Intrusive Thoughts Aren’t Intrusive After All

While undesirable thoughts may sound negative and uncontrollable to us, people can limit the awareness of unwanted memories. Anterior cingulate cortex (ACC), a brain region involved in cognitive control, was found to have the ability to detect and suppress unwanted memories via both proactive and reactive mechanisms.

A new study published in the Journal of Neuroscience by Maité Crespo García, a postdoctoral research associate at the University of Cambridge MRC Cognition and Brain Sciences Unit, shed light on the brain’s ability to suppress negative memories with the anterior cingulate cortex (ACC). 

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Detecting Emerging Bad Traces

In this research titled “Anterior Cingulate Cortex Signals the Need to Control Intrusive Thoughts During Motivated Forgetting”, researchers used simultaneous EEG-fMRI recordings to track interactions between the dorsal ACC (dACC), the right dorsolateral prefrontal cortex (rDLPFC), and the hippocampus during suppression. When undesirable thoughts emerge in both sexes, the ACC exerts a top-down inhibitory control on the hippocampus. While previous studies have shown neural mechanisms interact with the rDLPFC to inhibit hippocampal activity when unwanted memories surface, questions regarding how such mechanisms act remain unanswered.

The participants memorized sets of words (i.e., gate and train) and were asked to either recall a cue word’s pair (see gate, think about train) or only focus on the cue (see gate, only think about gate). During proactive memory suppression, the ACC increased activity within the first 500 milliseconds of the task. The researchers then examined variations in participants’ theta power and N2 amplitude EEG markers in the dACC that are believed to reflect the need for neural control.

The authors stated that during strong early EEG activity, hippocampal activity and blood oxygen dependent (BOLD) signals in the dACC and rDLPFC decreased, suggesting preempting retrieval reduces overall neural control demands.

Reactive Response to Intrusions 

If the “need for control” surfaces, the ACC activity increases within 500 milliseconds during the task, relaying control signals to the DLPFC to reduce hippocampal activity and memory recall, leading to “motivated forgetting”. When the memory is stopped early, the activity levels in the ACC and DLPFC decrease, if the memory is not suppressed in time, the ACC initiates an alarm. This increases activity in the ACC and the DLPFC to stop intrusive thoughts.

“This study provides evidence that theta mechanisms in dACC are key to triggering inhibitory control by rDLPFC during motivated forgetting. These mechanisms can be engaged rapidly by external warning stimuli, helping to rapidly preempt unwanted thoughts.”

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Author

Fujie Tham