The flow of human thoughts is frequently plagued by unwanted cognitive activity, which has the unfortunate power to interfere with task performance, planning, social behaviour, and many other aspects of our lives. Importantly, repetitive negative thoughts and memories play a major role in psychopathology and represent a fundamental transdiagnostic process which deserves experimental and clinical attention. Inhibitory deficits on the one hand and metacognitive beliefs on the other are thought to play a key role in maintaining intrusive repetitive memories and thoughts in a variety of mental health difficulties (Major Depressive Disorder, Post-Traumatic Stress Disorder, Obsessive-Compulsive Disorder, Generalized Anxiety Disorder).

This thesis argues against Daniel Wegner’s Ironic Process Theory (Chapter 1) and examines the impact of thought suppression on intrusive Autobiographical Memories with two studies: an fMRI study (Study 1, Chapter 2), and a behavioural study (Study 2, Chapter 3). These two studies represent the first attempt to employ the Autobiographical Think/No-Think task (ATNT), a novel version of the Think/No-Think task solely based on autobiographical memories provided by each participant. In particular, Study 1 investigates the neural correlates of the ATNT task using functional Magnetic Resonance Imaging, and Study 2 explores the introduction of trial-by-trial intrusion ratings in the ATNT task and considers the affective consequences of thought suppression using Skin Conductance Response (SCR). This thesis also probes for the first time the relationship between metacognitive beliefs, intrusive memories, and thought control abilities using the standard Think/No-Think paradigm and manipulating participants’ metacognitive beliefs about the usefulness and the uncontrollability of repetitive intrusive thinking (Study 3, Chapter 4). After a general discussion (Chapter 5), this thesis reflects on the philosophical and ethical implications of forgetting, from a personal, psychological, and historical point of view (Chapter 6).