On the ontological assumptions of the medical model of psychiatry: philosophical considerations and pragmatic tasks

Problems in Psychiatric Diagnosis

Horwitz asserts that "because [diagnostic psychiatry] uses symptoms to classify disorders, it also categorizes an enormous diversity of human emotions, conduct, and relationships as distinct pathological entities" [2]. At first blush, such an approach seems logical because precise diagnostic classifications can presumably distinguish between particular disease states and offer reliable information about etiology, prognosis, and treatment. In the The Myth of Mental Illness, Szasz disputed psychiatry's claims of medical legitimacy. Szasz was concerned about the validity of psychiatric concepts, and his critique raised questions about the evaluative nature of the psychiatric enterprise. To Szasz, psychiatry utilized terms (such as delusions, compulsions, and obsessions) that lacked the descriptive objectivity of other domains of medicine. Szasz did not deny that neuroanatomical lesions could result in dysfunctional behaviors, however, such abnormality is, strictly speaking, a brain disease. Labeling various forms of behavior as pathological "...rests on a serious, albeit simple, error: ... mistaking or confusing what is real with what is imitation; literal meaning with metaphorical meaning; medicine with morals" [3]. If psychiatry lacked terms that could definitively individuate normality from pathology, how could psychiatrists issue seemingly objective diagnoses and prognoses while relying on a predominantly subjective (and elastic) epistemology?

This conceptual tension in psychiatry mirrors larger debates about objectivity and normativity in the philosophy of science. In The Structure of Scientific Revolutions, Thomas Kuhn argued that science does not operate within an Archimedean framework, but instead, is sensitive to the normative practices of social communities [4]. Scientists (and clinicians) undergo training and develop expertise within localized academic institutions. As a consequence, intellectual traditions tend to bind scientists and clinicians within a coherent community of practitioners. Kuhn noted that members of a particular academic community tend to hold similar constructs and values about what constitute a good theory, and these values were largely assumed, unquestioned, and maintained as valid within the group. For Kuhn at least, the collective nature of scientific theory-building suggested that communities' values matter in the content of scientific discourse and theorization (and, we might add, clinical practice).

Postmodern criticisms of science generally impugn this relativistic bend, and pose the question: If science evolves within a cultural frame (just like other ideologies), then in what sense is it immune from the normative practices of society [5]? The crucial issue is not whether the unique status of science (and by extension, clinical medicine) hinges on cultural biases, but whether its epistemology is better than other ideologies at obtaining knowledge about the natural world. All ideologies manifest hegemonic assumptions about the nature of reality and being. However, unlike other ideologies, science also values a self-correcting process through which increasingly refined and robust characterizations about the natural world can be made over time. If new observations become difficult to reconcile with standing hegemonic beliefs, then those initial assumptions are usually abandoned. Thus, scientific epistemology allows for large scale reorganization of ontological assumptions, or what Kuhn called "paradigm shifts" [4].

In applying this framework to the medical model of psychiatry, we see a reliance upon four main ontological assumptions. These are 1) Realism: the claim that mental properties (such as desires, beliefs, and thoughts) are real phenomena and not merely artifacts of socio-cultural norms; 2) Naturalism: the concept that disturbances in neural structures are causally implicated in the formation and persistence of mental disorders; 3)Reductionism: the view that at some level, disturbances in neural structures are necessary to account for mental disorders, and 4) Essentialism: the assertion that mental disorders have underlying 'essences" that allow distinction of one type from another.

Are each and all of these assumptions warranted and necessary in order to arrive at a valid concept of mental disorder? We assert that naturalism, realism, and reductionism are reconcilable with advances in contemporary neuroscience, but that essentialism has proven to be, and may still be somewhat more problematic, vis-a-vis the medical model of psychiatry, at least to date. Let us examine each of these assumptions in turn.

Realism

The realist position asserts that terms used in scientific theories map onto actual properties in the external world, even if the relevant phenomena are not necessarily observable. So, for example, sodium-gated ion channels or serotonin receptors all do, in fact, exist. Their existence is not predicated upon our ability to perceive them through our senses. Another important aspect of realism is that properties referred to by scientific theories are independent of our linguistic practices or socio-cultural norms; hence, the amino acid glycine will always have a hydrogen atom as its functional group. This description holds true regardless of human circumstance.

