"The term 'cytoskeleton' is often used as if it described a single, unified structure, but the cytoskeleton of neurons, Human Brain Cells, and other eukaryotic cells, comprises 3 distinct, interacting structural complexes that have very different properties:
- microtubules (MTs)
- neurofilaments (NFs)
- and microfilaments (MFs).
"Each, 1., 2., 3., has a characteristic composition, structure and organization that may be further specialized in a particular cell type or subcellular domain. The defining structural elements have long been identifiable in electron micrographs (Fig. 8-1), and a considerable amount is known about the detailed organization of these components in neurons and glia. Each set of cytoskeletal structures is considered in turn.
"The key components of the intricate Microtubular subcellular architecture, are endowed with special electrical conduction mechanisms, called Memristors. (In Artificial Intelligence they are called Multidirectional Logic Gates) [Tuszynski, J.A., Friesen, D., Freedman, H. et al. Microtubules as Sub-Cellular Memristors. Sci Rep 10, 2108 (2020). https://doi.org/10.1038/s41598-020-58820-y]
Cells of eukaryotic organisms are elaborately subdivided into functionally-distinct intracellular membrane-bound compartments, which are called subcellular. [ Schuler D. (2004). Molecular analysis of a subcellular compartment: the magnetosome membrane in Magnetospirillum gryphiswaldense. Arch Microbiol. 181:1-7 ]
Now for the drilled-down details. “A particular effect observed in referenced (below) experiments shows that microtubules function as memristors. (In Artificial Intelligence called Logic Gates).
“Logical operations are necessary because they can be used to model the way that information flows through electrical circuits.”[Logical operation 11/16/2019 by Computer Hope]
“Three decades ago, British physicist Sir Roger Penrose introduced a key element of panpsychism with his theory that Consciousness is rooted in the statistical rules of quantum physics as they apply in the microscopic spaces between neurons in the brain.
“In 2006, German physicist Bernard Haisch, known both for his studies of active stars and his openness to unorthodox science, took Penrose’s idea a big step further.
“Haisch proposed that the quantum fields that permeate all of empty space (the so-called "quantum vacuum") produce and transmit consciousness, which then emerges into any sufficiently complex system with energy flowing through it, as in the Human Brain.
“One of the hallmarks of life is the ability of life to adjust its behavior in response to stimulus.
Matloff found a little-studied anomaly in stellar motion known as Paranego’s Discontinuity. On average, cooler stars orbit our galaxy more quickly than do hotter ones. Matloff noted the anomaly appears in stars that are cool enough to have molecules in their atmospheres, which greatly increases their chemical complexity.
Matloff noted further that some stars appear to emit jets that point in only one direction, an unbalanced process that could cause a star to alter its motion. He wondered: Could this actually be a willful process? Is there any way to tell?
“If Paranego’s Discontinuity is caused by something intrinsic in the stars, as Quantum Entangled Particles and Coherent Energy fields of Consciousness would be, it should be the same everywhere.
“Paranego’s Discontinuity means young thin disk stars (younger than a billion years) have lower velocity dispersions than old thin disk stars. This means that young thin disk stars have more circular orbits around the center of the Galaxy than do old thin disk stars. The young stars also stay closer to the Galactic plane. [Source https://www.physicsforums.com/threads/is-the-parenago-discontinuity-a-real-thing.925023/] [Parenago's Discontinuity, page 428 of Galactic Astronomy: Structure and Kinematics by Dmitri Mihalas and James Binney, 2nd edition.] [pages 93-100 of The Alchemy of the Heavens: Searching for Meaning in the Milky Way by Ken Croswell] [Source: https://www.physicsforums.com/threads/is-the-parenago-discontinuity-a-real-thing.925023/]
“Data from existing stellar catalogs seems to support the latter view, Matloff claims. Detailed results from the Gaia star-mapping space telescope, due in 2018, will provide a more stringent test.
