bioRxiv Subject Collection: Neuroscience's Journal

A Method for the Combined Functional Assessment of Photoreceptors and Ganglion Cells in Acute Retinal Explants
Significant progress has been made in studying the individual steps of retinal signaling, yet a comprehensive understanding of the functional interplay between photoreceptors, as input cells, and retinal ganglion cells (RGCs), as output cells, remains elusive. This connection is crucial to fully unravel the retina's computational capabilities and its role in visual processing. To address this gap, this study introduces a novel technique that combines two-photon (2P) autofluorescence microscopy with multi-electrode array (MEA) recordings, enabling simultaneous testing of photoreceptor and RGC function. Unlike traditional methods that target isolated cell classes or structural analysis, this integrated technique provides the basis to investigate input-output relationships within the retinal neural network, offering a deeper understanding of its dynamic activity and adaptability to cellular dropout.

Neural Dynamics of Tonic Cold Pain: A Novel Investigation of an In-Scanner Alternative to the Cold Pressor Test in Healthy Individuals
The cold pressor task (CPT) is widely used to study tonic pain during acute and chronic conditions and is often as used as a conditioning stimulus to activate descending pain control systems. However, logistical challenges in magnetic resonance imaging (MRI) limit its application, hindering the understanding of CPT's neural dynamics. To address this, we acquired resting-state functional MRI data from 30 healthy participants before, during, and after immersion in gelled-cold water, the closest in-scanner alternative to date to CPT for prolonged stimulation. Participants provided subjective pain intensity ratings after each scan, as well as average pain perceived during noxious stimulation, using a numeric rating scale (NRS). Following fMRI, participants rated their pain continuously during identical tonic noxious stimulation of the contralateral hand using a visual analogue scale (VAS). We employed three complementary methods to examine changes in brain function across fMRI conditions: a data-driven approach via independent component analysis (ICA), seed-to-whole-brain connectivity analysis with the periaqueductal grey (PAG) as seed, and spectral dynamic causal modelling (spDCM) to explore effective connectivity changes across the dorsal anterior cingulate cortex (dACC), anterior insulae (AI), thalamus, and PAG. NRS scores were significantly higher following tonic cold compared to baseline and recovery conditions. Continuous VAS reflected sustained mild-to-moderate pain over six minutes, with average VAS scores not significantly differing from NRS ratings recorded in the scanner. ICA identified engagement of descending pain control and sensorimotor networks during pain, with the latter persisting during recovery. Seed-based analysis revealed a disengagement between the PAG and cortical/subcortical regions involved in pain processing, such as the dACC, midcingulate cortex, AI, intraparietal sulcus, and precuneus. Finally, spDCM revealed tonic pain neural signature was most likely characterised by top-down inhibitory and bottom-up excitatory connections. This study establishes the cold gelled-water paradigm as a robust in-scanner alternative to CPT. By uncovering key neural dynamics of CPT, we provide new insights into the brain and brainstem mechanisms of tonic cold pain paradigms routinely used in psychophysical pain studies.

Spatial and feature-selective attention interact to drive selective coding in frontoparietal cortex
Attention enables the selective processing of relevant information. Two types of selective attention, spatial and feature attention, have separable neural effects but in real life are often used together. Here, we asked how these types of attention interact to affect information coding in a frontoparietal 'multiple-demand' (MD) network, essential for attentional control. Using functional magnetic resonance imaging (fMRI) with multivariate pattern analysis, we examined how covert attention to object features (colour or shape) and spatial locations (left or right) influences coding of task-related stimulus information. We found that spatial and feature attention interacted multiplicatively on information coding in MD and visual regions, such that there was above-chance decoding of the attended feature of the attended object and no detectable coding of visually equivalent but behaviourally irrelevant aspects of the visual display. The attended information had a multidimensional neural representation, with stimulus information (e.g., colour) and discrimination difficulty (distance from the categorical decision boundary) reflected in separate dimensions. Rather than boosting processing of whole objects or relevant features across space, our results suggest neural activity reflects precise tuning to relevant information, indicating a highly selective control process that codes behaviourally relevant information across multiple dimensions.

