Biology subjects

Somervail, R.

Publications and source records attributed to Somervail, R..

4 recordsLinked to original sources

bioRxiv2026

Distinct nigral and brainstem pathology markers map onto separable subthalamic electrophysiological signatures in Parkinson's disease

Subthalamic local field potentials (LFPs) are increasingly used as physiomarkers of the symptomatic state in Parkinsons disease, but their relationship to the underlying neurodegenerative pathology remains unclear. Here, we combined OFF-medication subthalamic LFP recordings with quantitative MRI markers of nigral and brainstem pathology in 33 people with Parkinsons disease. Distinct pathological markers mapped onto dissociable electrophysiological components. Substantia nigra pars compacta susceptibility was associated with increased occupancy, duration and rate of low-{beta} bursts, whereas nigral free water was associated with greater low-frequency aperiodic offset and a steeper slope. Pedunculopontine nucleus free-water- corrected axial diffusivity was selectively associated with high-frequency aperiodic activity, and this relationship strengthened with increasing nigral susceptibility, consistent with dopaminergic-state- dependent influences of extranigral pathology on subthalamic physiology. Only low-frequency aperiodic offset was also associated with contralateral bradykinesia. These findings indicate that the subthalamic LFP is not a unitary readout of dopamine loss or motor state, but an integrated physiological signal in which pathology across interconnected systems is expressed through separable oscillatory and aperiodic components. Chronically implanted devices may therefore provide physiological readouts of underlying disease biology alongside control signals for adaptive therapy.

neuroscience↗

bioRxiv2026

Spontaneous locus coeruleus bursts coincide withtransient global brain state changes similar to thoseelicited by surprise

Sudden and isolated sensory stimuli (SISS) engage the extralemniscal system and elicit widespread electrocortical responses in the brain. These responses, consisting of both time-domain transients and spectral changes, reflect a switch of the global brain state that likely prepares the organism for subsequent urgent behaviours. Crucially, SISS also elicit a short-latency phasic response in a key component of the extralemniscal system in the brainstem, the noradrenergic Locus Coeruleus (LC) nucleus. Such stimulus-evoked LC firing is associated with the electrocortical markers of extralemniscal activation. LC neurons also display burst-like firing spontaneously, i.e., without imposed sensory stimuli, for example, during quiet wakefulness, sleep, or anaesthesia. However, this phenomenon remains underexplored. We therefore measured, in freely behaving rats, the prefrontal electrocorticogram (ECoG) responses following spontaneous LC bursts. In addition, we compared these ECoG responses to those triggered by electrical LC stimulation or auditory SISS. We found that ECoG responses were proportional to the magnitude of the spontaneous LC bursts or microstimulation, and remarkably similar to those elicited by SISS. Finally, suppression of noradrenergic transmission with systemic clonidine administration attenuated the auditory-evoked ECoG response. These results suggest that LC plays a role in generating the transient brain state changes elicited by SISS.

neuroscience↗

bioRxiv2025

Electrical Spinal Imaging (ESI): Analysing spinal cord activity with non-invasive, high-resolution mapping

The spinal cord is the key bridge between the brain and the body. However, scientific understanding of healthy spinal cord function has historically been limited because noninvasive measures of its neural activity have proven exceptionally challenging. In this work, we describe a novel recording and analysis approach to obtain non-invasive, high-resolution images of the electrical activity of the spinal cord in humans (Electrical Spinal Imaging, ESI). ESI is analytically simple, easy to implement, and data-driven: it does not involve template-based strategies prone to produce spurious signals. Using this approach we provide a detailed description and physiological characterization of the spatiotemporal dynamics of the peripheral, spinal and cortical activity elicited by somatosensory stimulation. We also demonstrate that attention modulates post-synaptic activity at spinal cord level. Our method has enabled four new insights regarding spinal cord activity. (1) We identified three distinct responses in the time domain: sP9, sN13 and sP22. (2) The sP9 is a traveling wave reflecting the afferent volley entering the spinal cord through the dorsal root. (3) In contrast, the sN13 and sP22 reflect segmental post-synaptic activity. (4) While the sP9 response is first seen on the dorsal electrodes ipsilateral to the stimulated side, the sN13 and sP22 were not lateralised with respect to the side of stimulation. (5) Unimodal attention strongly modulates the amplitude of the sP22, but not that of the sP9 and sN13 components. The proposed method offers critical insights into the spatiotemporal dynamics of somatosensory processing within the spinal cord, paving the way for precise non-invasive functional monitoring of the spinal cord in basic and clinical neurophysiology.

neuroscience↗

bioRxiv2022

Egocentric value maps of the near-body environment

Body-part centric response fields are pervasive: they are observed in single neurons, fMRI, EEG, and multiple behavioural measures. This prevalence across scales and measures makes them excellent candidates for studying systems-level neuroscience. Nonetheless, they remain poorly understood because we lack a unifying formal explanation of their origins and role in wider brain function. Here, we provide such explanation. We use reinforcement learning to analytically explain the existence of body-part centric receptive fields, also known as peripersonal field. We then simulate multiple experimental findings considered foundational in the peripersonal space literature. Our results demonstrate that peripersonal fields naturally arise from two simple and plausible assumptions about living agents: 1) they experience reward when they contact objects in the environment, and 2) they act to maximise reward. These simple assumptions are enough to explain empirical findings on stimulus kinematics, tool use, valence, and network-architecture. Our explanation provides further insight. First, it offers multiple empirically testable predictions. Second, it offers a formal description of the notion that the world-agent state is encoded in parieto-premotor cortices, using motor primitives: peripersonal fields provide building blocks that together create a short-term model of the world near the agent in terms of its future states; a successor representation. This short-term, close-range egocentric peripersonal map is analogous to the long-term, long-range allocentric spatial map of place and grid cells, which underlie locomotion and navigation to reach distant objects. Together, these allocentric and egocentric maps allow efficient interactions with a changing environment across multiple spatial and temporal scales. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=149 SRC="FIGDIR/small/504456v1_ufig1.gif" ALT="Figure 1"> View larger version (68K): org.highwire.dtl.DTLVardef@1c9d635org.highwire.dtl.DTLVardef@e4b1corg.highwire.dtl.DTLVardef@65390borg.highwire.dtl.DTLVardef@1840160_HPS_FORMAT_FIGEXP M_FIG C_FIG

neuroscience↗