“Maybe we can move panpsychism from philosophy to observational astrophysics.”
"The only dominant theory of Consciousness says that it is associated with ‘complexity’ i.e. a system’s ability to act upon its own state and determine its own fate,” Humans have the same complexity. Humans can realize their conditions and react with improvements.
“Christof Koch of the Allen Institute for Brain Science, (inspired by Integrated Information Theory i.e. Consciousness is defined by the ability of a system to be influenced by its previous state and to influence its next state), says, “Theory states that Consciousness could exist in very simple systems. In principle, some purely physical systems that are not biological or organic may also be Conscious.”
Koch explains: “Human beings are more complex and have more self-awareness but other systems have awareness, though to a lesser degree. Humans may share the property of experience. Feeling and sharing various experience degrees influence the definition of consciousness: the ability to experience everything, from the most mundane to the most refined religious experience.”
“Despite their seeming similarities, Koch is dubious of Matloff’s volitional stars. What is distinctive about living things, according to his theory, is not that the stars are alive but that they are complex.
Although the sun is vastly bigger than a bacterium, from physics and mathematics perspectives, the sun is vastly simpler than a bacterium. Koch allows that a star may have an internal life that allows it to “feel,” but whatever that feeling is, it is much less than the feeling of being a one cell germ.
Human and Biological Consciousness are different than Universal and Physical Consciousness. “Even non-animal systems could have a small fraction of Consciousness,” Koch says.
“Consciousness is a characteristic of the inanimate, physical world.” From this perspective, the Universe may not be exactly Cognitive like thinking Humans, but Universe still has internal experiences, which are intimately tied to Human experiences.
Koch is dubious of every detail of Matloff’s volitional star theory. What is distinctive about living things, according to Koch’s theory, is not that they are alive, but that they are complex.
Physicist and mathematician Roger Penrose theories link Consciousness and Quantum Mechanics. He does not overtly identify himself as a panpsychist, but Penrose’s argument that self-awareness and free will begin with Quantum Events in the Brain, inevitably linksHuman minds with the cosmos. Penrose sums up this connection beautifully in his opus "The Road to Reality."
Penrose asserts, “The laws of physics produce complex systems, and these complex systems lead to Consciousness, which leads to mathematics, which can then lead to the very underlying laws of physics that gave rise to it.”
Despite his towering stature as a physicist and mathematician, Penrose has encountered resistance to his theory of Consciousness. Oddly, Penrose's colleagues have been more accepting of the implications of Quantum Mechanics interconnections to Cosmic-Consciousness and Human Consciousness . [Is The Universe Conscious, by Corey S. Powell, June 16, 2017, MACH, NBC]
Drs Stuart Hameroff and Roger Penrose Orch OR Theory conclude that consciousness derives from deeper-order, finer-scale quantum computations in microtubules inside brain neurons which
- 1) regulate neuronal membrane and synaptic activities
- 2) and connect brain processes to fundamental space-time geometry, the fine-scale structure of the universe.
7. “After 40 years of Consciousness research and new evidence, including research about the fundamentals of spirituality and the Soul, the conclusion by Dr Stuart Hameroff and collegial scientists, after their peer review, is that Human Consciousness NeuroBioPhysicsology is correct and Human Consciousness occurs secondary to Quantum Vibrations in brain microtubules.”
“If the connection to fundamental space-time geometry is also validated, Orch OR may provide a bridge between neuroscience and more spiritual approaches to consciousness. [Journal of Consciousness Studies, 21, No. 3–4, 2014, pp. 126–53 Correspondence: Stuart Hameroff M.D., Departments of Anesthesiology and Psychology, Center for Consciousness Studies]
“With resonances, orchestration, beats, and different scales, or octaves, microtubules are looking like musical instruments, at least metaphorically. In Orch OR, microtubule vibrations also correspond with fluctuations in the fine scale structure of space-time geometry, so in some sense, consciousness is the ‘music of the universe.”
