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ABSTRACT
This is a revision of Freud’s “Project for a Scientific Psychology: General Scheme.” It updates the original, sentence for sentence where possible, in light of contemporary neuroscientific knowledge. The principle revisions are as follows. (1) Freud’s conception of “quantity” (the precursor of “drive energy”) is replaced by the concept of “free energy.” This is the energy within a system that is not currently performing useful work. (2) Shannon’s conception of “information” is introduced, where information is equivalent to unpredictability, and is formally equivalent to “entropy” in physics. (3) In biology, the fundamental purpose of “homeostasis” is to resist entropy – i.e., to increase predictability. Homeostasis turns out to be the underlying mechanism of what Freud called the “principle of neuronal inertia.” (4) Freud’s conception of “contact barriers” (the physical vehicles of memory) is linked with the modern concepts of consolidation/reconsolidation, whereby more deeply consolidated predictions are less plastic (more resistant to change) than freshly consolidated ones. (5) Freud’s notion of sensory “excitation” is replaced with the concept of “prediction error,” where only that portion of sensory input which is not explained by outgoing predictions is propagated inwards for cognitive processing. (6) Freud’s conception of “bound” (inhibited) cathexis, the main vehicle of his “secondary process” and voluntary action is equated with the buffering function of “working memory”; and “freely mobile” cathexis (the vehicle of Freud’s “primary process”) is equated with the automatized response modes of the nondeclarative memory systems. (7) Freud’s notion of ω (the system “consciousness”) is replaced by the concept of “precision” modulation, also known as “arousal” and “postsynaptic gain.”
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Notes
1 Friston’s work builds directly upon Helmholtz’s insights, not least concerning the conservation of energy. The first law of thermodynamics states that energy is never lost or created, it is only transformed. The second law states that energy always dissipates during natural processes. The driving mechanism of self-organizing (e.g. living) systems is to resist this dissipative tendency, by minimizing free energy. That is the free energy principle.
2 Please note: the Greek letters used here are purely conventional; they have no literal meaning. Also, although the symbols denote concepts that are equivalent to those that Freud used, they are not identical with them; this is because the concepts have been substantively updated.
3 “Free energy.” There are various types of free energy. F denotes “variational” free energy, or Friston free energy for short. This is analogous to Helmholtz free energy, where there is an information exchange as opposed to a thermodynamic exchange between a system and its environment. (See Friston, Citation2009.)
4 In Shannon’s (Citation1948) mathematical treatment of “information,” the less predictable an event is, the more information it carries. The average information of a system is its entropy (a concept formally related to but not identical with free energy). Therefore, the less information required by a self-organizing system (i.e., the lower its uncertainty, the fewer yes/no questions it needs to ask), the better for the system. Uncertainty is, for obvious reasons, dangerous for biological systems.
5 This “orphan” sentence is a good example of the challenges posed by Freud’s dense text. In the original version, the sentence reads: “N and Qη – Similar experiments are now frequent.” There, N denoted “neurons” and Qη denoted “quantity of an intercellular order of magnitude.” What Freud meant to convey was that he was not the only scientist using these two basic ideas to conceptualize the dynamics of the nervous system; and I am trying to convey the same, in relation to neurons and information theory. – Incidentally, the neuron had only just been discovered at the time of Freud’s writing the “Project.”
6 Freud (Citation1915, pp. 121–122) defined drive as “the psychical representative of the stimuli originating from within the organism and reaching the mind, as a measure of the demand made upon the mind for work in consequence of its connection with the body.” Here, I am equating “drive” with F, bearing in mind that the “free energy” (F) within a system is the energy that is not currently performing useful work. Helmholtz contrasted it with “bound energy.”
7 The basic principle in question is the free energy principle, which is formulated in Friston’s law: “All the quantities that can change; i.e. that are part of the system, will change to minimise free energy” (Friston & Stephan, Citation2007). This law (like the law of affect, described below) is probabilistic; it applies only in the average case, i.e. over sufficient time periods. See Friston (Citation2009) for an introduction to this unifying principle of brain functioning.
8 The “principle of neuronal inertia” is the theoretical precursor of Freud’s “death drive.“ This is ironic because homeostasis is the grounding mechanism of all life.
