Neurons In Parietal Cortex Research Articles

Neural effects of continuous Theta-Burst Stimulation on single neurons in macaque parietal cortex

Neural effects of continuous Theta-Burst Stimulation on single neurons in macaque parietal cortex

Small numbers are sensed directly, high numbers constructed from size and density

Two theories compete to explain how we estimate the numerosity of visual object sets. The first suggests that the apparent numerosity is derived from an analysis of more low-level features like size and density of the set. The second theory suggests that numbers are sensed directly. Consistent with the latter claim is the existence of neurons in parietal cortex which are specialized for processing the numerosity of elements in the visual scene. However, recent evidence suggests that only low numbers can be sensed directly whereas the perception of high numbers is supported by the analysis of low-level features. Processing of low and high numbers, being located at different levels of the neural hierarchy should involve different receptive field sizes. Here, I tested this idea with visual adaptation. I measured the spatial spread of number adaptation for low and high numerosities. A focused adaptation spread of high numerosities suggested the involvement of early neural levels where receptive fields are comparably small and the broad spread for low numerosities was consistent with processing of number neurons which have larger receptive fields. These results provide evidence for the claim that different mechanism exist generating the perception of visual numerosity. Whereas low numbers are sensed directly as a primary visual attribute, the estimation of high numbers however likely depends on the area size over which the objects are spread.

Stirred, Not Shaken: Motor Control with Partially Mixed Selectivity

In this issue of Neuron, Zhang etal. (2017) demonstrate that neurons in human parietal cortex represent effector responses functionally segregated, while other movement variables are associated in a subordinated fashion. Such partially mixed selectivity facilitates efficient motor control in various behavioral contexts.

Dynamic Reorganization of Neuronal Activity Patterns in Parietal Cortex

Neuronal representations change as associations are learned between sensory stimuli and behavioral actions. However, it is poorly understood whether representations for learned associations stabilize in cortical association areas or continue to change following learning. We tracked the activity of posterior parietal cortex neurons for a month as mice stably performed a virtual-navigation task. The relationship between cells' activity and task features was mostly stable on single days but underwent major reorganization over weeks. The neurons informative about task features (trial type and maze locations) changed across days. Despite changes in individual cells, the population activity had statistically similar properties each day and stable information for over a week. As mice learned additional associations, new activity patterns emerged in the neurons used for existing representations without greatly affecting the rate of change of these representations. We propose that dynamic neuronal activity patterns could balance plasticity for learning and stability for memory.

Cognition: Neurons couple up to make decisions.

The use of state-of-the-art techniques to study neuronal activity during a navigational task involving sound stimuli broadens our understanding of how neuronal populations produce complex behaviours. See Letter p.92 Information must be represented at many timescales in the cortex, from precise millisecond tracking of rapidly fluctuating inputs to seconds-long representation of behavioural choice variables. Using calcium imaging data from mice performing a virtual reality auditory decision-making task, Christopher Harvey and colleagues analyse the population codes in the primary auditory and posterior parietal cortex that support choice behaviour. Parietal cortex neurons have stronger activity correlations and carry information over longer timescales than neurons in the auditory cortex, revealing that correlation is a cortical property that enables information coding by populations over different timescales.

Selective ligands for Na+/K+-ATPase α isoforms differentially and cooperatively regulate excitability of pyramidal neurons in distinct brain regions

Sodium-potassium ATPase (NaKA) is a plasma membrane enzyme responsible for influencing membrane physiology by direct electrogenic activity. It determines cellular excitability and synaptic neurotransmission, thus affecting learning and memory processes. A principle catalytic α subunit of NaKA has development-specific expression pattern. There are two α isoforms, α1 and α3, in adult brain neurons. Although NaKA is a housekeeping enzyme, the physiological differences between these two α isoforms in different brain regions have not been well explored. Endogenous cardiotonic steroids, including Marinobufagenin and Ouabain, control the cell homeostasis and cell functions via inhibiting NaKA. Here we employed selective inhibition of α1 and α3 NaKA isoforms by Marinobufagenin and Ouabain respectively, to measure the contribution of α subunits in cellular physiology of three distinct mouse brain regions. The results of the whole cell recording demonstrated that α1 isoform predominated in layer-5 pyramidal cells at rostral motor cortex, while α3 isoform governed the pyramidal neurons at hippocampal CA1 region and to a lesser extent the layer-5 pyramidal neurons of parietal cortex. Furthermore, selective α isoform inhibition induced differential effects on distinct physiological properties even within the same brain region. In addition, our results supported the existence of synergism between two NaKA α isoforms. To conclude, this systematic study of NaKA α isoforms demonstrated their broader roles in neuronal functioning in a region-specific manner.