“Microtubules (MTs), cylindrical protein polymers composed of tubulin dimers are key components of the cytoskeleton. They have been shown to increase solution’s ionic conductance and re-orient in the presence of electric fields.
“It has been hypothesized that MTs also possess intrinsic capacitive and inductive properties, leading to transistor-like behavior. Here, we show a theoretical basis and experimental support for the assertion that Microtubules (MTs) under specific circumstances behave consistently with the definition of a memristor.
“Their biophysical properties lead to pinched hysteretic current–voltage dependence as well a classic dependence of magnetic flux on electric charge.
“Based on the information about the structure of MTs we provide an estimate of their memristance. We discuss its significance for biology, especially neuroscience, and potential for nanotechnology applications.
Introduction: The term memristor is the contraction of memory and resistor and it was first proposed in 1971 as the fourth element of the electric circuits. 1.
A memristor is defined as a 2-terminal passive circuit element that provides a functional relation between electric charge and magnetic flux. 1,2.
“One of the possible breakthrough applications of memristors is ‘Neuromorphic Computing.’ 6. Memristance refers to a property of the memristor that is analogous to resistance but it also depends on the history of applied voltage or injected current, unlike in other electrical circuit elements.
“When the electrical charge flows in one direction, the resistance of some memristors increases while it decreases when the charge flows in the opposite direction or vice versa.
“If the applied voltage is turned off, the memristor retains the last resistance value that it exhibited. This history dependence of memristance is expressed via a self-crossing or pinched I–V loop, which is frequency dependent 3.6. and whose lobe area tends to zero as the frequency tends to infinity.
“This research provides indirect indication that MTs may function as nano-scale sub-cellular memristors with an enormous potential for storage of large amounts of biologically-relevant information.
“Their involvement in many biological functions, especially in cell morphology, mitosis, intracellular transport and neuronal migration makes them important biological structures, whose memristive properties would provide an extraordinary range of possibilities in the context of cell biology and neuroscience and also offer a great potential for hybrid nano-biotechnological advances using a combination of protein-based and synthetic components. {{{NeuroBioPhysicslolgy}}}
“The cytoskeleton of eukaryotic cells contains three main types of protein filaments, namely: Microtubules (MTs), actin filaments (AFs) and intermediate filaments (IFs).
“The cytoskeleton in addition to providing the necessary mechanical rigidity for cell morphology and localized force generation capabilities due to their polymerization dynamics, these protein polymers participate in a multitude of key biological functions including cell division, cell motility and intracellular transport.
“Additionally, MTsinside the cytoskeleton and other cytoskeletal filaments in neurons, have been hypothesized to store molecular bits of information that can build up memory at a sub-cellular level.
“MTs have also been proposed to transmit electrical signals in neuronal cells. 16,17,18,19,20. Importantly in this connection, both AFs and especially MTs possess highly electrically-charged surfaces, which enable them to conduct electrical signals via ionic cable-like transmission process. 21,22. It is important to note that MTs are very abundant in neurons where they form parallel bundles interconnected by MAPs (MT-associated proteins) resembling parallel processing computational architecture.
“It is not surprising to find that the key components of MTs intricate intracellular architecture are endowed with special electrical conduction properties.
“Hameroff published an Orch OR theory of ‘Consciousness’ update: ‘Consciousness in the Universe, a Review of the Orch OR Theory’ (Hameroff and Penrose, 2014a). Its key points:
- 1) Proto-conscious processes and Penrose objective reduction, ‘OR’, have been in the Universe all along, occurring in the fine scale structure of space-time geometry {{{ since the relic Higgs boson energy fields and relic Fermion particles }}}, thus shaping the material world.
- 2) Microtubules evolved in biology to compute and ‘orchestrate’ OR events into rich conscious experience and causal action (Orch OR), sequences of which give rise to our ‘stream of consciousness’.
