Biology subjects

Kass, R. E.

Publications and source records attributed to Kass, R. E..

5 recordsLinked to original sources

bioRxiv2026

A Population Coupling Model Identifies Reduced Propagation from V1 to Higher Visual Areas During Locomotion

Point process generalized linear models (GLMs) have been a major tool for studying coordinated activity across populations of neurons. These models typically quantify how the spiking of a single neuron depends on the past activity of other neurons at multiple time lags, and the resulting neuron-to-neuron interactions are then aggregated to obtain population-coupling effects. However, when neurons within the same population exhibit similar spiking patterns, explicitly modeling individual interactions can be redundant and can unnecessarily increase model complexity. In such cases, population-level formulations may offer a more efficient alternative. For example, biophysical population models often characterize circuit dynamics using the average firing rate across neurons within a population, and recent data-driven approaches have similarly demonstrated the utility of population-level statistics for capturing cross-population interactions. Motivated by this consideration, we reformulate the GLM framework to operate directly at the population level. The resulting model, which we call pop-GLM, provides a computationally efficient method for estimating coupling between populations. In a simulated dataset, we show that pop-GLM achieves greater sensitivity in detecting coupling effects and can account for trial-to-trial variation in stimulus drive, which would otherwise introduce bias. We also note that moving from single-neuron to population-level modeling requires a specific modification of the traditional GLM framework. We then apply pop-GLM to real data and find reduced functional connectivity from primary visual cortex (V1) to a higher visual area during locomotion, a change not detected by single-neuron GLMs.

neuroscience↗

bioRxiv2025

Relative timing and coupling of neural population bursts in large-scale recordings from multiple neuron populations

The onset of a sensory stimulus elicits transient bursts of activity in neural populations, which are presumed to convey information about the stimulus to downstream populations. The time at which these synchronized bursts reach their peak is highly variable across stimulus presentations, but the relative timing of bursts across interconnected brain regions may be less variable, especially for regions that are strongly functionally coupled. We developed a simple analytical framework that obtains good estimates of population burst times on a trial-by-trial basis, and of the correlations in the timing of evoked population bursts across areas. We show that this method performs well on simulated data, and is 85 to 90% faster than an alternative, recently-published method while also being much easier to apply. Using this new approach, we examined the relative timing of the first two population bursts following the onset of a drifting grating stimulus in large-scale recordings of spiking activity from six cortical visual areas and one visual thalamic nucleus in thirteen mice. The new method allowed us to identify mouse-to-mouse variation in peak times and region-to-region functional coupling. While all results were consistent with known anatomy and physiology, we found some sequences of activity across areas to be the same across all mice, while others varied with the individual. The general approach can thus produce sensitive analyses of timing relationships across neural populations. Significant StatementCareful analysis can reveal strong and precisely-timed interactions across multiple brain areas from small populations of spiking neurons. We developed a computationally efficient procedure that allowed us to examine the relative timing and coupling of 7 visual areas (6 cortical and one thalamic) and compare results in over 10 mice. The method can be used to track the flow of information across the brain in response to stimuli or during a behavioral task.

neuroscience↗

bioRxiv2018

Exploring spatio-temporal neural dynamics of the human visual cortex

The human visual cortex is organized in a hierarchical manner. Although a significant body of evidence has been accumulated in support of this hypothesis, specific details regarding the spatial and temporal information flow remain open. Here we present detailed spatio-temporal correlation profiles of neural activity with low-level and high-level features derived from a \"deep\" (8-layer) neural network pre-trained for object recognition. These correlation profiles indicate an early-to-late shift from low-level features to high-level features and from low-level regions to higher-level regions along the visual hierarchy, consistent with feedforward information flow. To refine our understanding of information flow, we computed three sets of features from the low-and high-level features provided by the neural network: object-category-relevant low-level features (the common components between low-level and high-level features), low-level features roughly orthogonal to high-level features (the residual Layer 1 features), and unique high-level features that were roughly orthogonal to low-level features (the residual Layer 7 features). Contrasting the correlation effects of the common components and the residual Layer 1 features, we observed that the early visual cortex exhibits a similar amount of correlation with the two feature sets early in time (60 to 120 ms), but in a later time window, the early visual cortex exhibits a higher and longer correlation effect with the common components/low-level task-relevant features as compared to the low-level residual features--an effect unlikely to arise from purely feedforward information flow. Overall, our results indicate that non-feedforward processes, for example, top-down influences from mental representations of categories, may facilitate differentiation between these two types of low-level features within the early visual cortex.

neuroscience↗

bioRxiv2016

Inter-Subject Alignment of MEG Datasets at the Neural Representational Space

Pooling neural imaging data across subjects requires aligning recordings from different subjects. In magnetoencephalography (MEG) recordings, sensors across subjects are poorly correlated both because of differences in the exact location of the sensors, and structural and functional differences in the brains. It is possible to achieve alignment by assuming that the same regions of different brains correspond across subjects. However, this relies on both the assumption that brain anatomy and function are well correlated, and the strong assumptions that go into solving the underdetermined inverse problem given the high dimensional source space. In this paper, we investigated an alternative method that bypasses source-localization. Instead, it analyzes the sensor recordings themselves and aligns their temporal signatures across subjects. We used a multivariate approach, multi-set canonical correlation analysis (M-CCA), to transform individual subject data to a low dimensional common representational space. We evaluated the robustness of this approach over a synthetic dataset, by examining the effect of different factors that add to the noise and individual differences in the data. On a MEG dataset, we demonstrated that M-CCA performs better than a method that assumes perfect sensor correspondence and a method that applies source localization. Lastly, we described how the standard M-CCA algorithm could be further improved with a regularization term that incorporates spatial sensor information.

neuroscience↗

bioRxiv2016

Ventral tegmental area neurons use an ensemble code for representing information about ongoing actions

Multiple and unpredictable numbers of actions are often required to achieve a goal. In order to organize behavior and allocate effort so that optimal behavioral policies can be selected, it is necessary to continually monitor ongoing actions. Real-time processing of information related to actions and outcomes is typically assigned to the prefrontal cortex and basal ganglia, but also depends on midbrain regions, especially the ventral tegmental area (VTA). We were interested in how individual VTA neurons, as well as networks within the VTA, encode salient events when an unpredictable number of serial actions are required to obtain a reward. We recorded from ensembles of putative dopamine and non-dopamine neurons in the VTA as animals performed multiple cued trials in a recording session where, in each trial, serial actions were randomly rewarded. While averaging population activity did not reveal a response pattern, we observed that different neurons selectively tuned to low, medium, or high numbered actions in a trial. This preferential tuning of putative dopamine and non-dopamine VTA neurons to different subsets of actions in a trial allowed information about binned action number to be decoded from the ensemble activity. At the network level, tuning curve similarity was positively associated with action-evoked noise correlations, suggesting that action number selectivity reflects functional connectivity within these networks. Analysis of phasic responses to cue and reward revealed that the requirement to execute multiple and uncertain numbers of actions weakens both cue-evoked responses and cue-reward response correlation. The functional connectivity and ensemble coding scheme that we observe here may allow VTA neurons to cooperatively provide a real-time account of ongoing behavior. These computations may be critical to cognitive and motivational functions that have long been associated with VTA dopamine neurons.

neuroscience↗