Substantia Nigra Integrity Correlates with Sequential Working Memory in Parkinson's Disease

Area of Science:

• Neuroscience
• Neurology
• Neuroimaging

Background:

• Sequential working memory is vital for daily activities.
• Parkinson's disease (PD) is linked to sequential working memory deficits and basal ganglia dysfunction.
• The substantia nigra (SN) plays a role in basal ganglia function.

Purpose of the Study:

• To investigate the relationship between substantia nigra (SN) integrity, basal ganglia function, and sequential working memory performance in Parkinson's disease (PD).
• To explore the neural mechanisms underlying sequencing deficits in PD using functional MRI (fMRI).

Main Methods:

• Neuromelanin-sensitive structural MRI was used to assess SN size in 29 PD patients and 29 healthy controls (HCs).
• fMRI was employed during a digit-ordering task (pure recall vs. reorder and recall) to examine brain activation and functional connectivity.
• Correlation analyses were performed to link SN integrity, basal ganglia activation, and task performance.

Main Results:

• PD patients exhibited smaller SNs, reduced accuracy in the digit-ordering task, and altered basal ganglia activation (caudate/pallidal hypoactivation, subthalamic hyperactivation) compared to HCs.
• Weakened functional connectivity between the SN and basal ganglia regions was observed in PD patients.
• Larger SN size in PD patients correlated with lower accuracy costs and greater caudate activation during sequencing, suggesting SN integrity influences task performance via caudate regulation.

Conclusions:

• Damage to the substantia nigra (SN) contributes to sequential working memory deficits in Parkinson's disease (PD), mediated by basal ganglia dysfunction.
• SN integrity appears to modulate task-dependent caudate activation, impacting sequencing performance in PD patients.
• While D2/3 receptor agonists influenced subthalamic activation in PD, this did not improve sequencing accuracy costs.