The contributions of posterior lateral temporal cortex to language and control networks
Within cognitive neuroscience, understanding how the brain supports the flexible use of language and meaning remains an ongoing challenge. In recent years, the Controlled Semantic Cognition framework has offered an account of the neural correlates of representation and control of meaningful information. The context-independent storage of semantic representations is subserved by the bilateral anterior temporal lobe hub and its connections to modality-specific spokes distributed throughout the cortex, while semantic control – the flexible, goal-oriented access and manipulation of this meaningful information – relies upon a left-lateralised set of frontal and temporal brain regions. However, we do not yet understand precisely how these two networks may integrate. Further, the set of regions supporting semantics overlaps somewhat with phonological processing, and the semantic control network is distinct, but overlapping with, the multiple demand network for domain-general executive control. This raises the question of how semantic representation and control might relate to other domains. The exact extent of this overlap, and the implications this has both for role of individual regions, is still uncertain. One such region is the posterior lateral temporal cortex (pLTC). Many disparate literatures have made claims about the function of the pLTC or subregions within, suggesting involvement in domains such as phonology, semantics, social processing, and both semantic and domain-general control. However, it remains unclear how this area is organised, including which subregions might be recruited by the different language, semantic and control networks in which the pLTC has been implicated, the domain-specificity of the control processes supported by these subregions, and whether the pLTC is a site of integration between networks. To address these questions, Chapters 2 and 3 employ activation likelihood estimation meta-analysis at the whole brain and region of interest (ROI) levels to compare the regions of consistent activation across domains. Then, Chapters 4 and 5 use task-based functional MRI with a factorial design in neurotypical participants, to explore the independent and interacting effects of stimulus domain and task process on the activation and connectivity of control regions. In Chapter 2, whole brain meta-analyses are used to delineate dimensions of functional organisation in the language network, highlighting the importance of language subdomain (semantic versus phonology), as well as the distinction between representation and control processes as key factors in determining the functional organisation of the language network. In Chapter 3, a large cross-domain meta-analysis within a bilateral pLTC ROI compares activation convergence across seven cognitive domains simultaneously (semantics, semantic control, phonology, tool processing, face processing, theory of mind and biological motion processing), in order to map out subregions within the pLTC that are shared and distinct across domains, and generate hypotheses about the cognitive processes that may be supported by these regions. From the meta-analyses, several hypotheses emerged regarding the domain-specificity of control regions, in particular the left pLTC, that warranted further testing. In Chapter 4, univariate whole brain analyses indicate that both task process and stimulus domain affect the activation of control networks and their constituent regions, separating these factors for the first time to give a more nuanced understanding of what is “special” about semantic control. ROI analyses also demonstrate that regions for semantic and non-semantic control are not homogenous in their profile of activity. Chapter 5 uses task-based psycho-physiological interaction analyses in an attempt to assess how the functional connectivity of key seeds in the left pLTC changes with task process and stimulus modality. Though these results are minimal and provide no insight, resting-state functional connectivity analyses on an independent fMRI dataset reveal different intrinsic connectivity for the left pMTG/STS versus pITG, giving a better understanding of the precise contributions of these pLTC subregions to semantic and control networks.
brain, cognitive neuroscience, control, language, posterior temporal lobe, semantics
Networked Digital Library of Theses and Dissertations