Retinal metric: a stimulus distance measure derived from population neural responses

The ability of the organism to distinguish between various stimuli is limited by the structure and noise in the population code of its sensory neurons. Here we infer a distance measure on the stimulus space directly from the recorded activity of 100 neurons in the salamander retina. In contrast to previously used measures of stimulus similarity, this "neural metric" tells us how distinguishable a pair of stimulus clips is to the retina, given the noise in the neural population response. We show that the retinal distance strongly deviates from Euclidean, or any static metric, yet has a simple structure: we identify the stimulus features that the neural population is jointly sensitive to, and show the SVM-like kernel function relating the stimulus and neural response spaces. We show that the non-Euclidean nature of the retinal distance has important consequences for neural decoding.Comment: 5 pages, 4 figures, to appear in Phys Rev Let

Segregation of object and background motion in the retina

An important task in vision is to detect objects moving within a stationary scene. During normal viewing this is complicated by the presence of eye movements that continually scan the image across the retina, even during fixation. To detect moving objects, the brain must distinguish local motion within the scene from the global retinal image drift due to fixational eye movements. We have found that this process begins in the retina: a subset of retinal ganglion cells responds to motion in the receptive field centre, but only if the wider surround moves with a different trajectory. This selectivity for differential motion is independent of direction, and can be explained by a model of retinal circuitry that invokes pooling over nonlinear interneurons. The suppression by global image motion is probably mediated by polyaxonal, wide-field amacrine cells with transient responses. We show how a population of ganglion cells selective for differential motion can rapidly flag moving objects, and even segregate multiple moving objects

"A renewed sense of purpose": mothers' and fathers' experience of having a child following a recent stillbirth.

Most research has focused on mothers' experiences of perinatal loss itself or on the subsequent pregnancy, whereas little attention has been paid to both parents' experiences of having a child following late perinatal loss and the experience of parenting this child. The current study therefore explored mothers' and fathers' experiences of becoming a parent to a child born after a recent stillbirth, covering the period of the second pregnancy and up to two years after the birth of the next baby. In depth interviews were conducted with 7 couples (14 participants). Couples were eligible if they previously had a stillbirth (after 24 weeks of gestation) and subsequently had another child (their first live baby) who was now under the age of 2 years. Couples who had more than one child after experiencing a stillbirth and those who were not fluent in English were excluded. Qualitative analysis of the interview data was conducted using Interpretive Phenomenological Analysis. Five superordinate themes emerged from the data: Living with uncertainty; Coping with uncertainty; Relationship with the next child; The continuing grief process; Identity as a parent. Overall, fathers' experiences were similar to those of mothers', including high levels of anxiety and guilt during the subsequent pregnancy and after the child was born. Coping strategies to address these were identified. Differences between mothers and fathers regarding the grief process during the subsequent pregnancy and after their second child was born were identified. Despite difficulties with bonding during pregnancy and at the time when the baby was born, parents' perceptions of their relationship with their subsequent child were positive. Findings highlight the importance of tailoring support systems not only according to mothers' but also to fathers' needs. Parents', and particularly fathers', reported lack of opportunities for grieving as well as the high level of anxiety of both parents about their baby's wellbeing during pregnancy and after birth implies a need for structured support. Difficulties experienced in bonding with the subsequent child during pregnancy and once the child is born need to be normalised

Refinement and Pattern Formation in Neural Circuits by the Interaction of Traveling Waves with Spike-Timing Dependent Plasticity

Traveling waves in the developing brain are a prominent source of highly correlated spiking activity that may instruct the refinement of neural circuits. A candidate mechanism for mediating such refinement is spike-timing dependent plasticity (STDP), which translates correlated activity patterns into changes in synaptic strength. To assess the potential of these phenomena to build useful structure in developing neural circuits, we examined the interaction of wave activity with STDP rules in simple, biologically plausible models of spiking neurons. We derive an expression for the synaptic strength dynamics showing that, by mapping the time dependence of STDP into spatial interactions, traveling waves can build periodic synaptic connectivity patterns into feedforward circuits with a broad class of experimentally observed STDP rules. The spatial scale of the connectivity patterns increases with wave speed and STDP time constants. We verify these results with simulations and demonstrate their robustness to likely sources of noise. We show how this pattern formation ability, which is analogous to solutions of reaction-diffusion systems that have been widely applied to biological pattern formation, can be harnessed to instruct the refinement of postsynaptic receptive fields. Our results hold for rich, complex wave patterns in two dimensions and over several orders of magnitude in wave speeds and STDP time constants, and they provide predictions that can be tested under existing experimental paradigms. Our model generalizes across brain areas and STDP rules, allowing broad application to the ubiquitous occurrence of traveling waves and to wave-like activity patterns induced by moving stimuli

Rehabilitation via home based gaming exercise for the upper-limb post stroke (RHOMBUS): results of an intervention feasibility trial

Innovate UK grant number 10418

Rehabilitation via HOMe Based gaming exercise for the Upper-limb post Stroke (RHOMBUS): a qualitative analysis of participants’ experience

