Mainstream Neuroscience Research Articles

Thinking about the action potential: the nerve signal as a window to the physical principles guiding neuronal excitability.

Ever since the work of Edgar Adrian, the neuronal action potential has been considered as an electric signal, modeled and interpreted using concepts and theories lent from electronic engineering. Accordingly, the electric action potential, as the prime manifestation of neuronal excitability, serving processing and reliable "long distance" communication of the information contained in the signal, was defined as a non-linear, self-propagating, regenerative, wave of electrical activity that travels along the surface of nerve cells. Thus, in the ground-breaking theory and mathematical model of Hodgkin and Huxley (HH), linking Nernst's treatment of the electrochemistry of semi-permeable membranes to the physical laws of electricity and Kelvin's cable theory, the electrical characteristics of the action potential are presented as the result of the depolarization-induced, voltage- and time-dependent opening and closure of ion channels in the membrane allowing the passive flow of charge, particularly in the form of Na+ and K+ -ions, into and out of the neuronal cytoplasm along the respective electrochemical ion gradient. In the model, which treats the membrane as a capacitor and ion channels as resistors, these changes in ionic conductance across the membrane cause a sudden and transient alteration of the transmembrane potential, i.e., the action potential, which is then carried forward and spreads over long(er) distances by means of both active and passive conduction dependent on local current flow by diffusion of Na+ ion in the neuronal cytoplasm. However, although highly successful in predicting and explaining many of the electric characteristics of the action potential, the HH model, nevertheless cannot accommodate the various non-electrical physical manifestations (mechanical, thermal and optical changes) that accompany action potential propagation, and for which there is ample experimental evidence. As such, the electrical conception of neuronal excitability appears to be incomplete and alternatives, aiming to improve, extend or even replace it, have been sought for. Commonly misunderstood as to their basic premises and the physical principles they are built on, and mistakenly perceived as a threat to the generally acknowledged explanatory power of the "classical" HH framework, these attempts to present a more complete picture of neuronal physiology, have met with fierce opposition from mainstream neuroscience and, as a consequence, currently remain underdeveloped and insufficiently tested. Here we present our perspective that this may be an unfortunate state of affairs as these different biophysics-informed approaches to incorporate also non-electrical signs of the action potential into the modeling and explanation of the nerve signal, in our view, are well suited to foster a new, more complete and better integrated understanding of the (multi)physical nature of neuronal excitability and signal transport and, hence, of neuronal function. In doing so, we will emphasize attempts to derive the different physical manifestations of the action potential from one common, macroscopic thermodynamics-based, framework treating the multiphysics of the nerve signal as the inevitable result of the collective material, i.e., physico-chemical, properties of the lipid bilayer neuronal membrane (in particular, the axolemma) and/or the so-called ectoplasm or membrane skeleton consisting of cytoskeletal protein polymers, in particular, actin fibrils. Potential consequences for our view of action potential physiology and role in neuronal function are identified and discussed.

Possible Role of Parvalbumin Interneurons in Meditation and Psychiatric Illness.

Parvalbumin (PV) interneurons are present in multiple brain regions and produce complex influences on brain functioning. An increasing number of research findings indicate that the function of these interneurons is more complex than solely to inhibit pyramidal neurons in the cortex. They generate feedback and feedforward inhibition of cortical neurons, and they are critically involved in the generation of neuronal network oscillation. These oscillations, generated by various brain regions, are linked to perceptions, thought processes, and cognitive functions, all of which, in turn, influence human emotions and behavior. Both animal and human studies consistently have found that meditation practice results in enhancement in the effects of alpha-, theta-, and gamma-frequency oscillations, which may correspond to positive changes in cognition, emotion, conscious awareness, and, subsequently, behavior. Although the study of meditation has moved into mainstream neuroscience research, the link between PV interneurons and any role they might play in meditative states remains elusive. This article is focused primarily on gamma-frequency oscillation, which is generated by PV interneurons, to develop insight and perspective into the role of PV interneurons in meditation. This article also points to new and emerging directions that address whether this role of PV interneurons in meditation extends to a beneficial, and potentially therapeutic, role in the treatment of common psychiatric disorders, including schizophrenia.

The thermodynamic theory of action potential propagation: a sound basis for unification of the physics of nerve impulses.

