Context-dependent spatially periodic activity in the human entorhinal cortex.

The spatially periodic activity of grid cells in the entorhinal cortex (EC) of the rodent, primate, and human provides a coordinate system that, together with the hippocampus, informs an individual of its location relative to the environment and encodes the memory of that location. Among the most defining features of grid-cell activity are the 60° rotational symmetry of grids and preservation of grid scale across environments. Grid cells, however, do display a limited degree of adaptation to environments. It remains unclear if this level of environment invariance generalizes to human grid-cell analogs, where the relative contribution of visual input to the multimodal sensory input of the EC is significantly larger than in rodents. Patients diagnosed with nontractable epilepsy who were implanted with entorhinal cortical electrodes performing virtual navigation tasks to memorized locations enabled us to investigate associations between grid-like patterns and environment. Here, we report that the activity of human entorhinal cortical neurons exhibits adaptive scaling in grid period, grid orientation, and rotational symmetry in close association with changes in environment size, shape, and visual cues, suggesting scale invariance of the frequency, rather than the wavelength, of spatially periodic activity. Our results demonstrate that neurons in the human EC represent space with an enhanced flexibility relative to neurons in rodents because they are endowed with adaptive scalability and context dependency.

Driving stroke quality improvement at scale in EDs across a nationwide network of hospitals: strategies and interventions.

OBJECTIVES: Reducing the treatment time while increasing the proportion of eligible stroke patients who receive intravenous tissue plasminogen activator (tPA) has been a priority for many quality improvement efforts. Recent studies have primarily focused on identifying interventions that reduce door-to-needle (DTN) time, while comparatively little has been done to determine whether these interventions also improve tPA rates. METHODS: In order to investigate interventions related to process improvements, an electronic dashboard serving as a stroke performance tool was implemented to store and retrieve patient outcome data. These data were used to study the efficacy of interventions designed to facilitate triage of stroke patients in the ED, and determine the individual interventions associated with the most significant improvements in the fraction of patients receiving tPA and in reducing the DTN time. Stroke performance data from the dashboard collected over a 2-year period (2015-2017) from 89 US hospitals were analysed with respect to interventions implemented by individual facilities, as verified by a hospital survey. RESULTS: A statistically significant association was found between increases in the fraction of patients receiving tPA and reductions in DTN time over the study period. These improvements in outcomes were most strongly associated with process interventions that allocate stroke-specific physical and human resources in the ED, most notably a designated emergency room space for stroke, and with workflows that decrease the time to key checkpoints for determining a patient's eligibility for tPA. CONCLUSIONS: Data from the stroke performance tool was leveraged to identify the programmes and process interventions that lead to improved patient outcomes and allow EDs to better prioritise process interventions and resources.

Higher Incidence of Ischemic Stroke in Patients Taking Novel Oral Anticoagulants.

Background and Purpose- The increased use of novel oral anticoagulants (NOACs) to control atrial fibrillation is largely driven by the assumption that they are equally effective as warfarin at preventing ischemic stroke while putting patients at lower risk of hemorrhages. To test this hypothesis, a retrospective study of the relative incidence of strokes among patients taking NOACs versus those taking warfarin is performed. Methods- Relative stroke incidence in the 2 groups of patients was compared using odds ratios and Fisher exact tests for significance using a data set of 71 365 on NOACs and 59 546 patients on warfarin. In addition, the 7033 patients with a record of both warfarin and NOAC use were analyzed as a separate cohort. Results- There is a significantly higher (odds ratio=1.29, <0.001) frequency of ischemic strokes among patients prescribed NOACs compared with those on warfarin. The relative frequency of ischemic strokes was also higher for every individual NOAC compared with warfarin (these higher frequencies are statistically significant for dabigatran and apixaban, though not for edoxaban and rivaroxaban). There is a lower incidence of intracranial hemorrhages and nontraumatic hemorrhages in general among patients taking NOACs, consistent with the published literature. Comparisons of the demographic and clinical profiles of the patients taking NOACs to those on warfarin do not show significantly higher background stroke risk in NOAC patients; in fact, patients on NOACs tend to be at lower background risk overall for ischemic strokes. Conclusions- Because NOAC use is associated with higher ischemic stroke risk together with a lower risk of hemorrhages than warfarin use, it can be concluded that patients on warfarin are more strongly anticoagulated. The observed effect could be a secondary consequence of dosage control or alternatively a result of different anticoagulant effects among the different medications.

In vivo measurements of limbic glutamate and GABA concentrations in epileptic patients during affective and cognitive tasks: A microdialysis study.