Reward Size Informs Repeat-Switch Decisions and Strongly Modulates the Activity of Neurons in Parietal Cortex.

Behavior is guided by previous experience. Good, positive outcomes drive a repetition of a previous behavior or choice, whereas poor or bad outcomes lead to an avoidance. How these basic drives are implemented by the brain has been of primary interest to psychology and neuroscience. We engaged animals in a choice task in which the size of a reward outcome strongly governed the animals' subsequent decision whether to repeat or switch the previous choice. We recorded the discharge activity of neurons implicated in reward-based choice in 2 regions of parietal cortex. We found that the tendency to retain previous choice following a large (small) reward was paralleled by a marked decrease (increase) in the activity of parietal neurons. This neural effect is independent of, and of sign opposite to, value-based modulations reported in parietal cortex previously. This effect shares the same basic properties with signals previously reported in the limbic system that detect the size of the recently obtained reward to mediate proper repeat-switch decisions. We conclude that the size of the obtained reward is a decision variable that guides the decision between retaining a choice or switching, and neurons in parietal cortex strongly respond to this novel decision variable.

Distinct relationships of parietal and prefrontal cortices to evidence accumulation.

Gradual accumulation of evidence is thought to be fundamental for decision-making, and its neural correlates have been found in multiple brain regions1–8. Here we develop a generalizable method to measure tuning curves that specify the relationship between neural responses and mentally-accumulated evidence, and apply it to distinguish the encoding of decision variables in posterior parietal cortex (PPC) and prefrontal cortex (frontal orienting fields, FOF). We recorded the firing rates of neurons in PPC and FOF from rats performing a perceptual decision-making task. Classical analyses uncovered correlates of accumulating evidence, similar to previous observations in primates and also similar across the two regions. However, tuning curve assays revealed that while the PPC encodes a graded value of the accumulating evidence, the FOF has a more categorical encoding that indicates, throughout the trial, the decision provisionally favored by the evidence accumulated so far. Contrary to current views3,5,7–9, this suggests that premotor activity in frontal cortex does not play a role in the accumulation process, but instead has a more categorical function, such as transforming accumulated evidence into a discrete choice. To causally probe the role of FOF activity, we optogenetically silenced it during different timepoints of the trial. Consistent with a role in committing to a categorical choice at the end of the evidence accumulation process, but not consistent with a role during the accumulation itself, a behavioral effect was observed only when FOF silencing occurred at the end of the perceptual stimulus. Our results place important constraints on the circuit logic of brain regions involved in decision-making.

Precision and neuronal dynamics in the human posterior parietal cortex during evidence accumulation

Primate studies show slow ramping activity in posterior parietal cortex (PPC) neurons during perceptual decision-making. These findings have inspired a rich theoretical literature to account for this activity. These accounts are largely unrelated to Bayesian theories of perception and predictive coding, a related formulation of perceptual inference in the cortical hierarchy. Here, we tested a key prediction of such hierarchical inference, namely that the estimated precision (reliability) of information ascending the cortical hierarchy plays a key role in determining both the speed of decision-making and the rate of increase of PPC activity. Using dynamic causal modelling of magnetoencephalographic (MEG) evoked responses, recorded during a simple perceptual decision-making task, we recover ramping-activity from an anatomically and functionally plausible network of regions, including early visual cortex, the middle temporal area (MT) and PPC. Precision, as reflected by the gain on pyramidal cell activity, was strongly correlated with both the speed of decision making and the slope of PPC ramping activity. Our findings indicate that the dynamics of neuronal activity in the human PPC during perceptual decision-making recapitulate those observed in the macaque, and in so doing we link observations from primate electrophysiology and human choice behaviour. Moreover, the synaptic gain control modulating these dynamics is consistent with predictive coding formulations of evidence accumulation.

Task-phase-specific dynamics of basal forebrain neuronal ensembles.

Cortically projecting basal forebrain neurons play a critical role in learning and attention, and their degeneration accompanies age-related impairments in cognition. Despite the impressive anatomical and cell-type complexity of this system, currently available data suggest that basal forebrain neurons lack complexity in their response fields, with activity primarily reflecting only macro-level brain states such as sleep and wake, onset of relevant stimuli and/or reward obtainment. The current study examined the spiking activity of basal forebrain neuron populations across multiple phases of a selective attention task, addressing, in particular, the issue of complexity in ensemble firing patterns across time. Clustering techniques applied to the full population revealed a large number of distinct categories of task-phase-specific activity patterns. Unique population firing-rate vectors defined each task phase and most categories of task-phase-specific firing had counterparts with opposing firing patterns. An analogous set of task-phase-specific firing patterns was also observed in a population of posterior parietal cortex neurons. Thus, consistent with the known anatomical complexity, basal forebrain population dynamics are capable of differentially modulating their cortical targets according to the unique sets of environmental stimuli, motor requirements, and cognitive processes associated with different task phases.

