In the mammalian central nervous system (CNS), each neuron receives signals from other neurons through numerous synapses located on its cell body and dendrites. Molecules involved in the postsynaptic signaling pathways need to be targeted to the appropriate subcellular domains at the right time during both synaptogenesis and the maintenance of synaptic functions. The presence of messenger RNAs (mRNAs) in dendrites offers a mechanism for synthesizing the appropriate molecules at the right place in response to local extracellular stimuli. Several dendritic (...) mRNAs have been identified, and the mechanisms controlling their localization are beginning to be understood. In many cell types, controls on mRNA stability play an important role in the regulation of gene expression, but it is unclear to what extent this type of control operates in dendrites. The regulation of protein synthesis and the control of mRNA stability in dendrites could have important implications for neuronal function. BioEssays 20:70–78, 1998. © 1998 John Wiley & Sons, Inc. (shrink)

In the mammalian central nervous system (CNS), each neuron receives signals from other neurons through numerous synapses located on its cell body and dendrites. Molecules involved in the postsynaptic signaling pathways need to be targeted to the appropriate subcellular domains at the right time during both synaptogenesis and the maintenance of synaptic functions. The presence of messenger RNAs (mRNAs) in dendrites offers a mechanism for synthesizing the appropriate molecules at the right place in response to local extracellular stimuli. Several dendritic (...) mRNAs have been identified, and the mechanisms controlling their localization are beginning to be understood. In many cell types, controls on mRNA stability play an important role in the regulation of gene expression, but it is unclear to what extent this type of control operates in dendrites. The regulation of protein synthesis and the control of mRNA stability in dendrites could have important implications for neuronal function. BioEssays 20:70–78, 1998. © 1998 John Wiley & Sons, Inc. (shrink)

We show that the quasi-order of continuous embeddability between finitely branching dendrites (a natural class of fairly simple compacta) is $\Sigma_1^1$ -complete. We also show that embeddability between countable linear orders with infinitely many colors is $\Sigma_1^1$ -complete.

It is proposed that a human conscious experience of the sort we report to each other reflects a direct causal interaction between a pattern of information about the world, encoded in a field of postsynaptic potentials, and a quantized mode of excitation occupying dendritic cytoskeleton. The requirement for a quantized account is seen simply as the need for an event of experience to be a single indivisible, but richly patterned, causal relation between information and an 'informee'. It is argued that (...) the informee is likely to be a higher-order quantized collective mode (much as proposed by Craddock and colleagues, 2017) with the biologically relevant dynamics likely also to be describable in classical terms. No specific interpretation of quantum theory is needed. In this scenario, anaesthetics would abrogate reportable experience by detuning parameters underpinning cytoskeletal informee modes, perhaps critically increasing associated impedence. It is also proposed that tuning and detuning of informee modes in individual dendritic trees by binding of accessory proteins to cytoskeleton plays a physiological role in short-term memory and truth evaluation through ascertainment of sequential signal pattern consonance. Components of this model may be involved in cellular adaptive responses in many types of organism. (shrink)

No one knows yet how to organize, in a simple yet predictive form, the knowledge concerning the anatomical, biophysical, and molecular properties of neurons that are accumulating in thousands of publications every year. The situation is not dissimilar to the state of Chemistry prior to Mendeleev's tabulation of the elements. We propose that the patterns of presence or absence of axons and dendrites within known anatomical parcels may serve as the key principle to define neuron types. Just as the positions (...) of the elements in the periodic table indicate their potential to combine into molecules, axonal and dendritic distributions provide the blueprint for network connectivity. Furthermore, among the features commonly employed to describe neurons, morphology is considerably robust to experimental conditions. At the same time, this core classification scheme is suitable for aggregating biochemical, physiological, and synaptic information. (shrink)

The ongoing steady nature of consciousness in everyday life implies that the underlying neural activity possesses a high level of stability. The prolonged cognitive events of sustained attention, imagery, and working memory also imply high stability of underlying neural activity. This paper proposes that stabilization of neural activity is produced by apical dendrite activity in pyramidal neurons within recurrent corticothalamic circuits, and proposes that the wave activities of apical dendrites that stabilize ongoing activity constitute the subjective impressions of an attended (...) object and the entire sensory background. The cortical minicolumn, as the functional unit of the cortex, is separated into an axis consisting of layer 5 pyramidal neurons and a surrounding shell consisting of layer 2/3 pyramidal neurons. It is proposed that apical dendrites of the axis generate sensory impressions, and basal dendrites of the shell process the brief-lasting input–output identifications of objects that give rise to ideas. (shrink)

