Exposure to Sleep, Rest, or Exercise Impacts Skill Memory Consolidation but so Too Can a Challenging Practice Schedule

A motor sequence task is a common procedural skill used to reveal offline performance gains. This task requires the performer execute a series of key presses that are spatially compatible with visual signals presented on a display as quickly and accurately as possible (A). A number of motor sequences (trials for three unique sequences, represented in black, gray, or white, are used for the purpose of illustration in this example) are practiced in either a repetitive (RP) or interleaved (IP) format during a period of training. For RP, all trials of practice for one of the sequences are completed during a period of training before any practice with an alternative motor sequence is introduced. Alternatively, in IP, during any period of practice, an equal number of trials for all of the to-be-learned sequences are experienced. However, the presentation of trials of practice for these to-be-learned sequences rarely, if ever, involve the execution of the same sequence on two consecutive trials within a single bout of training. The impact on performance following each of these training contexts is most commonly assessed during a delayed test usually administered 24–72 h later (not shown in diagram; Lin et al., 2011; Wright et al., 2016; B). Offline gain, defined as the difference between performance at the time of test and at the end of training in either a IP or RP format, is greater following IP compared with RP (Wright et al., 2016; Lin et al., 2011; C), and the difference in offline gain achieved following RP and IP is related to the difference in cortical excitability observed at M1 before a test administered 72 h after practice was completed between individuals assigned to IP and RP (Lin et al., 2011; D). tDCS involves the passage of direct current between two electrodes [anode (+), cathode (–)]. Anodal stimulation (e.g., 1 mA for 20 min) is a condition in which the anode is placed over the neural region being targeted resulting in an upregulation of activity at the stimulated site (e.g., M1) reflected in an increased MEP from the application of single-pulse TMS compared with sham stimulation (E). Applying anodal tDCS at right M1 while the learner performed a motor sequence task with the left hand during RP results in offline gains rather than the anticipated loss in performance commonly observed following RP when performed in the absence of stimulation (Kim and Wright, 2020; F).