Quantum physics in neuroscience and psychology: a neurophysical model of mind–brain interaction
Your brain is a time machine: the neuroscience and physics of time Buonomano is trying to reach a broad non-specialist audience and. That notion has always been met with skepticism, which is not . What if, Penrose asked, there are molecular structures in our brains that are. Making sense of the brain is another challenge entirely. Balasubramanian did his Ph.D. in theoretical particle physics at Princeton University and . Answering the mystery of what atoms do when liquids and gases meet.
Rather than attempting to get every detail right, like a physics teacher might require, software-powered physics engines take shortcuts. With this approach they can get most things just about right, and they can do it quickly.
This way, games can generate the outcome of a car crashing into a race barrier in real-time. Might this also be how the brain works? This idea has been explored from other angles, but the new study is the first one to look at the areas of the brain involved in interpreting physical events. The study involved four experiments, each building on the previous one.
All of them took place while participants were undergoing fMRIs functional magnetic resonance imaging. Participants were asked to judge either where the blocks would land if the tower toppled, or whether the tower had more blue or yellow blocks. Several areas of the brain responded more strongly when participants predicted how the blocks would fall. The dots interacted either like billiard balls following the laws of physics, or like people interacting socially for example, one could chase the other.
After eight seconds one dot disappeared. Two seconds later it reappeared. Participants predicted the path of the invisible dot during those two seconds and reported whether they were correct. Some areas of the brain were active in both cases, likely those involved in general problem-solving, prediction, and spatial reasoning.
Experiment 3 To explore whether looking at a physics event is enough to cause a strong reaction in the five regions of interest, participants watched short movies with varying amounts of physics content like a ball rolling. The more physics content in a movie, the stronger the responses in the regions of interest.
Thus, the structure of a proper physical theory must involve not only the part describing the behaviour of the not-directly experienced theoretically postulated entities, expressed in some appropriate symbolic language, but also a part describing the human experiences that are pertinent to these tests and applications, expressed in the language that we actually use to describe such experiences to ourselves and to each other.
And the theory must specify the connection between these two differently described and differently conceived parts of scientific practice.
Classic physics meets this final requirement in a trivial way. The relevant experiences of the human participants are taken to be direct apprehensions of the gross properties of large objects composed of huge numbers of their tiny atomic-scale parts.
These apprehensions of, for example, the perceived location and motion of a falling apple or the position of a pointer on a measuring device were taken to be passive: But the physicists who were examining the behaviours of systems that depend sensitively upon the behaviours of their tiny atomic-scale components found themselves forced to introduce a less trivial theoretical arrangement. In the new scheme the human agents are no longer passive observers.
They are considered to be active agents or participants. The participation of the agent continues to be important even when the only features of the physically described world being observed are large-scale properties of measuring devices. The sensitivity of the behaviour of the devices to the behaviour of some tiny atomic-scale particles propagates first to the devices and then to the observers in such a way that the choice made by an observer about what sort of knowledge to seek can profoundly affect the knowledge that can ever be received either by that observer himself or by any other observer with whom he can communicate.
Thus the choice made by the observer about how he or she will act at a macroscopic level has, at the practical level, a profound effect on the physical system being acted upon. That conclusion is not surprising. How one acts on a system would, in general, be expected to affect it.
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Nor is it shocking that the effect of the agent's actions upon the system being probed is specified by the quantum mechanical rules. But the essential point not to be overlooked is that the logical structure of the basic physical theory has become fundamentally transformed.
The agent's choice about how to act has been introduced into the scientific description at a basic level and in a way that specifies, mathematically, how his or her choice about how to act affects the physical system being acted upon.
The structure of quantum mechanics is such that, although the effect upon the observed system of the agent's choice about how to act is mathematically specified, the manner in which this choice itself is determined is not specified. This means that, in the treatment of experimental data, the choices made by human agents must be treated as freely chosen input variables, rather than as mechanical consequences of any known laws of nature.
Quantum theory thereby converts science's concept of us from that of a mechanical automaton, whose conscious choices are mere cogs in a gigantic mechanical machine, to that of agents whose conscious free choices affect the physically described world in a way specified by the theory. The approximation that reduces quantum theory to classic physics completely eliminates the important element of conscious free choice. Owing to the strangeness of the properties of nature entailed by the new mathematics, the Copenhagen strategy was to refrain from making any ordinary sort of ontological claims, but instead to take an essentially pragmatic stance.
