The effect of memory load on cortical activity in the spatial working memory circuit

Area of Science:

• Neuroscience
• Cognitive Neuroscience
• Cognitive Psychology

Background:

• Spatial working memory (SWM) is crucial for cognitive tasks.
• Neuroimaging and electrophysiology suggest frontal and parietal regions support SWM.
• The precise influence of memory load on SWM neural circuits requires further investigation.

Purpose of the Study:

• To investigate how memory load affects the neural activity within the spatial working memory circuit.
• To examine the relationship between memory load, behavioral performance, and brain activity during a delayed-response task.

Main Methods:

• Parametrically varied memory set size (1-4 spatial locations) in a delayed-response task.
• Utilized time-resolved functional Magnetic Resonance Imaging (fMRI) to monitor brain activity.
• Analyzed behavioral data including accuracy and reaction time.

Main Results:

• Behavioral performance (accuracy, reaction time) deteriorated with increasing memory load.
• Memory load modulated cortical activity across cue, delay, and response phases.
• Delay-related activity increased with load in some regions but decreased in the middle frontal gyrus and frontal eye fields, and plateaued in parietal areas at higher loads.
• Activity in the left posterior parietal cortex was lower during error trials compared to correct trials.

Conclusions:

• Neural activity in the spatial working memory circuit is sensitive to memory load.
• Attenuation of delay period activity represents a neural correlate of performance limitations under high memory load.
• Findings elucidate the neural mechanisms underlying capacity limits in spatial working memory.