychology became increasingly integrated with neuroscience. The analysis of subjective psychological experience in terms of physiological activity in the brain is understood as "reductionist," because it explains a "higher" order psychological phenomena (thinking, remembering, perceiving) in terms of a more basic physiological substrate (neurons firing).

This paper explores reductionistic approaches to cognitive science. Reductionism in cognitive science has both proponents and detractors. On the one end of the spectrum, John Bickle makes a case for "ruthless reductionism" -- the project of fully explaining cognitive phenomena such as thoughts, memory, attention, and even consciousness in terms of molecular biology. On the other end of the spectrum, cognitive scientists such as Anthony Chemero and Charles Heyser contend that an adequate scientific explanation of certain aspects of cognition will never be fully reduced to genetic or neurological processes, and that to try to force an explanation of all mental activity into such a reductionistic account will lead to bad science.

What is reductionism?

In order to understand what cognitive scientists mean by psycho-neural reductionism, imagine a hierarchy of observable phenomena that function at different levels. Subjective thought processes observable through introspection -- such as remembering the past, imagining places or people, or planning for the future -- represent the highest, most complex level of phenomena that cognitive scientists wish to explain. Since cognitive science is naturalistic in its assumptions, subjective states of mind must be somehow dependent on the firing of neurons in the brain. Whereas memories, feelings and symbolic thoughts have traditionally been considered to be "nonphysical" in some sense, the brain as a physical organ of thought is amenable to dissection or clinical observation in action using an fMRI. Accounting for higher level conscious processes in terms of more basic physiological processes of the brain can be considered a reduction of complex psychological phenomena into more fundamental biological substrate.

The brain can in turn be reduced to more basic biological components. The encephalon consists of neural tissue, which is a collection of cells, which in turn consist of proteins, which in turn are produced by the activity of DNA. Following the logic of reducing a complex thing to the interactions of its constituent parts, consciousness may be reduced to the functioning of a brain, the brain to a complex of neurons, the neurons to proteins, the proteins to RNA, the RNA to molecules. A ruthlessly reductive explanation might in principle be able to show a tight connection between thought at the highest level and the activity of DNA molecules at the lowest.

A related concept to reduction is emergence (O'Connor and Wong). If strict reductionism claims that a complex system is nothing but the sum of its parts, emergence claims that at a certain level of complexity, new properties emerge making the whole greater than the mere sum of its parts.

An observed phenomenon is understood as "emergent" if it appears different in kind from anything that can be found or observed when you break the system down to simpler pieces. The concept of non-emergence can be traced back to Ancient Greek philosophy. The Roman Atomist Lucretius attributed the doctrine of homeomeria to the Greek philosopher Anaxagoras (Patzia). In Lucretius'account, Anaxagoras assumed that the infinitesimally small units which constitute an object must have the same properties as the object. So atoms of water must be wet, atoms of iron must be hard, atoms of rose petals must be red, and so on. No matter how small you break down matter into its component pieces, the observable properties of the macro-object continue to be found at the lower levels. This misconception illustrates the fallacy of division, which is the false assumption that an attribute or quality of a whole object must also be an attribute or quality of its constituent parts.

Since we now know that physical qualities such as color or wetness do not describe matter at the molecular level, we can understand emergent properties as qualities that arise from the interactions of a system's component parts. At a certain level of complexity, smaller constituents of a system interact to produce patterns or phenomena that are not an aspect of those components in isolation. The new properties only emerge through interaction at a higher level of organization.

While a reductionistic explanation of a complex phenomenon into more fundamental processes is a goal of science, emergent phenomena at higher levels of organization must also be recognized to exist.

Ruthless reductionism and the Science of Research

John Bickle is a strong advocate for reducing neuroscientific research to the most basic explanatory level -- the actions of single cells, controlled ultimately by genetic switches. Bickle surveys research into the cellular basis of working memory, a feature of conscious experience. The scope of Bickle's reductionism proceeds from mind to molecule.

Bickle is a scientific optimist. He points to recent advances in neuroimaging techniques and successful reductionistic accounts of evolutionary and developmental processes in biology to the activity of DNA molecules. He predicts that cognitive science will enjoy similar success by following similar strategies. The ultimate goal of the reductionist cognitive neuroscience is to explain all behavior, cognition, and even consciousness itself in terms of molecular biology. Bickle calls this "ruthless reductionism."

