Recent advances in the neuroscience of spontaneous and off-task thought: implications for mental health

Abstract

People spend a remarkable 30-50% of awake life thinking about something other than what they are currently doing. These experiences of being "off-task" can be described as spontaneous thought when mental dynamics are relatively flexible. Here we review recent neuroscience developments in this area and consider implications for mental wellbeing and illness. We provide updated overviews of the roles of the default mode network and large-scale network dynamics, and we discuss emerging candidate mechanisms involving hippocampal memory (sharp-wave ripples, replay) and neuromodulatory (noradrenergic and serotonergic) systems. We explore how distinct brain states can be associated with or give rise to adaptive and maladaptive forms of thought linked to distinguishable mental health outcomes. We conclude by outlining new directions in the neuroscience of spontaneous and off-task thought that may clarify mechanisms, lead to personalized biomarkers, and facilitate therapy developments toward the goals of better understanding and improving mental health.

Figure 1:. Number of publications on spontaneous thought and mental health over the last two decades.

PubMed search query for Spontaneous Thought: (“spontaneous thought” OR “mind wandering” OR “task-unrelated thought” OR “stimulus-independent thought” OR “freely moving thought” OR “self-generated thought”). PubMed search query for Mental Health: (“mental health” OR “positive affect” OR “negative affect” OR “emotion” OR “mood” OR “sadness” OR “happiness” OR “distress” OR “emotional state” OR “depression” OR “anxiety” OR “ADHD” OR “schizophrenia”).

Figure 2:. Linking spontaneous thought and off-task thought phenomenology to neural measures with experience sampling.

(a) Schematic example of the use of online experience sampling to examine neural correlates and predictors of spontaneous thought and off-task thought. (b) Distinct techniques for examining causal brain relationships with spontaneous thought that provide insights at multiple spatial and temporal scales.

Figure 3:. Large-scale brain network predictive models of spontaneous fluctuations in experience sampling ratings.

(a) (Top) Connectivity features of an fMRI-based functional network model that is predictive of intra-subject off-task thought and on-task attention. (Bottom) The number of edges (pairs of regions) between multiple intrinsic networks that contribute to the model (reproduced with modification from.). (b) (Top) Implanted electrode locations and neuroanatomical regions involved in an iEEG-based functional network model that is predictive of subjective mood fluctuations. (Bottom) Connectivity features (beta-frequency coherence matrix) within a subnetwork involving strong amygdala-hippocampus coupling that is predictive of intra-subject mood ratings (reproduced with modification from).