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  • The VSWM network has an extensive interaction

    2018-10-25

    The VSWM network has an extensive interaction with the ventral attention network, which includes the inferior frontal gyrus, the ventral medial prefrontal and orbitofrontal cortex (OFC), and the temporoparietal junction and superior temporal cortex (Prado and Weissman, 2011; Weissman and Prado, 2012). The ventral attention network acts as a salience detection system, enabling the involuntarily reorientation of attention to unexpected external events (Corbetta et al., 2008; Vossel et al., 2014). This may be related to the role of the ventral attention network in reward processing, which also involves the ventral striatum, anterior cingulate and the limbic system (Kable and Glimcher, 2007; Kennerley and Wallis, 2009; Klingberg, 2010; Rushworth et al., 2011). It has been suggested that the OFC, together with other ventral frontal cortices, is specifically involved in processing the properties (quantity and quality) of reward-related stimuli (Howard et al., 2015; Pauli et al., 2012; Roesch and Olson, 2004). This enables the OFC to serve as a specialized short term memory buffer, monitoring which recent actions were rewarded and predicting which future actions are most likely to be rewarded (Kahnt et al., 2010). Individuals with ADHD show relatively low sensitivity to reward related information as compared with NC, evident in lower neural activity levels in the ventral striatum (Ströhle et al., 2008), and poor OFC responsiveness to reward (Cubillo et al., 2012; Wilbertz et al., 2012). The anterior insula plays a critical role in mediating between the ventral and dorsal executive networks (primarily in the right hemisphere), and GW5074 it exhibits significant functional connectivity to dorsal prefrontal GW5074 regions involved in goal-directed behavior (Eckert et al., 2009). A second key brain region playing a related role is the anterior cingulate, which interacts with primary sensory cortices in tasks that require action selection and attention control (Crottaz-Herbette and Menon, 2006; Silvetti et al., 2013). Despite primarily being associated with the limbic system, the anterior insula and the anterior cingulate are more recently considered as part of a salience detection network, and it is suggested that they complement the central executive network in risk/gain prediction (Menon and Uddin, 2010; Preuschoff et al., 2008; Späti et al., 2014; Taylor et al., 2009). Whenever decision switching or response inhibition is required, children with ADHD are likely to exhibit poor cognitive control associated with lower levels of neural activity in the anterior insula, as compared with NC subjects (Cubillo et al., 2010; Morein-Zamir et al., 2014). Since children with ADHD display increased reliance on external feedback and reward, we hypothesized that either the lack of trial-by-trial feedback (Wiersema et al., 2009), or an expectation for insignificant reward (Bitsakou et al., 2009), would result in an impaired VSWM performance in ADHD. Since the VSWM network and the processing of reward and feedback involve several brain regions, we expected impaired performances in ADHD to be associated with abnormal pattern of neural activity distributed across several brain regions, where the specific nature of this distributed pattern would depend on the characteristics of the performed task (i.e., conditioned by the expected reward size and feedback availability). In contrast, trial-by-trial feedback associated with large-reward simulate a scenario where there is an immediate association between a desired action and a rewarding outcome, and thus this may result with better VSWM performances in ADHD. Here we had two alternative hypotheses: (i) performance improvement in ADHD would be associated with brain activity becoming more normal-like. (ii) Performance improvement in ADHD would be associated with an engagement of a compensatory neural mechanism, which is not engaged in NC children.