- 3) Microtubules have quantum vibrational resonances (e.g. in megahertz) blocked by anesthetics and enhanced by psychoactive drugs. Interference of microtubule vibrations results in slower ‘beat frequencies’, accounting for electroencephalography (EEG) rhythms.
- 4) Therapies aimed at brain microtubules may be useful in a variety of neurological and psychiatric disorders.
- 5) Universal Consciousness is self-organization in the fine scale structure of space-time geometry, the ‘music of the universe’.
- 6) Orch OR is the most comprehensive, rigorous, and successful theory of Human Consciousness ever put forth.
- [148 S. HAMEROFF Copyright (c) Imprint Academic 2013 For personal use only -- not for reproduction For Orch OR, JCS, and TSC the future is bright. Congratulations and thanks to JCS, its readers, and to TSC participants, colleagues, critics, and students of consciousness everywhere. In the end, consciousness is all that really matters.]
==
“Memristors combine memory and cognitive logics in Human Microtubules, Microtubular responses to external and internal sensory inputs involve multidirectional reception, processing, integration for Neurophysiological actions, behaviors, self-awareness, self-modification and memorization through the Memristor’s Capacitor, Inductor, Resistor, Transistor i.e NeuroBioPhysicsological processing functions.
AI devices are attempting to simulate Human Microtubule NeuroBioPhysicsological processing functions in order “to perform a full set of logic operations at the same time as they function as nonvolatile memory.”
“Scientists have presented the actual physics of how a memristor functions, and have summarized the memristors basic operations in the reference listed below. The devices can adopt either high- or low-resistance states, which can be considered bits. A positive voltage above a specific threshold will set the memristor in its high-resistance state in as little as two microseconds. A negative voltage of the same magnitude toggles it to its low-resistance state.
“A key feature of memristors is that these states are stableand they act as nonvolatile memory. Reading their state can be accomplished by applying voltages smaller than the critical threshold, and determining how much current flows through.
“Although these devices are currently difficult to manufacture and the memristors aren't especially useful in isolation at the moment. The authors also point out that the use of implication is quite common among those who study formal logic, but is largely ignored by those designing logic schemes, who focus on what's easy to do in silicon. "The major lesson from this research," they write, "is that when confronted with a new device, one needs to determine whether it has a natural basis for computationthat is different from familiar paradigms." [Human adaptation form Memristors combine memory, logics set in one device, John Timmer, 4/7/2010, arsTechnica Nature, 2010. DOI: 10.1038/nature08940]
== See pictures
“Memristors represent the fourth electrical circuit element complementing resistors, capacitors and inductors.
“Hallmarks of memristive behavior include pinched and frequency-dependent I–V hysteresis loops and most importantly a functional dependence of the magnetic flux passing through an ideal memristor on its electrical charge. see picture aabove
A plot is a graphical technique for representing a data set, usually as a graph showing the relationship between two or more variables. The plot can be drawn by hand or by a computer. In the past, sometimes mechanical or electronic plotters were used.
- ▸ Concept: - Assumes special case of interfacial switching :
- §Current determined by layer resistivity, no influence by Schottky contact
- §Not proven, even not that it is interfacial and not filamentary (see further hysteresis loop) - Need to account for generation/recombination of oxygen vacancies;
- §Possibly by REDOX reactions at interface - We will have Oxygen Vacancy profiles (not 2 fixed levels, no abrupt transition...) Dirk Wouters ESA WS April 2015 Folie 13 Physical ?
