Differential Default Mode Network Response to Rest Cues in Adults with Attention Deficit Hyperactivity Disorder

• ¹ Ghent University, Department of Experimental-Clinical and Health Psychology, Belgium
• ² University of Southampton, Developmental Brain-Behaviour Unit, School of Psychology, United Kingdom

Introduction: The default mode network (DMN) is a robust and highly replicable set of brain regions denoting a task-independent, self-referential state, including medial prefrontal cortex (MPFC) and posterior cingulate cortex (PCC)/precuneus. From a functional perspective, the hallmark feature of the DMN is its activation during periods of rest, and its attenuation as one takes on attention-demanding activities (Raichle et al., 2001). Research into the pathophysiology of Attention Deficit Hyperactivity Disorder (ADHD) has implicated DMN dysregulation. The most recent findings show that individuals with ADHD fail to effectively suppress the DMN as they transition to attention-demanding tasks and that this appears to create interference with the ability to perform those tasks (Fassbender et al., 2009; Liddle et al., 2011; Sonuga-Barke & Castellanos, 2007). Furthermore, the functional connections of the network during rest are also reported to be altered and point to a reduced ability to efficiently modulate it (Castellanos et al., 2008; Fair et al., 2010; Tian et al., 2007). In the present study, we adopted a novel approach to investigate the state transitions in ADHD, by evaluating the DMN response upon the receipt of a cue signalling rest (i.e. rest cue) prior to the actual rest period. Hence, in this preliminary analysis we evaluated the DMN response to rest cues in a group of adults with ADHD and healthy controls.
Methods: We undertook a functional magnetic resonance (fMRI) study using an event-related cued state-switching paradigm, where predefined cues signalled either a rest period or a task trial. Eleven neurologically normal adults participated in the present study – 6 healthy controls and 5 with a clinical diagnosis of ADHD. In order to investigate group differences in rest cue related DMN response, brain activity was contrasted between the groups on a singled out cue phase.
Results: There were two key findings. First, the results indicate an up-regulation of the DMN upon the occurrence of a rest cue in both adults with ADHD and healthy controls, reflected in increased activation in the core regions of the DMN (MPFC, PCC/precuneus). Second, rest cues activated the DMN to a significantly lesser degree in adults with ADHD compared to healthy controls.
Conclusions: These preliminary results provide valuable insight into brain responses during the transition to rest periods, indicating an increase in DMN activation upon a cue signalling an upcoming rest period. This broadens our perception of the DMN, by showing that the network is highly sensitive and is rapidly modulated in response to a stimulus indicating the transition to an idle state. Moreover, our findings extend previous research reporting state-dependent DMN alterations in ADHD by showing decreased DMN up-regulation in ADHD during transition to a rest period. Thus, our results further implicate the DMN in the pathophysiology of ADHD, suggesting decreased DMN responsiveness to rest cues and tentatively point to a state modulation deficit in ADHD.