An RT/fMRI study showed a single cluster of activity that pertains to logical negation, distinct from clusters that were activated by numerical comparison and from the traditional language regions

Logical negation mapped onto the brain. Yosef Grodzinsky et al. Brain Structure and Function, November 4 2019. https://link.springer.com/article/10.1007/s00429-019-01975-w

Abstract: High-level cognitive capacities that serve communication, reasoning, and calculation are essential for finding our way in the world. But whether and to what extent these complex behaviors share the same neuronal substrate are still unresolved questions. The present study separated the aspects of logic from language and numerosity—mental faculties whose distinctness has been debated for centuries—and identified a new cytoarchitectonic area as correlate for an operation involving logical negation. A novel experimental paradigm that was implemented here in an RT/fMRI study showed a single cluster of activity that pertains to logical negation. It was distinct from clusters that were activated by numerical comparison and from the traditional language regions. The localization of this cluster was described by a newly identified cytoarchitectonic area in the left anterior insula, ventro-medial to Broca’s region. We provide evidence for the congruence between the histologically and functionally defined regions on multiple measures. Its position in the left anterior insula suggests that it functions as a mediator between language and reasoning areas.

Keywords: Language Logic Numerosity Functional neuroanatomy Functional neuroimaging Cytoarchitecture Brain mapping Negation Sentence verification Left anterior insula Modularity

Discussion 
Taken together, the anatomical and functional clusters exhibit bi-uniqueness: area Id7 is cytoarchitectonically distinct from its neighbors, and represents a new, independent cortical area of the anterior insula (Fig. 7, Movie). The functional NetNegInt coincides largely with Id7, overlaps with no other cortical region, and NetNegInt intensity correlates with RT at the individual participant level. 

At a minimum, these results allow us to conclude that there is a single, anatomically and functionally cohesive core area involved in negation—Id7/NetNegInt. It is distinct from areas 44, 45, long believed to support syntax and from areas supporting core compositional semantic processes in the left temporal pole (Del Prato and Pylkkänen 2014). This distinctness and cohesiveness illustrates how relatively small elements of cognition can be neurally individuated and correlated with cytoarchitectonically defined areas. It also supports a modular view of cognitive functioning (Fodor 1983) and moreover seems to provide an answer, albeit partial, to the perennial debate about language and logic. If evidence from neuroscience bears on the debate, then Frege, Russell, and their followers were right: language and at least some aspects of logic are distinct. Finally, our results suggest that the border between the insula and Broca’s region is where language stops and logic begins.

We are not in a position to establish a connection between our results and other roles attributed to the anterior insula such as interoception. Yet, there is a differ-ence in pattern: typically, the anterior insula is activated bilaterally (Zaccarella and Friederici 2015), and tends to co-activate with the anterior cingulate (Craig 2009; Engstrom et al. 2014), to which the left and right insulae appear to be massively connected (Mesulam and Mufson 1982) and have a similar histologic makeup (Ghaziri et al. 2017). Our study documented no bi-lateral co-activation. Recent lesion data, moreover, relate interoceptive deficits to regions that seem to exclude the here defined left Id7 (Salomon et al. 2018).

So what can we conclude and where do we go from here? Our experiment demonstrates that the processing of one log-ical connective, ¬, has a distinct neurocognitive signature, supported by a histologically coherent piece of neural tissue, the left Id7, that is, outside the traditional language regions, lying between them and decision making areas. While we believe that this set of findings provides the basis for an important argument for language–logic dissociation, we are aware that it is based on a single set of results, one that needs to be further enriched in the same spirit. Convergent results from related explorations of other logical connectives will no doubt help to bolster our claims. E.g., if experiments can be designed to successfully isolate disjunction, conjunction, and the like, and their results converge, solid foundations for a new perspective on language–logic relations would be constructed. 

ith this qualification, can we conclude that the phi-losophers were right? Gottlob Frege, in his Begriffschrift, famously asserted that linguistic rules relate to logic as the eye compares to a microscope (van Heijenoort 1967): language is flexible, but logic is more rigid—mediating between linguistic expressions and objects suitable to reasoning. While Frege and Russell had no cognitive perspective, let alone a neurological one, we feel free to add one and assign an anatomical construal of Frege’s assertion in regards to the spatial position of the left Id7: like a microscope, this area may “translate” linguistic objects into logical forms. A mediating role has already been proposed for the posteriorly adjacent, middle left insula, claimed to mediate between motor planning and speech (Dronkers 1996). In a similar vein, it is proposed that the left Id7 mediates between the language regions and prefrontal areas engaged in reasoning (Baggio et al. 2016; Monti et al. 2007). By doing so, it seems to play a crucial role in what could be a core neural network that underlies our humanity.