RNA-programmable cell type monitoring and manipulation in the human cortex with CellREADR
Reliable and systematic experimental access to diverse cell types is necessary for understanding the neural circuit organization, function, and pathophysiology of the human brain. Methods for targeting human neural populations are scarce and currently center around identifying and engineering transcriptional enhancers and viral capsids. Here we demonstrate the utility of CellREADR, a programmable RNA sensor-effector technology that couples cellular RNA sensing to effector protein translation, for accessing, monitoring, and manipulating specific neuron types in ex vivo human cortical tissues. We designed CellREADR constructs to target two distinct human neuron types, CALB2+ (calretinin) GABAergic interneurons and FOXP2+ (forkhead box protein P2) glutamatergic projection neurons, and validated cell targeting using histological, electrophysiological, and transcriptomic methods. CellREADR-mediated expression of optogenetic effectors and genetically-encoded calcium indicators allowed us to manipulate and monitor these neuronal populations in cortical microcircuits. We further demonstrate that AAV-based CellREADR and enhancer vectors can be jointly used to target different subpopulations in the same preparation. By demonstrating specific, reliable, and programmable experimental access to targeted cell types, our results highlight CellREADR's potential for studying human neural circuits and treating brain disorders with cell type resolution.

Universal rhythmic architecture uncovers distinct modes of neural dynamics
Understanding the organizing principles of brain activity can advance neuro-technology and medical diagnosis and treatment. A prominent principle promoted over the last century is that brain activity consists of electrical field potentials that oscillate at different frequency bands. However, this principle has been challenged on several grounds. Specifically, increasing evidence suggests that in some cases brain oscillations are manifested as transient bursts rather than sustained rhythms. In this paper, we examine the hypothesis that rhythmicity (sustained vs. bursty) is an additional dimension in the organization of brain function. To test this hypothesis, we segmented the neurophysiological spectrum of 859 participants encompassing a dozen datasets across species, recording techniques, ages 18-88, brain regions, and cognitive states in both health and disease, according to a novel measure of rhythmicity. Together with computer simulations and brain stimulation, we found a universal spectral architecture divisible into two categories: high-rhythmicity bands associated with sustained oscillations and novel low-rhythmicity bands dominated by brief oscillatory bursts. This universal architecture reveals stable features of the brain's mode of operation: sustained bands signify maintenance of ongoing activity, whereas transient bands signify the brain's response to change. Rhythmicity specifies a powerful, replicable, and accessible feature-set for neuro-technology and diagnosis, as well as cross-species comparisons.

Volitional Regulation and Transferable Patterns of Midbrain Oscillations
Dopaminergic brain areas are crucial for cognition and their dysregulation is linked to neuropsychiatric disorders typically treated with pharmacological interventions. These treatments often have side effects and variable effectiveness, underscoring the need for alternatives. We introduce the first demonstration of neurofeedback using local field potentials (LFP) from the ventral tegmental area (VTA). This approach leverages the real-time temporal resolution of LFP and ability to target deep brain. In our study, non-human primates learned to regulate VTA beta power using a customized normalized metric to stably quantify VTA LFP signal modulation. The subjects demonstrated flexible and specific control with different strategies for specific frequency bands, revealing new insights into the plasticity of VTA neurons contributing to oscillatory activity that is functionally relevant to many aspects of cognition. Excitingly, the subjects showed transferable patterns, a key criterion for clinical applications beyond training settings. This work provides a foundation for neurofeedback-based treatments, which may be a promising alternative to conventional approaches and open new avenues for understanding and managing neuropsychiatric disorders.

The association between oscillatory burst features and deviations during human working memory
Oscillatory power across multiple frequency bands has been associated with distinct working memory (WM) processes. Recent research has shown that previous observations based on averaged power are driven by the presence of transient, oscillatory burst-like events, particularly within the alpha, beta, and gamma bands. However, the interplay between alpha, beta and gamma bursts in human WM is not well understood. The current EEG study aimed to investigate the dynamics between alpha/beta and high frequency activity (HFA; 55-80 Hz) bursts in human WM, particularly burst features and error-related deviations during the encoding and maintenance of WM in healthy adults. Oscillatory burst features within the alpha, beta and HFA bands were examined at frontal and parietal electrodes in healthy young adults during a Sternberg working memory task. Averaged power dynamics were driven by oscillatory burst features, most consistently the burst rate and burst power. Alpha/beta and HFA bursts displayed complimentary roles in WM processes, in that alpha and beta bursting decreased during encoding and increased during delay, while HFA bursting had the opposite pattern, i.e., increased during encoding and decreased during the delay. The parietal electrode exhibited faster and stronger variation in burst features across WM stages than the frontal electrode. Critically, weaker variation across stages was associated with incorrect responses. Together, these results indicate that successful human WM is dependent on the rise and fall interplay between alpha/beta and HFA bursts, with such burst dynamics reflecting a novel target for development of treatment in clinical populations with WM deficits.