Bickle co-wrote with Alcino Silva an assessment of the current state of cognitive neuroscience. In their review, Silva and Bickle make suggestions for reforming the field along scientific lines so that more neuroscientists will pursue reductionist research agendas.

Science historian Thomas Kuhn proposed some general principles for how science advances as newer, more general paradigms with greater explanatory power displace older paradigms. Silva and Bickle find Kuhn's analysis too relativistic. They criticize the history and sociology of the science for its lack of scientific methodology. In place of the sociology of science, they propose a new scientific discipline called the "science of research" (SR).

SR entails less speculative philosophy of how science works, and more systematic hypothesis-testing. It is a results-oriented model that is itself scientific. Rather than studying general principles, Silva and Bickle propose conducting empirical investigations of particular research programs to provide practical advice for how to improve outcomes and advance the state of knowledge. For Silva and Bickle, a key goal of science is to explain natural phenomena by establishing networks of causal connections (108).

The Extended Mind Hypothesis

Anthony Chemero and Charles Heyser present a radical critique of psycho-neural reductionism, claiming that some cognitive processes extend beyond the bounds of the body. In light of this, they argue that cognitive and behavioral sciences are not reducible to neuroscience, even in principle (88).

To illustrate their reasoning, Chemero and Heyser critique a type of memory experiment which has been conducted on rodents. The experiments investigate the animals'exploratory behavior when objects are placed in their environment. When a novel object is introduced to the cage, exploration increases. In order to locate the brain regions responsible for the behavior, experimenters would examine how recognition memory is influenced under conditions involving drug and gene manipulation that target certain neural pathways.

Chemero and Heyser showed how these exploratory experiments were fatally flawed, since the experimenters failed to take into account the "affordances" of the objects they supplied for the rodents to explore. Affordances are "features of extended brain-body-environment systems" (Chemero and Heyser 74). Affordances provide "opportunities for action by animals in the environment" (74). For example, one type of textured wooden object with ridges and ledges of the right size might "afford" a climbing behavior, while a slick glass object of the same proportions would not afford this behavior. The relevant affordances in the memory research on rodents were the size and shape and other physical properties of the objects the experimenters introduced into the animals' cages. By varying certain physical properties of the objects to be explored, Chemero and Heyser were able to demonstrate that altering affordances of the objects did in fact influence the animals' exploratory behavior.

Chemero and Heyser argue that the experimenters' failure to attend to the affordances of the objects they used in the exploratory studies resulted from their reductionist assumptions. Since they were exclusively focused on brain physiology, they failed to sufficiently account for how aspects of an animal's external environment might influence its performance in a memory task.

Chemero and Heyser conclude:

"We believe that the conviction that psychological phenomena just are molecular and genetic phenomena, and that studying molecular and genetic phenomena just is doing psychology, leads to this neglect of behaviorally relevant aspects of the environment and thereby to flawed experimental design" (88).

Theoretical Implications of the Extended Mind for Cognitive Science

Chemero and Heyser argue that the subject matter of cognitive science will prove not to be reducible to neurophysiology, let alone molecular biology or genetics. The reason they give for this has to do with the nature of reductionism and the requirements for a comprehensive account of cognitive phenomena.

Extended cognition, Chemero and Heyser's preferred model for explaining some cognitive phenomena, is not reducible to neurophysiology or molecular biology because its subject matter includes information outside the thinking organism. If the subject matter of cognitive science is brain-body-environment systems, as Chemero and Heyser claim, then the most neuroscience can contribute is one important, though not comprehensive, aspect in the study of cognition. Cognitive science, conceived in this way, is not reducible to neuroscience even in principle.

Chemero and Heyser do not deny that some subset of subject matter of interest to cognitive science might be fully accountable in terms of neuroanatomy. They suggest long-term memory consolidation and long-term potentiation as good candidates for the reductive approach (89). Yet there are other cognitive phenomena in which the brain-body-environment approach is required. The question then becomes which approach will be more appropriate for a particular type of cognition, such as perception, social intelligence, developmental stages of childhood, sociolinguistics and motor control. So long as the reductionists limit their examples to certain types of mental phenomena, the approach appears plausible. When you consider other varieties of human cognition, the way forward is less clear.