Stimulus-free thoughts induce differential activation in the human default network

Area of Science:

• Neuroscience
• Cognitive Neuroscience
• Brain Imaging

Background:

• The function of the default network, a brain region network active during rest, remains debated.
• It is unclear if its activity is driven by external stimuli or internal thought content.
• Understanding the default network is crucial for comprehending brain function during rest and internal thought.

Purpose of the Study:

• To investigate whether stimulus-free thoughts can modulate default network activation.
• To determine the role of thought content in default network specialization.
• To introduce a novel experimental paradigm for studying the default network.

Main Methods:

• Eliciting sustained, stimulus-free thoughts using brief auditory cues.
• Measuring sustained brain activations (40s) during these stimulus-free conditions.
• Analyzing default network activity modulation based on different types of stimulus-free thought content.

Main Results:

• Sustained brain activations were observed during stimulus-free thought conditions, outlasting the initial cue.
• Default network activity was significantly modulated by the content of stimulus-free thoughts.
• Volitional-prospection thoughts preferentially activated the default network compared to other thought types.
• Several default network regions showed sustained above-rest activation during volitional-prospection.

Conclusions:

• Default network activation is modulated by thought content, even without external stimuli.
• This modulation highlights the importance of internal thought processes in default network specialization.
• The findings support the idea that intrinsically oriented processing is a core function of the default network.
• The study introduces a new stimulus-free experimental method for default network research.