Differences and similarities between human hippocampal low-frequency oscillations during navigation and mental simulation
Low frequency oscillations in the hippocampus emerge during by both spatial navigation and episodic memory function in humans. We have recently shown that in humans, memory-related processing is a stronger driver of low frequency oscillations than navigation. These findings and others support the idea that low-frequency oscillations are more strongly associated with a general memory function than with a specific role in spatial navigation. However, whether the low-frequency oscillations that support episodic memory and those during navigation could still share some similar functional roles remains unclear. In this study, patients undergoing intracranial electroencephalography (iEEG) monitoring performed a navigation task in which they navigated and performed internally directed route replay, similar to episodic memory. We trained a random forest classification model to use patterns in low-frequency power (2-12 Hz) to learn the position during navigation and subsequently used the same model to successfully decode position during mental simulation. We show that removal of background differences in power between navigation and mental simulation is critical to detecting the overlapping patterns. These results suggest that the low-frequency oscillations that emerge during navigation are more associated with a role in memory than specifically with a navigation related function.

Adult visual deprivation engages associative, presynaptic plasticity of thalamic input to cortex
Associative plasticity at thalamocortical synapses is thought to be constrained by age in the mammalian cortex. However, here we show for the first time that prolonged visual deprivation induces robust and reversible plasticity at synapses between first order visual thalamus and cortical layer 4 pyramidal neurons. The plasticity is associative and expressed by changes in presynaptic function, thereby amplifying and relaying the change in efferent drive to the visual cortex.

Seeing speech: neural mechanisms of cued speech perception in prelingually deaf and hearing users
For many deaf people, lip-reading plays a major role in verbal communication. However, lip movements are by nature ambiguous, so that lip reading does not allow for a full understanding of speech. The resulting language access difficulties may have serious consequences on language, cognitive and social development. Cued speech (CS) was developed to eliminate this ambiguity by complementing lip-reading with hand gestures, giving access to the entire phonological content of speech through the visual modality alone. Despite its proven efficiency for improving linguistic and communicative abilities, the mechanisms of CS perception remain largely unknown. The goal of the present study is to delineate the brain regions involved in cued speech perception and identify their role in visual and language-related processes. Three matched groups of participants were scanned during two fMRI experiments: Prelingually deaf users of cued speech, hearing users of cued speech, and naive hearing controls. In Experiment 1, we presented videos of silent CS sentences, isolated lip movements, isolated gestures, plus CS sentences with speech sounds and meaningless CS sentences. In Experiment 2, we presented pictures of faces, bodies, written words, tools, and houses in order to understand the contribution of category-specific visual regions to CS perception. We delineated a number of mostly left-hemisphere brain regions involved in CS perception. We first found that language areas were activated in all groups by both silent CS sentences and isolated lip movements, and by gestures in deaf participants only. Despite overlapping activations when perceiving CS, several findings differentiated experts from novices. As such, CS expertise was associated with a leftward functional lateralization of the lateral occipital cortex, possibly driven by the expert identification of hand gestures. The Visual Word Form Area, which supports the interface between vision and language during reading, did not contribute to CS perception. Moreover, the integration of lip movements and gestures took place in a temporal language-related region in deaf users, and in movement-related regions in hearing users, reflecting their different profile of expertise in CS comprehension and production. Finally, we observed a strong involvement of the Dorsal Attentional Network in hearing users of CS, and identified the neural correlates of the variability in individual proficiency. Cued speech constitutes a novel pathway for accessing core language processes, halfway between speech perception and reading. The current study provides a delineation of the common and specific brain structures supporting those different modalities of language input, paving the way for further research.

