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Abstract
Since cognitive neuroscience aims at giving an integrated account of mind and brain, its ontology should include both neural and cognitive entities and specify their relations. According to what we call the standard ontological framework of cognitive neuroscience (SOFCN), the aim of cognitive neuroscience should be to establish one-to-one mappings between neural and cognitive entities. Where such entities do not yet closely align, this can be achieved by reforming the cognitive ontology, the neural ontology, or both. In order to assess the limits and the possibilities of the SOFCN, we will examine a paradigmatic case study: the concept of Broca’s area, which indicates an alleged mapping between the left inferofrontal gyrus and the production of language. We review evidence showing that such a mapping does not hold, thus calling into question either the status of Broca’s area or the validity of the SOFCN. We then propose some strategies for addressing the issue and suggest that it may be solved within the SOFCN by adopting both of the following strategies: first, more accurately defining the relevant neural structures and second, switching the focus of neural ontology from structures to events, individuated by a where (neural structures) conjoint with a how (oscillatiory frequency).
Disclosure statement
No potential conflict of interest was reported by the authors.
Notes
1. A historical oddity: according to some historical sources, Leborgne actually had another speech automatism. “When [Mr Leborgne] was completely frustrated by his inability to express his thoughts he would utter the invocation, ‘Sacré nom de Dieu’” (Joynt, Citation1961, p. 954;. However, see the objection of Domanski, Citation2013; and a rebuttal by Code, Citation2013).
2. Broca himself proposed the term aphemia in order to describe Leborgne’s condition. However, Armand Trousseau argued in favor of the word aphasia. Though Broca never accepted it, the term aphasia eventually spread across the medical community (Ryalls, Citation1984). However, in the last few decades, doubts have been raised about the taxonomic utility of the concept of Broca’s aphasia (e.g., Caramazza, Citation1984; Schwartz, Citation1984).
3. We intentionally use the broad terminology “mental and neural entities” instead of more accepted pairs such as “cognitive functions / neural structures” (as cognitive neuroscientists would say) or “mental state / brain state” (as philosophers of mind would say). We do so in order to avoid commitment regarding the kind of entity to conceive of as mental (e.g., faculties, modules, or functions) or neural (e.g., bumps, regions, or networks). Furthermore, while the term “entities” usually refers either to objects or substances, throughout this paper we employ it in a broader, metaphysically non-committal manner, so that it may also indicate properties or events. The importance of this caveat will come to light in section 4.5.
4. While intuitively pointing toward a type-identity theory, the SOFCN is ultimately agnostic about the metaphysics of mind. Rightly so, since “Brain-behavior correlations are neutral on mind-brain metaphysics: substance dualism, emergentism, and reductionism, among other metaphysical positions, are equally consistent with these correlations” (Figdor, Citation2011).
5. For example, while assessing the evidence for the existence of some so-called “basic” emotions, Tracy and Randles claim that a “gold standard is the presence of neurons dedicated to the emotion’s activation” (Citation2011, p. 398). More recently, Poldrack and Yarkoni even commit themselves to the strong claim that “all else being equal, we believe that a model of psychological processes that also maps systematically onto known biological structures is strongly preferable over one that does not—often even when there are other grounds to prefer the latter” (Citation2016, p. 599).
6. Notably, mappings can occur at multiple levels of the hierarchy. Cognitive tasks are decomposed into many component operations, and should probably be localized into a complex network rather than onto a single area, each part of which might correspond to some component operation. In Petersen and Fiez’s efficacious slogan: “there is no ‘tennis forehand area’ to be discovered … Any task or ‘function’ utilizes a complex and distributed set of brain areas” (Citation1993, p. 513).
7. Noppeney, Friston, and Price (Citation2004) distinguish two different cases of degeneracy: degenerate functional neuroanatomy, involving multiple structurally distinct systems carrying out the same cognitive task but coexisting within a single brain, and degeneracy over subjects, when a “same task is supported by distinct neural structures in different subjects or in the same subjects at different times, for example following functional reorganization” (pp. 438–439). They also propose a strategy for mapping degenerate neuronal systems by combining functional neuroimaging and data from studies involving either actual or virtual lesion. (See also Henson Citation2005, pp. 224–225). Notice that accounting for degeneracy also defuses the objection to SOFCN based on neural plasticity, since neuroplasticity is but one (probably the major) cause of degeneracy.
8. “If there were ever a phrenological science, it would be the phrenology of convolutions [in the cortex], and not the phrenology of bumps [on the skull]” (Broca, Citation1861b, quoted in Fink et al. Citation2006, 255).
9. Seven years later, Dronkers’ team used magnetic resonance imaging (MRI) to reassess the brains of the most famous Broca’s aphasic patients, Mr Leborgne and Mr Lelong, following earlier attempts made with computerized tomography (Cabanis, Iba-Zizen, Abelanet, Monod-Broca, & Signoret, Citation1994; Signoret, Castaigne, Lhermitte, Abelanet, & Lavorel, Citation1984). While Broca, who decided not to cut the brains in order to conserve them, could only describe superficial lesions, Dronkers, Plaisant, Iba-Zizen, and Cabanis (Citation2007) discovered that in both brains the lesions extended far beyond the inferofrontal gyrus.
10. Price and Friston’s (Citation2005) mapping of the left posterior lateral fusiform with sensorimotor integration reflects a similar strategy. See Klein (Citation2012) and McCaffrey (Citation2015) for a critical discussion.
11. The problems we will frame in section 4.4. and section 4.5, as well as the answers we are going to suggest, are similar to Poeppel and Embick’s (Citation2005) discussion of the granularity mismatch (or map problem) and of the ontological incommensurability problem (or mappings problem) (see also Embick & Poeppel, Citation2015; Poeppel, Citation2012).
12. As noticed by Brown (Citation2006), the earliest wave of identity theorists in philosophy of mind, that is, Feigl (Citation1967), Place (Citation2004), and Smart (Citation1991), used to talk about brain or neural events or processes, whereas later identity theorists such as Armstrong (Citation1968) and Lewis (Citation1966) preferred to speak about “brain states”. We think that this was a step in the wrong direction, as it led many philosophers to reify brain entities, thus neglecting their intrinsically dynamic aspect.
13. To put it in the language of mechanistic accounts of explanation, the structure-function mapping envisaged by Price and Friston (Citation2005) corresponds to what Bechtel and Richardson (Citation2010) call direct or simple localization of some mental entity onto some part of the neural mechanism. We are proposing that mental entities should rather be mapped onto the operations of the mechanism.
14. While in the present paper we will not address many aspects of the mechanistic framework, since we are only concerned with taxonomical issues, it is worth noticing that Bechtel repeatedly stresses that in order to account for the fact that many biological systems are endogenously active (rather than merely reactive), mechanistic explanations must describe their nonlinear temporal dynamics, the most widespread of which are oscillatory mechanisms (Bechtel, Citation2011, 2012; Bechtel & Abrahamsen, Citation2009, 2013).
15. “Connections, even functional connections, do not provide information critical to understanding how the brain produces cognition. What is needed is not only what is connected, but how and in what directions regions of the brain are connected: what signals they convey and how those signals are acted upon as part of a neural computational process … the how is important for understanding the ways in which various parts of the brain combine their particular computations to support cognitive function.” (Kopell et al., Citation2014, p. 1319).
16. A procedure during which electrodes are implanted in the brain of epileptic patients for evaluating their cerebral activity.
17. “Broca’s area is not dedicated to a single kind of linguistic representation but is differentiated into adjacent but distinct circuits that process phonological, grammatical, and lexical information” (Sahin et al., Citation2009, p. 449).