Identifying motor learning deficits in neurological conditions: a critical analysis of a perennial problem

Identifying deficits in motor learning has the potential to serve as an indicator of brain function in several neurological conditions. However, evidence for motor learning deficits can be confounded by factors unrelated to learning. In this review, we critically examine the evidence for these deficits in neurological conditions, focusing both on conceptual and methodological issues. Across a wide range of neurological conditions, we found that a majority of evidence for motor learning deficits is difficult to clearly interpret as learning-related and is potentially confounded by the presence of baseline differences. In addition, the use of low sample sizes, short time durations of practice, and the narrow focus on sequence learning paradigms also raise questions about the validity and generality of this evidence. Given that deficits in motor learning have implications for the early detection of neurological status and the design of rehabilitation strategies, we highlight the need for greater rigor when addressing this important, but perennially challenging, question.