Electrophysiologial mapping of alpha and beta activity across the ventrolateral (motor) thalamus: a local field potential study

Objective: To map the distribution of alpha (8–12 Hz) and beta (13–30 Hz) activity across the ventrolateral (motor) thalamus

Introduction: Neural oscillations are thought to underlie coupling of spatially remote neurons and gating of information within the human sensorimotor system. Different frequency ranges have been associated with different movements: A tonic contraction elicits beta-band-activity¹, while a resting alpha rhythm at around 10 Hz can be observed over the motor cortex^2,3. Different kinds of movement also elicit activity in different areas in the motor network⁴.

Methods: We recorded local field potentials (LFP) from the ventrolateral thalamus in 4 dystonic patients (5 hemispheres, 12 trajectories) while they were undergoing deep brain stimulation surgery. Two one minute recordings were done at 1-mm-steps at 9 recording depths, spanning three of the motor nuclei of the thalamus (Voa, Vop and Vim), while patients were either resting or lifting their contralateral forearm leading to an isometric contraction. Simultaneously, EMG was recorded from 2 to 3 contralateral forearm muscles.

Results: There was a trend for alpha activity to decrease from anterodorsal to posteroventral direction, while beta activity increased (i.e. the Vim showed less alpha and more beta activity than more anterodorsal areas) as did the activity ratio between both frequency bands. Beta power increased during voluntary movement, while alpha power decreased.

Discussion: According to anatomical studies, Vim receives predominantly cerebellar input, whereas the Voa is part of the basalganglia-cortical loop, receiving mainly pallidal afferents. The results might imply that the cerebello-thalamo-cortical network including the Vim communicates predominantly in the beta-band, whereas the basalganglia-thalamo-cortical network might rely more on the alpha-band. Larger patient numbers are necessary to confirm the finding.

Literatur: 1. Salenius, S. and Hari, R. Synchronous cortical oscillatory activity during motor action. Current Opinion in Neurobiology 13, 678-684 (2003). 2. Salenius, S. et al. Cortical Control of Human Motoneuron Firing During Isometric Contraction. Journal of Neurophysiology 77, 3401-3405 (1997). 3. Pfurtscheller, G. et al. Foot and hand area mu rhythms. Int J Psychophysiol 26, 121-135 (1997). 4. Herz, D.M. et al. Task-specific modulation of effective connectivity during two simple unimanual motor tasks: a 122-channel EEG study. NeuroImage doi:10.1016/j.neuroimage.2011.11.042