_Figure 1. Dendrites and cell bodies of schematic neurons connected by dendritic-dendritic gap junctions form a laterally connected input_ _layer (“dendritic web”) within a neurocomputational architecture. Dendritic web dynamics are temporally coupled to gamma synchrony_ _EEG, and correspond with integration phases of “integrate and fire” cycles. Axonal firings provide input to, and output from, integration_ _phases (only one input, and three output axons are shown). Cell bodies/soma contain nuclei shown as black circles; microtubule networks_ _pervade the cytoplasm. According to the (...) Orch OR theory, gamma EEG-synchronized integration phases include quantum computations in_ _microtubule networks which culminate with conscious moments. Insert closeup shows a gap junction through which microtubule quantum_ _states entangle among different neurons, enabling macroscopic quantum states in dendritic webs extending throughout cortex and other_ _brain regions._. (shrink)

The electric activities of cortical pyramidal neurons are supported by structurally stable, morphologically complex axo-dendritic trees. Anatomical differences between axons and dendrites in regard to their length or caliber reflect the underlying functional specializations, for input or output of neural information, respectively. For a proper assessment of the computational capacity of pyramidal neurons, we have analyzed an extensive dataset of three-dimensional digital reconstructions from the NeuroMorphoOrg database, and quantified basic dendritic or axonal morphometric measures in different regions and layers of (...) the mouse, rat or human cerebral cortex. Physical estimates of the total number and type of ions involved in neuronal electric spiking based on the obtained morphometric data, combined with energetics of neurotransmitter release and signaling fueled by glucose consumed by the active brain, support highly efficient cerebral computation performed at the thermodynamically allowed Landauer limit for implementation of irreversible logical operations. Individual proton tunneling events in voltage-sensing S4 protein alpha-helices of Na+, K+ or Ca2+ ion channels are ideally suited to serve as single Landauer elementary logical operations that are then amplified by selective ionic currents traversing the open channel pores. This miniaturization of computational gating allows the execution of over 1.2 zetta logical operations per second in the human cerebral cortex without combusting the brain by the released heat. (shrink)

We present a theoretical view of the cellular foundations for network-level processes involved in producing our conscious experience. Inputs to apical synapses in layer 1 of a large subset of neocortical cells are summed at an integration zone near the top of their apical trunk. These inputs come from diverse sources and provide a context within which the transmission of information abstracted from sensory input to their basal and perisomatic synapses can be amplified when relevant. We argue that apical amplification (...) enables conscious perceptual experience and makes it more flexible, and thus more adaptive, by being sensitive to context. Apical amplification provides a possible mechanism for recurrent processing theory that avoids strong loops. It makes the broadcasting hypothesized by global neuronal workspace theories feasible while preserving the distinct contributions of the individual cells receiving the broadcast. It also provides mechanisms that contribute to the holistic aspects of integrated information theory. As apical amplification is highly dependent on cholinergic, aminergic, and other neuromodulators, it relates the specific contents of conscious experience to global mental states and to fluctuations in arousal when awake. We conclude that apical dendrites provide a cellular mechanism for the context-sensitive selective amplification that is a cardinal prerequisite of conscious perception. (shrink)