Heterogeneous, temporally consistent, and plastic brain development after preterm birth
The current view of neurodevelopment after preterm birth presents a strong paradox: diverse neurocognitive outcomes suggest heterogeneous neurodevelopment, yet numerous brain imaging studies focusing on average dysmaturation imply largely uniform aberrations across individuals. Here we show both, spatially heterogeneous individual brain abnormality patterns (IBAPs) but with consistent underlying biological mechanisms of injury and plasticity. Using cross-sectional structural magnetic resonance imaging data from preterm neonates and longitudinal data from preterm children and adults in a normative reference framework, we demonstrate that brain development after preterm birth is highly heterogeneous in both severity and patterns of deviations. Individual brain abnormalities were also consistent for their extent and location along the life course, associated with glial cell underpinnings, and plastic for influences of the early social environment. Thus, IBAPs of preterm birth are spatially heterogenous, temporally consistent for extent, spatial location, and cellular underpinnings, and plastic for social-environmental impacts. Our findings extend conventional views of preterm neurodevelopment, revealing a nuanced landscape of individual variation, with consistent commonalities between subjects. This integrated perspective of preterm neurodevelopment implies more targeted theranostic intervention strategies, specifically integrating brain charts and imaging at birth, as well as social interventions during early development.

The brain selectively allocates energy to functional brain networks under cognitive control
Network energy has been conceptualized based on structural balance theory in the physics of complex networks. We utilized this framework to assess the energy of functional brain networks under cognitive control and to understand how energy is allocated across canonical functional networks during various cognitive control tasks. We extracted network energy from functional connectivity patterns of subjects who underwent fMRI scans during cognitive tasks involving working memory, inhibitory control, and cognitive flexibility, in addition to task-free scans. We found that the energy of the whole-brain network increases when exposed to cognitive control tasks compared to the task-free resting state, which serves as a reference point. The brain selectively allocates this elevated energy to canonical functional networks; sensory networks receive more energy to support flexibility for processing sensory stimuli, while cognitive networks relevant to the task, functioning efficiently, require less energy. Furthermore, employing network energy, as a global network measure, improves the performance of predictive modeling, particularly in classifying cognitive control tasks and predicting chronological age. Our results highlight the robustness of this framework and the utility of network energy in understanding brain and cognitive mechanisms, including its promising potential as a biomarker for mental conditions and neurological disorders.

Symbolic and Non-Symbolic numbers differently affect centre identification in a number-line bisection task
Numerical and spatial representations are intertwined as in the Mental Number Line, where smaller numbers are on the left and larger numbers on the right. This relationship has been repeatedly demonstrated with various experimental approaches, such as the line bisection task. Spatial accuracy appears to be systematically distorted leftward for smaller digits by elaboration of spatial codes during number processing. Other studies have investigated perceptual and visuo-spatial attention bias using the digit line bisection task, suggesting that these effects may be related to a cognitive illusion in which the reference numbers project their values onto the straight line, creating an illusory lateral disparity. On the other hand, both dot arrays (non-symbolic stimuli) and arabic numbers (symbolic stimuli) demonstrate a privileged relation between spatial and numerical elaboration. The bias toward the larger numerosity flanker was attributed to a length illusion. There is, however, no consensus regarding whether physical features and symbolic and non-symbolic numerical representations exert the same influence over spatial ones. In the present study, we carried out a series of 4 Experiments to provide further evidence for a better understanding of the nature of this differential influence. All experiments presented the numbers in both symbolic and non-symbolic formats. In Experiment 1, the numbers "2-8" were presented in a variety of left-right orientations. In Experiment 2, the flankers were identical, "2-2" or "8-8", and symmetrically displaced with respect to the line. In Experiment 3, we employed asymmetrically distributed eight dots, or font sizes in "8-8" numerals, to create a perceptual imbalance. In Experiment 4, we replicated the manipulation used in Experiment 3, but with two dots and "2-2" numerals. The Non-Symbolic format induced stronger leftward biases, particularly when the larger numerosity (Experiment 1) or the denser stimuli near the line (Experiments 3 and 4) were on the left, while no bias emerged when flankers were numerically equivalent and symmetrical (Experiment 2). The left bias may result from a tendency to estimate the influence of stimulus perception associated with participant' scanning direction, similar to the direction of pseudoneglect. Conversely, the Symbolic format induced mostly right bias, possibly due to left-lateralized processing and a tendency to use a common strategy involving scanning from left to right. Altogether our data support the view that abstract numbers and non-symbolic magnitude affect perceptual and attentional biases, yet in distinctive ways.