The thermodynamic theory of action potential propagation challenges the conventional understanding of the nerve signal as an exclusively electrical phenomenon. Often misunderstood as to its basic tenets and predictions, the thermodynamic theory is virtually ignored in mainstream neuroscience. Addressing a broad audience of neuroscientists, we here attempt to stimulate interest in the theory. We do this by providing a concise overview of its background, discussion of its intimate connection to Albert Einstein's treatment of the thermodynamics of interfaces and outlining its potential contribution to the building of a physical brain theory firmly grounded in first principles and the biophysical reality of individual nerve cells. As such, the paper does not attempt to advocate the superiority of the thermodynamic theory over any other approach to model the nerve impulse, but is meant as an open invitation totheneuroscience community to experimentally test the assumptions and predictions of the theory on their validity.

Consciousness Regained: Disentangling Mechanisms, Brain Systems, and Behavioral Responses.

How consciousness (experience) arises from and relates to material brain processes (the "mind-body problem") has been pondered by thinkers for centuries, and is regarded as among the deepest unsolved problems in science, with wide-ranging theoretical, clinical, and ethical implications. Until the last few decades, this was largely seen as a philosophical topic, but not widely accepted in mainstream neuroscience. Since the 1980s, however, novel methods and theoretical advances have yielded remarkable results, opening up the field for scientific and clinical progress. Since a seminal paper by Crick and Koch (1998) claimed that a science of consciousness should first search for its neural correlates (NCC), a variety of correlates have been suggested, including both content-specific NCCs, determining particular phenomenal components within an experience, and the full NCC, the neural substrates supporting entire conscious experiences. In this review, we present recent progress on theoretical, experimental, and clinical issues. Specifically, we (1) review methodological advances that are important for dissociating conscious experience from related enabling and executive functions, (2) suggest how critically reconsidering the role of the frontal cortex may further delineate NCCs, (3) advocate the need for general, objective, brain-based measures of the capacity for consciousness that are independent of sensory processing and executive functions, and (4) show how animal studies can reveal population and network phenomena of relevance for understanding mechanisms of consciousness.

An issue whose time has come.

“Be careful, it's the third rail.” I received this strong advice to steer clear of studying sex differences from a senior colleague around the year 2000 when my research into brain mechanisms of emotional memory began drawing me into the issue of sex differences—or better yet, sex influences—on brain function. And in a way, he was right. For the vast majority of his long and distinguished neuroscience career, exploring sex influences was indeed a terrific way for a brain scientist not studying reproductive functions to lose credibility at best, and at worst, become a pariah in the eyes of the neuroscience mainstream. Why was studying sex differences so taboo? I believe there are several key reasons (for more detail, see Cahill, 2006; Cahill, 2014). First, most neuroscientists knew that sex influences on the brain exclusively concerned sex behaviors (e.g., mating), sex hormones, and a few small brain nuclei mostly in the hypothalamus. Second, most neuroscientists knew that, to the extent sex influences seemed to exist elsewhere, they were not fundamental; rather, they were of secondary importance-—something to be understood after determining the fundamental facts. Third, most neuroscientists knew that sex influences were do to undulating sex hormones, a pesky sort of feature essentially of the female, an unnecessary source of additional variability and one wisest to avoid in the search for the fundamental. This view in turn justified in brain science the still overriding reliance on the male as equal proxy for the female. Finally…politics. Due to a deeply ingrained, implicit (but false) assumption that “equal” means “the same,” most neuroscientists knew, and even feared that establishing that males and females are not the same in some aspect of brain function meant establishing that they were not equal. This assumption is false and deeply harmful, in particular to the health of women (see Cahill, 2014), but remains deeply impactful nonetheless. As a result of these powerful but misguided driving forces, today, sex influences of all types-and-sizes run unexamined and uncontrolled in neuroscience. Peruse the table of contents of any neuroscience journal and you will find that for easily over 95 percent of the studies one can (and in truth, should) ask “in males, or females, or both?” The answer is almost universally unknown, and worse, almost universally assumed not to matter. Fortunately, times are changing. The past 15 to 20 years in particular witnessed an explosion of research (despite the prevailing biases against the topic) documenting sex influences at all levels of brain function. So overpowering is the wave of research that the standard ways of dismissing sex influences (e.g., “They are all small and unreliable,” “They are all due to circulating hormones,” “They are all due to human culture,” and “They don't exist on the molecular level”) have all been swept away, at least for those cognizant of the research. This themed issue of the Journal of Neuroscience Research (JNR) heralds a zeitgeist shift. It is the first ever from a mainstream neuroscience journal entirely devoted to the issue of sex influences on brain/nervous system functioning. Papers from about 70 groups of authors, from those who have been investigating the issue for decades to those uncovering them only recently, forcefully document the fact that sex influences on brain function are ubiquitous, regularly reshaping findings—hence conclusions—at all levels of our field, and powerfully demonstrating how much “sex matters.” The fact that these ubiquitous sex influences are often unanticipated, or that we often cannot say conclusively what they “mean,” only heightens their evident importance, at least for those who believe that women should be treated equally with men by the biomedical research establishment. Consequently the papers in this issue force the conclusion that the status quo in neuroscience (whereby potential sex influences may be safely ignored or dismissed) is no longer scientifically defensible. And in fact, with this issue, JNR is indeed changing the neuroscience status quo. Coinciding with this issue (which will be permanently open access), JNR is announcing editorial policy changes whereby all new submissions to the journal must carefully attend to potential sex influences (see Editorial Comment by Prager, 2017). These new policies dovetail nicely with the new NIH requirements regarding the consideration of sex as a biological variable (see Clayton and Collins, 2014). The French novelist Victor Hugo said, ‘‘there is one thing more powerful than all the armies in the world, and that is an idea whose time has come.’’ The notion that sex matters fundamentally, powerfully, and pervasively for all of neuroscience (not just for reproduction) is an idea whose time indeed has come.