Love, fear, hope, calculus, and game shows-how do all these spring from a few delicate pounds of meat? Neurophysiologist Ian Glynn lays the foundation for answering this question in his expansive An Anatomy of Thought, but stops short of committing to one particular theory. The book is a pleasant challenge, presenting the reader with the latest research and thinking about neuroscience and how it relates to various models of consciousness. Combining the aim of a textbook with the style of a (...) popularization, it provides all the lay reader needs to know to participate in the philosophical debate that is redefining our attitudes about our minds. Drawing on the rich history of neurological case studies, Glynn picks through the building blocks of our nervous system, examines our visual and linguistic systems, and probes deeply into our higher thought processes. The stories of great scientists, like Ramon y Cajal, and famous patients, like Sperry's split-brained epileptics, illuminate the scientific issues Glynn selects as essential for understanding consciousness. Some might argue that his lengthy explorations of natural selection overemphasize evolutionary explanations of psychological phenomena, but they must also agree that evolutionary psychology has distanced itself mightily from social Darwinism in recent years and merits a reappraisal. The great consciousness debate may form the core of the 21st-century Zeitgeist; get ready for it with An Anatomy of Thought. -Rob Lightner From Publishers Weekly How do we know? What do we think? How could a philosophical problem-'the mind-body problem,' say-induce a headache? What can evolutionary theory, molecular biology, the history of medicine and experimental psychology tell us about the features of human consciousness, and (once again) how do we know? Glynn, a physician and Cambridge University professor, meticulously attempts to answer these questions and more, setting forth the results of all sorts of research relevant to our brains-from 19th-century dissections to Oliver Sacks-like case studies, work with monkeys and supercomputers, and the enduring puzzles of philosophy, which he rightly saves for near the end. After explaining evolution by natural selection and 'clearing away much dross,' Glynn lays out the experiments and theories that have shown 'how nerve cells can carry information about the body, how they can interact' and how sense organs work; demonstrates the 'mixture of parallel and hierarchical organization' in our brains and 'the striking localization of function within it'; considers where neuroscience is likely to go; and admits that, among the many fields of exciting research just ahead, 'we can be least confident of progress toward a complete, scientific explanation of our sensations and thoughts and feelings.' Other recent explaining-the-brain books have sometimes advanced simplistic, or implausibly grand, claims about the nature and features of consciousness in general. Instead, Glynn offers a patient, informative, well-laid-out researcher's-eye view of what we have learned, how we figured it out and what we still don't know about neurons, senses, feelings, brains and minds. (Apr.) Copyright 2000 Reed Business Information, Inc. From Library Journal The nature of consciousness, which perennially troubles the minds of scientists and philosophers, is the subject of an ever-growing body of literature. Two of the latest entries approach the topic from different perspectives. Glynn, a professor of physiology and head of the Physiological Laboratory at Cambridge, offers a comprehensive summary of what we know about the brain-both its evolution and its mechanisms. Among the topics he covers are natural selection, molecular evolution, nerves and the nervous system, sensory perception, and the specific structures responsible for our intellect. Using the mechanisms involved in vision and speech as models, Glynn skillfully describes various neurological deficiencies that can lead to 'disordered seeing' and problems with the use of language. He carefully distinguishes what we know through experimental evidence from what we know through the observation of patients with neurological damage. He also describes some of the major theories that attempt to explain why these structures arose. While his book concentrates on the structures that make up the mind, Glynn is well aware that some physical events appear explicable only in terms of conscious mental events-a situation that conflicts with the laws of modern physics. Only briefly, however, does he consider the various approaches that have been taken to deal with the issues of mind/body and free will. In contrast, this is the primary focus of The Physics of Consciousness. After reviewing the fundamentals of classic physics, Walker (who has a Ph.D. in physics) summarizes elements of the new physics in which our knowledge of space, time, matter, and energy are all dependent on the moment of observation. Walker explores the meaning of consciousness as a characteristic of the observer. In this context both the observer and the act of measurement are critical. In essence, Walker leads his reader on a journey through his concept of a 'quantum mind,' which can both affect matter (including other minds) and can be affected by other distant matter/minds. To break up what would otherwise be an extremely dense text, Walker also relates the very touching story of the loss of his high-school sweetheart to leukemia. Indeed, it is his memory of their relationship that drives Walker to seek an understanding of ultimate reality. At times, he has a tendency to be dogmatic-as when he concludes, 'our consciousness, our mind, and the will of God are the same mind.' While An Anatomy of Thought is appropriate for most academic libraries, the Physics of Consciousness will be most accessible to readers with some knowledge of advanced physics. -Laurie Bartolini, Illinois State Lib., Springfield Copyright 2000 Reed Business Information, Inc. From Booklist The codiscoverers of natural selection-Charles Darwin and Alfred Wallace-disagreed over the possibility of finding an evolutionary explanation for the human mind. Glynn here argues Darwin's side of the debate, tracing an eons-long path of development starting from simple amino acids floating in primal seas and extending through the erect hominids in which the powers of a massive brain first manifest themselves. Patiently adducing evidence of an evolutionary origin for the underlying molecular machinery, Glynn dissects the nerve centers that make possible speech and hearing, sight, and reading. Pressing deeper, he lays bare the cortical foundations of personality. But those who deal with the mind must attend also to the arguments advanced by philosophers. And it is when he turns from dendrites to syllogisms (especially the vexing mind-body paradox) that Glynn's empirical reasoning fails him. In the end, he concedes his perplexity in trying to conceive of an evolutionary origin for human consciousness. This concession may set the shade of Alfred Wallace to chortling, but it will draw readers into an honest confrontation with a profound enigma. Bryce Christensen. (shrink)

