Delineation of a task-demand dependent rostrocaudal gradient in the salience network

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The salience network is characterized by co-activation of the dorsal anterior cingulate and the bilateral insula, and has been assigned fundamental cognitive processes, such as signalling that a task context is important, or switching between other large-scale networks to facilitate access to attention. The dACC and insula have been proposed to follow a roughly rostral/caudal division; therefore, the salience network should also follow a rostrocaudal gradient, and delineation of this, and its functional significance, is an important first step in beginning to understanding the cognitive functions associated with the vast array of functional brain networks involved in an array of cognitive tasks. We have observed such a task-demand dependent rostrocaudal gradient in the salience network in our published studies, such that coordinated salience network activity is most posterior when sensorimotor processing is required, intermediate when externally oriented attention is required, and most anterior when reasoning and inner speech cognitive operations are executed. This organization is congruent with evolutionary theories of brain organization, with more frontal cognitive processing corresponding to exclusively human cognitive processes like reasoning and inner speech. To date this theory of task-demand dependent rostrocaudal gradient in the salience network has been developed based on observations across experiments, across samples, and across data collection sites. The proposed 5 year plan involves demonstrating control over these different configurations of the salience network using within-subjects manipulations of modality of stimulus presentation (visual, verbal and auditory) and modality of data collection (fMRI and EEG) using variations of the N-back and Sternberg working memory task platforms. Displays in the verbal modality include series of letters, nonsense syllables and words, presented visually or auditorily. Stimulus displays in the non-verbal modality include designs, spatial configurations or motions presented visually, or tones or other non-verbal sounds presented auditorily, possibly also depicting motion or spatial configurations. All networks that co-activate with the various salience configuration are anticipated to be modality dependent. The effect of each variable, and combinations, on performance and the rostrocaudal gradient of the salience network, is an important first step in beginning to understanding the cognitive functions associated with the vast array of functional brain networks. This will be explored over 10 multimodal experiments proposed to extend over 5 years. This research is important to Canadians because a precise understanding of the function of brain networks is required for manipulation of those brain networks, through brain training and/or neuromodulation, to enhance cognitive functioning.