Objective To report participants’ experiences of trial processes and use of the Neurofenix platform for home-based rehabilitation following stroke. The platform, consisting of the NeuroBall device and Neurofenix app, is a non-immersive virtual reality tool to facilitate upper limb rehabilitation following stroke. The platform has recently been evaluated and demonstrated to be safe and effective through a non-randomised feasibility trial (RHOMBUS). Design Qualitative approach using semistructured interviews. Interviews were audio recorded, transcribed verbatim and analysed using the framework method. Setting Participants’ homes, South-East England. Participants Purposeful sample of 18 adults (≥18 years), minimum 12 weeks following stroke, not receiving upper limb rehabilitation prior to the RHOMBUS trial, scoring 9–25 on the Motricity Index (elbow and shoulder), with sufficient cognitive and communicative abilities to participate. Results Five themes were developed which explored both trial processes and experiences of using the platform. Factors that influenced participant’s decision to take part in the trial, their perceptions of support provided during the trial and communication with the research team were found to be important contextual factors effecting participants’ overall experience. Specific themes around usability and comfort of the NeuroBall device, factors motivating persistence and perceived effectiveness of the intervention were highlighted as being central to the usability and acceptability of the platform. Conclusion This study demonstrated the overall acceptability of the platform and identified areas for enhancement which have since been implemented by Neurofenix. The findings add to the developing literature on the interface between virtual reality systems and user experience. Trial registration number ISRCTN60291412.Innovate UK (grant number: 104188

Rehabilitation using virtual gaming for Hospital and hOME Based training for the Upper limb post Stroke (RHOMBUS II): a feasibility randomised controlled trial

Meeting abstract presented at the 17th UK Stroke Forum Conference, 29th November – 1st December 2022, Liverpool ACC, UK.Introduction: Stroke survivors can experience persistent upper-limb (UL) weakness. Intense practice and repetition of movement are key to effective UL rehabilitation. Yet, practice falls short of the dosage needed to drive recovery. Technology offers solutions to increase training opportunities. The NeuroBall is a co-designed portable device for all-in-one arm training through a uniquely designed rehabilitation gaming app, displayed on a tablet computer. This study aimed to determine the safety, feasibility and acceptability of the NeuroBall in the subacute inpatient and ESD stroke pathways when practice can be most effective. Method: Single-site feasibility RCT with non-blinded outcomes at seven weeks. Twenty-four sub-acute stroke with new unilateral weakness were randomised (Intervention n=16; control n=8). Both groups received UL usual care; the intervention group, once trained, used the NeuroBall for seven weeks. Outcomes included arm impairment, arm function, pain, fatigue and self-efficacy for exercising alone, participant satisfaction, device usage and adverse events (AEs) and missing data. Results: Twenty-four participants were recruited, eighteen completed all stages. Outcome measures were suitable, and there was minimal missing data (less than 10%). Participants undertook an additional 13 hours of UL rehabilitation, completing an average of 15, 133 UL repetitions. The mean satisfaction score (QUEST) was 35/40. Eight AEs were reported, six in the intervention group and two in the control, five were unrelated, one related, one probable and one possibly. Conclusion: The NeuroBall is safe, enjoyable and easy to use for training the UL in the subacute stroke pathway both as an inpatient and early weeks at home

Receptive Field Inference with Localized Priors

The linear receptive field describes a mapping from sensory stimuli to a one-dimensional variable governing a neuron's spike response. However, traditional receptive field estimators such as the spike-triggered average converge slowly and often require large amounts of data. Bayesian methods seek to overcome this problem by biasing estimates towards solutions that are more likely a priori, typically those with small, smooth, or sparse coefficients. Here we introduce a novel Bayesian receptive field estimator designed to incorporate locality, a powerful form of prior information about receptive field structure. The key to our approach is a hierarchical receptive field model that flexibly adapts to localized structure in both spacetime and spatiotemporal frequency, using an inference method known as empirical Bayes. We refer to our method as automatic locality determination (ALD), and show that it can accurately recover various types of smooth, sparse, and localized receptive fields. We apply ALD to neural data from retinal ganglion cells and V1 simple cells, and find it achieves error rates several times lower than standard estimators. Thus, estimates of comparable accuracy can be achieved with substantially less data. Finally, we introduce a computationally efficient Markov Chain Monte Carlo (MCMC) algorithm for fully Bayesian inference under the ALD prior, yielding accurate Bayesian confidence intervals for small or noisy datasets

Rehabilitation Using Virtual Gaming For Hospital And Home- Based Training For The Upper Limb In Acute And Subacute Stroke (Rhombus Ii): Results Of A Feasibility RCT

Conference poster presented at the 19th UK Stroke Forum Conference, 1st–3rd December 2024, Liverpool ACC, UK.Introduction: Current provision of upper-limb (UL) rehabilitation during the early period post stroke is insufficient to optimise potential for recovery. Virtual reality systems, such as the Neurofenix platform, can help increase the intensity of UL rehabilitation across the stroke pathway. Method: A feasibility RCT was undertaken to determine the safety, feasibility and acceptability of the Neurofenix platform. Stroke survivors with UL weakness were recruited from in-patient or early supported discharge stroke teams. Both groups received usual care, the intervention group also had the Neurofenix platform for 7-weeks. Outcomes were assessed at baseline and 7-weeks. Safety was assessed through adverse events (AEs), pain, spasticity and fatigue. Feasibility was determined through training and support requirements, and acceptability through intervention fidelity and a satisfaction questionnaire. Results: 24 participants were randomised, n=16 to the intervention (13 women; mean (SD) age 66.5 (15) years; median (range) 9.5 (1-42) days post-stroke) and n=8 control group (4 women; mean (SD) age 64.6 (13.6) years; median (range) 17.5 (4-23) days post-stroke). 3 participants withdrew before 7-weeks, with 21 (intervention group n=15; control group n=6) included in the analysis. No significant between group differences in fatigue, spasticity, pain scores or total number of AEs. Median (IQR) time to train participants was 98 (64) minutes over 1-3 sessions. Participants trained with the platform for a median (range) of 11 (1-58) hours, equating to 94 minutes extra per week. Conclusion: The Neurofenix platform is safe, feasible and well-accepted across the hospital and home settings, supporting increased dose and intensity of essential early UL stroke rehabilitation