This introduction to the third and final part of the Common Knowledge symposium “Unsocial Thought, Uncommon Lives” is reprinted here in a special issue of representative pieces from the journal’s first twenty-five years. The title is taken from an article by Isaiah Berlin in CK. Perl’s essay argues against the Aristotelian presumption that “man is a social animal” and explains that the CK symposium on unsocial thought was meant to substantiate that “societies do as a rule smother instinctive behaviors, but (...) in the process they also as a rule incarnate the least respectable instincts with greater force than individuals can do independently.... If even heroism and altruism, let alone standard social conduct, are oblique expressions of aggression, cruelty, and the will to power, then the obvious conclusion to reach is that human beings are not fit company for each other.... The standard means of veering off from this conclusion is to blame one’s own society, or aspects of contemporary society, and then to propose improvements. Historically, evidence suggests, efforts of this kind are opportunities for controversy and thus for exercise of the will to power. Social order is such that even the discussion of social order occasions conflict.” Perl goes on to argue that individualists and communitarians are “fundamentally in accord”: they are “teams” agreeing to the rules of a dubious conflict from which only “stylites, dendrites, and mendicants” have done what is required to exempt themselves. (shrink)

We argue that prediction success maximization is a basic objective of cognition and cortex, that it is compatible with but distinct from prediction error minimization, that neither objective requires subtractive coding, that there is clear neurobiological evidence for the amplification of predicted signals, and that we are unconvinced by evidence proposed in support of subtractive coding. We outline recent discoveries showing that pyramidal cells on which our cognitive capabilities depend usually transmit information about input to their basal dendrites and amplify (...) that transmission when input to their distal apical dendrites provides a context that agrees with the feedforward basal input in that both are depolarizing, i.e., both are excitatory rather than inhibitory. Though these intracellular discoveries require a level of technical expertise that is beyond the current abilities of most neuroscience labs, they are not controversial and acclaimed as groundbreaking. We note that this cellular cooperative context-sensitivity greatly enhances the cognitive capabilities of the mammalian neocortex, and that much remains to be discovered concerning its evolution, development, and pathology. (shrink)

At the global as well as local scales, some of the geometry of types of neuron arbors—both dendrites and axons—appears to be self-organizing: Their morphogenesis behaves like flowing water, that is, fluid dynamically; waterflow in branching networks in turn acts like a tree composed of cords under tension, that is, vector mechanically. Branch diameters and angles and junction sites conform significantly to this model. The result is that such neuron tree samples globally minimize their total volume—rather than, for example, surface (...) area or branch length. In addition, the arbors perform well at generating the cheapest topology interconnecting their terminals: their large-scale layouts are among the best of all such possible connecting patterns, approaching 5% of optimum. This model also applies comparably to arterial and river networks. S1063-651X 99 16205-6.. (shrink)

I propose that primary conscious awareness arises from synchronized activity in dendrites of neurons in dorsal thalamic nuclei, mediated particularly by inhibitory interactions with thalamic reticular neurons. In support, I offer four evidential pillars: consciousness is restricted to the results of cortical computations; thalamus is the common locus of action of brain injury in vegetative state and of general anesthetics; the anatomy and physiology of the thalamus imply a central role in consciousness; neural synchronization is a neural correlate of consciousness.

In the beginning of the 20th century the groundbreaking work of Ramon y Cajal firmly established the neuron doctrine, according to which neurons are the basic structural and functional units of the nervous system. Von Weldeyer coined the term “neuron” in 1891, but the huge leap forward in neuroscience was due to Cajal’s meticulous microscopic observations of brain sections stained with an improved version of Golgi’s la reazione nera (black reaction). The latter improvement of Golgi’s technique made it possible to (...) visualize the arborizations of single neurons that were “colored brownish black even to their finest branchlets, standing out with unsurpassable clarity upon a transparent yellow background. All was sharp as a sketch with Chinese ink”. The high quality of both the visualization of individual nerve cells and the work performed on studying the anatomy of the central nervous system lead Ramon y Cajal to the conclusion that axons output the nervous impulses to the dendrites or the soma of other target neurons. (shrink)

