Abstract
Recently we found that modulation depth of beta power during movement increases with practice over sensory-motor areas in normal subjects but not in patients with Parkinson's disease (PD). As such changes might reflect use-dependent modifications, we concluded that reduction of beta enhancement in PD represents saturation of cortical plasticity. A few questions remained open: What is the relation between these EEG changes and retention of motor skills? Would a second task exposure restore beta modulation enhancement in PD? Do practice-induced increases of beta modulation occur within each block? We thus recorded EEG in patients with PD and age-matched controls in two consecutive days during a 40-min reaching task divided in fifteen blocks of 56 movements each. The results confirmed that, with practice, beta modulation depth over the contralateral sensory-motor area significantly increased across blocks in controls but not in PD, while performance improved in both groups without significant correlations between behavioral and EEG data. The same changes were seen the following day in both groups. Also, beta modulation increased within each block with similar values in both groups and such increases were partially transferred to the successive block in controls, but not in PD. Retention of performance improvement was present in the controls but not in the patients and correlated with the increase in day 1 modulation depth. Therefore, the lack of practice-related increase beta modulation in PD is likely due to deficient potentiation mechanisms that permit between-block saving of beta power enhancement and trigger mechanisms of memory formation.
Highlights
Movement is accompanied by EEG changes of beta oscillations over the sensory-motor areas, with a power decrease before movement onset, a negative peak during execution and a post-movement increase (Pfurtscheller and Lopes da Silva, 1999; Toma et al, 2002)
Other support comes from our previous finding that movement-related beta modulation does not significantly increase with practice in patients with Parkinson’s disease (PD) (Moisello et al, 2015b), a disease that is accompanied by a decrease of skill retention (Marinelli et al, 2009; Bedard and Sanes, 2011; Isaias et al, 2011; Moisello et al, 2015a) and by deficits in the induction of use-dependent and long term potentiation (LTP)-like plasticity (Morgante et al, 2006; Kishore et al, 2012; Koch, 2013)
The results of this paper confirm our previous findings that the depth of movement-related beta modulation increases across performance blocks in normal subjects but not in patients with PD, while performance improves in both groups (Moisello et al, 2015b)
Summary
Movement is accompanied by EEG changes of beta oscillations over the sensory-motor areas, with a power decrease before movement onset, a negative peak during execution (event-related desynchronization, ERD) and a post-movement increase (eventrelated synchronization, ERS) (Pfurtscheller and Lopes da Silva, 1999; Toma et al, 2002). Increases of beta power have been associated with high GABA levels in animal and human studies (Jensen et al, 2005; Roopun et al, 2006; Yamawaki et al, 2008; Hall et al, 2010, 2011; Muthukumaraswamy et al, 2013; Rossiter et al, 2014) and decreases in cortical excitability in humans (Hsu et al, 2011; Noh et al, 2012; McAllister et al, 2013) These two lines of evidence are not incompatible: the repetitive pattern of alternate activation and inactivation of the sensory and motor areas during the continuous, uninterrupted practice of a task likely triggers the induction of long term potentiation (LTP) that may reinforce existing sensory-motor memories (or internal models) or create new ones, resulting in skill enhancement. On a second exposure to the task the following day, enhancement of performance should occur in normal subjects but not in patients with PD, while beta modulation should show similar changes in both groups as in day 1
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