Independent basal ganglia neural populations encode speech production and ambient-noise levels

The basal ganglia's (BG) contribution to motor control is thought to involve invigorating movement based on environmental constraints, yet this has primarily been studied in the limb system. We hypothesized that the BG similarly regulate the respiratory and articulatory systems during speech. We recorded local field potentials and single-unit activity from the subthalamic nucleus (STN) and globus pallidus (GP) in humans during a speech task where the Lombard Effect was used to modulate environmental constraints. GP and STN exhibited distinct temporal profiles during speech production. Neither region robustly encoded produced speech intensity. Instead, neural populations tracked ambient background noise levels, even during baseline, with high decoding accuracy. The ambient-noise-modulated sites were an independent population from speech-modulated sites. We theorize that the code is leveraged in downstream BG-cortical loop nodes to invigorate speech oro-motor gestures and co-speech manual limb gestures, both of which respond to ambient noise levels to maintain high-fidelity communication.