Excitation at widely dispersed loci in the cerebral cortex may represent a neural correlate of consciousness. Accordingly, each unique combination of excited neurons would determine the content of a conscious moment. This conceptualization would be strengthened if we could identify what orchestrates the various combinations of excited neurons. In the present paper, cholinergic afferents to the cerebral cortex are hypothesized to enhance activity at specific cortical circuits and determine the content of a conscious moment by activating certain combinations of postsynaptic (...) sites in select cortical modules. It is proposed that these selections are enabled by learning-related restructuring that simultaneously adjusts the cytoskeletal matrix at specific constellations of postsynaptic sites giving all a similar geometry. The underlying mechanism of conscious awareness hypothetically involves cholinergic mediation of linkages between microtubules and microtubule-associated protein-2 . The first reason for proposing this mechanism is that previous studies indicate cognitive-related changes in MAP-2 occur in cholinoceptive cells within discrete cortical modules. These cortical modules are found throughout the cerebral cortex, measure 1–2 mm2, and contain approximately 103–104cholinoceptive cells that are enriched with MAP-2. The subsectors of the hippocampus may function similarly to cortical modules. The second reason for proposing the current mechanism is that the MAP-2 rich cells throughout the cerebral cortex correspond almost exactly with the cortical cells containing muscarinic receptors. Many of these cholinoceptive, MAP-2 rich cells are large pyramidal cell types, but some are also small pyramidal cells and nonpyramidal types. The third reason for proposing the current mechanism is that cholinergic afferents are module-specific; cholinergic axons terminate wholly within individual cortical modules. The cholinergic afferents may be unique in this regard. Finally, the tapering apical dendrites of pyramidal cells are proposed as primary sites for cholinergic mediation of linkages between MAP-2 and microtubules because especially high amounts of MAP-2 are found here. Also, the possibility is raised that muscarinic actions on MAP-2 could modulate microtubular coherence and self-collapse, phenomena that have been suggested to underlie consciousness. (shrink)

Insights into the role of sleep in the molecular mechanisms of memory consolidation may come from studies of activity-dependent synaptic plasticity, such as long-term potentiation (LTP). This commentary posits a specific contribution of sleep to LTP stabilization, in which mRNA transported to dendrites during wakefulness is translated during sleep. Brain-derived neurotrophic factor may drive the translation of newly transported and resident mRNA.

The idea that individual nerve cells might have conscious experiences has been around ever since cells were identified in the seventeenth century, but in the era of modern neuroscience the case for individual human neuronal experience has received little attention. A series of arguments will be presented suggesting that all the human conscious experiences that we talk about are events in individual neurons, not global to the brain or organism. We conclude that cellular consciousness is the only plausible way to (...) explain ‘our’ experiences within current physics and biology, however implausible it might at first seem. This implies that our experiences are multiple in space as well as time, consistent with the neuroscience watchword that there is ‘no single place where everything comes together in the brain’. The central argument is that events of experience must involve rich integration of information and individual neurons are the only places in brains where integration of information occurs. Any more global ‘binding’ is neither required nor physically possible. The detailed nature of events of integration of signals in a neuron’s dendrites remains uncertain but recent developments provide some candidates. (shrink)

Quartz & Sejnowski (Q&S) disregard evidence that suggests that their view of dendrites is inadequate and they ignore recent results concerning the role of neurotrophic factors in synaptic remodelling. They misrepresent neuronal selectionism and thus erect a straw-man argument. Finally, the results discussed in section 4.2 require neuronal proliferation, but this does not occur during the period of neuronal development of relevance here. Footnotes1 Address correspondence to TE at [email protected].

There is evidence for increase, followed by decline, in synaptic numbers during development. Dendrites do not function in isolation. A constructive neuronal process may underpin a selectionist cognitive process. The environment shapes both ontogeny and phylogeny. Phylogenetic natural selection and neural selection are compatible. Natural selection can yield both constructivist and selectionist solution to adaptuive problems.

