Biology subjects

Gamez, J.

Publications and source records attributed to Gamez, J..

5 recordsLinked to original sources

bioRxiv2026

The Compositional Encoding of Hand-Eye Coordinated Movements for Single Neurons in the Posterior Parietal Cortex

Human posterior parietal cortex (PPC) is thought to play an important role in hand-eye coordination, yet the underlying encoding mechanisms remain uncertain. We recorded 412 single neurons across 11 sessions from motor cortex (MC; n=251) and PPC (n=161) in a single human participant performing a hand-eye (H-E) coordinated center-out task. While MC neurons showed little to no modulation by eye movements, 79% of PPC neurons had neural representations that were additively separable into independent hand- and eye-movement tuning curves. Due to this separability, neural representations could be separated and additively recomposed while maintaining structure similarity. Consequently, compositional decoders trained solely on single-effector movements could match the performance of decoders trained on coordinated H-E movements (hand: 66% vs 69%; eye: 34% vs 36%). These results show that, during simple center-out tasks, MC hand movement codes are unaffected by eye movements and that compositionality can be used to modularly decode H-E coordinated movements in PPC.

neuroscience↗

bioRxiv2025

Hierarchical and Context-Dependent Encoding of Actions in Human Posterior Parietal and Motor Cortex

Action understanding requires internal models that link vision to motor goals. In monkeys, mirror neurons demonstrate motor resonance during observation, but single-unit evidence in humans is limited, leaving open whether such representations rely solely on motor resonance. We recorded neural activity from motor cortex (MC) and superior parietal lobule (SPL) in two tetraplegic participants implanted with Utah arrays while they intended or observed hand actions. MC strongly encoded intention but showed only weak, feature-specific overlap during observation, evident primarily at the population level. SPL, in contrast, supported shared models across intended movement and observation formats at both single-unit and population levels. In variants with incongruent instructed and observed actions, SPL encoded observed actions only when behaviorally relevant, whereas MC remained intention-dominant. Our results identify a context-dependent gating mechanism in SPL and suggest a hierarchical organization in which MC maintains intention-specific codes while SPL flexibly links observed input with internal goals to support action understanding.

neuroscience↗

bioRxiv2025

Manifold properties in the macaque medial premotor cortex during switching from attending to tapping to a metronome

Animals synchronize their movements with external rhythms to coordinate perception and action, but the neural population mechanisms that allow them to attend and then initiate and sustain these rhythms remain unclear. Using high-density recordings from the medial premotor cortex (MPC) of two macaque monkeys, we investigated neural dynamics during an attend-then-synchronize tapping task with visual metronomes. We found low-dimensional neural manifolds that capture neural population trajectories. During the attention phase, trajectories exhibited increasing amplitude and oscillatory modulation along successive stimuli, consistent with a resonant-like mechanism. Transition to tapping was marked by a reliable shift into a distinct manifold subspace, enabling accurate decoding of the switch in behavior. In addition, large amplitude and oscillatory indices were higher in successful tapping synchronization trials than in incorrect ones. These findings demonstrate that macaque MPC activity evolves along smooth, low-dimensional trajectories whose geometry governs different perceptual and motor aspects of tapping synchronization.

animal behavior and cognition↗

bioRxiv2022

Premotor population dynamics as neural substrate for auditory and visual rhythmic entrainment

The neural substrate for beat extraction and response entrainment to auditory and visual rhythms is still unknown. Here we analyzed the population activity of hundreds of medial premotor neurons of monkeys performing an isochronous tapping guided by brief flashing stimuli or auditory tones. The animals showed a strong bias towards visual than auditory metronomes, with rhythmic tapping that was more precise and accurate on the former. The population dynamics shared the following properties across modalities: the circular dynamics of the neural trajectories formed a regenerating loop for every produced interval; the trajectories converged in similar state space at tapping times resetting the clock; the tempo of the synchronized tapping was encoded in the trajectories by a combination of amplitude modulation and temporal scaling. In addition, the modality induced a displacement in the neural trajectories in auditory and visual subspaces without greatly altering time keeping mechanism. These results suggest that the interaction between the MPC amodal internal representation of pulse and a modality specific external input generates a neural rhythmic clock whose dynamics governs rhythmic tapping execution across senses.

neuroscience↗

bioRxiv2018

The amplitude in periodic neural state trajectories underlies the tempo of rhythmic tapping

Our motor commands can be exquisitely timed according to the demands of the environment, and the ability to generate rhythms of different tempos is a hallmark of musical cognition. Yet, the neuronal basis behind rhythmic tapping remains elusive. Here we found that the activity of hundreds of primate MPC neurons show a strong periodic pattern that becomes evident when their activity is projected into a lower dimensional state space. We show that different tempos are encoded by circular trajectories that travelled at a constant speed but with different radii, and that this neuronal code is highly resilient to the number of participating neurons. Crucially, the changes in the amplitude of the oscillatory dynamics in neuronal state space are a signature of beat-based timing, regardless of whether it is guided by an external metronome or is internally controlled and is not the result of repetitive motor commands. Furthermore, the increase in amplitude and variability of the neural trajectories accounted for the scalar property of interval timing. In addition, we found that the interval-dependent increments in the radius of periodic neural trajectories are the result of larger number of neurons engaged in the production of longer intervals. Our results support the notion that beat-based timing during rhythmic behaviors is encoded in the radial curvature of periodic MPC neural population trajectories.

neuroscience↗