Limbic system structures such as the amygdala (AMG) and the hippocampus (HIPP) are involved in affective and cognitive processing. However, because of the limitations in noninvasive technology, absolute concentrations of the neurotransmitters underlying limbic system engagement are not known. Here, we report changes in the concentrations of the neurotransmitters glutamate (Glu) and gamma-aminobutyric acid (GABA) in the HIPP and the AMG of patients with nonlesional temporal lobe epilepsy undergoing surgery for intracranial subdural and depth electrode implantation. We utilized an in-vivo microdialysis technique while subjects were engaged in cognitive tasks with or without emotional content. The performance of an emotion learning task (EmoLearn) was associated with a significant increase in the concentration of glutamate in the HIPP when images with high valence content were processed, as compared to its concentration while processing images with low valence. In addition, significantly decreased levels of glutamate were found in the AMG when images with predominantly low valence content were processed, as compared to its concentration at baseline. The processing of face stimuli with anger/fear content (FaceMatch task) was accompanied with significantly decreased concentrations of GABA in the AMG and HIPP compared to its levels at the baseline. The processing of shapes on the other hand was accompanied with a significantly decreased concentration of the glutamate in the AMG as well as in the HIPP compared to the baseline. Finally, the performance of a nondeclarative memory task (weather prediction task-WPT) was associated with relatively large and opposite changes in the GABA levels compared to the baseline in the AMG (decrease) and the HIPP (increase). These data are relevant for showing an involvement of the amygdala and the hippocampus in emotional processing and provide additional neurochemical clues towards a more refined model of the functional circuitry of the human limbic system.

Neurons in the basal forebrain project to the cortex in a complex topographic organization that reflects corticocortical connectivity patterns: an experimental study based on retrograde tracing and 3D reconstruction.

The most prominent feature of the Basal Forebrain (BF) is the collection of large cortically projecting neurons (basal nucleus of Meynert) that serve as the primary source of cholinergic input to the entire cortical mantle. Despite its broad involvement in cortical activation, attention, and memory, the functional details of the BF are not well understood due to the anatomical complexity of the region. This study tested the hypothesis that basalocortical connections reflect cortical connectivity patterns. Distinct retrograde tracers were deposited into various frontal and posterior cortical areas, and retrogradely labeled cholinergic and noncholinergic neurons were mapped in the BF. Concurrently, we mapped retrogradely labeled cells in posterior cortical areas that project to various frontal areas, and all cell populations were combined in the same coordinate system. Our studies suggest that the cholinergic and noncholinergic projections to the neocortex are not diffuse, but instead, are organized into segregated or overlapping pools of projection neurons. The extent of overlap between BF populations projecting to the cortex depends on the degree of connectivity between the cortical targets of these projection populations. We suggest that the organization of projections from the BF may enable parallel modulation of multiple groupings of interconnected yet nonadjacent cortical areas.

Event as the central construal of psychological time in humans.

Time is a fundamental dimension of our perception and mental construction of reality. It enables resolving changes in our environment without a direct sensory representation of elapsed time. Therefore, the concept of time is inferential by nature, but the units of subjective time that provide meaningful segmentation of the influx of sensory input remain to be determined. In this review, we posit that events are the construal instances of time perception as they provide a reproducible and consistent segmentation of the content. In that light, we discuss the implications of this proposal by looking at "events" and their role in subjective time experience from cultural anthropological and ontogenetic perspectives, as well as their relevance for episodic memory. Furthermore, we discuss the significance of "events" for the two critical aspects of subjective time-duration and order. Because segmentation involves parsing event streams according to causal sequences, we also consider the role of causality in developing the concept of directionality of mental timelines. We offer a fresh perspective on representing past and future events before age 5 by an egocentric bi-directional timeline model before acquiring the allocentric concept of absolute time. Finally, we illustrate how the relationship between events and durations can resolve contradictory experimental results. Although "time" warrants a comprehensive interdisciplinary approach, we focus this review on "time perception", the experience of time, without attempting to provide an all encompassing overview of the rich philosophical, physical, psychological, cognitive, linguistic, and neurophysiological context.

Functional architecture of the forebrain cholinergic system in rodents.

The basal forebrain cholinergic system (BFCS) participates in functions that are global across the brain, such as sleep-wake cycles, but also participates in capacities that are more behaviorally and anatomically specific, including sensory perception. To better understand the underlying organization principles of the BFCS, more and higher quality anatomical data and analysis is needed. Here, we created a "virtual Basal Forebrain", combining data from numerous rats with cortical retrograde tracer injections into a common 3D reference coordinate space and developed a "spatial density correlation" methodology to analyze patterns in BFCS cortical projection targets, revealing that the BFCS is organized into three principal networks: somatosensory-motor, auditory, and visual. Within each network, clusters of cholinergic cells with increasing complexity innervate cortical targets. These networks represent hierarchically organized building blocks that may enable the BFCS to coordinate spatially selective signaling, including parallel modulation of multiple functionally interconnected yet diverse groups of cortical areas.

