Rumination may promote ineffective behavior that ultimately harms mental health, although the mechanisms are
unclear. Recent research suggests rumination, which is defined as dwelling on the possible significance and
implications of one’s distress and problems, may promote ineffective behavior by disrupting reinforcement
learning (RL). RL refers to the suite of processes that enable adjusting expectations, when an experience differs
from expected, and then taking appropriate action. RL is a ubiquitous process that is necessary for effective
behavior. Hence, rumination’s disruption of RL may represent an upstream process that helps explain
rumination’s link to various ineffective behaviors. This raises the prospect of intervening to prevent rumination
from disrupting RL, thereby making behavior more effective, and ultimately improving mental health. However,
the recent research showing rumination disrupts RL is currently unclear on if rumination disrupts the RL
mechanisms of learning (adjusting expectations) or choice (taking appropriate action). Different mechanisms
would have distinct translational implications, hence clarity on the specific mechanisms is critically needed.
Therefore, the objectives of this project are to dissociate rumination’s effects on the learning and choice
components of RL, and to apply computational modeling and electroencephalography (EEG) to identify the
specific mechanisms of these components it impairs. The central hypotheses are that rumination disrupts RL by
impairing the following RL mechanisms: guidance by working memory that accelerates learning, long-term
punishment learning, and cognitive control that enables effective choice. To test these hypotheses, the within-
subject effects of ruminative (RUM) vs. neutral (NEU) thinking on mechanisms that guide learning (Aim 1) and
choice (Aim 2) in RL will be investigated. To ensure generalization to clinical rumination, all participants (N=60)
in this single-visit experimental study will meet criteria for Major Depressive Disorder or Generalized Anxiety
Disorder. To ensure feasibility, recruitment will be embedded in a large-scale external project that conducts
diagnostic interviews. Aim 1 will examine if RUM (vs. NEU) leads to slower acquisition of contingencies by
disrupting working memory, and causes working memory to represent punishment experiences more strongly
during initial learning, thereby disrupting long-term punishment learning. Aim 2 will examine if RUM (vs. NEU)
disrupts cognitive control in a task where Pavlovian (instinctual) and instrumental (goal-directed) impulses
conflict, and cognitive control is needed to override the former. These aims are integrated with a training plan to
broaden and deepen the applicant’s background in computational neuroscience, to enable him to acquire
specialized skills in this area (hierarchical Bayesian computational modeling and EEG), and to facilitate his
development of a programmatic and competitive translational research program. This training is essential to the
applicant’s transition to an independent, productive research career in the NIMH priority area of computational
psychiatry.