Collapse of Interictal Suppressive Networks Permits Seizure Spread
How do networks in the brain limit seizure activity? In the Interictal Suppression Hypothesis (ISH), we recently postulated that high inward connectivity to seizure onset zones (SOZs) from non-involved zones (NIZs) is a sign of broader network suppression at rest. If broad networks appear to be responsible for interictal SOZ suppression, what changes during seizure initiation, spread, and termination? For patients with drug resistant epilepsy, intracranial monitoring offers a view into the electrographic networks which organize around and in response to the SOZ. In this manuscript, we investigate network dynamics in the peri-ictal periods to assess possible mechanisms of seizure suppression and the consequences of this suppression being overwhelmed. Peri-ictal network dynamics were derived from stereo electroencephalography (SEEG) recordings from 75 patients with drug-resistant epilepsy undergoing pre-surgical evaluation at Vanderbilt University Medical Center. We computed directed connectivity from 5-second windows in the periods between, immediately before, during, and after seizures. After aligning all network connectivity matrices between seizures and patients, we calculated net connectivity changes from the SOZ, propagative zone (PZ), and NIZ. Across all seizure types, we observed two distinct phases as seizures initiated and evolved: a large rapid increase in directed communication towards the SOZ from NIZ followed by a collapse in network connectivity. During this first phase, SOZs could be distinguished from all other regions (One-Way ANOVA, p=8.32x10-19 - 2.22x10-7, lower range to upper range of p-values). In the second phase and post-ictal period, SOZ inward connectivity decreased yet remained distinct (One-Way ANOVA, p= 2.58x10-10-1.66x10-2). Furthermore, NIZs appeared to drive the increase in inward SOZ connectivity while global connectivity between NIZs concordantly decreased. Stratifying by seizure subtype, we found that consciousness-impairing seizures show loss of inward connectivity from the NIZ earlier than conscious sparing seizures (one-way ANOVA, p<0.01 after false discovery correction). Tracking network reorganization against a surrogate for seizure involvement highlighted a possible antagonism between seizure propagation to the NIZ and the NIZ's ability to maintain high connectivity to the SOZ. Finally, we found that inclusion of peri-ictal connectivity improved SOZ classification accuracy from previous models to a combined area under the curve of 93%. Overall, NIZs appear to actively respond to seizure onset and increase inhibitory signaling towards the SOZ, possibly in an attempt to thwart seizure activity. This inhibition appears to be insufficient to prevent seizure onset, and furthermore, loss of normal communication in the rest of the brain between NIZs may contribute to loss of consciousness during larger seizures. Dynamic connectivity patterns uncovered in this work may: i) allow more accurate delineation of surgical targets in focal epilepsy, ii) reveal why inward suppression of SOZs interictally may nonetheless be insufficient to prevent all seizures, and iii) provide insight into mechanisms of loss of consciousness during certain seizures.

Sense of control buffers against stress
Stress is one of the most pervasive causes of mental ill-health across the lifespan. Subjective dimensions of stress perception, such as perceived control, are especially potent in shaping stress responses. While the impact of reduced or no control over stress is well understood, much less is known about whether heightened feelings of control buffer against the negative impact of later stress. We designed a novel paradigm with excellent psychometric properties to sensitively capture and induce different states of subjective control. Across two studies with a total of 768 neurotypical adults, we show a robust association between sense of control and stress as well as symptoms of mental ill-health. More importantly, in a subsample of 295 participants we show that compared to a neutral control group, inducing a heightened state of subjective control buffers against the impact of later stress. These findings demonstrate a causal role for a heightened sense of control in mitigating the negative impact of stressful experiences and spell out important directions for future preventative interventions.