Realism entails that a mental realm does not exist separately from the physical, and so an acceptance of realism necessitates a rejection of dualism. Simply, there is not an ontologically separate mental world, independent of its physical instantiation in the brain. The idea of an overriding mind, metaphysically independent of the brain, becomes untenable when we realize that lesions to various regions of the brain have profound consequences for subsequent subjective experience. How would the mental realm causally interact with an aphasic's brain, given the loss of linguistic capabilities due to an insult to the superior temporal gyrus or Broca's area? Similarly, how are we to account for the gradual loss of cognitive function in patients with Alzheimer's disease?

To experience disease is to be in a certain experiential state. To use a rather overplayed computational metaphor, to have such an experience requires that one have the requisite "hardware" (brain) and "software" (mind). A rejection of dualism would logically mean that all mental disorders are (in some way) biologically based. The tenet claims that every mental process, pathological or otherwise, arises in and from the brain [6]. It is important to note that nothing has been claimed about how neural structures causally produce mental states (naturalism), or whether mental states are best understood through their more basic, physical components (reductionism).

Realism has been a rather controversial assumption in the philosophy of psychiatry. An objection to the realist case is that there is no reason to claim that mental properties, such as beliefs, doubts, desires, and fears actually exist in the natural world. Moreover, as matter of fact, such mental properties do depend on the normative constraints of local communities. According to Cash, "...people's intentions, beliefs, thoughts and decisions are different in kind, not just in scale, from causal mechanisms in the brain. The nature of this 'difference in kind' can be revealed by considering the nature of the public criteria we use to ascribe intentional states to one another" [7]. The veridicality of intentional states often depends upon the requisite conditions; intentional states can mean or be about something. The property of aboutness cannot be mapped onto reality in any law-like way.

One can sidestep this criticism by noting that realism is best approached as an epistemological constraint. It is not the case that the tentative plausibility of a certain theoretical term commits us to finding its 'real world" equivalent. The validity of theoretical terms, that is, their ability to appropriately map onto real world properties, is completely contingent on the congruency of the associated theory with other established scientific principles. Critics of realism often conflate the object of scientific knowledge with the process of knowledge construction. Fundamentally, science is an interpretative process; it is something people do. Given that science is a project of collaboration, it is empirically impure, relying on built-in explanations that become embedded in the process of theory development. This does not mean that science is merely a by-product of cultural practices. Roy Bhaskar articulates the problem in this way:

"[M]en in their social activity produce knowledge which is a social product much like any other, which is no more independent of its production and the men who produce it than motor cars, armchairs and books... and which is no less subject to change than any other commodity. This is one side of 'knowledge'. The other is that knowledge is 'of' things which are not produced by men at all: the specific gravity of mercury, the process of electrolysis, the mechanism of light propagation. None of these 'objects of knowledge' depend upon human activity. If men ceased to exist sound would continue to travel and heavy bodies fall to earth in exactly the same way, though ex hypothesi there would be no one to know it" [8].

Knowledge, in the form of theories and explanations, is interpretational and should be regarded as a changeable social product. This does not mean that the object of any such knowledge is always dependent upon socio-cultural constructions. Science describes entities of nature, but "proof" comes through our success in interpreting, interacting with, manipulating (and often, controlling) them.

Naturalism

Naturalistic theories of mind generally assume that mental properties, such as thoughts or beliefs, are derived from neurobiological structures in a causally relevant way. In order to legitimize the naturalistic characterization of a mental disorder, the observed clinical expressions of behavior should have causal roots in biology. This is not to claim that all mental behavior should only be understood through biology, but rather that we - as dynamic organisms within complex environments - will undoubtedly be influenced by a variety of interacting variables, including biology.

A pressing question in naturalistic theories is how is it, exactly, that neurobiological disorders can be causally linked to certain behavioral outcomes? The steps implicated in the causal chains from the biochemical to the behavioral level(s) are vast and endless, and as Hume noted, we cannot "see" causation [9]. In science, we observe event regularities, and if such regularities occur with sufficient frequency, then we tentatively accept these observations as truly causal. Such observations are affirmed through the use of statistical theories, which provide a mathematical measure for the probability of an event occurring solely by chance.

