Subcortical loop activation during selection of currently relevant memories

Area of Science:

• Neuroscience
• Cognitive Psychology
• Neuroimaging

Background:

• The anterior limbic system, particularly the orbitofrontal cortex (OFC), is crucial for aligning thought and behavior with current reality.
• The OFC appears to function by suppressing irrelevant memories before conscious recognition.

Purpose of the Study:

• To investigate the specific anatomical connections through which the OFC exerts its influence on memory suppression.
• To understand the neural mechanisms underlying the OFC's role in maintaining awareness of ongoing reality.

Main Methods:

• Utilized H(2)(15)O Positron Emission Tomography (PET) scanning in healthy subjects.
• Employed continuous recognition tasks with varied stimuli (designs, words, nonwords) across multiple runs.
• Analyzed brain activation patterns during tasks requiring selective memory retrieval and suppression of prior familiarity.

Main Results:

• Initial runs showed medial temporal and right orbitofrontal activation, associated with familiarity judgments.
• Later runs, requiring selection of currently relevant memories, revealed left orbitofrontal activation.
• Significant activation was also observed in the ventral striatum, caudate nucleus, substantia nigra, and medial thalamus during later runs.

Conclusions:

• The OFC modulates memory representation via subcortical pathways, including the basal ganglia and thalamus.
• These findings suggest a role for the dopaminergic reward system in the neural monitoring of ongoing reality during cognitive tasks.