Pallidal gamma-band oscillatory activity reflects modulation of motor gain according to behavioral requirements in dystonia patients

Introduction:

Complementing previous data on the role of the globus pallidus internus (GPi) in error-detection, the present study focuses on the interplay between changes in oscillatory activity and the behavioral requirements of suppression and selection of responses in a rection-time conflict task, which elicits laterality mistakes in the motor responses.

Method:

We recorded local field potentials (LFPs) bipolarly from adjacent contact pairs located in the GPi in nine patients undergoing deep brain stimulation for therapy resistant idiopathic dystonia during performance of a flanker task. Changes in response-locked spectral power were assessed by computing the wavelet energy of the LFP signal in [–1000, 1000]ms and then normalizing with the prestimulus baseline level, separately for incongruent correct (IC) and error (IF) trials. Permutation tests were performed with the difference in sample means as test statistic.

Results:

We found a significant (pthr=0.0026) interaction between factors Laterality (contralateral, ipsilateral) and Response-type (IF, IC) in the gamma band: (i) from –300 to –100 ms, prior to response and (ii) between –50 and 50 ms around response-onset. Post-hoc analyses revealed a decrease in gamma band activity prior to response onset in IC trials, larger in the contralateral GPi, that was absent in IF epochs. Furthermore, in the contralateral GPi a significant increase in gamma activity at button press was larger in IC compared to IF trials (pthr=0.005).

Conclusions:

Here, prominent pallidal gamma-band oscillatory response-locked changes converged with the time scales of inhibition and selection of conflicting responses in the flanker task. Similar to the reported role of pallidal gamma bursts in enhancing motor gain (Brücke et al., in press), we propose reduced gamma-band oscillatory GPi activity as a candidate to mediate active suppression of motor responses with corresponding adjustment of movement parameters by reducing motor gain.

Literatur: Brücke C, Huebl J, Schönecker T, Neumann JW, Yarrow K, Kupsch A, Blahak C, Lütjens G, Brown P, Krauss JK, Schneider GH, Kühn AA. Scaling of movement is related to pallidal gamma oscillations in patients with dystonia. Journal of Neuroscience. In press.