RESUMO
Delayed Information Processing Speed (IPS) often underlies attention deficits and is particularly evident in patients with traumatic brain injury, Parkinson's disease, depression, dementia, and multiple sclerosis. Therefore, it is of interest to determine the brain network that is responsible for such essential cognitive function to understand IPS deficits and to develop effective rehabilitation programs. We assessed brain functional connectivity and effective connectivity during the performance of an adapted version of the Symbol Digit Modalities Test. Using dynamic causal modeling, we focused on obtaining a network model for IPS function in healthy subjects. Sixteen right-handed volunteers (seven women, age: 29.7⯱â¯5.0 years) were included in the study after giving written consent for participating. Functional magnetic resonance images were acquired in a 3T scanner. According to our results, two systems interact during the IPS task performance. One is formed by frontoparietal and fronto-occipital networks, related to the control of goal-directed (top-down) selection for stimuli and response, while the second is composed of the temporoparietal and inferior frontal cortices, which are associated with stimulus-driven attention in the brain. Additionally, the default-mode network showed a significant correlation with networks positively associated with the task, mainly those related to visual detection and processing, indicating its relevant role in functional integration involving IPS. Therefore, an IPS-related network was proposed through a methodology that may be useful for future studies considering other cognitive functions and tasks, clinical groups, and longitudinal assessments.
Assuntos
Encéfalo/fisiologia , Cognição/fisiologia , Adulto , Mapeamento Encefálico , Feminino , Humanos , Imageamento por Ressonância Magnética , Masculino , Vias Neurais/fisiologia , Testes NeuropsicológicosRESUMO
Action update, substituting a prepotent behavior with a new action, allows the organism to counteract surprising environmental demands. However, action update fails when the organism is uncertain about when to release the substituting behavior, when it faces temporal uncertainty. Predictive coding states that accurate perception demands minimization of precise prediction errors. Activity of the right anterior insula (rAI) is associated with temporal uncertainty. Therefore, we hypothesize that temporal uncertainty during action update would cause the AI to decrease the sensitivity to ascending prediction errors. Moreover, action update requires response inhibition which recruits the frontostriatal indirect pathway associated with motor control. Therefore, we also hypothesize that temporal estimation errors modulate frontostriatal connections. To test these hypotheses, we collected fMRI data when participants performed an action-update paradigm within the context of temporal estimation. We fit dynamic causal models to the imaging data. Competing models comprised the inferior occipital gyrus (IOG), right supramarginal gyrus (rSMG), rAI, right presupplementary motor area (rPreSMA), and the right striatum (rSTR). The winning model showed that temporal uncertainty drove activity into the rAI and decreased insular sensitivity to ascending prediction errors, as shown by weak connectivity strength of rSMGârAI connections. Moreover, temporal estimation errors weakened rPreSMAârSTR connections and also modulated rAIârSTR connections, causing the disruption of action update. Results provide information about the neurophysiological implementation of the so-called horse-race model of action control. We suggest that, contrary to what might be believed, unsuccessful action update could be a homeostatic process that represents a Bayes optimal encoding of uncertainty.