Microscale visualization of cellular features in adult macaque visual cortex.

Expansion microscopy and light sheet imaging enable fine-scale resolution of intracellular features that comprise neural circuits. Most current techniques visualize sparsely distributed features across whole brains or densely distributed features within individual brain regions. Here, we visualize dense distributions of immunolabeled proteins across early visual cortical areas in adult macaque monkeys.

Ultra-high density electrodes improve detection, yield, and cell type identification in neuronal recordings.

To understand the neural basis of behavior, it is essential to sensitively and accurately measure neural activity at single neuron and single spike resolution. Extracellular electrophysiology delivers this, but it has biases in the neurons it detects and it imperfectly resolves their action potentials. To minimize these limitations, we developed a silicon probe with much smaller and denser recording sites than previous designs, called Neuropixels Ultra ().

Dissociation in neuronal encoding of object versus surface motion in the primate brain.

A paradox exists in our understanding of motion processing in the primate visual system: neurons in the dorsal motion processing stream often strikingly fail to encode long-range and perceptually salient jumps of a moving stimulus. Psychophysical studies suggest that such long-range motion, which requires integration over more distant parts of the visual field, may be based on higher-order motion processing mechanisms that rely on feature or object tracking. Here, we demonstrate that ventral visual area V4, long recognized as critical for processing static scenes, includes neurons that maintain direction selectivity for long-range motion, even when conflicting local motion is present.

Accounting for Bias in the Estimation of between Two Sets of Noisy Neural Responses.

The Pearson correlation coefficient squared, , is an important tool used in the analysis of neural data to quantify the similarity between neural tuning curves. Yet this metric is biased by trial-to-trial variability; as trial-to-trial variability increases, measured correlation decreases. Major lines of research are confounded by this bias, including those involving the study of invariance of neural tuning across conditions and the analysis of the similarity of tuning across neurons.

Age differences in brain activity in dorsolateral prefrontal cortex and supplementary motor areas during three different walking speed tasks.

Background: Functional Near-Infrared Spectrometry (fNIRS) is a novel neuroimaging method that can detect brain activity during functional activities. The prefrontal cortex and supplemental motor area (SMA) are active during normal and fast speed walking. However, it is unclear how age difference affects brain activity in the dorsolateral prefrontal cortex (DLPFC) and SMA when walking at different speeds.

Perceptual Texture Dimensions Modulate Neuronal Response Dynamics in Visual Cortical Area V4.

Texture is an important visual attribute for surface pattern discrimination and therefore object segmentation, but the neural bases of texture perception are largely unknown. Previously, we demonstrated that the responses of V4 neurons to naturalistic texture patches are sensitive to four key features of human texture perception: coarseness, directionality, regularity, and contrast. To begin to understand how distinct texture perception emerges from the dynamics of neuronal responses, in 2 macaque monkeys (1 male, 1 female), we investigated the relative contribution of the four texture attributes to V4 responses in terms of the strength and timing of response modulation.

The unbiased estimation of the fraction of variance explained by a model.

The correlation coefficient squared, r2, is commonly used to validate quantitative models on neural data, yet it is biased by trial-to-trial variability: as trial-to-trial variability increases, measured correlation to a model's predictions decreases. As a result, models that perfectly explain neural tuning can appear to perform poorly. Many solutions to this problem have been proposed, but no consensus has been reached on which is the least biased estimator.

Validation of perceived physical fatigability using the simplified-Chinese version of the Pittsburgh Fatigability Scale.

Background: The Pittsburgh Fatigability Scale (PFS) was developed to capture fatigue and demand in a single tool, filling a gap that no validated questionnaire existed to measure perceived fatigability. Since fatigability is a more sensitive measure of a person's susceptibility to fatigue, we validated the simplified-Chinese version of the PFS among Chinese community-dwelling older adults.

Methods: This cross-sectional study was conducted in an urban community in Beijing between November 2018 and July 2019.

Accounting for Biases in the Estimation of Neuronal Signal Correlation.

Signal correlation () is commonly defined as the correlation between the tuning curves of two neurons and is widely used as a metric of tuning similarity. It is fundamental to how populations of neurons represent stimuli and has been central to many studies of neural coding. Yet the classic estimate, Pearson's correlation coefficient, [Formula: see text], between the average responses of two neurons to a set of stimuli suffers from confounding biases.

A cross-sectional study of functional and metabolic changes during aging through the lifespan in male mice.

Aging is associated with distinct phenotypical, physiological, and functional changes, leading to disease and death. The progression of aging-related traits varies widely among individuals, influenced by their environment, lifestyle, and genetics. In this study, we conducted physiologic and functional tests cross-sectionally throughout the entire lifespan of male C57BL/6N mice.

Neural Coding for Shape and Texture in Macaque Area V4.

The distinct visual sensations of shape and texture have been studied separately in cortex; therefore, it remains unknown whether separate neuronal populations encode each of these properties or one population carries a joint encoding. We directly compared shape and texture selectivity of individual V4 neurons in awake macaques (1 male, 1 female) and found that V4 neurons lie along a continuum from strong tuning for boundary curvature of shapes to strong tuning for perceptual dimensions of texture. Among neurons tuned to both attributes, tuning for shape and texture were largely separable, with the latter delayed by ∼30 ms.

