Out of our skull, in our skin: the Microbiota-Gut-Brain axis and the Extended Cognition Thesis

Abstract

According to a shared functionalist view in philosophy of mind, a cognitive system, and cognitive function thereof, is based on the components of the organism it is realized by which, indeed, play a causal role in regulating our cognitive processes. This led philosophers to suggest also that, thus, cognition could be seen as an extended process, whose vehicle can extend not only outside the brain but also beyond bodily boundaries, on different kinds of devices. This is what we call the ‘Externally Extended Cognition Thesis.’ This notion has generated a lively debate. Here, we offer a novel notion of extended cognition, according to which cognition can be seen as being realized (and expanded) outside the brain, but still inside the body. This is what we call the ‘Internally Extended Cognition Thesis’. Not only our thesis but also our approach while defending it is innovative. The argument we offer is supported by recent empirical findings in the life sciences and biomedicine, which suggest that the gut microbiota’s activity has a functional role in regulating our cognitive processes and behaviors. In doing so, we embrace the holobiont-perspective, according to which it is possible to claim that what we call biological individuals are not autonomous entities with clear boundaries, but should rather be seen as networks of multiple interactions among species. Thus, by analyzing different sets of evidence in light of the holobiont-perspective, we argue that the gut microbiota could be seen as a component of our organism. On the basis of the philosophical interpretation of this evidence, however, we also suggest that there are no impediments standing the way of considering the gut microbiota also as a functional extension of our cognitive system. If so, this amounts to extending cognition out of ‘our skull’, though still confining it within ‘our body’: to ‘our gut’. This is an instance of the ‘Internally Extended Cognition Thesis,’ whose benefits for an original (biologically informed) theory of extended cognition are discussed.

Maternal antibiotics disrupt microbiome, behavior, and temperature regulation in unexposed infant mice

“…Gut microbiome–brain interactions, both as a construct (Boem et al., 2021; Martin et al., 2018; Sarkar et al., 2018) and as a constellation of phenomena (Cusick et al., 2021; Cussotto et al., 2018; Nagpal & Cryan, 2021), have stimulated vigorous activity in basic, translational, and clinical research. Among the many remarkable findings are data suggesting links between early life ABx exposure, GI issues—including dysbiosis—and ASDs (e.g., Adams et al., 2007; Atladóttir et al., 2012; Axelsson et al., 2019b; Bittker & Bell, 2018; Guisso et al., 2018; Hisle‐Gorman et al., 2018; Vargason et al., 2019).…”

Bacterial communication

“…First, bacteria also seem to employ quorum sensing to communicate with plants and animals (Lowery et al, 2008). This idea might have potential implications for other philosophical claims, such as the suggestion that microbiota 'extend our minds' (Boem et al 2021). Secondly, it has been suggested that bacteria like B. subtillis communicate using electrical signals, which might have close analogies with neuronal communication by means of action potentials (Prindle et al 2015;Beagle and Lockless, 2015).…”

A pluralistic view of holobionts in the context of process ontology

“…Should a holobiont be considered a physiological organism? Three arguments, namely (i) activity, (ii) spatiotemporal position, and (iii) tolerance of the immune system, support the physiological concept of the holobiont as a genuine organism (Bordenstein and Theis, 2015;Stencel and Proszewska, 2018;Triviño and Suárez, 2020;Boem et al, 2021).…”