Does sonification of action simulation training impact corticospinal excitability and audiomotor plasticity?

Abstract

Sonification is a sensory augmentation strategy whereby a sound is associated with, and modulated by, movement. Evidence suggests that sonification could be a viable strategy to maximize learning and rehabilitation. Recent studies investigated sonification of action observation, reporting beneficial effects, especially in Parkinson's disease. However, research on simulation training-a training regime based on action observation and motor imagery, in which actions are internally simulated, without physical execution-suggest that action observation alone is suboptimal, compared to the combined use of action observation and motor imagery. In this study, we explored the effects of sonified action observation and motor imagery on corticospinal excitability, as well as to evaluate the extent of practice-dependent plasticity induced by this training. Nineteen participants were recruited to complete a practice session based on combined and congruent action observation and motor imagery (AOMI) and physical imitation of the same action. Prior to the beginning, participants were randomly assigned to one of two groups, one group (nine participants) completed the practice block with sonified AOMI, while the other group (ten participants) completed the practice without extrinsic auditory information and served as control group. To investigate practice-induced plasticity, participants completed two auditory paired associative stimulation (aPAS) protocols, one completed after the practice block, and another one completed alone, without additional interventions, at least 7 days before the practice. After the practice block, both groups significantly increased their corticospinal excitability, but sonification did not exert additional benefits, compared to non-sonified conditions. In addition, aPAS significantly increased corticospinal excitability when completed alone, but when it was primed by a practice block, no modulatory effects on corticospinal excitability were found. It is possible that sonification of combined action observation and motor imagery may not be a useful strategy to improve corticospinal, but further studies are needed to explore its relationship with performance improvements. We also confirm the neuromodulatory effect of aPAS, but its interaction with audiomotor practice remain unclear.

Keywords: Metaplasticity; Paired associative stimulation; Plasticity; Sensory augmentation; Sonification; Transcranial magnetic stimulation.

Fig. 1

Schematic representation of the experimental design. a Participants visited the laboratory on two non-consecutive sessions. Session 1 was designed to investigate the effect of aPAS on corticospinal excitability. On the second session, participants engaged in a single practice block, followed by another aPAS protocol, to investigate the interaction between practice and PAS. Measures of corticospinal excitability on the first visit were obtained before and after the completion of the aPAS protocol. For the second visit, corticospinal excitability was measured at three timepoints: before the training (PRE), after the training (POST1) and after the aPAS (POST2). b Schematic representation of the practice session. Participants first observed a blue cross, representing a ‘ready’ cue, then engaged in AOMI; the SON group heard the sonification sound concurrently. After this, another blue cross appeared, after which participants either imagined (MI; cloud icon) or executed (PE; battery icon) the same action. When a white cross appeared, participants did nothing for a 5 s period. c Details of the aPAS protocol. For each audiomotor training, the TMS pulse was delivered 100 ms after the onset of the sound. The sound lasted for 3 s (yellow box). The audiomotor training was delivered every 4–6 s (blue box)

Fig. 2

Corticospinal excitability measures before and after aPAS. On the first visit, both SON and CON completed the same protocol, so the data shown represent the group average of both groups (n = 19) a MEPs collected at 130% rMT, b MEPmax of the IO curve sigmoid fitting; c slope of the IO curve sigmoid fitting; d sigmoid fitting of the nine IO curve stimulation intensities for pre- and post-aPAS. White circles represent individual data, while black rectangles represent group means. *: p < 0.05; **: p < 0.01

Fig. 3

Second visit. MEPs were collected at three time points: Before the practice session (PRE), after the practice session (POST 1), and after the aPAS (POST 2). a Corticospinal excitability on the second visit for SON and CON groups. b Sigmoid fitting of the 9 IO curve stimulation intensities for PRE and POST 1 and POST2 for CON group (upper panel) and SON group (lower panel). c Between-days effects of aPAS on corticospinal excitability. In session 1, aPAS was the only intervention, while on session 2, aPAS was administered after the practice block. Circles and triangles represent individual values for SON and CON group, respectively. Black rectangles represent group means. *p < 0.05