Children and adults rely on different heuristics for estimation of durations.

Time is a uniquely human yet culturally ubiquitous concept acquired over childhood and provides an underlying dimension for episodic memory and estimating durations. Because time, unlike distance, lacks a sensory representation, we hypothesized that subjects at different ages attribute different meanings to it when comparing durations; pre-kindergarten children compare the density of events, while adults use the concept of observer-independent absolute time. We asked groups of pre-kindergarteners, school-age children, and adults to compare the durations of an "eventful" and "uneventful" video, both 1-minute long but durations unknown to subjects. In addition, participants were asked to express the durations of both videos non-verbally with simple hand gestures. Statistical analysis has revealed highly polarized temporal biases in each group, where pre-kindergarteners estimated the duration of the eventful video as "longer." In contrast, the school-age group of children and adults claimed the same about the uneventful video. The tendency to represent temporal durations with a horizontal hand gesture was evident among all three groups, with an increasing prevalence with age. These results support the hypothesis that pre-kindergarten-age children use heuristics to estimate time, and they convert from availability to sampling heuristics between pre-kindergarten and school age.

Phase coding of spatial representations in the human entorhinal cortex.

The grid-like activity pattern of cells in the mammalian entorhinal cortex provides an internal reference frame for allocentric self-localization. The same neurons maintain robust phase couplings with local field oscillations. We found that neurons of the human entorhinal cortex display consistent spatial and temporal phase locking between spikes and slow gamma band local field potentials (LFPs) during virtual navigation. The phase locking maintained an environment-specific map over time. The phase tuning of spikes to the slow gamma band LFP revealed spatially periodic phase grids with environment-dependent scaling and consistent alignment with the environment. Using a Bayesian decoding model, we could predict the avatar's position with near perfect accuracy and, to a lesser extent, that of heading direction as well. These results imply that the phase of spikes relative to spatially modulated gamma oscillations encode allocentric spatial positions. We posit that a joint spatiotemporal phase code can implement the combined neural representation of space and time in the human entorhinal cortex.

Persistent dynamic attractors in activity patterns of cultured neuronal networks.

Three remarkable features of the nervous system--complex spatiotemporal patterns, oscillations, and persistent activity--are fundamental to such diverse functions as stereotypical motor behavior, working memory, and awareness. Here we report that cultured cortical networks spontaneously generate a hierarchical structure of periodic activity with a strongly stereotyped population-wide spatiotemporal structure demonstrating all three fundamental properties in a recurring pattern. During these "superbursts," the firing sequence of the culture periodically converges to a dynamic attractor orbit. Precursors of oscillations and persistent activity have previously been reported as intrinsic properties of the neurons. However, complex spatiotemporal patterns that are coordinated in a large population of neurons and persist over several hours--and thus are capable of representing and preserving information--cannot be explained by known oscillatory properties of isolated neurons. Instead, the complexity of the observed spatiotemporal patterns implies large-scale self-organization of neurons interacting in a precise temporal order even in vitro, in cultures usually considered to have random connectivity.

Glutamate and GABA concentration changes in the globus pallidus internus of Parkinson's patients during performance of implicit and declarative memory tasks: a report of two subjects.

The basal ganglia, typically associated with motor function, are involved in human cognitive processes, as demonstrated in behavioral, lesion, and noninvasive functional neuroimaging studies. Here we report task-contingent changes in concentrations of the neurotransmitters glutamate (Glu) and gamma-aminobutyric acid (GABA) in the globus pallidus internus (GPi) of two patients with Parkinson's disease undergoing deep brain stimulation surgery by utilizing in-vivo microdialysis measurements during performance of implicit and declarative memory tasks. Performance of an implicit memory task (weather prediction task-WPT) was associated with increased levels of glutamate and GABA in the GPi compared to their concentrations at baseline. On the other hand, performance of a declarative memory task (verbal learning task-VLT) was associated with decreased levels of glutamate and GABA in GPi compared to baseline during the encoding and immediate recall phase with less conclusive results during the delayed recall phase. These results are in line with hypothesized changes in these neurotransmitter levels: an increase of excitatory (Glu) input from subthalamic nucleus (STN) to GPi during implicit memory task performance and a decrease of inhibitory inputs (GABA) from globus pallidus externus (GPe) and striatum to GPi during declarative memory performance. Consistent with our previous report on in-vivo neurotransmitter changes during tasks in STN, these data provide corroborative evidence for the direct involvement of basal ganglia in cognitive functions and complements our model of the functional circuitry of basal ganglia in the healthy and Parkinson's disease affected brain.