In a companion review1 we discussed the data supporting the conclusion that at least two subtypes of spectrin exist in mammalian brain. One form is found in the cell bodies, dendrites, and post‐synaptic terminals of neurons (brain spectrin(240/235E)) and the other subtype is located in the axons and presynaptic terminals (brain spectrin(240/235)). Our recent understanding of brain spectrin subtype localization suggests a possible explanation for a conundrum concerning brain 4.1 localization. Amelin, an immunoreactive analogue of red blood cell (rbc) cytoskeletal (...) protein 4.1, is localized in neuronal cell bodies and dendrites when brain sections are stained with antibody against rbc protein 4.1. However, it has recently been suggested that synapsin I, a neuron‐specific phosphoprotein associated with the cytoplasmic surface of small synaptic vesicles, is related to erythrocyte 4.1. In this review we hypothesize that there are at least two forms of brain 4.1: a cell body/dendritic form (amelin) which is detected with rbc protein 4.1 antibody, and a unique form found exclusively in the presynaptic terminal (synapsin I). The binding of synapsin I to brain spectrin(240/235), and its ability to stimulate the spectrin/F‐actin interaction in a phosphorylation‐dependent manner suggests a model for the regulation of synaptic transmission mediated by the neuronal cytoskeleton. (shrink)

Mormyrid teleosts have Purkinje cells with palisade dendrites, which probably represent coincidence detectors of parallel fiber activity. Their existence strongly supports the ideas of Braitenberg et al. on cerebellar function. However, the organization of mormyrid granule cells and parallel fibers suggests that a key to cerebellar function is not in interactions within one wave, but between twoopposite tidal waves.

Neurofilaments and microtubules are important components of the neuronal cytoskeleton. In axons or dendrites, these filaments are aligned in parallel arrays, and separated from one another by nonrandom distances. This distinctive organization has been attributed to cross bridges formed by NF side arms or microtubule‐associated proteins. We recently proposed a polymer‐brush‐based mechanism for regulating interactions between neurofilaments and between microtubules. In this model, the side arms of neurofilaments and the projection domains of microtubule‐associated proteins are highly unstructured and exert long‐range (...) repulsive forces that are largely entropic in origin; these forces then act to organize the cytoskeleton in axons and dendrites. Here, we review the biochemical, biophysical, genetic and cell biological data for the polymer‐brush and cross‐bridging models. We explore how the data traditionally used to support cross bridging may be reconciled with a polymer‐brush mechanism and compare the implications of recent experimental insights into axonal transport and physiology for each model. BioEssays 26:1017–1025, 2004. © 2004 Wiley Periodicals, Inc. (shrink)

The tidal-wave theory is inspired by the particular morphology of the cerebellar cortex. It elegantly attributes function to the anisotropy of the cerebellar wiring and the geometry of Purkinje cell dendrites. In this commentary, physiological considerations are used to elaborate temporal and spatial constraints of the tidal-wave theory. It is shown, first, that limitations of temporal precision in the cortical inputs to the mammalian cerebellum delimit the spatial resolution of an input sequence (i.e., the minimal distance along the parallel fibers (...) which can detect sequential input) to the range of a millimeter at best. Second, temporal characteristics of Purkinje cell postsynaptic potentials are argued to predict a distance of at least several millimeters along the parallel fiber beam in order to generate a sequence in the cerebellar output. It is concluded that the implementation of tidal waves as a general principle of cerebellar function is questionable as there exist cerebelli too small to match these constraints. (shrink)

The strong correlation between the geometry of the dendritic tree and the specific function of motoneurons suggests that their synaptic contacts are established on a selective stochastic basis with the characteristic form of dendrites being the source of selection in the frog. A compromise is suggested according to which specific structures may have evolved on a selective stochastic basis and “constructive learning” could be the source of selection in the cortex.

Where is consciousness? Neurobiological theories of consciousness look primarily to synaptic firing and “spike codes” as the physical substrate of consciousness, although the specific mechanisms of consciousness remain unknown. Synaptic firing results from electrochemical processes in neuron axons and dendrites. All neurons also produce electromagnetic (EM) fields due to various mechanisms, including the electric potential created by transmembrane ion flows, known as “local field potentials,” but there are also more meso-scale and macro-scale EM fields present in the brain. The functional (...) role of these EM fields has long been a source of debate. We suggest that these fields, in both their local and global forms, may be the primary seat of consciousness, working as a gestalt with synaptic firing and other aspects of neuroanatomy to produce the marvelous complexity of minds. We call this assertion the “electromagnetic field hypothesis.” The neuroanatomy of the brain produces the local and global EM fields but these fields are not identical with the anatomy of the brain. These fields are produced by, but not identical with, the brain, in the same manner that twigs and leaves are produced by a tree’s branches and trunk but are not the same as the branches and trunk. As such, the EM fields represent the more granular, both spatially and temporally, aspects of the brain’s structure and functioning than the neuroanatomy of the brain. The brain’s various EM fields seem to be more sensitive to small changes than the neuroanatomy of the brain. We discuss issues with the spike code approach as well as the various lines of evidence supporting our argument that the brain’s EM fields may be the primary seat of consciousness. This evidence (which occupies most of the paper) suggests that oscillating neural EM fields may make firing in neural circuits oscillate, and these oscillating circuits. may help unify and guide conscious cognition. (shrink)