- • Movement of boundary is essentially FIELD driven, not CURRENT driven
- • Further (for memory it needs to be) very non-linear: (good threshold behavior) – dW(t)/dt = m(E).E
- • Link to current as through relation of electric current in the device with field : i ~ E – However, also in principle non-linear over whole operation range (including ‘”switching”) (and different from drift non-linearity
- • In memory we want at low fields (ideally) NO ion drift BUT measurable (state dependent) current, and “state change” only at high field: – Same integral of current at low field has different effect than integral of current at high field ànot accounted for ? A correspondence may be possible in principle but would be magical in practice because different energy barrier for electronic and ionic conduction Name des/der Vortragenden Folie 14 Hysteresis curve
- ▸ Theory : - Each point on the pinched hysteresis is a stable point - Limited change of dynamics over the complete range :
- §as only linearly depending on the current level ▸ Real device: - In different parts of the hysteresis, very different dynamics: - Below Vt (SET) and Vtrans(RESET) NO change of state - 3 regions of state change:
- §Snapback : very rapid initial set (impossible to control intermediate state)
- §Second part of SET: state depending on CURRENT LEVEL (not charge) * microscopic still voltage controlled
- §RESET: Voltage controlled Dirk Wouters ESA WS April 2015 Folie 15 Model calculations Real device Hysteresis shape : memristor vs real Memristive modeling - Three b
- [Workshop on Memristive systems for Space applications 30 April 2015 ESTEC, Noordwijk, NL, by Dirk J. Wouters and Eike Linn RWTH Aachen, Institut für Werkstoffe der Elektrotechnik, Aachen, Germany ESA WS April 2015 Folie 2]
- • ^A particular effect observed in our experiments shows that microtubules function as memristors.
- • Memristors represent the fourth element of the electrical circuits complementing resistors, capacitors and inductors.
- • Hallmarks of memristive behavior include
- • pinched and frequency-dependent I-V hysteresis loops. Memristive affect on current flux passing through Memristor voltage-current plane.
- • circuits containing conventional nonlinear devices and linear (directly proportional changes) accumulating elements are described which generate pinched hysteresis loops.
- • and most importantly, a functional dependence of the magnetic flux passing through an ideal memristor on its electrical charge.
- • In this research provided both theoretical and experimental evidence that microtubules act according to the definition of a memeristor.
- • Their biophysical properties lead to pinched hysteretic I-V dependence
- • as well a classic dependence of magnetic flux on charge.
- • In this research estimates of microtubule memristance reveal the significance for neuroscience and nanotechnology.
- • Memristor electrical resistance is not constant but depends on the history of current that had previously flowed through the device, i.e., its present resistance depends on how much electric charge has flowed in what direction through it in the past; the device remembers its history — the so-called non-volatility property.
- [2] When the electric power supply is turned off, the memristor remembers its most recent resistance until it is turned on again.
- [3][4] [1 Chua, L. O. (1971), "Memristor—The Missing Circuit Element (reprint on CiteSeerX)", IEEE Transactions on Circuit Theory, CT-18 (5): 507–519, CiteSeerX 10.1.1.189.3614 ]
- [2.Chua, Leon (1 March 2011). "Resistance switching memories are memristors" (PDF). Applied Physics A. 102 (4): 765–783. Bibcode:2011ApPhA.102..765C]
- [3.Strukov, Dmitri B.; Snider, Gregory S.; Stewart, Duncan R.; Williams, R. Stanley (2008).
- "The missing memristor found"(PDF). Nature. 453 (7191): 80–83. Bibcode:2008Natur.453...80S] [4.Memristor FAQ, Hewlett-Packard, retrieved 2010-09-03 [Wikipedia} ]
“MTs have been experimentally demonstrated to respond to externally-applied electric fields in vitro exhibiting alignment and drift effects along field lines23,24,25. Researchers reported the results from their four-probe measurements of both DC and AC conductive properties. The values of DC conductivity of MTs, found using a 200 nm gap, were reported to be in a very broad range from 10−1 to 102 S/m. In fact, they found MTs at particular frequency values to become almost 1000-fold more conductive than their DC estimates, reportedly showing surprisingly high values for MT conductivities between 103 and up to 105 S/m31. These effects were interpreted as being due to MT’s ballistic conductivity property. It was also claimed by these authors but not proven that the high conductivity at specific frequency ranges arises from the water content inside the MT lumen. 32.
