Trends in Cognitive Sciences
Volume 5, Issue 11, 1 November 2001, Pages 472-478
Journal home page for Trends in Cognitive Sciences

Opinion
A quantum approach to visual consciousness

https://doi.org/10.1016/S1364-6613(00)01774-5Get rights and content

Abstract

A theoretical approach relying on quantum computation in microtubules within neurons can potentially resolve the enigmatic features of visual consciousness, but raises other questions. For example, how can delicate quantum states, which in the technological realm demand extreme cold and isolation to avoid environmental ‘decoherence’, manage to survive in the warm, wet brain? And if such states could survive within neuronal cell interiors, how could quantum states grow to encompass the whole brain? We present a physiological model for visual consciousness that can accommodate brain-wide quantum computation according to the Penrose–Hameroff ‘Orch OR’ model. In this view, visual consciousness occurs as a series of several-hundred-millisecond epochs, each comprising ‘crescendo sequences’ of quantum computations occurring at ∼40 Hz.

Section snippets

Is quantum computation feasible in the brain?

Orch OR and other quantum models are viewed skeptically for seemingly good reasons. Technological quantum computation requires isolation and extreme cold to avoid rapid decoherence by environmental thermal interactions, yet the brain operates at about 310 K. Quantum states in microtubules within neurons and glial cells would need to be isolated or shielded long enough to reach threshold for Orch OR in neurophysiologically relevant time scales (i.e. ranging from roughly 25 ms to several hundred

Neuroanatomical and neurophysiological substrates for Orch OR

At the cellular level, the most likely site for Orch OR related to rudimentary visual consciousness is within dendrites and cell bodies of the pyramidal cells in layer 5 of visual cortex (see Fig. 1). Pribram 15 and Eccles 16, among others, have argued that consciousness occurs primarily in dendrites, with axons serving to execute and communicate results of conscious dendritic processes. Pribram 15 emphasized ‘horizontal’ dendrodendritic connections (e.g. via electrotonic gap junctions) in

Rudimentary visual consciousness

Having examined the underlying neuroanatomy and physiology that could support Orch OR, we now turn to how this mechanism might give rise to visual consciousness. It is generally agreed that ten or more cortical areas are involved in vision and that the main pathway for visual input is from the retina to lateral geniculate of the thalamus and then directly to striate cortex (V1) 29. Some neuroscientists believe V1 to be a site for conscious vision; however, many agree with the suggestion of

Conclusion

We have presented a seemingly radical model of quantum computation in visual cortex to address the exceedingly difficult features of visual consciousness. According to the Orch OR model, subjective, phenomenal conscious vision depends on quantum computation in microtubules. We have outlined explanations of how quantum states can occur at the temperatures at which the brain operates, and remain stable for time periods commensurate with neurophysiological events. We propose that quantum states

Questions for future research

  • How are certain objects or aspects of a visual scene selected for attention?

  • How is it that inputs from different parts of the visual field, as well as visual inputs arriving at different times, are globally integrated into unitary visual objects and scenes (spatial and temporal binding)?

  • What are the neural and physical mechanisms whereby objects and scenes become subjectively conscious, and what exactly is phenomenal visual consciousness (the ‘hard problem’ of phenomenal vision)?

Glossary

acetylcholine
a neurotransmitter found in the peripheral and central nervous systems required for movement, memory, attention and consciousness.
actin
filamentous cytoskeletal protein, which polymerizes to form cytoplasmic gel.
CaMK II
(calcium/calmodulin-dependent kinase II) a protein molecule that adds phosphoryl groups to other molecules as a mechanism of activation.
cholinergic
an action or neuronal system utilizing acetylcholine.
cytoskeleton
the internal scaffolding (microtubules, MAP-2, actin,

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