Intersection of microwire electrodes with proximal CA1 stratum-pyramidale neurons at insertion for multiunit recordings predicted by a 3-D computer model.

It is of broad interest in the context of neuronal multiunit extracellular recordings to understand electrode-tissue interactions in order to maximize the number of recordable units and to minimize experimental artifacts due to mechanical tissue alteration. Toward this goal, a computer model of microwire electrode insertion in hippocampus CA1 area was developed, firstly to provide estimates of the number of electrode-neuron intersections affecting recordable (local) neurons and, secondly, to determine optimal insertion/electrode parameters that minimize the number of intersections. The model predicts that in hippocampus CA1 area, using an electrode 50 microm in diameter, only 10% of the recordable neurons (those within 50 microm of the electrode), would remain collision free. Moreover, the model also predicts that inhibitory neurons are less prone to be intersected by the electrode, resulting in a 2 to threefold higher percentage of collision-free interneurons than expected from the relative densities of pyramidal cells and interneurons. Furthermore, the model confirms, in agreement with experimental observations, that electrode tilting with respect to the main neuronal axis increases the number of intact neurons (fourfold for a 50-microm electrode at 45 degrees when compared to 0 degrees , i.e., an insertion normal to the cell body layer).

Motor cortex stimulation for neuropathic pain syndromes: a case series experience.

Neuropathic pain is a chronic condition lacking effective management and responding poorly to standard treatment protocols. Motor cortex stimulation has emerged as a new and promising therapeutic tool with outcomes potentially affected by the specific causes and location. In this study we report a series of eight cases in the neurosurgery practice of one of the authors (R.J.B.), including neuropathic pain syndromes of trigeminal or thalamic origin with or without anesthesia dolorosa. Pain relief was evaluated on the basis of comparison of Visual Analog scores at baseline and at 3 months after surgery. In addition, we assessed differences in pain relief outcomes between cases with trigeminal neuralgia and thalamic stroke, as well as cases with or without anesthesia dolorosa (i.e. pain with numbness of the affected area). Visual Analog Scale scores showed a statistically significant decrease of 4.19 (P=0.002) at 3 months follow-up compared with baseline. Pain relief levels in four of five patients in the subgroup with facial pain were higher than 50%, and none of the patients in the subgroup with thalamic and phantom limb pain showed such a good outcome. Furthermore, we found larger pain relief levels in facial pain conditions with versus without anesthesia dolorosa. These results point to utility of motor cortex stimulation in relieving neuropathic pain, as well as better outcomes for patients with facial pain and anesthesia dolorosa. Future studies should incorporate methods to noninvasively trial those patients who may benefit from surgical implantation to predict the outcomes and maximize their negative predictive value.

Reference frames in virtual spatial navigation are viewpoint dependent.

Spatial navigation in the mammalian brain relies on a cognitive map of the environment. Such cognitive maps enable us, for example, to take the optimal route from a given location to a known target. The formation of these maps is naturally influenced by our perception of the environment, meaning it is dependent on factors such as our viewpoint and choice of reference frame. Yet, it is unknown how these factors influence the construction of cognitive maps. Here, we evaluated how various combinations of viewpoints and reference frames affect subjects' performance when they navigated in a bounded virtual environment without landmarks. We measured both their path length and time efficiency and found that (1) ground perspective was associated with egocentric frame of reference, (2) aerial perspective was associated with allocentric frame of reference, (3) there was no appreciable performance difference between first and third person egocentric viewing positions and (4) while none of these effects were dependent on gender, males tended to perform better in general. Our study provides evidence that there are inherent associations between visual perspectives and cognitive reference frames. This result has implications about the mechanisms of path integration in the human brain and may also inspire designs of virtual reality applications. Lastly, we demonstrated the effective use of a tablet PC and spatial navigation tasks for studying spatial and cognitive aspects of human memory.

Changes in GABA and glutamate concentrations during memory tasks in patients with Parkinson's disease undergoing DBS surgery.

