ارتباطات عصبی سرکوب افکار

The present report used functional magnetic resonance imaging (fMRI) to examine the neural correlates of thought suppression. Subjects were imaged while alternately (i) attempting to suppress a particular thought, (ii) attempting to suppress all thoughts, or (iii) thinking freely about any thought. Suppression of a particular thought, when compared to the free-thought control condition, revealed greater activation in the anterior cingulate. When the task of suppressing all conscious thoughts was compared to free-thought, a more distributed network of brain regions, including the anterior cingulate and the insula, was activated. These findings are consistent with previous research on cognitive control and may provide potential insights into psychological disorders involving recurring, intrusive thoughts.

A fundamental human capacity is the ability to regulate and control our thoughts and behaviors. Neural substrates of cognitive control have been investigated using a variety of methods that require suppression of actions (Bush et al., 1998 and Casey et al., 1997; Garavan, Ross, & Stein, 1999; Gondo, Shimonaka, Senda, Mishina, & Toyama, 2000; Kawashima et al., 1996; Kiehl, Smith, Hare, & Liddle, 2000; Leung, Skudlarski, Gatenby, Peterson, & Gore, 2000; MacDonald, Cohen, Stenger, & Carter, 2000). The procedures used in these studies require participants to inhibit behavior, such as refraining from making a button press in a go/no-go task (e.g. Gondo et al., 2000, Kawashima et al., 1996 and Kiehl et al., 2000; Konishi, Nakajima, Uchida, Sekihara, & Miyashita, 1998; Liddle, Kiehl, & Smith, 2001) or inhibiting reading while naming the color in which a word is written (i.e. the Stoop task) (Bush et al., 1998 and Leung et al., 2000). Less attention, however, has focused on the brain regions that are involved in the regulation of mental contents, such as when people are instructed to control their thoughts or memories (Bunge, Ochsner, Desmond, Glover, & Gabrieli, 2001; Wegner & Wenzlaff, 1996). Although regulating the contents of consciousness requires substantial cognitive effort (Wenzlaff & Wegner, 2000), thought control does not require the suppression of an overt motoric or verbal response. Thus, it is unclear whether similar neural mechanisms are involved in this variant of cognitive control. Noting this ambiguity, the present study investigates the neural mechanisms that underlie directed thought suppression. Mental control is required for people to function effectively in their daily lives. Successfully controlling our thoughts is difficult; unwanted worries intrude and thoughts frequently wander when they should be focused on the task or goal at hand (Wenzlaff & Wegner, 2000). These intrusive thoughts often arise automatically, without any conscious effort to call them forth. Difficulties with mental control and inhibition are core symptoms in various clinical disorders (Purdon, 1999), such as post-traumatic stress disorder (PTSD) (e.g. Davies & Clark, 1998; Steil & Ehlers, 2000), attention-deficit hyperactivity disorder (ADHD) (e.g. Caplan, Guthrie, Tang, Nuechterlein, & Asarnow, 2001), obsessive–compulsive disorder (OCD) (e.g. Purdon, 2001; Tolin, Abramowitz, Hamlin, Foa, & Synodi, 2002), and depression (Beck, Rush, Shaw, & Emery, 1979; Greenberger & Padesky, 1995; Reynolds & Wells, 1999). Each of these disorders has been linked to deficits in the ability to regulate or suppress unwanted thoughts. The combined evidence from these several patient groups also raises the possibility that cognitive control over thoughts and actions may share common underlying neural mechanisms. Thus, understanding the neural basis of mental control over everyday thoughts in healthy individuals may provide insights into the cognitive processes associated with these various psychological disorders. Cognitive control of thoughts and actions may involve similar component processes and therefore recruit common brain regions. Action inhibition typically involves activation of the anterior cingulate (Braver, Barch, Gray, Molfese, & Snyder, 2001; Liddle et al., 2001 and MacDonald et al., 2000) and the prefrontal cortex (Casey et al., 1997; Dove, Pollman, Schubert, Wiggins, & von Cramon, 2000; Logan & Cowan, 1984; Miller, 2000). The anterior cingulate is active across a variety of tasks that require inhibition of prepotent responses, such as the Stroop task (Peterson et al., 1999) and the go/no-go task (Casey et al., 1997, Kiehl et al., 2000 and Liddle et al., 2001). Additionally, research has shown that there is diminished anterior cingulate activity in patients with PTSD when they are responding to emotional words, suggesting that this structure may play a key role in the ability to suppress intrusive thoughts (Shin et al., 2001). Recent studies have also implicated the insula in aspects of cognitive control (Bunge, Klingberg, Torkel, Jacobson, & Gabrieli, 2000; Dove et al., 2000; Garavan et al., 1999; Rubia et al., 2001). Garavan et al., using event-related fMRI, showed right insula activation during a task that required inhibition of prepotent motor responses to target letters (Garavan et al., 1999). Similarly, Dove et al. reported insula activity during task switching (Dove et al., 2000). Thus, the accumulated evidence to date suggests that the insula may be an important brain region in the network that subserves cognitive control. Extending work of this kind, the present research used fMRI to identify the neural substrates of intentional thought suppression. Specifically, subjects were imaged during three task conditions: (1) trying to suppress a specific, unwanted thought; (2) trying to suppress all conscious thought; and (3) thinking freely about anything.