Task-based changes in proton MR spectroscopy signal during configural working memory in human medial temporal lobe

Area of Science:

• Neuroimaging
• Cognitive Neuroscience
• Biochemistry

Background:

• Understanding brain function during working memory is crucial for cognitive neuroscience.
• Medial temporal lobe structures are vital for memory processes.
• Cholinergic systems play a role in cognitive functions, including memory.

Purpose of the Study:

• To detect local cholinergic changes in the human medial temporal lobe during configural working memory performance.
• To investigate the role of choline-containing metabolites in configural visual working memory.

Main Methods:

• Proton magnetic resonance spectroscopy (¹H-MRS) at 3T was used to measure metabolite concentrations in the medial temporal lobe.
• Measurements were taken during a configural visual working memory task (cWMT) with blocks of rest, memorization, active maintenance, and recognition.
• Choline-containing metabolites (Cho) were referenced to creatine + phosphocreatine (Cre) to account for task-based BOLD T₂* effects.

Main Results:

• A significant increase in the Cho/Cre ratio was observed during active memory maintenance compared to rest (P = 0.0042).
• Behavioral accuracy during the task correlated with subsequent memory retention (r = 0.48, P = 0.027).
• Quality assurance revealed task-based changes in Cre signal individually and when used as a reference (NAA/Cre, P = 0.00079).

Conclusions:

• Increases in the medial temporal lobe ¹H-MRS Cho/Cre ratio occur during configural working memory maintenance.
• These findings suggest potential involvement of cholinergic activity, but cannot be definitively assumed due to similar changes in non-cholinergic metabolites.
• Caution is advised regarding the use of creatine as an internal standard for task-based ¹H-MRS measurements.