“Based on the above overview of the reported effects of MTs on the conducting properties of solutions containing MTs, it can be concluded that MTs act as conducting cables for charge transport, showing increased conductivity compared to the solution itself as well as possessing electric capacitance that is due to counter-ion condensation and the formation of a charge-separation double layer involving negative MT surface charges and positive counter-ions.
“It was further hypothesized previously that MTs may also have intrinsic inductance due to the possibility of solenoidal flow of ionic charges, which put together with other observed properties and a non-linear capacitance due to highly limited number of counter-ions they can attract, leads to a transistor-like behavior with the observed injected current amplification 33,38. Below, we argue that in addition to the already demonstrated unusual electrical conduction properties described above, MTs also behave as nano-scale sub-cellular memristive devices. In Fig. 1 we show how the effects of ionic charge propagation along an MT affect the conformations of the negatively-charged C-termini and also how these ionic flows may involve penetration into the MT lumen. These effects will be discussed below in the paper in connection with memristive behavior or MTs.
Figure 1 Schematics displaying ionic movement along an MT. Conformational changes in C-termini on the MT surface both alter ionic flows and respond to them, creating a non-linear transmission line. (A–C) display charge transport along the MT length and outside it. (D) displays charge transport across the MT surface into its lumen.
Microtubules as Memristors: It important to note that this effect is similar to the situation arising with current flows along memristors, which affect the state of the memristor. 7. Since the counter-ions act as electric charge carriers in the ionic currents facilitated by MTs functioning as nonlinear cables, the variable-diameter pipe analogy appears to be suitable for the description of MT conductivity.
If a DC current, i(t), is applied across a memristor, the memristance will not have a constant value, but will vary with time. This is because the memristance M(q) = df(q)/dq is not a function of i, but rather it is a function of the time integral of i(t), namely, the charge q, where f(q) is the slope of the flux versus charge, a characteristic curve defining the memristor. After the current drops to zero at t = T, the memristance retains its last value M(T). In other words, the memristor remembers the latest value of M(t) until the currentdrops to zero. This property is directly responsible for the memory of the device. It is important to understand that what is remembered is the value of memristance, and not the value of the voltage, or current. Hence memristance represents the “memory” property of the device.
We have previously reported impedance measurements for MTs and tubulin solutions under various conditions in Santelices et al. 32 where details of the methodology used can be found. Such experiments, performing current-voltage measurements at both AC and DC voltages can potentially validate the memristive properties of MTs. Here, we report for the first time the observed hysteretic behavior of the buffer solution with ensembles of MTs.
Specifically, by reversing the voltage applied we were able to observe a characteristic pinched hysteresis loop for memristors, which is shown in Fig. 3. A combined effect is shown for MTs and the buffer in which they are solubilized and a net effect on MTs by themselves where we have subtracted the contribution of the buffer.
Conclusions: “In this research we have provided theoretical and experimental evidence in support of the hypothesis that MTs are intracellular memristors. MTs have highly negative linear charge densities, which are screened by counterions surrounding MTs from both outer and inner surfaces. The same counterions anchored by negative charges within the Bjerrum regions stay in fixed states until injected currents or potential gradients push them away from the MT vicinity.
“Ionic motion is guided by MT geometry but there are numerous intricacies due to the presence of nanopores on the MT surface, which enable ionic motion in and out of the lumen. Moreover, the highly charged C-termini decorate the MT surface in a periodic pattern and can fluctuate between at least two conformational states: outstretched and bound to the MT surface.
“Transitions between these two states are susceptible to local electrostatic potentials and hence interact with ionic flows. We believe that these conformational transitions are responsible for memristive properties of MTs. In Fig. 5 we show an illustrative comparison between a TiO2 memristor where oxygen vacancies play the role of memory carriers and an MT memristor where ionic species are memory carriers.
“Overall our findings in the above experiments and simulations seem to indicate that MTs can propagate, and amplify, electric signals via ionic flows along the MT surface, through the lumen and across their nanopores.
