Biology subjects

Schurger, A.

Publications and source records attributed to Schurger, A..

8 recordsLinked to original sources

bioRxiv2026

Real-time intracortical decoding from human motor cortex reveals a task-independent commitment to act that aligns with conscious intent

Preparatory neural signals that precede movement onset are well established. However, whether they mark a commitment to act, align with conscious intention, or are subject to voluntary control remains under debate. We addressed these questions with a closed-loop experiment: a strategic timing game where a virtual opponent monitored intracortical sensorimotor activity and preempted participants' actions when their intention to move was detected. In three people with tetraplegia and preserved wrist extension, movement onset was reliably predicted from motor cortex 250-400 ms before action. Although participants attempted to act unpredictably, they were preempted on 94% of trials -and movement output generally followed despite the opponent's interruption. Participants reported intending to act on 88% of preemptions. The same decoder accurately predicted participants' actions in a non-competitive task, without retraining. These findings identify a late, task-independent motor-cortical state marking a voluntary commitment to act, which participants report as an intention when interrupted.

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bioRxiv2026

A neural circuit mechanism for abstract free choice

Making abstract free choices, such as arbitrary decisions between comparable options formed independently of specific motor plans, is central to everyday behavior. Yet, the neural mechanisms underlying free choice remain poorly understood. Using a delayed-response paradigm (N=80), we dissociated abstract goal selection (color choice) from later motor response mapping. We found that freely chosen goals elicit slower responses and lower goal-switching costs than instructed goals. We developed a hierarchical attractor network model in which symmetry-breaking attractor dynamics drive free goal selection, and conjunctive representations translate these abstract goals into motor output. Freely chosen goals converged on less extreme fixed points than instructed ones, accounting for their slower, more variable responses. Consistent with our model, human EEG activity (N=30) sequentially encoded goal, conjunctive, and response representations, with conjunctive representations specifically coupled to behavioral variability. Our findings offer plausible circuit-level mechanisms for how abstract free choices are made and translated into action. HighlightsO_LIFree-instructed differences persist when goal selection and response mapping are dissociated C_LIO_LIAbstract free choices elicit reduced goal-switching costs relative to instructed ones C_LIO_LISymmetry-breaking attractor dynamics explain behavioral signatures of free choice C_LIO_LIEEG signals sequentially encode abstract goal, conjunctive, and response representations C_LIO_LIConjunctive representations, but not goal or response, were coupled to behavior C_LI

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bioRxiv2025

A Caveat Regarding the Unfolding Argument: Implications of Plasticity for Computational Theories of Consciousness

The unfolding argument in the neuroscience of consciousness posits that causal structure cannot account for consciousness because any recurrent neural network (RNN) can be "unfolded" into a functionally equivalent feedforward neural network (FNN) with identical input-output behavior. Subsequent debate has focused on dynamical properties and philosophy of science critiques. We examine a boundary condition on the unfolding argument for RNN systems with rapid plasticity in their connection weights. We demonstrate through rigorous mathematical proofs that rapid plasticity negates the functional equivalence between RNN and FNN. Our proofs address history-dependent plasticity, dynamical systems analysis, information-theoretic considerations, perturbational stability, complexity growth, and resource limitations. We demonstrate that neuronal systems that possess properties such as plasticity, history-dependence, and complex temporal information encoding have features that cannot be captured by a static FNN. We show that plasticity is a concrete instance of lenient dependency between behavioral and internal observables, restoring empirical testability to theories that incorporate plasticity on perception-relevant timescales. Our results do not establish that recurrence, plasticity, or process are necessary for consciousness; they establish that the unfolding argument does not preclude empirical investigation of whether these properties matter.

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bioRxiv2024

Pupil dilations prior to freely timed actions reflect the reported timing of conscious intention

Freely timed actions are typically preceded by a slow anticipatory buildup of cortical brain activity, which has been extensively studied. However, such free actions are also preceded by slow pupil dilations in both humans and other animals, which have barely been examined. We investigated the neurocognitive significance of antecedent pupil dilations (APDs) in a voluntary-action paradigm. Participants performed self-paced actions and reported the timing of movement, conscious intention, or other events using a clock. APDs began a second or more before movement, and control conditions suggest that they did not reflect processing related to reporting demands, motor execution, or general anticipation. Critically, APD timing covaried with the reported timing of intention awareness but did not covary with the reported timing of overt movement or an external stimulus. Furthermore, decoding algorithms could distinguish APDs with above-chance accuracy more than 500 milliseconds before button-press. Our results suggest that APDs reflect a shift in awareness prior to movement onset and potentially offer a non-invasive method of predicting spontaneous movements before they occur. Highlights: 1. Freely timed movements are preceded by antecedent pupil dilations (APDs). 2. APDs do not reflect reporting, motor execution, or general anticipation. 3. APDs are informative of upcoming movements 500+ milliseconds before button-press. 4. APD timing specifically correlates with timing of intention awareness.