Thus, the theory was formulated basically as a set of practical rules for how scientists should go about the tasks of acquiring, manipulating and using knowledge. This change in perspective is captured by Heisenberg's famous statement: The conception of the objective reality of the elementary particles has thus evaporated not into the cloud of some obscure new reality concept, but into the transparent clarity of a mathematics that represents no longer the behavior of the particle but rather our knowledge of this behavior.
Heisenbergp. The key idea is more concretely expressed in statements such as: The freedom of experimentation, presupposed in classic physics, is of course retained and corresponds to the free choice of experimental arrangement for which the mathematical structure of the quantum mechanical formalism offers the appropriate latitude. Bohrp. In order to achieve this re-conceptualization of physics the Copenhagen formulation separates the physical universe into two parts, which are described in two different languages.
One part is the observing human agent plus its measuring devices. The other part of nature is the system that the agent is acting upon. That part is described in physical terms—in terms of mathematical properties assigned to tiny space—time regions. In particular, it brings a crucial part of doing science, namely our choices about how we will probe nature, directly into the causal structure.
It specifies the effects of these probing actions upon the systems being probed. This approach works very well in practice. However, the body and brain of the human agent, and also their devices, are composed of atomic constituents. Hence a complete theory ought to be able to describe these systems in physical terms.
The great mathematician and logician John von Neumann formulated quantum theory in a rigorous way that allows the bodies and brains of the agents, along with their measuring devices, to be shifted into the physically described world. At each step the crucial act of choosing or deciding between possible optional observing actions remains undetermined by the physical observed system. This act of choosing is always ascribed to the observing agent.
It is described in psychological terms, and is, in practice, the stream of consciousness of the agent. At each step the direct effect of the conscious act is upon the part of the physically described world that is closest to the psychologically described world.
This means that, in the end, the causal effect of the agent's mental action is on their own brain, or some significant part of their brain.
Process 2 is the analogue in quantum theory of the process in classic physics that takes the state of a system at one time to its state at a later time.
This process 2, like its classic analogue, is local and deterministic. However, process 2 by itself is not the whole story: For example, if process 2 were, from the time of the big bang, the only process in nature, then the quantum state centre point of the moon would represent a structure smeared out over a large part of the sky, and each human body—brain would likewise be represented by a structure smeared out continuously over a huge region.
Process 2 generates a cloud of possible worlds, instead of the one world we actually experience. Any physical theory must, in order to be complete, specify how the elements of the theory are connected to human experience.
In classic physics this connection is part of a metaphysical superstructure: But in quantum theory a linkage of the mathematically described physical state to human experiences is contained in the mathematically specified dynamic. This connection is not passive. It is not a mere witnessing of a physical feature of nature. Instead, it injects into the physical state of the system being acted upon specific properties that depend upon choices made by the agent.
Quantum theory is built upon the practical concept of intentional actions by agents. Each such action is a preparation that is expected or intended to produce an experiential response or feedback. Quantum theory is thus an information-based theory built upon the preparative actions of information-seeking agents. Probing actions of this kind are not only performed by scientists. Every healthy and alert infant is continually engaged in making wilful efforts that produce experiential feedbacks and he or she soon begins to form expectations about what sorts of feedbacks are probable to follow from some particular kind of effort.
Thus, both empirical science and normal human life are based on paired realities of this action—response kind, and our physical and psychological theories are both basically attempting to understand these linked realities within a rational conceptual framework.
Science would be difficult to pursue if scientists could make no such judgements about what they are experiencing.
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All known physical theories involve idealizations of one kind or another. In quantum theory the main idealization is not that every object is made up of miniature planet-like objects. It is rather that there are agents that perform intentional acts each of which can result in feedback that may or may not conform to a certain criterion associated with that act.
One piece of information is introduced into the world in which that agent lives, according to whether or not the feedback conforms to that criterion. The answer places the agent on one or the other of two alternative possible branches of the course of world history.
These remarks reveal the enormous difference between classic physics and quantum physics. In classic physics the elemental ingredients are tiny invisible bits of matter that are idealized miniaturized versions of the planets that we see in the heavens and that move in ways unaffected by our scrutiny, whereas in quantum physics the elemental ingredients are intentional preparative actions by agents, the feedbacks arising from these actions and the effects of these actions upon the physically described states of the probed systems.
