The Hippocampus Preorders Movements for Skilled Action Sequences

Given its associative binding capacity, the hippocampus is essential for the formation of conscious long-term memories. Yewbrey and Kornysheva propose a new role for the hippocampus in non-conscious procedural memory, and they suggest that the hippocampus pre-orders movements for skilled action sequences. However, this interpretation raises concerns, particularly in light of the operationalization of the procedural memory task that involved the hippocampus.
First, it cannot be neglected that learning new motor skills (even complex, novel musical sequences) is possible in amnesic patients with bilateral hippocampal damage or resection.
In healthy individuals, the learning of new motor sequences is initially supported by the declarative memory system (e.g., following instructions, processing feedback). This role diminishes as learning progresses with repetition and the task becomes automated.
The same applies to the paradigm used in the study. It addresses procedural memory but places an additional demand to learn an association of an abstract fractal image with a specific motor sequence and to integrate feedback on the performance. Associative learning and retrieval as well as learning from feedback require conscious memory processing.
Moreover, the results section lacks critical information (positive predictive value, receiver operating characteristics curves) necessary to demonstrate any predictive power of hippocampal activity regarding the sequencing of upcoming movements, which is the study’s major claim.
In conclusion, learning new motor skills is possible without the hippocampus. The hippocampus-dependent conscious memory system may, however, play a temporary supportive role regarding the procedural memory but is no part of it. Yewbrey and Kornysheva provide no compelling evidence for a new role of the hippocampus in procedural memory.