Based on neurobiological data, modern concepts of self-organization and a careful rationale, the hypothesis is put forward that the fleeting, highly ordered patterns of electric and/or magnetic fields, generated by assemblies of dendritic trees of specialized neuronal networks, should be thought of as the end-product of chaotic, dynamically governed self-organization. Such patterns encode for subjective experiences such as pain and pleasure, or perceiving colours. Because by quantum mechanical definition virtual photons are the theoretical constituents of electric and magnetic fields, the (...) former hypothesis can be re-formulated as follows: it is the highly ordered patterns of virtual photons that encode for subjective experiences. Arguments are then given that consciousness did not emerge during evolution only after neuronal networks had been formed able to generate electric and/or magnetic fields of sufficient complexity but, rather, that subjectivity already existed in a very elementary form as a fundamental property of the omnipresent virtual photons, i.e., of matter. The contribution of neuronal networks to consciousness was to generate highly ordered patterns of germs of subjectivity , so allowing complex subjective experiences. Due to the omnipresence of virtual photons, it follows finally that the whole universe must be imbued with subjectivity. An experimental strategy is proposed to test the hypothesis. (shrink)

Mammalian neural cells contain at least two forms of brain spectrin: brain spectrin (240/235) which is located primarily in the axons and presynaptic terminals of neurons, and brain spectrin (240/235E) which is found in the cell bodies, dendrites and postsynaptic terminals of neurones. Brain spectrin (240/235E) is also found in certain glial cell types. Antibodies against red blood cell spectrin detect only brain spectrin (240/235E), while antibodies against brain spectrin isolated from axonal and synaptic membranes detect brain spectrin (240/235). Previous (...) apparent discrepancies in the literature concerning brain spectrin localization at the light microscope level were undoubtedly due to different laboratories detecting distinct brain spectrin subtypes, based on the particular antibody being utilized for immunohistochemistry. In this review we (1) discuss the data supporting the presence of at least two distinct subtypes of mammalian brain spectrin, (2) explain how these results reconcile previous discrepancies concerning the localization of spectrin within neural cells, and (3) suggest the future implications of these findings. (shrink)

Growth cones are the highly motile structures found at the tips of growing axons and dendrites (neurites), which extend from neurones, during the development of the nervous system. They function both as detectors and transducers of extrinsic guidance cues and as regions where the neurite cytoskeleton is assembled. Without concerted neurite assembly, advance cannot occur. Assembly of the neurite cytoskeleton in growing neurites chiefly involves microtubule assembly at the growth cone. Some of the factors that may influence microtubule assembly in (...) growth cones are becoming apparent and include posttranslational modification of tubulin itself and microtubule associated proteins, particularly tau and MAP1B. (shrink)

The temporal profile of dendritic branching in developing neurons is an interplay between the proliferating number of branching sites and the branching rates at these individual sites. The eventual metrical structure of dendritic arborizations is the outcome of joint processes of branching and elongation of outgrowing neurites. Dendritic growth models have shown to be powerful tools for quantitatively studying the rules of outgrowth, aiming at reproducing the shape characteristics in observed dendritic arborizations. Recent model studies, focusing on the branching process, (...) have predicted strongly decreasing branching rates during dendritic outgrowth. The implications of these findings for the metrical development of outgrowing dendrites will be discussed. (shrink)

Neurons have developed elaborate mechanisms for sorting of proteins to their destination in dendrites and axons as well as dynamic local trafficking. Recent evidence suggests that polarized axonal sorting of β‐site converting enzyme 1 (BACE1), a type I transmembrane aspartyl protease involved in Alzheimer's disease (AD) pathogenesis, entails an unusual journey. In hippocampal neurons, BACE1 internalized from dendrites is conveyed in recycling endosomes via unidirectional retrograde transport towards the soma and sorted to axons where BACE1 becomes enriched. In comparison to (...) other transmembrane proteins that undergo transcytosis or elimination in somatodendritic compartment, vectorial transport of internalized BACE1 in dendrites is unique and intriguing. Dysfunction of protein transport contributes to pathogenesis of AD and other neurodegenerative diseases. Therefore, characterization of BACE1 transcytosis is an important addition to the multiple lines of evidence that highlight the crucial role played by endosomal trafficking pathway as well as axonal sorting mechanisms in AD pathogenesis. (shrink)