9 The (Bayesian) terms “prior” and “posterior” here refer to the fact that the actions and perceptions of a self-organizing system entail experiments which test hypotheses generated by its predictive model. Prior hypotheses are supplanted by posterior ones which take account of the outcome of each experiment. See Hohwy (Citation2013) and Clark (Citation2015) for accessible accounts of the “Bayesian brain.”
10 Freud conceptualized this compromise, his “constancy principle,” as a special case of Fechner’s “tendency towards stability.” – The simplest neural contrivance that gives expression to this imperative is the default-mode SEEKING system, described below, which engages proactively with sources of uncertainty (see Panksepp, Citation1998).
11 Cathexis will be further defined below.
12 F can also be defined roughly as the sum of squared prediction error.
13 See Mesulam (Citation2000).
14 Cf. Freud’s concept of “contact barriers,” which is here replaced by a broader conception of resistance.
15 See Felleman and Van Essen (Citation1991).
16 See Tozzi et al. (Citation2016): “Maximizing mutual information [i.e. minimizing demand for information flow] and minimizing metabolic costs are two sides of the same coin.”
17 These terms are used by Hohwy (Citation2013) and Clark (Citation2015) respectively, but by no means only by them.
18 See Friston (Citation2005) for a review.
19 I am disregarding the interneurons here.
20 “Neurons that fire together, wire together” (Hebb, Citation1949).
21 Freud linked this magnitude with Fechner’s law: “Sensation varies with the logarithm of the intensity of the stimulus.”
22 Technically, free energy may be decomposed into accuracy and complexity. Model evidence is the difference between accuracy and complexity, since models with minimum F provide accurate explanations of data under complexity costs, which in turn means that reducing model complexity improves model generalizability but at the cost of accuracy. The balance between accuracy and complexity determines a model’s efficiency. In biology, efficiency is everything. (In Bayesian terms: “likelihood” must be assessed in relation to “probability,” to prevent over-fitting.)
23 The nondeclarative and declarative systems are equivalent to Freud’s unconscious and preconscious systems respectively. (The term “declarative” implies “capable of becoming conscious.”) The pivotal topic of consciousness is discussed below, as is its relationship to plasticity.
24 Cf. the concept of “working memory,” discussed further below. Mental work here refers to ψ cathexis in the face of e. In physiological terms, a “cathected” ψ trace is subject to reconsolidation, which is predictive work in progress. This mechanism will become clearer below, when the concept of “precision” is introduced.
25 Despite being so obvious, this simple mechanism has enormous clinical ramifications.
26 Q in itself is “unknowable.”
27 Cf. Wheeler (Citation1990): “That which we call reality arises in the last analysis from the posing of yes/no questions and the registering of equipment-evoked responses; in short […] all things physical are information-theoretic in origin.”
28 I.e. through reconsolidation.
29 Error and prediction units are both assumed to be pyramidal neurons, although they have different patterns of connectivity. In cortex, the former originate in supragranular layers and terminate (centripetally) in layer 4 spiny stellate cells; the latter originate in infragranular layers and target (centrifugally) infra and supragranular cells. However, it is important to say that prediction units are very far indeed from being limited to the cortex.
30 This is post-synaptic modulation; see below.
31 Panksepp (Citation1998). “Sensory affects” are discussed below. I do not use Panksepp’s term for the interoceptive bodily affects because it can cause confusion: as we shall see, all affects are homeostatic.
32 As we shall see later, it demands engagement with our representations of the external world.
33 Emotional needs, unlike bodily ones, pertain in large measure to other agents in the world, the behaviour of which is far less predictable than that of inanimate objects. – Please note: learning does not update reflexes and instincts; it supplements them.
34 See Bowlby (Citation1969).
35 Consider the common phobias.
36 Panksepp (Citation1998), Merker (Citation2007).
37 White et al. (Citation2017).
38 The earlier quotation above from Wheeler (Citation1990) is preceded by the following passage: “It from Bit. Otherwise put, every it – every particle, every field of force, even the spacetime continuum itself – derives its function, its meaning, its very existence entirely – even if in some contexts indirectly – from the apparatus-elicited answers to yes or no questions, binary choices, bits. It from Bit symbolizes the idea that every item of the physical world has at bottom – at a very deep bottom, in most instances – an immaterial source and explanation.”
39 See Kihlstrom (Citation1996) and Bargh and Chartrand (Citation1999) for reviews of the literature on unconscious cognition.