“Simulations suggest that these flows are sensitive to the dynamics of the C-terminal region, and consequently are tubulin isotype-dependent since various tubulin isotypes are characterized, among other properties, by C-termini differences.
“So far there seems to be no direct experimental verification of role of the MT cytoskeleton in electrical signal conduction in neurons. However, there is significant indirect experimental evidence in support of MT’s being involved in human cognition and hence potentially in neuronal signaling. In Fig. 6 we show the distribution of MTs within the axons of neurons, which is intended to visualize how signals carried by ionic flows along MTs can be incorporated into the functions of neurons by interactions with MAPs, which can then be coupled to axoplasmic transport and can affect ion channels, for example.
“MTs form a complex ionic circuit within a neuron. A schematic displaying the role of MTs as individual circuit elements that transfer signals along a neuron. MAPs link MTs, enhancing long-range ionic transport across the neuronal cytoskeleton.
“The neuronal cytoskeleton has been purported to play a crucial role in learning processes and memory formation, which has been documented and reviewed 21,22,38. Most eukaryotic cells exhibit MT dynamic instability with periods of growth interspersed with catastrophes and rescue events.
“However, MTs in neurons are less dynamic and more stable due to their interconnections with MAPs. However, reorganization of the MTs and MAPs in the neuronal cytoskeleton is known to occur during learning, which has been seen to correlate with an increase in MT numbers, and has also been shown to be impaired by the MT depolymerizing agent colchicine.
“This appears to indicate that learning involves dynamic MTs 21,44. Work on the molecular basis of memory has implicated CaMKII (calcium/calmodulin-dependent protein kinase II) as crucial to LTP (long-term potentiation) contributing to learning and the memory formation 45,46.
“CaMKII also phosphorylates both α- and β-tubulin directly in the C-terminal region of the protein47. An atomic-resolution model of MT phosphorylation by CaMKII 18 demonstrates an intricate and potentially massive molecular code of information encryption in the structure of neuronal MTs, especially in dendrites, and this can be directly linked to current flows, which we argue possess memristive properties along MTs.
“Enzymatic reactions of this type may trigger MT matrix reorganization, which is required for memory formation and learning.
“A mechanistic understanding of memory encoding at the intracellular level now emerges, which is not only dynamic but inherently linked to subtle conductive properties of MTs, especially their memristive ionic conduction characteristics as argued in this paper. 48.
“There are several clear advantages offered by MTs as intracellular memristors. Tubulin is one of the most abundant proteins in neurons,
and MTs are exceptionally well-conserved, spatio-temporally ubiquitous proteins.
“This suggests a widespread nature of MT memristors within the cell. Additionally, post-translational modifications (PTMs) on C-termini tails of tubulin that vary depending on the local and global MT environment may lead to complex attenuations in memristive action, depending on the positioning of MTs within the cell and on the cell type.
“The presence of MAPs provides further advantages and complexity to MT networks, creating connections among adjacent MTs (see Fig. 6) and establishing contacts between MTs and various macromolecules.
“While it is well-known that proteins degrade and denature over time, which would affect the endurance of MT-based memristors, some of it may be mitigated by stabilizing MTs via MAPs and pharmacological agents such as taxol.
“On the other hand, limited durability of MT-based devices offers new avenues such as the ability to construct evolvable bio-electronic devices or biodegradable or self-destructing ones.
Our discovery that MTs are biological memristors could, for example, help resolve the unknown origin of the ****impressive memory capabilities exhibited by the amoeba, which do not have neurons, let alone a brain, but are loaded with MTs ****.
“In general, MTs may offer numerous advantages over silicon-based technology. Microtubules are biological, biodegradable materials and hence offer an environmental advantage over seminconducting materials.
They are very abundant in all eukaryotic organisms and highly conserved through evolution indicating their importance to living systems.