A latch on priming.

A latch on priming.

A slippery slope: estimated slant of hills increases with distance.

The slopes of hills tend to be greatly overestimated. Previous studies have found that slope estimates are significantly greater when estimated verbally than with a proprioceptive measure. It has yet to be determined whether these estimates are made for the entire extent of the slope, or whether the estimates in closest proximity are estimated using a different process. Since some parietal cortex neurons respond differently to objects within arm's reach, short-distance slope estimation may utilize these or analogous neurons. Alternatively, greater implied effort might make longer slopes seem steeper. We determined that both verbal and proprioceptive reports of slope are overestimates that increase logarithmically with distance from the observer, contradicting both theories. Consistent with previous work, proprioceptive estimates were more accurate at all ranges. Our results can be interpreted as a function of the angle between the observer's gaze and the plane of the hill, modified by depth cues available at only near distances.

Eye-Centered Representation of Optic Flow Tuning in the Ventral Intraparietal Area

Reference frames are important for understanding sensory processing in the cortex. Previous work showed that vestibular heading signals in the ventral intraparietal area (VIP) are represented in body-centered coordinates. In contrast, vestibular heading tuning in the medial superior temporal area (MSTd) is approximately head centered. We considered the hypothesis that visual heading signals (from optic flow) in VIP might also be transformed into a body-centered representation, unlike visual heading tuning in MSTd, which is approximately eye centered. We distinguished among eye-centered, head-centered, and body-centered spatial reference frames by systematically varying both eye and head positions while rhesus monkeys viewed optic flow stimuli depicting various headings. We found that heading tuning of VIP neurons based on optic flow generally shifted with eye position, indicating an eye-centered spatial reference frame. This is similar to the representation of visual heading signals in MSTd, but contrasts sharply with the body-centered representation of vestibular heading signals in VIP. These findings demonstrate a clear dissociation between the spatial reference frames of visual and vestibular signals in VIP, and emphasize that frames of reference for neurons in parietal cortex can depend on the type of sensory stimulation.

Body-Centered, Mixed, but not Hand-Centered Coding of Visual Targets in the Medial Posterior Parietal Cortex During Reaches in 3D Space

The frames of reference used by neurons in posterior parietal cortex (PPC) to encode spatial locations during arm reaching movements is a debated topic in modern neurophysiology. Traditionally, target location, encoded in retinocentric reference frame (RF) in caudal PPC, was assumed to be serially transformed to body-centered and then hand-centered coordinates rostrally. However, recent studies suggest that these transformations occur within a single area. The caudal PPC area V6A has been shown to represent reach targets in eye-centered, body-centered, and a combination of both RFs, but the presence of hand-centered coding has not been yet investigated. To examine this issue, 141 single neurons were recorded from V6A in 2 Macaca fascicularis monkeys while they performed a foveated reaching task in darkness. The targets were presented at different distances and lateralities from the body and were reached from initial hand positions located at different depths. Most V6A cells used body-centered, or mixed body- and hand-centered coordinates. Only a few neurons used pure hand-centered coordinates, thus clearly distinguishing V6A from nearby PPC regions. Our findings support the view of a gradual RF transformation in PPC and also highlight the impact of mixed frames of reference.

The amount and composition of monkey parietal cortex neurons that are active during functionally different behaviors

The amount and composition of monkey parietal cortex neurons that are active during functionally different behaviors

Structural and Histochemical Changes in Rat Parietal Cortex Neurons during Biliary Drainage

The aim of the study reported here was to assess structural and metabolic changes in rat parietal cortex neurons during complete external bile drainage. Quantitative histochemical and electron microscopic methods were used. The findings showed that drainage of bile from the body led to gradual increases in the numbers of hyperchromic pyknotic neurons and ghost cells, death and reductions in the numbers of neurons, and increases in the number of glial cells in all layers of the parietal cortex. There was a gradual decrease in neuron size, with loss of sphericity (elongation). The cytoplasm showed decreases in succinate dehydrogenase, NADH, NADPH, and glucose-6-phosphate dehydrogenases, and decreases in RNA content, though these changes were accompanied by activation of lactate dehydrogenase and acid phosphatase. Nuclei and organelles (mitochondria, endoplasmic reticulum, Golgi complexes) underwent destructive changes, which were accompanied by increase in the numbers and sizes of lysosomes and phagosomes. Some neurons showed activation of the nuclear apparatus and increases in the relative content of free ribosomes. Thus, loss of bile from the body induced progressive increases in structural and metabolic changes in parietal cortex neurons, leading to the death of some and compensatory changes in others.