Until now direct neurochemical measurements during memory tasks have not been accomplished in the human basal ganglia. It has been proposed, based on both functional imaging studies and psychometric testing in normal subjects and in patients with Parkinson's disease (PD), that the basal ganglia is responsible for the performance of feedback-contingent implicit memory tasks. To measure neurotransmitters, we used in vivo microdialysis during deep brain stimulation (DBS) surgery. We show in the right subthalamic nucleus (STN) of patients with PD a task-dependent change in the concentrations of glutamate and GABA during an implicit memory task relative to baseline, while no difference was found between declarative memory tasks. The five patients studied had a significant decrease in the percent concentration of GABA and glutamate during the performance of the weather prediction task (WPT). We hypothesize, based on current models of basal ganglia function, that this decrease in the concentration is consistent with expected dysfunction in basal ganglia networks in patients with PD.

Binding by asynchrony: the neuronal phase code.

Neurons display continuous subthreshold oscillations and discrete action potentials (APs). When APs are phase-locked to the subthreshold oscillation, we hypothesize they represent two types of information: the presence/absence of a sensory feature and the phase of subthreshold oscillation. If subthreshold oscillation phases are neuron-specific, then the sources of APs can be recovered based on the AP times. If the spatial information about the stimulus is converted to AP phases, then APs from multiple neurons can be combined into a single axon and the spatial configuration reconstructed elsewhere. For the reconstruction to be successful, we introduce two assumptions: that a subthreshold oscillation field has a constant phase gradient and that coincidences between APs and intracellular subthreshold oscillations are neuron-specific as defined by the "interference principle." Under these assumptions, a phase-coding model enables information transfer between structures and reproduces experimental phenomenons such as phase precession, grid cell architecture, and phase modulation of cortical spikes. This article reviews a recently proposed neuronal algorithm for information encoding and decoding from the phase of APs (Nadasdy, 2009). The focus is given to the principles common across different systems instead of emphasizing system specific differences.

Clustering of large cell populations: method and application to the basal forebrain cholinergic system.

Functionally related groups of neurons spatially cluster together in the brain. To detect groups of functionally related neurons from 3D histological data, we developed an objective clustering method that provides a description of detected cell clusters that is quantitative and amenable to visual exploration. This method is based on bubble clustering (Gupta and Ghosh, 2008). Our implementation consists of three steps: (i) an initial data exploration for scanning the clustering parameter space; (ii) determination of the optimal clustering parameters; and (iii) final clustering. We designed this algorithm to flexibly detect clusters without assumptions about the underlying cell distribution within a cluster or the number and sizes of clusters. We implemented the clustering function as an integral part of the neuroanatomical data visualization software Virtual RatBrain (http://www.virtualratbrain.org). We applied this algorithm to the basal forebrain cholinergic system, which consists of a diffuse but inhomogeneous population of neurons (Zaborszky, 1992). With this clustering method, we confirmed the inhomogeneity in this system, defined cell clusters, quantified and localized them, and determined the cell density within clusters. Furthermore, by applying the clustering method to multiple specimens from both rat and monkey, we found that cholinergic clusters display remarkable cross-species preservation of cell density within clusters. This method is efficient not only for clustering cell body distributions but may also be used to study other distributed neuronal structural elements, including synapses, receptors, dendritic spines and molecular markers.

Information encoding and reconstruction from the phase of action potentials.

Fundamental questions in neural coding are how neurons encode, transfer, and reconstruct information from the pattern of action potentials (APs) exchanged between different brain structures. We propose a general model of neural coding where neurons encode information by the phase of their APs relative to their subthreshold membrane oscillations. We demonstrate by means of simulations that AP phase retains the spatial and temporal content of the input under the assumption that the membrane potential oscillations are coherent across neurons and between structures and have a constant spatial phase gradient. The model explains many unresolved physiological observations and makes a number of concrete, testable predictions about the relationship between APs, local field potentials, and subthreshold membrane oscillations, and provides an estimate of the spatio-temporal precision of neuronal information processing.

Temporally precise cortical firing patterns are associated with distinct action segments.

Despite many reports indicating the existence of precise firing sequences in cortical activity, serious objections have been raised regarding the statistics used to detect them and the relations of these sequences to behavior. We show that in behaving monkeys, pairs of spikes from different neurons tend to prefer certain time delays when measured in relation to a specific behavior. Single-unit activity was recorded from eight microelectrodes inserted into the motor and premotor cortices of two monkeys while they were performing continuous drawinglike hand movements. Repeated scribbling paths, termed drawing components, were extracted by data-mining techniques. The set of the least predictable relations between drawing components and pairs of neurons was determined and represented by one statistic termed the relations score. The chance probability of the relations score was evaluated by teetering the spike times: 1,000 surrogates were generated by randomly teetering the original time of each spike in a small window. In nine of 13 experimental days the precision was better than 12 ms and, in the best case, spike precision reached 0.5 ms.