Ok References to the 2015 paper I’m following are in this section of the “Changes of Mind” paper

Ok References to the 2015 paper I’m following are in this section of the “Changes of Mind” paper

Changing movements requires updates of motor commands in primary motor cortex, which in turn relies on dynamic re-programming of motor plans in a network of areas including preSMA, premotor cortex, inferior frontal gyrus and basal ganglia (Wise & Mauritz, 1985; Leuthold & Jentzsch, 2002; Nachev et al., 2005; Buch et al., 2010; Neubert, Mars, Buch, Olivier, & Rushworth, 2010; Pastor-Bernier, Tremblay, & Cisek, 2012; Kaufman et al., 2015; Roberts & Husain, 2015; Saberi-Moghadam, Ferrari-Toniolo, Ferraina, Caminiti, & Battaglia-Mayer, 2016). The mechanisms through which these areas drive changes in motor output involve both 1) inhibitory activity that cancels an initial motor plan and 2) excitatory activity that initiates the new motor plan (Mars, Piekema, Coles, Hulstijn, & Toni, 2007; Buch et al., 2010). Interestingly, it has been shown that the very same neural circuits in premotor cortex that programmed an initial response during motor planning are also involved in changing motor plans later on – when target locations change before movement onset (Wise & Mauritz, 1985), or even during ongoing movement execution when online changes are necessary (Pastor-Bernier et al., 2012; Kaufman et al., 2015). This indicates a remarkable continuity of the processes that shape movements as they evolve.

Reprogramming of movements incurs a cost, resulting in response slowing and larger P3 amplitudes in the EEG when a switch from one motor plan to another one is necessary (Fleming et al., 2009; Orban de Xivry & Lefèvre, 2016). However, the motor system has several mechanisms in place that make motor switches as efficient as possible. For example, under target uncertainty, labile motor plans are generated, which can be reprogrammed more flexibly to accommodate new motor commands (Gallivan, Bowman, Chapman, Wolpert, & Flanagan, 2016). Similarly, when motor intentions are generated endogenously, they are kept more flexible than when they are instructed, further facilitating switching (Fleming et al., 2009). Additionally, the motor system operates in a highly parallel manner where alternative movement representations can be activated simultaneously (Jentzsch, Leuthold, & Ridderinkhof, 2004; Cisek, 2007; Stewart et al., 2014; Gallivan et al., 2015). Such parallel motor representations have been observed in dorsal premotor cortex (Cisek & Kalaska, 2002, 2005; Pastor-Bernier & Cisek, 2011), posterior parietal cortex (Baldauf, Cui, & Andersen, 2008; Cui & Andersen, 2011) and anterior intraparietal area (Baumann, Fluet, & Scherberger, 2009; Gallivan & Wood, 2009). Once a movement has been initiated, alternative movement representations remain activated, even when the action alternative is not available anymore in the external environment (Filevich & Haggard, 2013). This suggests that the motor system does not only represent a single movement that is currently selected for execution, but instead, maintains representations of counterfactual motor actions that are available in a current context. This in turn can facilitate switches between different movements after action onset (Fleming et al., 2009).

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