Modeling diverse responses to filled and outline shapes in macaque V4.

Visual area V4 is an important midlevel cortical processing stage that subserves object recognition in primates. Studies investigating shape coding in V4 have largely probed neuronal responses with filled shapes, i.e.

Of Aging Mice and Men: Gait Speed Decline Is a Translatable Trait, With Species-Specific Underlying Properties.

In the last two decades, great strides were made in our ability to extend the life span of model organisms through dietary and other manipulations. Survival curves provide evidence of altered aging processes but are uninformative on what lead to that increase in life span. Longitudinal assessments of health and function during intervention studies could help in the identification of predictive biomarkers for health and survival.

Prediagnostic markers of idiopathic Parkinson's disease: Gait, visuospatial ability and executive function.

Background: Idiopathic Parkinson's disease (IPD) has a long preclinical phase.

Research Question: This study assesses data on prediagnostic markers of IPD from a longitudinal, natural history study of aging.

Methods: Participants were selected from the database of the Baltimore Longitudinal Study of Aging, and included 10 prediagnosed IPD cases (eight men and two women) and 30 age and sex matched healthy controls.

Reduced vestibular function is associated with longer, slower steps in healthy adults during normal speed walking.

Background: Vestibular signals contribute to balance and walking. With aging, vestibular function declines and gait speed decreases. Vestibular loss contributes to decreasing gait speed, but this influence could be linked to spatial and/or temporal aspects of gait.

'Artiphysiology' reveals V4-like shape tuning in a deep network trained for image classification.

Deep networks provide a potentially rich interconnection between neuroscientific and artificial approaches to understanding visual intelligence, but the relationship between artificial and neural representations of complex visual form has not been elucidated at the level of single-unit selectivity. Taking the approach of an electrophysiologist to characterizing single CNN units, we found many units exhibit translation-invariant boundary curvature selectivity approaching that of exemplar neurons in the primate mid-level visual area V4. For some V4-like units, particularly in middle layers, the natural images that drove them best were qualitatively consistent with selectivity for object boundaries.

β-amyloid deposition is associated with gait variability in usual aging.

Background: Higher amyloid burden predicts gait slowing in aging. Whether and which gait characteristics are associated with amyloid burden is less clear. Gait variability may be more sensitive to amyloid burden than mean gait characteristics.

Relationship Between Head-Turn Gait Speed and Lateral Balance Function in Community-Dwelling Older Adults.

Objective: To determine and compare gait speed during head-forward and side-to-side head-turn walking in individuals with lower versus greater lateral balance.

Design: Cross-sectional study.

Setting: University research laboratory.

Single and multiple step balance recovery responses can be different at first step lift-off following lateral waist-pull perturbations in older adults.

An inability to recover lateral balance with a single step is predictive of future falls in older adults. This study investigated if balance stability at first step lift-off (FSLO) would be different between multiple and single stepping responses to lateral perturbations. 54 healthy older adults received left and right waist-pulls at 5 different intensities (levels 1-5).

The brain map of gait variability in aging, cognitive impairment and dementia-A systematic review.

While gait variability may reflect subtle changes due to aging or cognitive impairment (CI), associated brain characteristics remain unclear. We summarize structural and functional neuroimaging findings associated with gait variability in older adults with and without CI and dementia. We identified 17 eligible studies; all were cross-sectional; few examined multiple brain areas.

Role of Hip Abductor Muscle Composition and Torque in Protective Stepping for Lateral Balance Recovery in Older Adults.

Objectives: To examine differences in hip abductor strength and composition between older adults who primarily use medial step versus cross-step recovery strategies to lateral balance perturbations.

Design: Cross-sectional.

Setting: University research laboratory.

A Model of Binocular Motion Integration in MT Neurons.

Unlabelled: Primate cortical area MT plays a central role in visual motion perception, but models of this area have largely overlooked the binocular integration of motion signals. Recent electrophysiological studies tested binocular integration in MT and found surprisingly that MT neurons lose their hallmark "pattern motion" selectivity when stimuli are presented dichoptically and that many neurons are selective for motion-in-depth (MID). By unifying these novel observations with insights from monocular, frontoparallel motion studies concurrently in a binocular MT motion model, we generated clear, testable predictions about the circuitry and mechanisms underlying visual motion processing.

Kinematic and behavioral analyses of protective stepping strategies and risk for falls among community living older adults.

Background: Protective stepping evoked by externally applied lateral perturbations reveals balance deficits underlying falls. However, a lack of comprehensive information about the control of different stepping strategies in relation to the magnitude of perturbation limits understanding of balance control in relation to age and fall status. The aim of this study was to investigate different protective stepping strategies and their kinematic and behavioral control characteristics in response to different magnitudes of lateral waist-pulls between older fallers and non-fallers.

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.

Mechanisms for Rapid Adaptive Control of Motion Processing in Macaque Visual Cortex.

Unlabelled: A key feature of neural networks is their ability to rapidly adjust their function, including signal gain and temporal dynamics, in response to changes in sensory inputs. These adjustments are thought to be important for optimizing the sensitivity of the system, yet their mechanisms remain poorly understood. We studied adaptive changes in temporal integration in direction-selective cells in macaque primary visual cortex, where specific hypotheses have been proposed to account for rapid adaptation.