Delta band oscillations predict hand selection for reaching


Current models emphasize that action selection is achieved by competitive interactions between co-existing motor plans afforded by target stimuli (Cisek and Kalaska 2010). We tested the hypothesis that action selection is influenced by the intrinsic excitability of the sensorimotor regions that encode those motor plans. We used a hand selection task in which subjects reached toward visual targets with the hand of their choice. We identified the target locations for which left and right hands were chosen equally often (see Oliveira et al., 2010), and then had subjects perform multiple trials toward these targets while recording electroencephalography (EEG). Data were binned according to the hand being selected. We measured delta band oscillations (2-4Hz) at electrodes overlaying the left and right primary motor cortices (M1), since excitability of neuronal ensembles fluctuates according to the phase of delta (Lakatos et al., 2008). Delta band inter-trial coherence at target onset was significantly greater over M1 contralateral to the selected hand than over ipsilateral M1 (p<0.001). Specifically, contralateral M1 was systematically in the delta through (mean=229º), which is considered the excitable phase of delta (Whittingstall and Logothetis 2009). Furthermore, delta phase of contralateral M1 predicted reach reaction times (p<0.01). These data demonstrate that the M1 in the most excitable phase of delta at target onset determines the hand to be selected, possibly by responding with greater gain to incoming target stimuli. This suggests that action selection is influenced by the instantaneous excitability of the sensorimotor regions in which motor plans are encoded.

Acknowledgments: NSERC; FRQ-S