171 research outputs found
Remarks on the number of tubulin dimers per neuron and implications for Hameroff-Penrose Orch OR
No full textStuart Hameroff has wrongly estimated that a typical brain neuron has 10^7^ tubulin dimers and wrongly attributed this result to Yu and Baas, J. Neurosci. 1994; 14: 2818-2829. In this letter we show that Hameroff’s estimate is based on misunderstanding of the results provided by Yu and Baas, who actually measured the total microtubule length in a single axonal projection with length of 56 μm in a differentiating in vitro stage 3 embryonic hippocampal neuron. In order to visualize how big Hameroff’s error is, we have reconstructed two of the studied by Yu and Baas embryonic hippocampal neurons with Neuromantic v1.6.3 and compared them with previously published reconstructions of adult hippocampal neurons. Correct calculations show that an adult differentiated pyramidal neuron in vivo has approximately 1.3×10^9^ tubulin dimers incorporated in cytoskeletal microtubules. This estimate has profound implications for the Hameroff-Penrose Orch OR model, because it sets limitations on the number of quantum coherent neurons and implies that if 100% of the neuronal microtubules are quantum coherent for 25 ms then Hameroff-Penrose Orch OR conscious events should involve only 15 pyramidal neurons
Cytoskeletal signaling: is memory encoded in microtubule lattices by CaMKII phosphorylation?
No full textMemory is attributed to strengthened synaptic connections among particular brain neurons, yet synaptic membrane components are transient, whereas memories can endure. This suggests synaptic information is encoded and 'hard-wired' elsewhere, e.g. at molecular levels within the post-synaptic neuron. In long-term potentiation (LTP), a cellular and molecular model for memory, post-synaptic calcium ion (Ca²⁺) flux activates the hexagonal Ca²⁺-calmodulin dependent kinase II (CaMKII), a dodacameric holoenzyme containing 2 hexagonal sets of 6 kinase domains. Each kinase domain can either phosphorylate substrate proteins, or not (i.e. encoding one bit). Thus each set of extended CaMKII kinases can potentially encode synaptic Ca²⁺ information via phosphorylation as ordered arrays of binary 'bits'. Candidate sites for CaMKII phosphorylation-encoded molecular memory include microtubules (MTs), cylindrical organelles whose surfaces represent a regular lattice with a pattern of hexagonal polymers of the protein tubulin. Using molecular mechanics modeling and electrostatic profiling, we find that spatial dimensions and geometry of the extended CaMKII kinase domains precisely match those of MT hexagonal lattices. This suggests sets of six CaMKII kinase domains phosphorylate hexagonal MT lattice neighborhoods collectively, e.g. conveying synaptic information as ordered arrays of six "bits", and thus "bytes", with 64 to 5,281 possible bit states per CaMKII-MT byte. Signaling and encoding in MTs and other cytoskeletal structures offer rapid, robust solid-state information processing which may reflect a general code for MT-based memory and information processing within neurons and other eukaryotic cells
Quantum computation in brain microtubules? The Penrose–Hameroff ‘Orch OR‘ model of consciousness
No full textPlenary debate: Quantum effects in biology: trivial or not?
No full textCopyright © World Scientific Publishing CompanyDerek Abbott, Julio Gea-Banacloche, Paul C. W. Davies, Stuart Hameroff, Anton Zeilinger, Jens Eisert, Howard Wiseman, Sergey M. Bezrukov and Hans Frauenfelde
How quantum brain biology can rescue conscious free will
No full textConscious ‘free will’ is problematic because 1) brain mechanisms causing consciousness are unknown, 2) measurable brain activity correlating with conscious perception apparently occurs too late for real-time conscious response, consciousness thus being considered ‘epiphenomenal illusion’, and 3) determinism, i.e. our actions and the world around us seem algorithmic and inevitable. The Penrose-Hameroff theory of ‘orchestrated objective reduction’ (‘Orch OR’) identifies discrete conscious moments with quantum computations in microtubules inside brain neurons, e.g. 40 per second in concert with gamma synchrony EEG. Microtubules organize neuronal interiors and regulate synapses. In Orch OR, microtubule quantum computations occur in integration phases in dendrites and cell bodies of integrate-and-fire brain neurons connected and synchronized by gap junctions, allowing entanglement of microtubules among many neurons. Quantum computations in entangled microtubules terminate by Penrose ‘objective reduction’ (‘OR’), a proposal for quantum state reduction and conscious moments linked to fundamental spacetime geometry. Each OR reduction selects microtubule states which can trigger axonal firings, and control behavior. The quantum computations are ‘orchestrated’ by synaptic inputs and memory (thus ‘Orch OR’). If correct, Orch OR can account for conscious causal agency, resolving problem 1. Regarding problem 2, Orch OR can cause temporal non-locality, sending quantum information backward in classical time, enabling conscious control of behavior. Three lines of evidence for brain backward time effects are presented. Regarding problem 3) Penrose OR (and Orch OR) invoke non-computable influences from information embedded in spacetime geometry, potentially avoiding algorithmic determinism. In summary, Orch OR can account for real-time conscious causal agency, avoiding the need for consciousness to be seen as epiphenomenal illusion. Orch OR can rescue conscious free will
"Funda-Mentality": is the conscious mind subtly linked to a basic level of the universe?