This radical restructuring of the form of physical theory grew out of a seminal discovery by Heisenberg. That discovery was that in order to get a satisfactory quantum generalization of a classic theory one must replace various numbers in the classic theory by actions operators. A key difference between numbers and actions is that if A and B are two actions then AB represents the action obtained by performing the action A upon the action B.
But for numbers the order does not matter: The difference between quantum physics and its classic approximation resides in the fact that in the quantum case certain differences AB—BA are proportional to a number measured by Max Planck inand called Planck's constant. Setting those differences to zero gives the classic approximation.
Thus quantum theory is closely connected to classic physics, but is incompatible with it, because certain non-zero quantities must be replaced by zero to obtain the classic approximation. The intentional actions of agents are represented mathematically in Heisenberg's space of actions. A description of how it operates follows.
Each intentional action depends, of course, on the intention of the agent and upon the state of the system upon which this action acts. Each of these two aspects of nature is represented within Heisenberg's space of actions by an action.
We shall denote the action or operator that represents the state being acted upon by the symbol S. An intentional act is an action that is intended to produce a feedback of a certain conceived or imagined kind. Of course, no intentional act is certain: The effect of this intentional mental act is represented mathematically by an equation that is one of the key components of quantum theory.
This equation represents, within quantum mathematics, the effect of process 1 action upon the quantum state S of the system being acted upon. Thus, an effect of the probing action is injected into the mathematical description of the physical system being acted upon. The operator P is important. That particular retained part is determined by the choice made by the agent.
Notice that process 1 produces the sum of the two alternative possible feedbacks, not just one or the other. But that is not correct. This is a key point. It can be made absolutely clear by noticing that S can be written as a sum of four parts, only two of which survive the process 1 action: This formula is a strict identity. The dedicated reader can quickly verify it by collecting the contributions of the four occurring terms PSP, PS, SP and S, and verifying that all terms but S cancel out.
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This identity shows that the state S is a sum of four parts, two of which are eliminated by process 1. But this means that process 1 has a non-trivial effect upon the state being acted upon: This result is the first key point: Nature's subsequent choice we shall call process 3. Orthodox quantum theory is formulated in a realistic and practical way.
It is structured around the activities of human agents, who are considered able to freely elect to probe nature in any one of many possible ways.
Bohr emphasized the freedom of the experimenters in passages such as the one already quoted earlier, or the similar: The foundation of the description of the experimental conditions as well as our freedom to choose them is fully retained. Those quantum laws are the only precise laws of nature recognized by that theory. The von Neumann generalization leaves this freedom intact. That assumption would have been reasonable during the nineteenth century.
But now, in the twenty-first century, it is rationally untenable. Quantum theory must be used in principle because the behaviour of the brain depends sensitively upon atomic, molecular and ionic processes, and these processes in the brain often involve large quantum effects. To study quantum effects in brains within an orthodox i. Copenhagen or von Neumann quantum theory one must use the von Neumann formulation. This is because Copenhagen quantum theory is formulated in a way that leaves out the quantum dynamics of the human observer's body and brain.
But von Neumann quantum theory takes the physical system S upon which the crucial process 1 acts to be precisely the brain of the agent, or some part of it. Thus process 1 describes here an interaction between a person's stream of consciousness, described in mentalistic terms, and an activity in their brain, described in physical terms.
A key question is the quantitative magnitude of quantum effects in the brain. They must be large in order for deviations from classic physics to play any significant role. To examine this quantitative question we consider the quantum dynamics of nerve terminals. Nerve terminals are essential connecting links between nerve cells. The general way they work is reasonably well understood. When an action potential travelling along a nerve fibre reaches a nerve terminal, a host of ion channels open.
Calcium ions enter through these channels into the interior of the terminal. These ions migrate from the channel exits to release sites on vesicles containing neurotransmitter molecules.
At their narrowest points, calcium ion channels are less than a nanometre in diameter Cataldi et al. This extreme smallness of the opening in the calcium ion channels has profound quantum mechanical implications. The narrowness of the channel restricts the lateral spatial dimension.
Consequently, the lateral velocity is forced by the quantum uncertainty principle to become large. This causes the quantum cloud of possibilities associated with the calcium ion to fan out over an increasing area as it moves away from the tiny channel to the target region where the ion will be absorbed as a whole, or not absorbed at all, on some small triggering site. This spreading of this ion wave packet means that the ion may or may not be absorbed on the small triggering site.