In this commentary, arguments are made for a dendritic code being preferable to a temporal synaptic code as a model of conscious experience. A temporal firing pattern is a product of an ongoing neural computation; hence, it is based on a neural algorithm and an algorithm may not provide the most suitable model for conscious experience. Reiteration of a temporal firing code as suggested in a preceding article (Helekar, 1999) does not necessarily improve the situation. The alternative model presented here (...) is that certain synaptic activity patterns, possibly those possessing universal features as suggested by Helekar, can become encoded in the dendritic structure. Following dendritic encoding, quantum phenomena in those specific dendrite sets could illuminate the static image of that encoded synaptic activity. It is the activation of the static image that would be equivalent to conscious experience; thus, conscious awareness would not be directly affiliated with synaptic activity. This dendrite encoding model may go farther than other models to explain the gestalt nature of consciousness, insofar as quantum entanglement could produce an interconnectedness between specific sets of dendrites-an interconnectedness that need not be based on neural computation or neural connections. (shrink)

In the present work, the microstructure of the melt-spun Al 90 Ce 10 alloy has been characterized using X-ray diffraction and transmission electron microscopy together with energy-dispersive spectrometry. It has been found that the microstructure of the melt-spun Al 90 Ce 10 alloy is composed of the amorphous phase, f -Al, f -Al 11 Ce 3 , Al 3 Ce and unidentified phases, quite different from that of the ingot-like alloy consisting of coarse primary f -Al- f -Al 11 Ce (...) 3 dendrites embedded in the f -Al- f -Al 11 Ce 3 eutectic matrix. Moreover, the amorphous phase is dominant in the melt-spun Al 90 Ce 10 alloy according to the XRD and TEM results. Al 3 Ce particles, less than 100 nm in size, are dispersed in the partial amorphous phase. Polygonal f -Al 11 Ce 3 crystals embedded in the f -Al matrix are also observed. The presence of the hexagonal, kite-like and petal-like intermetallic particles surrounded by the amorphous phase indicates that there exist micro-inhomogeneous structures in the Al 90 Ce 10 melt. These results demonstrate that the overheating of the melt has a significant effect on the amorphization of the Al 90 Ce 10 alloy. (shrink)

As bridges or brains become bigger or smaller, the changes pose problems of design thatneed to be solved. Larger brains could have larger or more neurons, or both. With largerneurons, it becomes difficult to maintain conduction times over longer axons andelectrical cable properties over longer dendrites. With more neurons, it becomes difficultfor each neuron to maintain its proportion of connections with other neurons. Theseproblems are addressed by making brains more modular, thereby reducing the lengths ofmany connections, and by altering functions. (...) Smaller brains may not have enoughneurons for all circuits, and they may lose modules and functions. Mammals with moreneocortex tend to have more cortical areas and more columns and types of columnswithin the larger areas. (shrink)

The ability to predict is the most importantability of the brain. Somehow, the cortex isable to extract regularities from theenvironment and use those regularities as abasis for prediction. This is a most remarkableskill, considering that behaviourallysignificant environmental regularities are noteasy to discern: they operate not only betweenpairs of simple environmental conditions, astraditional associationism has assumed, butamong complex functions of conditions that areorders of complexity removed from raw sensoryinputs. We propose that the brain's basicmechanism for discovering such complexregularities is implemented in (...) the dendritictrees of individual pyramidal cells in thecerebral cortex. Pyramidal cells have 5–8principal dendrites, each of which is capableof learning nonlinear input-to-outputtransfer functions. We propose that eachdendrite is trained, in learning its transferfunction, by all the other principal dendritesof the same cell. These dendrites teach eachother to respond to their separate inputs with matching outputs. Exposed to differentbut related information about the sensoryenvironment, principal dendrites of the samecell tune to functions over environmentalconditions that, while different, are correlated . As a result, the cell as awhole tunes to the source of the regularitiesdiscovered by the cooperating dendrites,creating a new representation. When organizedinto feed-forward/feedback layers, pyramidalcells can build their discoveries on thediscoveries of other cells, graduallyuncovering nature's hidden order. Theresulting associative network is powerfulenough to meet a troubling traditionalobjection to associationism: that it is toosimple an architecture to implement rationalprocesses. (shrink)