Self-specific processing in the default network: a single-pulse TMS study.

Area of Science:

• Cognitive Neuroscience
• Neuroimaging
• Brain Stimulation

Background:

• Neuroimaging studies identify a network including medial prefrontal cortex (MPFC), precuneus, and parietal cortex for self-related processing.
• Criticism suggests this network overlaps with the brain's default mode network, questioning its self-specificity.
• The self-reference effect (SRE) demonstrates superior performance for self-related stimuli.

Purpose of the Study:

• To investigate the self-specificity of the neural network associated with self-related processing.
• To determine the causal role of specific brain regions (MPFC, parietal cortex) in the SRE using transcranial magnetic stimulation (TMS).
• To differentiate between self-specific processing and general cortical activity within the default network.

Main Methods:

• Healthy volunteers performed a task rating adjectives as self- or other-related, exhibiting the SRE.
• Single-pulse TMS was applied to the medial prefrontal cortex (MPFC), left parietal cortex, and right parietal cortex at various stimulus onset asynchronies (SOAs).
• The impact of TMS on the SRE was measured by changes in performance accuracy and reaction time.

Main Results:

• TMS applied to the left parietal cortex significantly suppressed the SRE between 160 and 480 ms after stimulus onset.
• TMS to the right parietal cortex also suppressed the SRE, but at later SOAs compared to the left parietal cortex.
• Disruption of the MPFC with TMS had no significant effect on the SRE.

Conclusions:

• The findings provide evidence for a self-specific processing system involving the parietal cortex.
• Lateral inferior parietal cortices play a critical, time-dependent role in ongoing self-awareness and the SRE.
• The MPFC may not be specifically involved in self-referential processing, challenging previous interpretations of the default network's function.