Double dissociation of working memory load effects induced by bilateral parietal modulation

Area of Science:

• Neuroscience
• Cognitive Psychology
• Brain Stimulation

Background:

• Bilateral posterior parietal cortex (PPC) is crucial for verbal working memory (WM), with increased activation and decreased performance at higher cognitive loads.
• Task practice and familiarity can enhance WM performance and alter PPC activity patterns.

Purpose of the Study:

• To investigate the effects of different transcranial direct current stimulation (tDCS) modulations on PPC activity and verbal WM performance after increased task familiarity.
• To determine if specific tDCS interventions can modulate PPC engagement differently for varying working memory loads.

Main Methods:

• Participants completed a verbal n-back task (1-back vs. 2-back) after initial practice.
• Bilateral tDCS was applied over the PPC using three conditions: left anodal-right cathodal, left cathodal-right anodal, and sham.
• Behavioral performance (reaction times) was assessed before and after tDCS application.

Main Results:

• A significant interaction between tDCS condition and task load was observed.
• In the 1-back task, left anodal-right cathodal tDCS impaired reaction time improvements seen in other conditions.
• In the 2-back task, left cathodal-right anodal tDCS similarly impaired performance improvements.

Conclusions:

• The findings demonstrate a double dissociation, indicating differential engagement of PPC hemispheres or altered interhemispheric balance based on tDCS.
• These effects are not due to task difficulty but likely reflect distinct processing strategies employed for different WM loads.
• Task-specific tDCS over the PPC can modify cognitive performance by influencing strategy selection after task familiarization.