The interplay between executive functions and updating predictive representations
Modifying habits, particularly unwanted behaviors, is often challenging. Cognitive research has focused on understanding the mechanisms underlying habit formation and how habits can be rewired. A key mechanism is statistical learning, the continuous, implicit extraction of probabilistic patterns from the environment, which forms the basis of predictive processing. However, the interplay between executive functions (EF) and the rewiring - or updating - of these probabilistic representations remains largely unexplored. To address this gap, we conducted an experiment consisting of four sessions: 1) Learning Phase - acquisition of probabilistic representations, 2) Rewiring Phase - updating these probabilistic representations, 3) Retrieval Phase - accessing learned representations, and 4) EF assessment, targeting five key aspects: attentional control, inhibition, working memory, flexibility, and verbal fluency. We focused on the relationship between these EF measures and the updating of previously acquired knowledge using an interindividual differences approach. Our results revealed a positive relationship between rewiring and inhibition, suggesting that better inhibitory control may facilitate the adaptive restructuring of probabilistic predictive representations. Conversely, a negative relationship was identified between rewiring and semantic fluency, implying that certain underlying aspects of verbal fluency tasks, such as access to long-term memory representations, may hinder the updating process. We interpret this relationship through the lens of competitive memory network models. Our findings indicate that the rewiring of implicit probabilistic representations is a multifaceted cognitive process requiring both the suppression of proactive interference from prior knowledge through cognitive inhibition and a strong reliance on model-free functioning.

Lesions of anterior cingulate cortex disrupt an electrophysiological signature of reward processing in humans
The reward positivity (RewP) is an event-related brain potential (ERP) component associated with feedback and reward processing. Although the component is said to be generated in anterior cingulate cortex (ACC), this inference is disputed because of the inverse problem. Recently, by conducting a current source density analysis of intracranial electroencephalogram (EEG) data recorded from a large cohort of epilepsy patients, we provided direct evidence that the RewP is produced by a circumscribed region in caudal ACC corresponding to Brodmann areas 24c and 32. In the present study we confirm that this brain area is the source of the RewP by examining the effects of damage to frontal cortex on RewP amplitude. We recorded scalp EEG from 68 stroke patients with damage to frontal cortex while they engaged in a trial-and-error guessing task used to elicit a canonical RewP. Application of non-parametric voxel-based lesion-symptom mapping to the lesion data revealed that damage to Brodmann areas 24c and 3 attenuated RewP amplitude, whereas damage to other parts of frontal cortex did not affect it. These results provide causal evidence that the caudal ACC generates the RewP and underscore the contribution of this brain region toward motivating extended behaviors.

Peripheral immune cell response to stimulation stratifies Parkinson's disease progression from prodromal to clinical stages
The motor stage of idiopathic Parkinson's disease (iPD) can be preceded for years by a prodromal stage characterized by non-motor symptoms like REM sleep behavior disorder (RBD). Here, we show that multiple stages of iPD, including the pre-motor prodromal stage, can be stratified according to the inflammatory and immunometabolic responses to stimulation of peripheral blood mononuclear cells ex vivo. We identified increased stimulation-dependent secretion of TNF, IL-1{beta}, and IL-8 in monocytes from RBD patients and showed diminished proinflammatory cytokine secretion in monocytes and T cells in early and moderate stages of PD. Mechanistically, immune activation revealed deficits in CD8+ T-cell mitochondrial health in moderate PD, and relative mitochondrial health in CD8+ T cells was positively correlated with stimulation-dependent T-cell cytokine secretion across the PD spectrum. Dysregulated immunometabolism may drive peripheral inflammation and PD progression, and ex vivo stimulation-based assays have potential to reveal novel biomarkers for patient stratification and progression with immune endophenotypes.

The Impact of Instrumental Music on Dual-task Interference in a Simulated Driving Environment
Numerous drivers engage in both listening to music and undertaking secondary tasks while driving. Secondary tasks have been shown to have a negative impact on driving performance. However, the effect of music on driving performance can vary, either improving or impairing it. Nevertheless, the influence of background music on dual-task interference remains uncertain. In this study, we aimed to investigate the impact of instrumental background music on dual-task performance within a simulated driving environment. Twenty-four participants performed a color-discrimination task followed by a driving lane-change task. The results indicated that music enhanced accuracy in the lane-change task without a corresponding increase in reaction time (RT), both in single- and dual-task conditions. Additionally, when the time gap between the two tasks was 600 ms, RT for the lane-change task decreased with high music tempo. However, RT for the lane-change task did not exhibit any changes in response to music tempo when the onset time between the two tasks was short (100 ms), as well as in the single-task condition. Notably, participants' perceived workload did not significantly differ across the various task conditions. These findings emphasize the potential of background music to improve dual-task performance, particularly when considering the temporal gap between tasks.