Multisensory and unisensory neurons in ferret parietal cortex exhibit distinct functional properties

Despite the fact that unisensory and multisensory neurons are comingled in every neural structure in which they have been identified, no systematic comparison of their response features has been conducted. Towards that goal, the present study was designed to examine and compare measures of response magnitude, latency, duration and spontaneous activity in unisensory and bimodal neurons from the ferret parietal cortex. Using multichannel single-unit recording, bimodal neurons were observed to demonstrate significantly higher response levels and spontaneous discharge rates than did their unisensory counterparts. These results suggest that, rather than merely reflect different connectional arrangements, unisensory and multisensory neurons are likely to differ at the cellular level. Thus, it can no longer be assumed that the different populations of bimodal and unisensory neurons within a neural region respond similarly to a given external stimulus.

Neural Mechanisms of Speed-Accuracy Tradeoff

Intelligent agents balance speed of responding withaccuracy of deciding. Stochastic accumulator models commonly explain this speed-accuracy tradeoff by strategic adjustment of response threshold. Several laboratories identify specific neurons in prefrontal and parietal cortex with this accumulation process, yet no neurophysiological correlates of speed-accuracy tradeoff have been described. We trained macaque monkeys to trade speed for accuracy on cue during visual search and recorded the activity of neurons in the frontal eye field. Unpredicted by any model, we discovered that speed-accuracy tradeoff is accomplished through several distinct adjustments. Visually responsive neurons modulated baseline firing rate, sensory gain, and the duration of perceptual processing. Movement neurons triggered responses with activity modulated in a direction opposite of model predictions. Thus, current stochastic accumulator models provide an incomplete description of the neural processes accomplishing speed-accuracy tradeoffs. The diversity of neural mechanisms was reconciled with the accumulator framework through an integrated accumulator model constrained by requirements of the motor system.

Neuroprotective effect of erythropoietin on nandrolone decanoate-induced brain injury in rats

Anabolic–androgenic steroids (AAS) are used in the medical treatment of many disorders. Erythropoietin (EPO) is a hematopoietic cytokine that has anti-apoptotic, anti-oxidative, and anti-inflammatory effects. The aim of the present study is to investigate the neuroprotective effects of EPO in the hippocampus, parietal cortex and prefrontal cortex, in brain damage due to nandrolone decanoate. 35 Wistar male rats were randomly divided into: (1) control group, (2) sham group, (3) nandrolone decanoate group (ND, intramuscular, 10mg/(kgweek), 8 weeks), (4) ND+low dose EPO treated group (ND+L-EPO) and (5) ND+high dose EPO treated group (ND+H-EPO). EPO was administrated by intraperitoneal injection at a dose of 100U/(kgday) for L-EPO treatment and at a dose of 500U/(kgday) for H-EPO treatment during 8 weeks. The number of neurons of CA1, CA2, CA3 and dentate gyrus of hippocampus, parietal cortex and prefrontal cortex were significantly less in the ND group compared with the control group. Treatment with H-EPO significantly preserved the number of neurons in hippocampus when compared with ND administrated. Besides, H-EPO treatment decreased the number of TUNEL-positive and active caspase-3 positive cells and MDA levels and increased GPx levels when compared to ND group. In conclusion, abuse of AAS causes reduction in the number of neurons in hippocampus, parietal cortex and prefrontal cortex regions and increases oxidative damage and therefore H-EPO may be useful as a neuroprotective agent in brain injury.

Neural Dynamics of Choice: Single-Trial Analysis of Decision-Related Activity in Parietal Cortex

Previous neurophysiological studies of perceptual decision-making have focused on single-unit activity, providing insufficient information about how individual decisions are accomplished. For the first time, we recorded simultaneously from multiple decision-related neurons in parietal cortex of monkeys performing a perceptual decision task and used these recordings to analyze the neural dynamics during single trials. We demonstrate that decision-related lateral intraparietal area neurons typically undergo gradual changes in firing rate during individual decisions, as predicted by mechanisms based on continuous integration of sensory evidence. Furthermore, we identify individual decisions that can be described as a change of mind: the decision circuitry was transiently in a state associated with a different choice before transitioning into a state associated with the final choice. These changes of mind reflected in monkey neural activity share similarities with previously reported changes of mind reflected in human behavior.