The beauty of language structure: a single-case fMRI study of palindrome creation

Leon-Cabrera, Patricia; Guillamon, Antoni; Vega, David Cucurell; Rodriguez-Fornells, Antoni · 2021 · Crossref

DOI: 10.31234/osf.io/mt2wa

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Summary

This study investigates the neural mechanisms underlying palindrome creation, a complex linguistic activity driven by intrinsic curiosity and aesthetic appreciation of structural symmetry. While language is typically analyzed for its communicative function, less is known about the cognitive processes involved in formal language play. The authors hypothesized that palindrome creation, which requires balancing structural constraints with semantic meaning, engages domain-specific language networks and domain-general cognitive control systems. To test this, they conducted a single-case functional magnetic resonance imaging (fMRI) study on TL, an experienced palindrome creator, to identify the brain regions recruited during this effortful task. The experimental design employed a blocked fMRI paradigm where TL covertly generated palindromic sentences from 12 seed-words categorized as either "easy" or "difficult" based on expert ratings. These palindrome blocks were interleaved with resting periods and a verbal working memory (1-back) task to control for general cognitive load. Data were analyzed using whole-brain contrasts comparing palindrome generation to rest (Pal > Rest) and to the working memory task (Pal > WM). Additionally, the study examined the effects of task difficulty (Difficult > Easy) and successful resolution (Solved > Unsolved) by contrasting brain activity based on TL’s post-scan recall. Results indicated that palindrome creation significantly activated bilateral dorsolateral prefrontal cortex (dlPFC) regions, including the left inferior frontal gyrus (Broca’s area) and middle frontal gyrus, as well as bilateral parietal lobes. The Pal > WM contrast highlighted engagement of the left dorsal frontoparietal language network, associated with controlled linguistic processing and phonological manipulation, while showing minimal activation in ventral temporal regions typically linked to semantic processing. This suggests a reliance on structural and orthographic constraints rather than deep semantic retrieval. Furthermore, increased difficulty and successful palindrome resolution were both associated with heightened activation in the right frontopolar cortex (BA 10), a region implicated in exploratory behavior and uncertainty monitoring. The activation pattern also showed substantial overlap with the multiple demand cortex, particularly in parietal areas, indicating the involvement of domain-general cognitive control networks. The findings demonstrate that palindrome creation relies on a hybrid neural architecture combining domain-specific language circuits for phonological and orthographic manipulation with domain-general executive control systems for managing complex constraints. The specific recruitment of the right frontopolar cortex during difficult and successful trials supports the hypothesis that this activity is driven by curiosity and exploratory information seeking. The study provides the first neuroimaging evidence for the neural basis of this ludo-linguistic behavior, highlighting how structural aesthetic pursuits engage high-level cognitive control and specialized language processing pathways distinct from standard semantic comprehension.

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• executive function