Functional MRI investigations of human temporoparietal junction: attention, response inhibition, theory of mind, and long-term meditation effects
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The human cortical temporoparietal junction (TPJ) has been implicated in cognitive processes including attentional reorienting, social cognition, and behavioral inhibition. Functional organization of TPJ remains unclear due to individual differences in anatomy. This dissertation describes functional magnetic resonance imaging (fMRI) experiments examining TPJ at the level of individuals. A method to localize TPJ using fMRI in individual subjects was developed and tested. TPJ subregions for social cognition, behavioral inhibition, and attention reorienting were parcellated. Finally, differences in attention networks between practitioners of focused attention meditation and matched control participants were investigated. Fifty individuals (ages 20-58; 21 women) participated. Experiment 1 (n=10) developed and tested a novel fMRI paradigm ('CueBall') that combined two forms of attentional reorienting; participants directed and shifted attention in a spatial cueing task and were distracted by the infrequent and unexpected presentation of task-irrelevant images ('oddballs'). The contrast of 'oddball distractor' to 'non-oddball' trials robustly identified TPJ in individual brains. Bilateral subdivisions of TPJ were identified in the fundus of the superior temporal sulcus (STS) and in ventral supramarginal gyrus (SMG). Experiment 2 (n=10, including one individual from Experiment 1) employed the CueBall task along with a Stop Signal task and a Theory of Mind task to determine whether these disparate tasks recruit common or distinct cortical areas. The data demonstrated functional overlap in anterior TPJ between the attention and behavioral inhibition tasks and in posterior TPJ for attention and Theory of Mind. Experiment 3 (n=30) investigated neural correlates of focused attention meditation training in the dorsal attention network (DAN), the default mode network (DMN), and ventral attention network (VAN). Meditators demonstrated an increased magnitude of differential activation in DAN vs. DMN in a sustained attention task, relative to matched controls. In contrast, attentional reorienting did not reveal attention network differences between meditators and controls. Taken together, this work validates an attentional fMRI tool, helps disambiguate functional organization of the TPJ, and demonstrates neural correlates of improved attention in humans with meditation experience.