Hippocampal GABA enables inhibitory control over unwanted thoughts

Area of Science:

• Neuroscience
• Cognitive Psychology
• Psychiatry

Background:

• Intrusive thoughts and hallucinations are common in psychiatric disorders.
• Deficient prefrontal cortex inhibitory control is often implicated, but hippocampal hyperactivity due to GABAergic dysfunction is also observed.
• The precise role of hippocampal GABA in thought suppression remains unclear.

Purpose of the Study:

• To investigate the role of hippocampal GABAergic inhibition in the neural pathway of thought suppression.
• To determine the relationship between hippocampal GABA concentrations and mnemonic control.
• To elucidate the fronto-hippocampal mechanisms underlying voluntary control over awareness.

Main Methods:

• Functional magnetic resonance imaging (fMRI) was used to monitor brain activity during thought suppression tasks.
• ¹H magnetic resonance spectroscopy (MRS) measured resting concentrations of hippocampal GABA.
• Participants viewed reminders of unwanted thoughts and attempted to suppress retrieval.

Main Results:

• Thought suppression led to reduced hippocampal activity and impaired memory for suppressed content.
• Higher resting hippocampal GABA concentrations predicted enhanced mnemonic control.
• Increased hippocampal GABA correlated with stronger fronto-hippocampal coupling during suppression, but not with prefrontal GABA levels.
• Action suppression did not involve the identified fronto-hippocampal pathway.

Conclusions:

• Hippocampal GABAergic inhibition is a critical component of the fronto-hippocampal pathway for thought suppression.
• Local hippocampal interneurons appear to mediate the control over intrusive thoughts.
• This study provides a mechanistic model for how voluntary control over awareness is achieved.