Negotiating neuroscience: LeDoux’s “dramatic ensemble”

Some argue we now live in a “brain society” in which our subjectivity is increasingly mediated through neurological discourses. Unless we are to surrender neuroscience to neoliberal colonisation, we need to articulate effective forms of engagement with this discipline. One route is to read mainstream neuroscience texts for resistances they offer to the homo economicus. Instead of a terrain that inevitably leads to neoliberal conclusions, we find a materiality in excess of dubious ideological circumscriptions. In this article we engage with Joseph LeDoux’s notion of the self as a “dramatic ensemble,” where the self is a vulnerable, constantly reiterated achievement marked by the partial and passing play of dominances. Simultaneously, however, LeDoux undermines this account by evoking a traditional notion of the self. This play of tensions is articulated and an argument is made to privilege a subjectivity which both resists LeDoux’s flight from his own implications and neoliberal assumptions of subjectivity.

Neuronal Modulation in the Prefrontal Cortex in a Transitive Inference Task: Evidence of Neuronal Correlates of Mental Schema Management.

In cognitive neuroscience, it is unknown how information that leads to inferential deductions are encoded and manipulated at the neuronal level. We addressed this question by recording single-unit activity from the dorsolateral prefrontal cortex of monkeys that were performing a transitive inference (TI) task. The TI required one to choose the higher ranked of two items, based on previous, indirect experience. Our results demonstrated that single-neuron activity supports the construction of an abstract, mental schema of ordered items in solving the task and that this representation is independent of the reward value that is experienced for the single items. These findings identify the neural substrates of abstract mental representations that support inferential thinking.

The neurobiology of MMN and implications for schizophrenia

Although the scientific community appears to know a lot about MMN, about its neural generators and the computational processes that underlie its generation, do we have sufficient knowledge to understand what causes the reduction of MMN amplitude in schizophrenia? Here we attempt to integrate the evidence presented in this series of papers for the special issue on MMN in schizophrenia together with evidence from other new relevant research and ask—what have we learnt? While MMN research was the purview for decades of psychophysiologists interested in event-related potentials derived from scalp recorded EEG, it is now part of mainstream neuroscience research attracting the interest of basic auditory neuroscientists, neurobiologists and computational modellers. The confluence of these developments together with increasing clinical research has certainly advanced our understanding of the causes of reduced MMN in schizophrenia as this integrative review attempts to demonstrate—but much remains to be learnt. Future advances will rely on the application of multiple methodologies and approaches in order to arrive at better understanding of the neurobiology of MMN and implications for schizophrenia.

Interaction between Neurogenesis and Hippocampal Memory System: New Vistas.

During the last decade, the questions on the functionality of adult neurogenesis have changed their emphasis from if to how the adult-born neurons participate in a variety of memory processes. The emerging answers are complex because we are overwhelmed by a variety of behavioral tasks that apparently require new neurons to be performed optimally. With few exceptions, the hippocampal memory system seems to use the newly generated neurons for multiple roles. Adult neurogenesis has given the dentate gyrus new capabilities not previously thought possible within the scope of traditional synaptic plasticity. Looking at these new developments from the perspective of past discoveries, the science of adult neurogenesis has emerged from its initial phase of being, first, a surprising oddity and, later, exciting possibility, to the present state of being an integral part of mainstream neuroscience. The answers to many remaining questions regarding adult neurogenesis will come along only with our growing understanding of the functionality of the brain as a whole. This, in turn, will require integration of multiple levels of organization from molecules and cells to circuits and systems, ultimately resulting in comprehension of behavioral outcomes.

