The neural basis of positive and negative affect

Abstract

Recent research suggests that cognitive-affective regulation is accomplished through large-scale brain networks. Amongst these networks, a unifying triple network model that includes the default mode network (DMN), salience and emotion network (SEN), and cognitive control network (CCN) appears to underpin a range of cognitive and affective processes that play significant roles in susceptibility of individuals to psychopathologies. Three studies were conducted to understand the relationships between affective traits, namely trait positive affect (PA) and negative affect (NA), and the triple-network in healthy individuals and the neural alterations in depression.

Study 1 examined the presentation of trait PA and NA in terms of the intra- and inter- network connectivity in the triple-network in healthy adults (n = 63). It was found that compared to DMN and CCN, PA was more related to the SEN, including the within-SEN connectivity, and the connectivity between SEN and DMN, CCN and other brain regions. NA was associated with some connections within SEN and within DMN to a lesser extent. The findings corroborated that NA and PA are two distinct components of affect and have different neural underpinnings.

Study 2 further examined the presentation of trait PA and NA in terms of the structure size of regions in the triple-network in healthy adults with the high-resolution magnetic resonance imaging (MRI) (n = 63). It was found that PA was negatively correlated with the gray matter volume (GMV) of posterior cingulate cortex (PCC) within DMN, and the GMV of dorsolateral prefrontal cortex (DLPFC) within CCN, but was not correlated with the GMV of any structures in SEN. In contrast, NA was negatively correlated with the GMV of nucleus accumbens (NAcc) within SEN. Integrating the findings from Study 1 and 2, a more complete picture of the neural correlates and connectivity underpinning PA and NA in healthy population in the three networks is depicted.

Study 3 moved on to investigate the alterations of the intra- and inter-network functional connectivity and regional structural size in the triple-network in people with Major Depressive Disorder (MDD) who commonly display low PA and high NA (MDD: n = 51, healthy control: n = 45). Aberrant connectivity within DMN but not within SEN or CCN was found in people with MDD compared to healthy controls. They also showed altered connectivity between DMN and SEN, between DMN and CCN and between the three networks and other brain regions. People with MDD also showed widespread volumetric reduction across the three networks.

Overall, the findings of this thesis corroborate that MDD is underpinned by altered triple-network related to PA and NA. Our findings offer significant insights into the implications of the triple network model in affective traits and affective psychopathology, which may guide the development of interventions for affective disorders.