“Due to the diversity of C-termini sequences, which are cell-type and species-specific, there is a huge potential for designing an array of MT-based memristors with functional differences. This can be further amplified by post-translational modifications.
Finally, MTs can form bioelectric circuits through their natural connections to MAPs, hence an enormous spectrum of circuit geometries is possible to be created even by self-organization processes. [Tuszynski, J.A., Friesen, D., Freedman, H. et al. Microtubules as Sub-Cellular Memristors. Sci Rep 10, 2108 (2020). https://doi.org/10.1038/s41598-020-58820-y]
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“Memristors represent the 4th element of the electrical circuits complementing resistors, capacitors and inductors. “Hallmarks of memristive behavior include:
- pinched and frequency-dependent I-V hysteresis loops .
- and most importantly, a functional dependence of the magnetic flux passing through an ideal Memristor on its electrical charge. Memristive affect on current flux passing through Memristor voltage-current plane.
“Research provided both theoretical and experimental evidence that microtubules act according to the definition of a memeristor. “Their biophysical properties lead to pinched hysteretic I-V dependence as well a classic dependence of magnetic flux on charge.
In this research estimates of microtubule memristance reveal the significance for neuroscience and nanotechnology.
Memristor electrical resistance is not constant but depends on the history of current that had previously flowed through the device, i.e., its present resistance depends on how much electric charge has flowed in what direction through it in the past; the device remembers its history — the so-called non-volatility property.[2] When the electric power supply is turned off, the memristor remembers its most recent resistance until it is turned on again.[3][4]
- [1 Chua, L. O. (1971), "Memristor—The Missing Circuit Element (reprint on CiteSeerX)", IEEE Transactions on Circuit Theory, CT-18 (5): 507–519, CiteSeerX 10.1.1.189.3614 ]
- [2.Chua, Leon (1 March 2011). "Resistance switching memories are memristors" (PDF). Applied Physics A. 102 (4): 765–783. Bibcode:2011ApPhA.102..765C]
- [3.Strukov, Dmitri B.; Snider, Gregory S.; Stewart, Duncan R.; Williams, R. Stanley (2008). "The missing memristor found"(PDF). Nature. 453 (7191): 80–83. Bibcode:2008Natur.453...80S]
- [4.Memristor FAQ, Hewlett-Packard, retrieved 2010-09-03 [Wikipedia} ]
- • “Microtubules (MTs) are cylindrical protein filaments that play crucial roles in eukaryotic cell functions.
- • They are particularly important in both axons and dendrites of neurons, hence their prominence in biophysical models of consciousness.
- • ^The building block of microtubules, the heterodimer of alpha and beta tubulin has been well characterized crystallographically, which allowed us to build atomic-level models of tubulin and microtubules.
- • These models reveal complex electrostatic properties of microtubules, molecular mechanics, structural stability, hydrogen-bond interactions as well as conductive properties in ionic solutions.
- • This research reports the recent experimental results of the effects MTs, and tubulin dimers have on ionic solution’s AC conductance.
- • Using a microelectrode system we have measured the AC conductivity and capacitance in a number of tubulin and microtubule solutions between 1 kHz and 1 MHz range of electric field frequencies. MTs in a low ionic solution increase solution conductance by 6% at 100 kHz, and this effect increases as the concentration of MTs increases. We model the possibility that this effect is due to ions being able to use MTs as a low-resistance cable as predicted in earlier publications.
- • Conversely, tubulin dimers decrease solution conductance by 5% at 100 kHz under similar conditions indicating that a transformation from depolymerized to polymerized tubulin corresponds to an insulator-conductor transition with major implications for cell division and the function of neurons.
- • We model these effects as being due to tubulin attracting counter-ion charges and lowering their mobility when depolymerized and directing their flows when polymerized. MTs show the ability to modulate the buffer solution’s conductance and capacitance and act as low resistance pathways for ions.
- • ^This has significant implications for biological information processing, especially in neurons, and for intracellular electrical communication in general
1. A. See slide above in photos