Conferences and Conclusions at the Year's Close

As we head towards the end of the year, it is a good time to reflect back on the most important stories and developments of the last twelve months, particularly in the light of the recent conference held by the Society for Neuroscience, which clearly demonstrated some of the ways in which the field is changing and growing. At the same time, our thoughts may also turn towards the year ahead and the new questions and breakthroughs that it may bring. The Year in Review Quantum neuroscience has generated some intriguing results in 2013, and it has also expanded into the public consciousness, with stories on quantum effects in nature being publicized by a number of newspapers. NeuroQuantology has itself published some interesting work over the course of the year, including the special supplement on Everett's Quantum Mechanics, and articles on neurophilosophy, consciousness and the quantum model of reality. The range of topics covered in NeuroQuantology has been vast, and with such diverse work going on, it is hardly surprising that quantum biology is becoming a term that a growing number of people are learning to recognize. Neuroscience - 2013 The year 2013 has produced some interesting and important advances in the fields of neuroscience and quantum biology, many of which fell under discussion during the Neuroscience 2013 conference, which was held between November 9 and 13 in San Diego, California. The conference, which was organized by the Society for Neuroscience, attracted more than 30,000 attendees from across the globe, making it one of the largest neuroscience meetings in the world. Among the research stories from the conference that made the biggest impact, particularly in the mainstream media, was the work conducted on the neuroscience of drug addiction. Findings presented at the conference included work into the use of magnetic stimulation to enable people to quit smoking, and stimulation of the subthalamic nucleus of rats to reduce their appetite for heroin. Other researchers had focused on the motivation of addicts and the long-term effects of vicodin use and other addictive substances. Drug abuse was described as causing improper regulation of the stress response in the brain, potentially increasing the desire to continue taking drugs, while individuals who had experienced damage to the insula were found to be less prone to gambling addiction. Other highlights of the conference included a lecture on the relationship between neuroscience and society, given by the president of Pixar, Ed Catmull, and the Symposium on Creativity, in which artists and scientists came together to discuss how neuroscience can help us to understand the creative process. The conference also gave attendees the chance to look forward and consider how the field of neuroscience is changing, with presentations on the new brain initiatives being created in both the United States and Europe, and a special series of lectures on the idea of creating a map of the entire network of cells making up the brain. Quantum Biology at Neuroscience - 2013 The broad focus of the conference enabled presenters to cover a wide range of topics in neuroscience, and although the majority of the work was dedicated to more traditional views of neuroscience, there were some presentations that explored quantum effects in the brain and in experimental methods, as well as other emerging approaches to neuroscience. The use of quantum dots was discussed by several research teams, indicating that this type of technology is becoming more widespread within neuroscience, although the study of quantum effects in the brain was not common among the studies presented at the meeting. As quantum neuroscience continues to produce the types of results that have been reported in Neuroquantology and elsewhere during the last year, we may hope to see more presentations on quantum effects in the brain being made at these mainstream neuroscience events, rather than being restricted to the more specialized meetings targeted at quantum biologists. Neuroscience - 2014 Looking back over the last year, it is clear that some important advances have been made in neuroscience and quantum biology, many of which were presented at the Society of Neuroscience's conference, but there are still many more questions left unanswered for us to puzzle over in 2014 and beyond. The increasing familiarity of neuroscientists with quantum ideas, particularly in the form of the use of quantum dots and similar technologies, may help to increase interest in the field over the next year, and quantum biology could well be better represented at next year's Society of Neuroscience meeting, which will be held between November 15 and 19 in Washington DC.

As experiências de quase morte (EQM) podem contribuir para o debate sobre a consciência?

The NDE is an altered state of consciousness which in the West has stereotyped content and emotional experience. Some features of the experience are trans-cultural and suggest either a similar brain mechanism or access to a transcendent reality. Individual features of the experience point more persuasively to transcendence than to simple limited brain mechanisms. Moreover there are, so far, no reductionist explanations which can account satisfactorily for some of its features; the meeting of dead relatives, the apparent sightedness in the blind during an NDE, the apparent acquisition after an NDE of psychic and spiritual gifts, accounts of healing occurring during an NDE, and of veridical experience during the resuscitation after a cardiac arrest. Although non-local mind would explain many of the NDE features, non locality is not yet accepted by mainstream neuroscience. Only those theories based on a wider understanding of mind could fully explain the subjective experience of the NDEr.

