Visual working memory for action: Evidence for using motor representations in encoding visuo-spatial stimulus sequences

Introduction: The neurobiological substrates of action-oriented visual working memory are not well understood.

Aim: To elucidate the neural correlates of translating visuo-spatial stimulus sequences into delayed (memory-guided) sequential actions. Specifically, we aimed to clarify whether motor representations are already involved in encoding visual sequences to be reproduced subsequently.

Methods: Using functional magnetic resonance imaging, we measured brain activity in 36 healthy adults while they encoded sequences of 4 – 7 dots appearing on fingers of a left or right schematic hand. After delays of either 500 or 7000 ms, these sequences were to be reproduced with the corresponding fingers.

Results: Recall became less accurate with longer sequences and was initiated faster after long delays. Across both hands, encoding and recall activated bilateral prefrontal, premotor, superior and inferior parietal regions as well as the basal ganglia, whereas hand-specific activity was found (albeit to a lesser degree during encoding) in contralateral premotor, sensorimotor and superior parietal cortex. Activation differences after long versus short delays were restricted to motor-related regions, indicating that rehearsal during long delays might have facilitated the conversion of the memorised sequence into concrete motor programmes at recall. Furthermore, basal ganglia activity during encoding selectively predicted correct recall.

Conclusion: Taken together, the results suggest that to-be-reproduced visuo-spatial sequences are encoded as prospective action representations (“motor intentions”), possibly in addition to retrospective sensory codes. Overall, our study supports and extends multi-component models of working memory, highlighting the notion that sensory input can be coded in multiple ways depending on what the memorandum is to be used for.