Divisive Normalization and Neuronal Oscillations in a Single Hierarchical Framework of Selective Visual Attention

Divisive normalization models of covert attention commonly use spike rate modulations as indicators of the effect of top-down attention. In addition, an increasing number of studies have shown that top-down attention increases the synchronization of neuronal oscillations as well, particularly in gamma-band frequencies (25–100 Hz). Although modulations of spike rate and synchronous oscillations are not mutually exclusive as mechanisms of attention, there has thus far been little effort to integrate these concepts into a single framework of attention. Here, we aim to provide such a unified framework by expanding the normalization model of attention with a multi-level hierarchical structure and a time dimension; allowing the simulation of a recently reported backward progression of attentional effects along the visual cortical hierarchy. A simple cascade of normalization models simulating different cortical areas is shown to cause signal degradation and a loss of stimulus discriminability over time. To negate this degradation and ensure stable neuronal stimulus representations, we incorporate a kind of oscillatory phase entrainment into our model that has previously been proposed as the “communication-through-coherence” (CTC) hypothesis. Our analysis shows that divisive normalization and oscillation models can complement each other in a unified account of the neural mechanisms of selective visual attention. The resulting hierarchical normalization and oscillation (HNO) model reproduces several additional spatial and temporal aspects of attentional modulation and predicts a latency effect on neuronal responses as a result of cued attention

Occlusion-related lateral connections stabilize kinetic depth stimuli through perceptual coupling

Local sensory information is often ambiguous forcing the brain to integrate spatiotemporally separated information for stable conscious perception. Lateral connections between clusters of similarly tuned neurons in the visual cortex are a potential neural substrate for the coupling of spatially separated visual information. Ecological optics suggests that perceptual coupling of visual information is particularly beneficial in occlusion situations. Here we present a novel neural network model and a series of human psychophysical experiments that can together explain the perceptual coupling of kinetic depth stimuli with activity-driven lateral information sharing in the far depth plane. Our most striking finding is the perceptual coupling of an ambiguous kinetic depth cylinder with a coaxially presented and disparity defined cylinder backside, while a similar frontside fails to evoke coupling. Altogether, our findings are consistent with the idea that clusters of similarly tuned far depth neurons share spatially separated motion information in order to resolve local perceptual ambiguities. The classification of far depth in the facilitation mechanism results from a combination of absolute and relative depth that suggests a functional role of these lateral connections in the perception of partially occluded objects

Suppression of parkinsonian tremor with deep brain stimulation and auditory cueing

The aim of this pilot study is to test whether the combination of DBS and auditory cueing has an enhanced effect on tremor reduction. Therefore, in a group of seven PD patients receiving STN-DBS, tremor occurrence in both hands and both feet was sequentially tested while performing repetitive movements cued by an auditory signal

Global and Local Visual Processing: Influence of Perceptual Field Variables

The Global Precedence Effect (GPE) suggests that the processing of global properties of a visual stimulus precedes the processing of local properties. The generality of this theory was argued for four decades during different known Perceptual Field Variables. The effect size of various PFVs, regarding the findings during these four decades, were pooled in our recent meta-analysis study. Pursuing the study, in the present paper, we explore the effects of Congruency, Size, and Sparsity and their interaction on global advantage in two different experiments with different task paradigms; Matching judgment and Similarity judgment. Upon results of these experiments, Congruency and Size have significant effects and Sparsity has small effects. Also, the task paradigm and its interaction with other PFVs are shown significant effects in this study, which shows the prominence of the role of task paradigms in evaluating PFVs' effects on GPE. Also, we found that the effects of these parameters were not specific to the special condition that individuals were instructed to retinal stabilize. So, the experiments were more extendible to daily human behavior

Neural activity in the rat basal ganglia

Objectives: Pathological oscillations in the beta frequencies (8-30Hz) have been found in the local field potentials of Parkinson's disease (PD) patients and non-human primate models of PD1. In particular, these synchronizations appear in the subthalamic nucleus (STN), a common target for deep brain stimulation (DBS) for medically intractable PD2. DBS and dopamine replacement therapy have been shown to reduce these oscillations and ameliorate the motor symptoms of PD. To better understand the origin and mechanisms of these synchronizations, we performed in vitro multielectrode recordings from the rat basal ganglia that support the detection of synchronous activity from numerous neurons. Methods: 300-400 μm basal ganglia slices were obtained from Wistar rats (postnatal days 15-60) using a vibratome and warmed up to room temperature in a holding chamber. The slices were transferred onto a 3D multielectrode array (Ayanda Systems) for recording and continuously perfused with carbogenated artificial cerebral spinal fluid at 36 °C. Neural signals were measured and filtered with a 60 channel amplifier (Multichannel Systems GmbH) and visualized in LabView. Action potentials were detected from the extracellular signal using a 5 standard deviation voltage threshold and sorted into different neuronal units using principal component analysis. Further signal analysis was performed in Matlab to analyze the neuronal firing patterns and measure the extent of synchronous firing. Results: Our preliminary results identified three distinct firing patterns in the STN and substantia nigra. Most neurons exhibited regular spike trains (60%) while others were random (30%) or bursty (10%). The addition of dopamine however reduced the percentage of cells with bursty and random firing patterns. Additionally, we found a very low incidence of synchronizations. Taken together, these results form the basis with which to compare firing patterns in an animal model of PD. Conclusions: Multi-electrode array recordings from the basal ganglia can reveal changes in their neurophysiological properties and measure the amount of synchronization between different neurons. We intend to use this technique to investigate pathological firing patterns in the basal ganglia in a rotenone rat model of PD. Using a combination of chemical and electrical stimulation, we will explore contributions from different nuclei of the basal ganglia to the network behavior. This would allow us to build more realistic models of the basal ganglia and lead to better therapies for PD