Multiple Functions of Endocannabinoid Signaling in the Brain

Despite being regarded as a hippie science for decades, cannabinoid research has finally found its well-deserved position in mainstream neuroscience. A series of groundbreaking discoveries revealed that endocannabinoid molecules are as widespread and important as conventional neurotransmitters such as glutamate or GABA, yet they act in profoundly unconventional ways. We aim to illustrate how uncovering the molecular, anatomical, and physiological characteristics of endocannabinoid signaling has revealed new mechanistic insights into several fundamental phenomena in synaptic physiology. First, we summarize unexpected advances in the molecular complexity of biogenesis and inactivation of the two endocannabinoids, anandamide and 2-arachidonoylglycerol. Then, we show how these new metabolic routes are integrated into well-known intracellular signaling pathways. These endocannabinoid-producing signalosomes operate in phasic and tonic modes, thereby differentially governing homeostatic, short-term, and long-term synaptic plasticity throughout the brain. Finally, we discuss how cell type- and synapse-specific refinement of endocannabinoid signaling may explain the characteristic behavioral effects of cannabinoids.

Seeing Minds in Behavior: Descriptive Mentalism

One of the core debates in the history of psychology is about the relationship between mind and behavior, or at least between particular mental phenomenon and associated behavioral phenomenon. Descriptive mentalism is the belief that this relationship is primarily descriptive; mental terms describe something about the behavior of the organism in question. This approach offers the potential to clarify many persistent problems in psychological theory and empirical investigation. The logic of descriptive mentalism is here displayed, starting with E. B. Holt's elaboration of William James's work, and continuing through to the comparatively recent contributions of Nicholas S. Thompson. Understanding descriptive mentalism offers a key to reintegrating insights from behaviorist psychology with mainstream psychology and neuroscience.

The Need for the Emergence of Mathematical Neuroscience: Beyond Computation and Simulation

The Need for the Emergence of Mathematical Neuroscience: Beyond Computation and Simulation

A self-referencing glutamate biosensor for measuring real time neuronal glutamate flux

Quantification of neurotransmitter transport dynamics is hindered by a lack of sufficient tools to directly monitor bioactive flux under physiological conditions. Traditional techniques for studying neurotransmitter release/uptake require inferences from non-selective electrical recordings, are invasive/destructive, and/or suffer from poor temporal resolution. Recent advances in electrochemical biosensors have enhanced in vitro and in vivo detection of neurotransmitter concentration under physiological/pathophysiological conditions. The use of enzymatic biosensors with performance enhancing materials (e.g., carbon nanotubes) has been a major focus for many of these advances. However, these techniques are not used as mainstream neuroscience research tools, due to relatively low sensitivity, excessive drift/noise, low signal-to-noise ratio, and inability to quantify rapid neurochemical kinetics during synaptic transmission. A sensing technique known as self-referencing overcomes many of these problems, and allows non-invasive quantification of biophysical transport. This work presents a self-referencing CNT modified glutamate oxidase biosensor for monitoring glutamate flux near neural/neuronal cells. Concentration of basal glutamate was similar to other in vivo and in vitro measurements. The biosensor was used in self-referencing (oscillating) mode to measure net glutamate flux near neural cells during electrical stimulation. Prior to stimulation, the average influx was 33.9±6.4fmolcm−2s−1). Glutamate efflux took place immediately following stimulation, and was always followed by uptake in the 50–150fmolcm−2s−1 range. Uptake was inhibited using threo-β-benzyloxyaspartate, and average surface flux in replicate cells (1.1±7.4fmolcm−2s−1) was significantly lower than uninhibited cells. The technique is extremely valuable for studying neuropathological conditions related to neurotransmission under dynamic physiological conditions.

Reviewing Multi-Disciplinary Papers: a Challenge in Neuroscience?

