Schweitzer, J. | bioRxiv Science

bioRxiv2025

Independent Basal Ganglia Neural Populations Encode Speech Production and Ambient-Noise Levels

The function of the basal ganglia (BG), a set of nuclei deep in the brain, is still under debate despite their clinical relevance. Lines of evidence from non-human primate and human experiments suggest that one key causal contribution of the adult primate BG is invigoration of movement according to environmental and energetic constraints. Previous studies have come to this conclusion using primarily limb motor control tasks. We hypothesized BG are also important for invigorating the respiratory, vocal, and articulatory motor systems during speech production. To test this, we used a rare clinical opportunity to record local field potentials-broadband gamma activity (LFP-BGA) and single unit (SU) activity from human basal ganglia during deep brain stimulation implant surgeries. Participants repeated sentences aloud in the operating room. We modulated environmental and energetic constraints of speech production by inducing the Lombard Effect, wherein people reliably increase the intensity of their voice in the presence of background noise. Participants increased voice intensity, pitch, vowel space size, and respiratory depth in the presence of ambient noise. [~]40% of LFP and SU sites were modulated by speech production. Comparing globus pallidus (GP) LFP-BGA, herein reported for the first time during speech, to subthalamic nucleus (STN) LFP-BGA revealed GP activated after STN. STN was more coincident with the speech preparatory period and GP more coincident with speech onset, suggesting differential roles in speech production. We found only weak evidence that STN or GP activity encodes the level of produced speech intensity. Instead, we found that LFP-BGA and SU-FR robustly track the ambient background noise levels. Linear decoding from SU-firing rate revealed we could infer the background noise levels with >75% accuracy in any given time point in the trial, including baseline. Importantly, the ambient-noise-modulated sites were an independent population from speech-modulated sites. We conclude that human BG encode the energetic constraints of communication. 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.

neuroscience↗

bioRxiv2023

Evolution of rarity and phylogeny determine above- and belowground biomass in plant-plant interactions

Rare species are often considered inferior competitors due to occupancy of small ranges, specific habitats, and small local populations. However, the phylogenetic relatedness and rarity level of interacting species in plant-plant interactions are not often considered when predicting the competitive response of rare plants. We used a common garden of 25 species of Tasmanian Eucalyptus, varying in rarity to allow us to differentiate the competitive abilities of rare versus common species when grown in mixtures varying in phylogenetic relatedness and rarity. We demonstrate increased biomass production of rare plant species when interacting with genetically intermediate neighbors through synergistic non-additive effects not seen in common species. Additionally, we also find that all plants, regardless of rarity status, maintain 47% greater aboveground and 69% greater belowground biomass when interacting with common species compared to the rarest species. However, species-specific interactions with one particular common species, E. globulus, yielded a 97% increase in biomass compared to average biomass yields in other interactions, suggesting the importance of E. globulus integration into rare species restoration plantings. These results are important because they suggest that the evolutionary processes driving species rarity and the phylogenetic divergence of traits interact to drive ecological dynamics of plant-plant interactions in non-additive ways. Through the ecological and evolutionary consideration of performance traits, rarity, and species-specific effects, we can more accurately predict plant-plant interaction dynamics varying in rarity and relatedness across the landscape.

ecology↗