Effective connectivity of ascending and descending frontalthalamic pathways during sustained attention: Complex brain network interactions in adolescence

Abstract

Frontal-thalamic interactions are crucial for bottom-up gating and top-down control, yet have not been well studied from brain network perspectives. We applied network modeling of fMRI signals (Dynamic Causal Modeling; DCM) to investigate frontal-thalamic interactions during an attention task with parametrically varying levels of demand. fMRI was collected while subjects participated in a sustained continuous performance task with low and high attention demands. 162 competing model architectures were employed in DCM to evaluate hypotheses on bilateral frontal-thalamic connections and their modulation by attention demand, selected at a second level using Bayesian Model Selection. The model architecture evinced significant contextual modulation by attention of ascending (thalamus → dPFC) and descending (dPFC → thalamus) pathways. However, modulation of these pathways was asymmetric: While positive modulation of the ascending pathway was comparable across attention demand, modulation of the descending pathway was significantly greater when attention demands were increased. Increased modulation of the (dPFC → thalamus) pathway in response to increased attention demand constitutes novel evidence of attention-related gain in the connectivity of the descending attention pathway. By comparison demand-independent modulation of the ascending (thalamus → dPFC) pathway suggests unbiased thalamic inputs to the cortex in the context of the paradigm.

Hyper-modulation of brain networks by the amygdala among women with Borderline Personality Disorder: Network signatures of affective interference during cognitive processing

“…The choice of seed and the psychological context are free parameters of the model, and are chosen based on prior knowledge regarding task characteristics and the putative network relationships of the seed (Friston et al, 1997; Horwitz et al, 2005; Wadehra, Pruitt, Murphy, & Diwadkar, 2013; Woodcock et al, 2016). PPIs constitute a model of directed functional connectivity and are distinguishable from more sophisticated models of brain network function (e.g., dynamic causal models) that provide estimates of effective connectivity, or causal interactions exerted between neuronal populations (Friston et al, 2012; Diwadkar et al, 2014; Jagtap & Diwadkar, 2016). Given our focus on assessing “bottom-up” network profiles in BPD, the amygdala was a logical choice of seed.…”

Response Hand and Motor Set Differentially Modulate the Connectivity of Brain Pathways During Simple Uni-manual Motor Behavior

“…These effects are broadly consistent with previous independent studies using a similar paradigm (Asemi et al, 2015), and suggest that the induction of a motor set unfolds inherent representations of the dominant right hand through increased synchrony between key sub-networks. Moreover, these sub-networks include regions such as the thalamus and the parietal cortex that are committed to attention processing (Corbetta et al, 1998; Jagtap & Diwadkar, 2016), and the primary motor cortex (M1) and SMA wherein hand dominance is strongly expressed (Bernard & Seidler, 2012); d) In investigating hand-related differences within each task condition, the random condition induced the greatest modulation (Figure 5), specifically when responding with the non-dominant left hand. These effects are intriguing for multiple reasons: First, as previously noted the unpredictability of onsets during the random condition is challenging enough to preempt the establishment of a motor set during task epochs (Asemi et al, 2015) resulting in reactive responding.…”

Brain network dysfunction in youth with obsessive-compulsive disorder induced by simple uni-manual behavior: The role of the dorsal anterior cingulate cortex

“…The thalamus is an important center that gates sensory inputs and projects outputs to cortical and subcortical targets (Haber and Calzavara, 2009), and studies suggest that the activity of thalamic nuclei are highly susceptible to descending frontal inputs (Haber and McFarland, 2001), and that descending network effects are detectable with network modeling (Jagtap and Diwadkar, 2016). Thus, the hyper-modulation of the thalamus across conditions suggests plausibly exaggerated mechanisms of “top-down” control of frontal-thalamic processing units in OCD.…”

“…In our ongoing analyses, we are attempting stronger connectivity analyses employing fuller measures of effective connectivity (Friston et al, 2003; Jagtap and Diwadkar, 2016), and are exploring relationships between the degree of network dysfunction in OCD and clinical dimensions. We also note that we are limited in addressing the correspondence between the observed behavioral effects (see Results) and the compelling fMRI network effects as we are compromised by the smaller sample size of the behavioral analyses.…”