Neuroscience sees itself as multidisciplinary field and, indeed, it was probably among the first biological disciplines which benefited by an influx of trained scientists from other domains like physics and engineering (De Schutter 2008). But while neuroscience made good use of the additional expertise to advance technologies to study the brain, it stayed firmly with its biologically roots as far as its appreciation for theory goes. More than two decades after the declaration of computational neuroscience as a subfield (Sejnowski et al. 1988) we must conclude that its impact on mainstream neuroscience remains limited and, in particular, most neuroscientists deny theory a strong role in their scientific approaches. This may seem a rather negative view at a time when experimentalists attend a growing number of computational neuroscience summer courses and when a small modeling section is often included in regular papers. We have indeed progressed compared to the early nineties when one wondered whether experimentalists and modelers could just get along (Bower and Koch, 1992). But after a grace period, when it was fairly easy to publish purely theoretical studies in mainstream neuroscience journals (e.g. Szilagyi and De Schutter 2004; Maex and De Schutter 1998, 2003), the balance may have shifted. In fact, all the journals referred to have recently rejected several manuscripts of which I was a co-author because, summarizing, this was purely theoretical work and needed experimental verification. Conversely, studies where I collaborated with experimentalists to produce combined modeling and experimental studies were recently accepted in even higher ranked journals (Santamaria et al. 2006; Steuber et al. 2007). While I laud the combined modeling-experiment study, as it has promoted a strong interest among experimentalists in applying modeling techniques, I worry that in the last few years this has led to a shift in the perception of what is the proper ‘place’ of modeling. It may have devalued pure theoretical work, shifting it to specialized journals as it is perceived as of ‘no interest’ to mainstream neuroscientists. It was never the intention of computational and theoretical neuroscience to become just a tool in the toolbox of experimentalists. Moreover, the combined approach seems to have generated a new class of experimentalists who call themselves modeling specialists, sometimes with little or no expertise to validate this claim. In fact, though second guessing who your reviewers are can be a dangerous game, I am convinced that, in the cases referred to earlier, pure modeling papers were reviewed exclusively by experimentalists despite the assurance of one of the editors that both reviewers “have done much modeling in their time”. We typically get two kinds of negative comments indicating the mindset of these reviewers. The first is the Neuroinform DOI 10.1007/s12021-008-9034-x

The molecules of social recognition memory: Implications for social cognition, extended mind, and neuroethics

Social cognition, cognitive neuroscience, and neuroethics have reached a synthesis of late, but some troubling features are present. The neuroscience that currently dominates the study of social cognition is exclusively cognitive neuroscience, as contrasted with the cellular and increasingly molecular emphasis that has gripped mainstream neuroscience over the past three decades. Furthermore, the recent field of molecular and cellular cognition has begun to unravel some molecular mechanisms involved in social cognition, especially pertaining to the consolidation of memories of particular conspecific organisms. Some new experimental techniques for positive interventions into these hypothesized mechanisms offer opportunities for establishing direct causal linkages between intra-neuronal molecular events and the behaviors used to measure social cognitive phenomena. Predicted results from an experiment described below also cast doubt on the application of the “extended mind” approach from recent cognitive science to ground the neuroscience of social cognition. Since neuroethics relies heavily on our best neuroscience of social cognition, that field may soon need to extend its attention beyond cognitive neuroscience, and into neuroscience’s cellular and molecular mainstream.

On the nature of neural information: A critique of the received view 50 years later

We offer a critical review of the concept of neural information, as received within mainstream neuroscience from Artificial Intelligence. This conception of information is constructed as a conditional probability of a stimulus given a certain neural activation, a correlation that cannot be accessed by the organism and fails to explain its causal organization. We reconstruct an alternative conception of neural information: a pattern of signals that is selected by the organism (as an autonomous system) to contribute to its self-maintenance in virtue of its correlation with external conditions, a correlation that might further be evaluated by the very system.

Understanding Neural Complexity: A Role For Reduction

Psychoneural reduction is under attack again, only this time from a former ally: cognitive neuroscience. It has become popular to think of the brain as a complex system whose theoretically important properties emerge from dynamic, non-linear interactions between its component parts. ``Emergence'' is supposed to replace reduction: the latter is thought to be incapable of explaining the brain qua complex system. Rather than engage this issue at the level of theories of reduction versus theories of emergence, I here emphasize a role that reductionism plays – and will continue to play – even if neuroscience adopts this ``complex systems'' view. In detailed investigations into the function of complex neural circuits, certain questions can only be addressed by moving down levels and scales. This role for reduction also finds a place for approaches that dominate mainstream neuroscience, like the widespread use of experimental techniques and theories from molecular biology and biochemistry. These are difficult to reconcile with the anti-reductionist sentiments of the ``complex systems'' branch of cognitive neuroscience.