The effect of doorway characteristics on freezing of gait in Parkinson’s disease

Background: Freezing of gait is a debilitating symptom in Parkinson’s disease, during which a sudden motor block prevents someone from moving forward. Remarkably, doorways can provoke freezing. Most research has focused on the influence of doorway width, and little is known about other doorway characteristics influencing doorway freezing. Objective: Firstly, to provide guidelines on how to design doorways for people with freezing. Secondly, to compare people with doorway freezing to people without doorway freezing, and to explore the underlying mechanisms of doorway freezing. Methods: We designed a web-based, structured survey consisting of two parts. Part I (n = 171 responders), open to people with Parkinson’s disease with freezing in general, aimed to compare people with doorway freezing to people without doorway freezing. We explored underlying processes related to doorway freezing with the Gait-Specific Attention Profile (G-SAP), inquiring about conscious movement processes occurring during doorway passing. Part II (n = 60), open for people experiencing weekly doorway freezing episodes, inquired about the influence of specific doorway characteristics on freezing. Results: People with doorway freezing (69% of Part I) had higher freezing severity, longer disease duration, and scored higher on all sub scores of the G-SAP (indicating heightened motor, attentional, and emotional thoughts when passing through doorways) than people without doorway freezing. The main categories provoking doorway freezing were: dimensions of the door and surroundings, clutter around the door, lighting conditions, and automatic doors. Conclusion: We provide recommendations on how to maximally avoid freezing in a practical setting. Furthermore, we suggest that doorways trigger freezing based on visuomotor, attentional, and emotional processes.</p

The role of wrist-worn technology in the management of Parkinson’s disease in daily life: A narrative review

Parkinson’s disease (PD) is a neurodegenerative disorder that affects millions of people worldwide. Its slow and heterogeneous progression over time makes timely diagnosis challenging. Wrist-worn digital devices, particularly smartwatches, are currently the most popular tools in the PD research field due to their convenience for long-term daily life monitoring. While wrist-worn sensing devices have garnered significant interest, their value for daily practice is still unclear. In this narrative review, we survey demographic, clinical and technological information from 39 articles across four public databases. Wrist-worn technology mainly monitors motor symptoms and sleep disorders of patients in daily life. We find that accelerometers are the most commonly used sensors to measure the movement of people living with PD. There are few studies on monitoring the disease progression compared to symptom classification. We conclude that wrist-worn sensing technology might be useful to assist in the management of PD through an automatic assessment based on patient-provided daily living information

Synchronization of the parkinsonian globus pallidus by gap junctions

We introduce pallidal gap junctional coupling as a possible mechanism for synchronization of the GPe after dopamine depletion. In a confocal imaging study, we show the presence of the neural gap junction protein Cx36 in the human GPe, including a possible remodeling process in PD patients. Dopamine has been shown to down-regulate the conductance of gap junctions in different regions of the brain [2,3], making dopamine depletion a possible candidate for increased influence of gap junctional coupling in PD

Effect of noise on mutually inhibiting pyramidal cells in visual cortex: foundation of stochasticity in bi-stable perception

Bi-stable perception has been an important tool to investigate how visual input is interpreted and how it reaches consciousness. To explain the mechanisms of this phenomenon, it has been assumed that a mutual inhibition circuit plays a key role. It is possible that this circuit functions to resolve ambiguity of input image by quickly shifting the balance of competing signals in response to conflicting features. Recently we established an in vitro neural recording system combined with computerized connections mediated by model neurons and synapses (“dynamic clamp” system). With this system, mutual inhibition circuit between two pyramidal cells from primary visual cortex were established by model inhibitory neurons and model synapses. Simultaneous injection of depolarizing current to the two pyramidal cells caused bi-stable activities: dominance of neural activities alternated between the two neurons with an interval of several seconds. We report the effect of adding noise to the (real) pyramidal cells and the (model) inhibitory neurons. Both excitatory and inhibitory synaptic conductance noise was modelled and given to these neurons while the pyramidal cells were exhibiting bi-stable activity. The histogram of the dominant activity durations showed gamma-like skewed distributions. The skewedness was enhanced by increasing the standard deviation of the conductance noise and the durations decreased overall. While adaptation of the dominant neuron and recovery (from adaptation) of the suppressed neuron caused a decrease and increase of their excitabilities, the fluctuation of membrane potentials due to the given conductance noise appeared to facilitate the reversal of the dominance