Functional systems as explanatory tools in psychiatry

ABSTRACT

Here we defend the view that one ought to categorize and classify at least some mental disorders as clusters of interrelated dysfunctions of (usually, several) cognitive capacities – that is, the kinds of capacities that are postulated in cognitive science; capacities that are understood as entities that are primarily individuated in cognitive-functional terms (CF-systems); systems that have a set of peculiar properties in their manner of operation when processing information or representations. Usually, some of the mental disorders postulated in psychiatry are clinically heterogeneous with respect to their symptoms, and tend to be comorbid – that is, one disorder is often accompanied by other disorders – for example, schizophrenia often comes with major depression. We argue that describing the manner in which CF-systems operate within themselves and with other CF-systems as well as with stimuli and other kinds of information can best explain why certain mental disorders are very heterogeneous with respect to their symptoms, and why comorbidity is so frequent among these disorders. A consequence is that both within-category heterogeneity and comorbodity are not necessarily indications of defective classifications but are rather a consequence of the actual cognitive functional architecture itself and are therefore to be expected in these cases.

KEYWORDS:

• Variation
• combinability
• multiple realization
• comorbidity
• within-category heterogeneity
• mental disorders

Acknowledgements

The authors would like to thank the anonymous referees for their relevant and valuable comments to this paper.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Notes

1 We defend this view in García et al. (2022).

2 Thus, in this sense psychology and biology are not structurally very different; in the latter as well as in the former, variation and variability are the norm.

3 Of course, some versions of these views have already seen the light in one form or another (see e.g. Carruthers 2005; Sperber 2001). Rather it is the combination of ideas and some of the ideas themselves contained in this paper that are new, for example, the novel concept of cognitive variation (García 2010).

4 The notion of part that is required by our characterization of a functional system is not based upon spatiotemporal contiguity. See Craver and Tabery (2015 §2.2) for a discussion of what may be involved in the notion of part required both for mechanisms and for our functional systems.

5 Notice that a CF-system could but need not be modular, that is, need not be encapsulated, or domain specific, or have many of the properties that some modularists assign to the systems they postulate (Carruthers 2005; Sperber 2001).

6 There are a number of different ways of understanding the notion of levels of organization, but the main idea is that some scientific disciplines are more basic than others – for example, physics is more basic than chemistry, and this one is more basic than biology, and biology is more basic than cognitive science, and so on. Some researchers even think that within these sciences, some parts of them are more basic than others, for example, molecular biology is more basic than physiology (see, e.g. Piccinini and Craver 2011; Striedter and Northcut 1991). See Eronen (2015) for arguments against any view that postulates the existence of levels of organization or description of any sort.

7 As we shall see below in this section, the distinction between CF-organization and implementation is closely related to our distinction between simple and complex CF-systems. In philosophy of psychology and biology it is commonly accepted that some cognitive and biological systems are multiply realized at lower levels. See Striedter and Northcutt (1991), Abouheif (1997) in different areas of biology, and Aizawa (2018) in vision theory.

8 We are using this example of CF-analysis in cognitive psychology as an illustration of the kinds of functional organizations that are oftentimes postulated in this discipline; however, this should not be taken as an endorsement of Baddeley’s particular CF-analysis of working memory. Yet there are many other examples of cognitive systems composed of functional parts, for example, Conway’s CF-analyses of episodic memory (2005) and Hassabis and Maguire’s functional analysis of autobiographical memory (2007).

9 Thus, being a simple system is level-relative; a functional system may be simple at the cognitive level but not at the neural level.

10 The distinction between cognitively simple and complex functional systems is crucial for understanding the within-category heterogeneity and comorbidity observed in psychiatric diagnostics. Cognitively simple systems cannot be further analyzed at the cognitive level, indicating a separation between the cognitive and neural levels. Multiple realizability supports this distinction by suggesting that different kinds of neural mechanisms can underlie the same kind of cognitive function. Accepting the nomological possibility of cognitive-neural multiple realizability (together with the idea of cognitive functional variability) explains some cases of within-category heterogeneity and comorbidity observed in mental disorders. These ideas will be discussed in Sections 4 and 5 of the paper.

11 A number of different, and often incompatible things have been said about the cognitive function of mirror neurons themselves and about their functional role in larger CF-systems. We do not enter into this discussion here; for our purposes we simply assume that the function of a single mirror neuron is to ‘correlate’ or ‘integrate’ sensory and motor information.

12 Elsewhere [García et al. manuscript 2022], we have argued that conceiving cognitive functional capacities as natural kinds in a sense inspired by Richard Boyd’s notion (1999, 2010) is theoretically adequate and fruitful.

13 By ‘cognitive character’ we mean things like the kinds of CF-subsystems that a CF-system has as parts, or the kinds of causal interactions two or more of these subsystems exhibit, the kinds of cognitive outcome the CF-system typically produces or should produce, the types of informational inputs that activate it, the cognitive dispositions that constitute the parts, the parts of the parts, etc., that is, the cognitive characteristics that the CF-system has.

14 Thus, as we understand implementation, it is a one-to-many relationship between kinds belonging to different levels of organization; furthermore, it is an explanatory relationship between different-level kinds: reference to each of the multiple lower-level kinds explains how some (but not all) of the tokens of the higher-level kind perform their functions.

15 When we talk about some CF-systems be more complex that others, what we mean is the following: Let X and Y be CF-systems, in our sense, we will then say that X is more complex than Y whenever Y is a sub-system of X, or when Y is a subsystem of a subsystem of X, or when Y is a subsystem, of a subsystem, of a subsystem of X, and so on.

Additional information

Funding

Salcedo-Gómez thanks the Direccion General de Asuntos del Personal Academico, Universidad Nacional Autonoma de Mexico [DGAPA-UNAM] Postdoctoral Fellowship Program for its support during the writing of this paper.

Notes on contributors

M. Salcedo-Gómez

Mariana Salcedo-Gómez focuses her research on the philosophy of psychiatry and of the cognitive sciences. She is particularly interested in the assumptions associated with the models of mental disorders’ classification and diagnosis – e.g., DSM and RDoC.

Claudia-Lorena García

Claudia-Lorena García has been researching for at least the last 15 years, on the topics of the philosophy of cognitive science, evolutionary biology and the construction of the concepts, and ideas that would facilitate the integration of these two disciplines.