No full textAge-old battle lines over the puzzling nature of mental experience are shaping a modern resurgence in the study of consciousness. On one side are the long-dominant "physicalists" who view consciousness as an emergent property of the brain's neural networks. On the alternative, rebellious side are those who see a necessary added ingredient: proto-conscious experience intrinsic to reality, perhaps understandable through modern physics (panpsychists, pan-experientialists, "funda-mentalists"). It is argued here that the physicalist premise alone is unable to solve completely the difficult issues of consciousness and that to do so will require supplemental panpsychist/pan-experiential philosophy expressed in modern physics. In one scheme proto-conscious experience is a basic property of physical reality accessible to a quantum process associated with brain activity. The proposed process is Roger Penrose's "objective reduction" (OR), a self-organizing "collapse" of the quantum wave function related to instability at the most basic level of space-time geometry. In the Penrose- Hameroff model of "orchestrated objective reduction" (Orch OR), OR quantum computation occurs in cytoskeletal microtubules within the brain's neurons. The basic thesis is that consciousness involves brain activities coupled to a self-organizing ripples in fundamental reality
The feasibility of coherent energy transfer in microtubules.
No full textIt was once purported that biological systems were far too \u27warm and wet\u27 to support quantum phenomena mainly owing to thermal effects disrupting quantum coherence. However, recent experimental results and theoretical analyses have shown that thermal energy may assist, rather than disrupt, quantum coherent transport, especially in the \u27dry\u27 hydrophobic interiors of biomolecules. Specifically, evidence has been accumulating for the necessary involvement of quantum coherent energy transfer between uniquely arranged chromophores in light harvesting photosynthetic complexes. The \u27tubulin\u27 subunit proteins, which comprise microtubules, also possess a distinct architecture of chromophores, namely aromatic amino acids, including tryptophan. The geometry and dipolar properties of these aromatics are similar to those found in photosynthetic units indicating that tubulin may support coherent energy transfer. Tubulin aggregated into microtubule geometric lattices may support such energy transfer, which could be important for biological signalling and communication essential to living processes. Here, we perform a computational investigation of energy transfer between chromophoric amino acids in tubulin via dipole excitations coupled to the surrounding thermal environment. We present the spatial structure and energetic properties of the tryptophan residues in the microtubule constituent protein tubulin. Plausibility arguments for the conditions favouring a quantum mechanism of signal propagation along a microtubule are provided. Overall, we find that coherent energy transfer in tubulin and microtubules is biologically feasible
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Transcranial Ultrasound as Therapy for Patients with Alzheimer's Disease and Other Dementias
No full textAlzheimer's disease is a progressive disorder that can affect cognitive and mental functions, and is the most common form of dementia. In upcoming years, the number of people expected to get Alzheimer's disease is expected to increase significantly due to so-called 'baby boomers' reaching advanced age. Clinical trials regarding dementia are critical in advancing Alzheimer's therapy, but drugs have been ineffective thus far. Rather than drugs, non-invasive brain stimulation techniques have had encouraging results. In animals, low to moderate transcranial ultrasound ('TUS') improves memory, and in humans, TUS causes improvements in mood. The application of TUS in humans is a promising therapy for neuronal growth, cognitive function, and mental state of mind. This paper reviews potential use of TUS for Alzheimer’s disease and dementia
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