While the development of statistical methods has refined the scientific process, the act of establishing causal relationships in the world long predates the development of statistics, or even mathematics. Such reasoning is possible because human beings have the capacity to reason inductively and infer logical relationships from data in, and obtained from the environment. Children as young as three years old can make appropriate judgments about novel stimuli and causally link processes they have only observed in operation [10].

These types of observations have prompted many philosophers (since Hume) to posit that causality can, at best, be understood as event regularities. We cannot determine by reasoning alone which of the observed (or potentially unobserved) effects actually cause the phenomena in question. To arrive at such conclusions, however, is to be led astray by words. As Ross states, "...to the extent that we have culturally universal intuitions about causation, this is a fact about our ethology and cognitive dispositions, rather than a fact about the general structure of the world" [11]. In other words, naturalistic intuitions are not evidence of their content.

Reductionism

Over the last few decades, neuroscience has elucidated a biological basis for several mental disorders. These developments have fuelled the quest to explain mental properties by reducing them to an interaction of their putative substrates. Given that interactions of neurobiological structures are causally implicated in aberrant of behavior, a logical paradigm would grant underlying genetic and biochemical entities explanatory primacy. Subjective experience and cultural influences can play a role in psychiatric disorders, but the "true" explanatory locus would rest in pathological structures and functions.

Many of these overly reductionist tendencies can be assuaged by revisiting some of Dennett's work that attempts to clarify the relations and predictions of mentalistic behavior through the use of three levels of explanatory abstraction [12]. The first is the Physical Stance, in which behavior could be predicted, in principle, from physical laws governing the interactions of material components. The second is the Design Stance, which predicts behavior, not from an understanding of the physical constitution of the mind, but through an understanding of the mind's purpose, function, and design. The final level of abstraction is the Intentional Stance, which requires neither an understanding of the physical constitution of the mind nor any design principles, but instead predicts behavior by considering what moves a rational agent would make in a given circumstance.

The brain and its potential representations are a primary focus of neuroscience, and neuroscientific information sustains both an evolving philosophy of mind, and the profession and practice of psychiatry. But it is important to recall that neuroscience, as a science, remains a process, and in so far as people are working on the common project of explanation, the objects of knowledge need to be interpreted. Normativity cannot be expunged from science, nor should it be. We make sense of the world and explain it with our theories, and it is inevitable that practical considerations will play an important role in theory choice. This means that reductionism need not be the raison d'être for the naturalistic project, but neither should it imply that reductionism is not possible, in principle. It is important to note that defining mental content in this way becomes a practical consideration. Accordingly, behavior can be interpreted using a level of abstraction that depends upon the needs of the investigator (and/or clinician).

Essentialism

A more controversial ontological assumption of the medical model of psychiatry is essentialism. This is the claim that psychiatric disorders, as defined by clinical nosology, map onto reality in a discrete way, and that these disorders possess essential properties, without which they would not be what they are. We argue that this assumption is highly questionable, and that as currently conceived, is anachronistic at best, and remains inconsistent with scientific thinking (at worst), and therefore is in need of re-examination and revision.

Science routinely organizes its body of knowledge into categories. How we sort things into categories largely depends on what measures we value. That is, we classify objects for a particular reason or to serve a specific function; to these ends, classification schemes cannot be arbitrary or random assortments. As Sadler notes, "...this non-arbitrariness is essential to a classification because it provides the basis for users with common purposes to talk about the same things. For us to discuss 'major depression' productively, we have to agree, in large part, about what major depression is, and in what practical context such a notion arises" [13].

An important concern for classification is the concept of validity. The validity of a category is related to the degree that it fits within a consonant body of explanatory theories. So, to group lungfish and cows in a similar category would require that there are genuine motivations for doing so. If one were an evolutionary biologist, such a grouping would align with what is known about macro-evolutionary processes. If one were a fisherman, the validity of such a pairing would seem impractical.

