Correlation between cortical plasticity, motor learning and BDNF genotype in healthy subjects

Abstract

There is good evidence that synaptic plasticity in human motor cortex is involved in behavioural motor learning; in addition, it is now possible to probe mechanisms of synaptic plasticity using a variety of transcranial brain-stimulation protocols. Interactions between these protocols suggest that they both utilise common mechanisms. The aim of the present experiments was to test how well responsiveness to brain-stimulation protocols and behavioural motor learning correlate with each other in a sample of 21 healthy volunteers. We also examined whether any of these measures were influenced by the presence of a Val66Met polymorphism in the BDNF gene since this is another factor that has been suggested to be able to predict response to tests of synaptic plasticity. In 3 different experimental sessions, volunteers underwent 5-Hz rTMS, intermittent theta-burst stimulation (iTBS) and a motor learning task. Blood samples were collected from each subject for BDNF genotyping. As expected, both 5-Hz rTMS and iTBS significantly facilitated MEPs. Similarly, as expected, kinematic variables of finger movement significantly improved during the motor learning task. Although there was a significant correlation between the effect of iTBS and 5-Hz rTMS, there was no relationship in each subject between the amount of TMS-induced plasticity and the increase in kinematic variables during motor learning. Val66Val and Val66Met carriers did not differ in their response to any of the protocols. The present results emphasise that although some TMS measures of cortical plasticity may correlate with each other, they may not always relate directly to measures of behavioural learning. Similarly, presence of the Val66Met BDNF polymorphism also does not reliably predict responsiveness in small groups of individuals. Individual success in behavioural learning is unlikely to be closely related to any single measure of synaptic plasticity.

Neuroplasticity in Depressed Individuals Compared with Healthy Controls

“…There are several possible explanations for the lack of relationship. There may be only partial overlap between the cortical processes moderated by brain stimulation and those involved in motor learning protocols (Li Voti et al, 2011). For example, performance of the rotor pursuit task used in this study also involves visual and subcortical striatal systems (Rajji et al, 2011).…”

A comparison of neuroplastic responses to non-invasive brain stimulation protocols and motor learning in healthy adults

“…Indeed, Di Lazzaro and colleagues have shown that while PAS and iTBS act primarily on cortical circuits generating late I-waves [3,4], cTBS acts primarily on cortical circuits generating I1 [5,6]. Li Voti and colleagues [17] examined the relationship between neuroplastic responses to different NBS protocols within a group of individuals and showed a positive relationship between the neuroplastic responses to 5 Hz repetitive TMS (rTMS) and iTBS. This suggests that 5Hz rTMS and iTBS engage common mechanisms important for short-term plasticity [17].…”

“…Li Voti and colleagues [17] examined the relationship between neuroplastic responses to different NBS protocols within a group of individuals and showed a positive relationship between the neuroplastic responses to 5 Hz repetitive TMS (rTMS) and iTBS. This suggests that 5Hz rTMS and iTBS engage common mechanisms important for short-term plasticity [17]. Relationships between multiple NBS protocols thought to be mediated by LTP-like mechanisms, however, were not examined.…”

“…There was no significant difference in RMT at baseline and immediately following TBS (cTBS: t (17) (Fig. 1C).…”

“…Figure 1 shows mean peak acceleration of thumb abduction movements with MT and mean MEP amplitude following MT, cTBS, iTBS, and PAS. The peak acceleration of thumb abductions increased with MT, both across the two major training blocks (F (1,17) Fig. 1B).…”