Accordingly, the contents of the vesicle may or may not be released. Consequently, the quantum state of the brain has a part in which the neurotransmitter is released and a part in which the neurotransmitter is not released. This quantum splitting occurs at every one of the trillions of nerve terminals. This means that the quantum state of the brain splits into a vast host of classically conceived possibilities, one for each possible combination of the release-or-no-release options at each of the nerve terminals.
In fact, because of uncertainties on timings and locations, what is generated by the physical processes in the brain will be not a single discrete set of non-overlapping physical possibilities but rather a huge smear of classically conceived possibilities.
This focus on the motions of calcium ions in nerve terminals is not meant to suggest that this particular effect is the only place where quantum effects enter into the brain process, or that the quantum process 1 acts locally at these sites.
What is needed here is only the existence of some large quantum of effect. The focus upon these calcium ions stems from the facts that i in this case the various sizes dimensions needed to estimate the magnitude of the quantum effects are empirically known, and ii that the release of neurotransmitter into synaptic clefts is known to play a significant role in brain dynamics.
The brain matter is warm and wet and is continually interacting intensely with its environment. It might be thought that the strong quantum decoherence effects associated with these conditions would wash out all quantum effects, beyond localized chemical processes that can be conceived to be imbedded in an essentially classic world. Strong decoherence effects are certainly present, but they are automatically taken into account in the von Neumann formulation employed here.
The existence of strong decoherence effects makes the main consequences of quantum theory being discussed here more easily accessible to neuroscientists by effectively reducing the complex quantum state of the brain to a collection of almost classically describable possibilities. Because of the uncertainties introduced at the ionic, atomic, molecular and electronic levels, the brain state will develop not into one single classically describable macroscopic state, as it does in classic physics, but into a continuous distribution of parallel virtual states of this kind.
Process 1 must then be invoked to allow definite empirical predictions to be extracted from this continuous smear of parallel overlapping almost-classic possibilities generated by process 2. The exact details of the plan will, for a classic model, obviously depend upon the exact values of many noisy and uncontrolled variables. The contemporary physical model accounts for these uncertainties in brain dynamics. As long as the brain dynamic is controlled wholly by process 2—which is the quantum generalization of the Newtonian laws of motion of classic physics—all of the various alternative possible plans of action will exist in parallel, with no one plan of action singled out as the one that will actually be experienced.
Some process beyond the local deterministic process 2 is required to pick out one experienced course of physical events from the smeared-out mass of possibilities generated by all of the alternative possible combinations of vesicle releases at all of the trillions of nerve terminals.
As already emphasized, this other process is process 1. This process brings in a choice that is not determined by any currently known law of nature, yet has a definite effect upon the brain of the chooser. The process 1 choice picks an operator P and also a time t at which P acts. The action P cannot act at a point in the brain, because action at a point would dump a huge in principle infinite amount of energy into the brain, which would then explode.
The operator P must, therefore, act non-locally, over a potentially large part of the brain. In examining the question of the nature of the effect in the brain of process 2 we focused on the separate motions of the individual particles. But the physical structures in terms of which the action of process 1 is naturally expressed are not the separate motions of individual particles.
They are, rather, the quasi-stable macroscopic degrees of freedom. The brain structures selected by the action of P must enjoy the stability, endurance and causal linkages needed to bring the intended experiential feedbacks into being. These functional structures are probably more like the lowest-energy state of the simple harmonic oscillator, which is completely stable, or like the states obtained from such lowest-energy states by spatial displacements and shifts in velocity.
These shifted states tend to endure as oscillating states. In other words, in order to create the needed causal structure the projection operator P corresponding to an intentional action ought to pick out functionally pertinent quasi-stable oscillating states of macroscopic subsystems of the brain. The state associated with a process 1 preparatory intervention should be a functionally important brain analogue of a collection of oscillating modes of a drumhead, in which large assemblies of particles are moving in a coordinated way.
Such an enduring structure in the brain can serve as a trigger and coordinator of further coordinated activities. It is the brain's template for the intended action. It is a pattern of neuroelectrical activity that, if held in place long enough, will tend to generate a physical action in the brain that will tend to produce the intended experiential feedback. On the other hand, a person's intentions are surely related in some way to their historical past. This means that the laws of contemporary orthodox quantum theory, although restrictive and important, do not provide a complete picture.
In spite of this, orthodox quantum theory, while making no claim to ontological completeness, is able to achieve a certain kind of pragmatic completeness.