A criticism of the construct of essentialism is found in the later work of Ludwig Wittgenstein. Summarizing the Wittgensteinian view, Garth Hallett writes:

Suppose I show someone various multi-coloured pictures, and say: "The colour you see in all these is called "yellow ochre"... Then he can look at, point to, the common thing." But "compare this case: I show him samples of different shades of blue and say: "The colour that is common to all these is what I call "blue"."' Now what can be looked at or pointed to save the varied hues of blue? And don't say, "There must be something common, or they would not, be called 'blue,"' "but look and see whether there is anything in common at all" [14].

The crucial argument here is that the property of "blue" is reliant, to some extent, upon practical considerations and constraints.

Yet, a form essentialism persists in psychiatry. This is clearly articulated by Robins and Guze who claim that, "...the finding of an increased prevalence of the same disorder among the close relatives of the original patients strongly indicates that one is dealing with a valid entity" [15]. In this framework, genetic and biochemical factors are attributed as primary causes, and the role of psychiatry is to locate these pathological qualities within the physical brain. While experience does play a role in one's mental health, this model is decidedly oriented toward brain function. In this way, genetic and biochemical causes are seen as exerting their influences uni-directionally and any/all manifest symptoms are the consequence of unique and individuated etiologies.

The medical model of psychiatry views the current classifications as representing discrete organic disease states as opposed to heterogeneous symptom clusters. Validation of these symptom clusters often occurs via post-hoc quantitative and statistical analyses (such as hierarchical cluster analysis or pattern recognition paradigms) of the clinical data to ascertain which combinations of symptoms tend to group together. The problem with creating these types of discrete definitions for many contemporary psychiatric conditions is that "...no amount of clustering can get around the fact that several variables used in such models may have little or no biological plausibility" [16]. Without clear biological mechanisms, it is unclear whether symptom clusters represent different ways of labeling the same affliction, socio-cultural influences, or other biological confounds. Peter Zachar and Nick Haslam have presented a strong case that psychiatric categories do not uniformly individuate to underlying essences, but are defined, to a large part, by practical considerations [17–24]. In many ways, this recalls the Szaszian argument for mental illness as "myth" - here literally used to denote a practical, explanatory narrative.

We do not refute, or even doubt that practical considerations are important to define the threshold(s) at which a particular set of signs and symptoms may be deemed clinically relevant. But, if we are to regard essentialism as critical to the medical model of psychiatry, and adopt practice standards in accordance, then the task at hand is to establish how and what essential criteria are pertinent to any construct of normality and order (versus abnormality and disorder), as relates to brain function, mental processes and expressions of cognition, emotion and behavior (within a social milieu). Toward this end, we have posited that one such "essential" element of normality is non-linear adaptive properties within and between particular brain networks; thus progressive linearity would be aberrant and could manifest effects from the cellular to the cognitive-behavioral (and even socio-cultural) levels [25]. In this way, mental disorders would occur as a spectrum of possible effects. We maintain that particular genotypic factors predispose endo- and exophenotypes that are differentially expressed through interaction(s) with internal and external environmental influences throughout the lifespan, thereby grounding neuropsychiatric syndromes to underlying biological factors [25, 26].

This acknowledges causal determinants of psychiatric disorders (at least at formal and material levels), and while accepting a form of token physicalism (i.e.- that particular mental events occur as result of some physical function(s) or dysfunction(s)), allows for appreciation of both emergence and the bio-psychosocial influence of environments. As well, the spectrum disorder concept satisfies the criteria that define the medical model (i.e.- realism, naturalism, reductionism, essentialism). In this light, a spectrum disorder can be considered to 1) involve neural substrates (i.e.- realism); 2) represent a disturbance in the natural function of the substrate(s) or system (i.e.-. naturalism); 3) be a perturbation or disruption of some underlying and/or contributory component(s) of the bio-psychosocial organism (i.e.- reductionism - in this case as token physicalism), and 4) manifest a particular "eidos" that defines its aberrant qualities - in this case the progressive loss of non-linear adaptability and the resultant effects on neural function, cognition, emotion and behavior (i.e.- essentialism).