What types of priming did your review consider?

We considered types of priming that do not involve electrical stimulation such as non-invasive brain stimulation. 

The non-stimulation-based priming methods include motor imagery, action observation, movement-based priming, aerobic exercise and mirror therapy. 

The priming activity needed to occur within 30 minutes of task specific practice.

How are these modalities of priming hypothesised to work?

It is hypothesised that priming increases cortical excitability, which can boost neuroplasticity during physical practice, leading to improved functional outcomes. 

Aerobic exercise also increases the level of brain-derived neurotrophic factor, which can improve neuroplasticity.

What outcome measures did the review consider?

We primarily considered activity outcomes such as measures of walking or the ability to perform upper limb tasks. 

The most common measure of lower limb activity was walking speed (included in 10 trials).

The most common measures of upper limb activity were the Box and Block Test (included in three trials) and the Action
Research Arm Test (included in three trials).

The secondary outcomes we considered were motor impairment outcomes such as measures of strength and
coordination. 

The most common measure of motor impairment was the Fugl-Meyer Assessment tool (included in 12 trials).

How did priming affect activity-related outcomes? 

The only type of priming that appeared to make a difference to activity-related outcomes was motor imagery, often called mental practice. 

The effect of motor imagery priming with task practice, compared to task practice alone, had a standardised mean difference of 0.48—indicating a moderate effect size. 

The 95 per cent confidence interval was 0.13 to 0.82, which indicates that we can be 95 per cent confident that the true effect lies between a small and a large effect.

What about impairment outcomes?

The only type of priming that appeared to make a difference to impairment outcomes was also motor imagery. 

Comparing the effect of motor imagery priming with task practice against task practice alone resulted in a standardised mean difference of 0.51—indicating a moderate effect size.

The 95 per cent confidence interval was 0.12 to 0.89, which means that we can be 95 per cent confident that the true effect lies
between a small and a large effect.

Where does future research in this area need to focus?

Most of the included trials involved stroke survivors who were more than six months post-stroke. 

All the motor imagery priming trials were interventions that targeted lower limb skills in participants with moderate
to severe levels of disability. 

Future research could look at establishing the effect of priming in individuals who have recently experienced a stroke.

Additionally, examining the effect of motor imagery priming on upper limb outcomes and in people with mild impairments after stroke may be beneficial.

>>Vaughan Nicholson APAM is a senior lecturer at the Australian Catholic University. His research investigates the effects of motor imagery training and exercise interventions on function in older adults.

>>Simone Dorsch APAM is an associate professor at the Australian Catholic University and a director of the StrokeEd collaboration. Her research investigates the associations between impairments and activity limitations after stroke and strategies to increase the amount of practice after stroke.