40 Brentano (Citation1874).
41 Technically, as we know, the most salient signal is the one which provides the greatest opportunity for minimizing F.
42 And which, please recall, can be both grabbed and assigned.
43 “Freely mobile” cathexis is automatized.
44 Cf. Freud (Citation1920, p. 25): “Consciousness arises instead of a memory trace.” Conversely, a memory trace arises instead of consciousness; when consciousness ceases, certainty is restored.
45 See Pfaff (Citation2005).
46 See Merker (Citation2007), Solms (Citation2013).
47 The law of affect states: “If a behaviour is consistently accompanied by pleasure it will increase, and if it is consistently accompanied by unpleasure it will decrease.” This law is attributable to Panksepp (Citation1998) who derived it from Thorndike’s (Citation1911) law of effect.
48 The first scientist to arrive at this important insight was Fotopoulou (Citation2013).
49 The terms “easy” and “hard” here refer to Chalmers (Citation1995). The hard problem is addressed in far greater detail in Solms (Citation2021).
50 See the “Key to Abbreviations.” Please note that these quantities are vectors, apart from ω and F which are scalars. The dot notation in the equations below implies a dot product (i.e. matrix or vector multiplication).
51 As stated above, these simplified equations effectively reduce free energy to the likelihood of a Gaussian distribution. In fuller treatments, one would also need to consider hierarchical generative models (with precisions at each level) and accommodate conditional uncertainty about external states. Furthermore, the equations lump all sensory prediction errors together – including the endogenous and exogenous modalities.
52 Technically, this is called a “gradient descent,” where the gradient is the rate of change of free energy with precision.
53 Under our simplifying assumptions about the encoding of Bayesian beliefs.
54 Unlike Freud, I am using the term “nucleus” here to denote what is conventionally called the “subpallium.” I have already divided the prosencephalon into its telencephalic and diencephalic components. However, the diencephalic structure I discussed previously was the hypothalamus only, the role of which (as a source of endogenous e) is clarified further in this section. The functional-anatomical situation is complicated: the diencephalon includes nuclei (e.g. the lateral geniculate, mentioned before) which clearly belong to the φ system and others (e.g. the subthalamic nucleus) which are functionally inextricable from the basal ganglia – i.e. the “nucleus” of ψ which I am discussing here – and yet others (e.g. the intralaminar nuclei) which form part of the ω system. These complexities were not recognized in Freud’s times.
55 I.e. affects arising from vegetative needs. See Note 31.
56 This apparently occurs in some psychosomatic diseases. The potential consequences of reducing precision on strong emotional error signals are less catastrophic, in the short term at least, as we have long known from “hysteria.”
57 Hence “infantile amnesia,” which applies only to episodic and semantic (declarative) memories.
58 Confidence in an e value is inversely proportional to that in its prior prediction, so if the error = 0, the prediction = 1.
59 Cf. the PANIC/GRIEF category described above. This does not imply, as Freud thought, that the need for attachment “leans upon” the need for nourishment (cf. “anaclisis”); these are independent needs and both must be met.
60 This corresponds to the distinction between “bound” and “freely mobile” cathexis, mentioned above.
61 Cf. the important paper on this by Carhart-Harris and Friston (Citation2010).
62 See the classical descriptions of this by Riggs and Ratliff (Citation1951) and Ditchburn and Ginsborg (Citation1952).
63 See Rizzolatti and Craighero (Citation2004) for a review.
64 Vittorio Gallese’s group describe what happens when mirror-neuron activity is not inhibited in this way, as occurs in schizophrenics who fail to distinguish the perceived object from themselves (Ebisch et al., Citation2012).
65 In babies, ω modulation is entirely in the hands of the midbrain decision triangle: in the “id.”
66 Please note, this is not an homogenous cathexis. When sleep is prioritized it remains possible for ψ to “listen out” for salient e signals such as, for example, the sound of a baby crying. Here the prediction (the wish) that “the baby will not cry” is assigned a low ω value so that the relevant e signal can attain a sufficiently high magnitude to cause re-prioritization of one’s needs from sleep to CARE. Likewise, a sufficiently high e signal emanating from anywhere in φ will always be capable of grabbing attention in the manner described before.
67 See the end of Section 3.
68 See Solms (Citation2011) for a review.
69 See Hobson and Friston (Citation2012).
70 Freud (Citation1900).
71 Here we have a deep mechanical account of the principle of constancy.
72 Although Freud (Citation1920) later forgot this.