The Functional Role of Large-scale Brain Network Coordination in Placebo-induced Anxiolysis

Summary & key facts

This study used brain imaging to see how simply expecting an anti-anxiety treatment that was actually a placebo changes large-scale brain networks. The researchers found that a brain area called the rostral anterior cingulate cortex increased its ongoing communication with the brain's salience network, while the salience network's reaction to threat cues went down. They also saw stronger connections inside the default mode network, which supports inward-focused thought. These network shifts were linked to lower steady anxiety and lower baseline alertness, suggesting the placebo made people’s brains turn attention inward and damp down threat signals.

Key facts:

• The team measured patterns of brain networks when people were either focused on things outside them or on their own thoughts while they believed they had taken an anxiety-reducing drug that was actually a placebo.
• Under the placebo, the salience network — the brain system that helps spot and react to important or threatening signals — showed an overall decrease in activity, especially when threat cues appeared.
• A region called the rostral anterior cingulate cortex, which is involved in emotion and regulation, showed stronger ongoing communication with the salience network under placebo. This stronger link was associated with reductions in steady anxiety and in baseline arousal, meaning people felt less constantly alert.
• The default mode network, a brain system tied to inward-focused thinking and daydreaming, showed stronger internal connections under placebo. These stronger connections also predicted reductions in anxiety.
• Together, the findings suggest placebo anxiety relief involves both a drop in attention to external threat and a shift toward more internal, calm mental states. The results show correlations in brain activity and anxiety levels, but they do not prove the brain changes cause the anxiety reductions or guarantee clinical benefit without more research.

Abstract

Anxiety reduction through mere expectation of anxiolytic treatment effects (placebo anxiolysis) has enormous clinical importance. Recent behavioral and electrophysiological data suggest that placebo anxiolysis involves reduced vigilance and enhanced internalization of attention; however, the underlying neurobiological mechanisms are not yet clear. Given the fundamental function of intrinsic connectivity networks (ICNs) in basic cognitive processes, we investigated ICN activity patterns associated with externally and internally directed mental states under the influence of an anxiolytic placebo medication. Based on recent findings, we specifically analyzed the functional role of the rostral anterior cingulate cortex (rACC) in coordinating placebo-dependent cue-related (phasic) and cue-unrelated (sustained) network activity. Under placebo, we observed a down-regulation of the entire salience network (SN), particularly in response to threatening cues. The rACC exhibited enhanced cue-unrelated functional connectivity (FC) with the SN, which correlated with reductions in tonic arousal and anxiety. Hence, apart from the frequently reported modulation of aversive cue responses, the rACC appears to be crucially involved in exerting a tonically dampening control over salience-responsive structures. In line with a more internally directed mental state, we also found enhanced FC within the default mode network (DMN), again predicting reductions in anxiety under placebo.

Topics

Mental Health and Psychiatry Neuroscience, Education and Cognitive Function Pain Management and Placebo Effect

Categories

Cognitive Neuroscience Life Sciences Neuroscience

Tags

Alternative medicine Functional connectivity Medicine Neuroscience Pathology Physical medicine and rehabilitation Physics Placebo Psychology Quantum mechanics Scale (ratio)

Conditions & symptoms

Anxiety Anxiety or worry