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bioRxiv2023

Probing for Intentions: The Early Readiness Potential does not Reflect Awareness of Motor Preparation

Voluntary actions are typically preceded by the Readiness Potential (RP), a negative midfrontal EEG deflection that begins [~]2 seconds before movement. What cognitive and neural process the RP reflects and how it relates to conscious intention remain unclear due to conflicting findings. We investigated the neural basis and cognitive significance of the RP in a novel probe-based paradigm. Contrary to prior reports, we found that pre-probe RP buildups were not related to reported awareness of motor preparation. Computational modeling suggested that the best explanation for these results is via metacognitive access to stochastic accumulation. Reported preparation was also related to beta desynchronization over contralateral motor cortex shortly before probe onset. We conclude that the RP may be metacognitively accessible in response to external task demands but does not reflect the onset of a conscious intention. We discuss implications of these findings for voluntary action initiation and intention awareness. HighlightsO_LIWe investigate the mechanisms underlying voluntary action initiation in a new probe paradigm. C_LIO_LIContrary to prior results, the readiness does not reflect reported awareness of motor preparation. C_LIO_LIComputational modeling supports stochastic accumulation over linear ballistic accumulation and classic RP models. C_LIO_LIReported awareness of motor preparation may emerge from metacognitive access to stochastic accumulation. C_LIO_LITime-frequency analysis suggests reported awareness may also relate to pre-probe beta desynchronization. C_LI

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bioRxiv2023

Slow ramping emerges from spontaneous fluctuations in spiking neural networks

Highlights1. We reveal a mechanism for slow-ramping signals before spontaneous voluntary movements. 2. Slow synapses stabilize spontaneous fluctuations in spiking neural network. 3. We validate model predictions in human frontal cortical single-neuron recordings. 4. The model recreates the readiness potential in an EEG proxy signal. 5. Neurons that ramp together had correlated activity before ramping onset. The capacity to initiate actions endogenously is critical for goal-directed behavior. Spontaneous voluntary actions are typically preceded by slow-ramping activity in medial frontal cortex that begins around two seconds before movement, which may reflect spontaneous fluctuations that influence action timing. However, the mechanisms by which these slow ramping signals emerge from single-neuron and network dynamics remain poorly understood. Here, we developed a spiking neural-network model that produces spontaneous slow ramping activity in single neurons and population activity with onsets [~]2 seconds before threshold crossings. A key prediction of our model is that neurons that ramp together have correlated firing patterns before ramping onset. We confirmed this model-derived hypothesis in a dataset of human single neuron recordings from medial frontal cortex. Our results suggest that slow ramping signals reflect bounded spontaneous fluctuations that emerge from quasi-winner-take-all dynamics in clustered networks that are temporally stabilized by slow-acting synapses.

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bioRxiv2021

Movement-Preceding Neural Activity under Parametrically Varying Levels of Time Pressure

Self-initiated movements are known to be preceded by the readiness potential or RP, a gradual increase in surface-negativity of cortical potentials that can begin up to 1 second or more before movement onset. The RP has been extensively studied for decades, and yet we still lack a clear understanding of its functional role. Attempts to model the RP as an accumulation-to-bound process suggest that this signal is a by-product of time-locking to crests in neural noise rather than the outcome of a pre-conscious decision to initiate a movement. One parameter of the model accounts for the imperative to move now, with cued movements having a strong imperative and purely spontaneous movements having no imperative. Two different variants of the model have been proposed, and both predict a decrease in the (negative) amplitude of the early RP as the imperative grows stronger. In order to test this empirically, we conducted an experiment where subjects produced self-initiated movements under varying levels of time pressure, and we investigated the amplitude, shape, and latency of the RP as a function of the imperative to move, operationalised as a time limit. We identified distinct changes in the amplitude of the early RP that grew non-linearly as the time limit grew shorter. Thus these data did not support the prediction made by the model. In addition, our results confirm that the shape of the RP is not stereotypically negative, being either positive or absent in about half of the subjects.

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bioRxiv2017

Human Self-Initiated Action Is Preceded By A Reliable Process Of Noise Reduction

A gradual buildup of electrical potential over motor areas precedes self-initiated movements. Recently, such \"readiness potentials\" (RPs) were attributed to stochastic fluctuations in neural activity. We developed a new experimental paradigm that operationalised self-initiated actions as endogenous skip responses while waiting for target stimuli in a perceptual decision task. We compared these to a block of trials where participants could not choose when to skip, but were instead instructed to skip. Frequency and timing of motor action were therefore balanced across blocks, so that conditions differed only in how the timing of skip decisions was generated. We reasoned that across-trial variability of EEG could carry as much information about the source of skip decisions as the mean RP. EEG variability decreased more markedly prior to self-initiated compared to externally-triggered skip actions. This convergence suggests a consistent preparatory process prior to self-initiated action. A leaky stochastic accumulator model could reproduce this convergence given the additional assumption of a systematic decrease in input noise prior to self-initiated actions. Our results may provide a novel neurophysiological perspective on the topical debate regarding whether self-initiated actions arise from a deterministic neurocognitive process, or from neural stochasticity. We suggest that the key precursor of self-initiated action may manifest as a reduction in neural noise.

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