The neural representation of intrusive thoughts

0 Center for Lifespan Psychology, Max Planck Institute for Human Development , Lentzeallee 94, 14195 Berlin 1 Clinic for Psychiatry and Psychotherapy, Charite University Medicine , St. Hedwig Krankenhaus, Groe Hamburger Strae 5-11, 10115 Berlin 2 Faculty of Psychology and Educational Sciences, Department of Experimental Psychology and Ghent Institute for Functional and Metabolic Imaging, Ghent University , Henri Dunantlaan 2, 9000 Gent, Belgium 3 Aging Research Center, Karolinska Institutet, Stockholm University , Schweden 4 Department of Psychology, Lund University , Box 214, 221 00 Lund 5 Leibniz-Institut fur Neurobiologie , Brenneckestr. 6, 39118 Magdeburg, Germany 6 German Institute for International Educational Research , Schlostrae 29, 60486 Frankfurt am Main Based on the philosophical notion that language embodies thought we investigated whether a habitual tendency for intrusive thought that younger and older participants report over a period of 100 sessions, spread out over about 6 months, is associated with brain regions related to language production. In favour of this hypothesis, we found that individual differences in habitual intrusive thoughts are correlated with activity in the left inferior frontal gyrus (IFG, Brocas area) as well as the cingulate cortex (CC) during a two-choice reaction-time task in fMRI. Participants who habitually tended to experience intrusive thoughts showed greater activity during task-free (baseline) compared to task periods in brain regions involved in language production. Task performance was unrelated to individual differences in intrusive thoughts. We conclude that intrusive thoughts may be represented in a language-like format and that individuals reporting a habitually higher tendency for intrusive thoughts may have stronger and more habitual inner speech processes. - Humans spend a good deal of their waking time engaged in so-called inner speech with natural language sentences occupying the stream of their conscious mentality (Sokolov, 1972). In philosophy, the question of how thought and language are related has long been debated (Carruthers, 2002). The assumption that language plays a direct role in normal human cognition has been put forward and implies that thought requires language (Wittgenstein 1953; Davidson 1975; McDowell 1994). Another view suggests that language is an inputoutput system for central cognition and is therefore only a channel to transfer thoughts out of or into the mind (Cummins, 1996). A third view would argue that language is one among several possible formats in which thoughts can be processed (Kosslyn et al., 2003). In this study, we focus on a particular kind of thought, namely intrusive thoughts. Intrusive thoughts have been defined as unwelcome repetitive thoughts, images or impulses (Rachman, 1981). In the last decades, clinical psychologists have empirically investigated the role of unwanted, intrusive thoughts in pathologies, such as obsessive compulsive disorders (Julien et al., 2007), depression (Wenzlaff et al., 1988, Cooney et al., 2010), post-traumatic stress disorder (Sprung, 2008) and generalized anxiety disorder (Ruscio and Borkovec, 2004). But also healthy individuals experience intrusive thoughts that are comparable to clinical obsessions in form and content (Rachman and de Silva, 1978; Purdon and Clark, 1993; Langlois et al., 2002). Here, we assessed the habitual tendency for intrusive thoughts by means of three items (Today, I cannot get certain thoughts out of my mind; Today, I keep thinking about something over and over again; Today, I have difficulties suppressing thoughts about myself) experienced by younger and older healthy participants over about 100 days during which participants took part in a micro-longitudinal study of day-to-day variability in cognitive performance. Given that these items were assessed a 100 times over a period of about 6 months, intrusive thoughts, as assessed in the present study, may qualify as indicating the habit to ruminate. We performed a functional magnetic resonance imaging (fMRI) session with a two-choice reaction time (RT) task before and after the 100 days of intrusive thought assessment. Based on previous neuroimaging studies on mind wandering (Mason et al., 2007; Wang et al., 2009) we reasoned that a stronger tendency for intrusive thought would manifest in more presence of these thoughts during task-free periods. We focused on the two-choice RT data instead of data from memory tasks (working and episodic memory), which were also administered within the scope of the present study, because the memory tasks are known to involve articulatory rehearsal processes (Logie et al., 2003; Nixon et al., 2004). We reasoned that strong involvement of inner speech during task performance might preclude or confound the detection of hypothesized inner speech processes during task-free baseline activity. Based on the notion that intrusive thoughts are represented in a language format, we investigated whether the reported habit for intrusive thoughts is associated with activity in brain regions related to language production, particularly the left inferior frontal gyrus (IFG, Brocas area), which has been associated with verbalizing and inner speech processes in previous neuroimaging studies (McGuire et al., 1996a, b; Morin and Michaud, 2007). Based on the notion that participants who show a stronger habitual tendency for intrusive thoughts also ruminate more in the task free periods, we predicted to find a positive correlation between the tendency for intrusive thoughts and brain activity in language related regions during task-free baseline periods. This question was addressed by correlating self-reported habitual tendency for intrusive thoughts with the contrast of brain activity in the task-free baseline > task performance. In addition, we examined the generality of our findings by testing whether they hold before and after the 100 days of assessment and cognitive practice. METHODS Participants The parent sample of this study consisted of 101 adults aged 2032 years and 103 adults aged 6580 years who participated in over 100 days of daily assessments of cognitive performance over a period of 6 months. Participants of this parent sample were asked to take part in imaging, and those volunteering were screened for eligibility. As a result, the effective samples consisted of 24 younger adults (Mage 25.2; s.d.age 3.2, rangeage 20.531.1) and 15 older adults (Mage 70.2; s.d.age 4.0, rangeage 65.080.4). Participants were right-handed, had normal or corrected-to-normal vision and reported no history of cardiovascular disease (except treated hypertension), diabetes, neurological or psychiatric conditions, or drug/alcohol abuse and no use of anti-seizure or antidepressant drugs. Participants in the effective sample completed pre-test imaging, about 100 days assessment of primarily cognitive performance, and post-test imaging and showed no imaging (...truncated)