Biology subjects

Herz, A. V. M.

Publications and source records attributed to Herz, A. V. M..

5 recordsLinked to original sources

bioRxiv2026

On the neural origin of hexadirectional fMRI modulations

When human beings navigate through an environment, a conceptual space, memories or even imagined spaces, fMRI signals in select brain regions vary with movement direction, alternating in strength with a periodicity of 60 degrees. At the cellular level, certain neurons called grid-cells form a hexagonal lattice representation of physical space. Given that the axes of the lattices align across neurons, the concerted directional and spatial firing of populations of these neurons may form the basis of the hexadirectional modulation of the fMRI signal. However, the exact link between the two remains unclear. Multiple mechanisms have been proposed that could couple neuronal activity to the fMRI signal. These include (1) preferential neuronal discharge when the direction of motion coincides with the lattice axes, (2) repetition suppression when multiple fields are traversed in succession, or alternatively, (3) a nonlinear transduction step. Here, we propose targeted experiments that can distinguish these mechanisms, for which we assess the expected effect sizes via simulations. In particular, by introducing calibrated pauses between linear path segments, it is possible to differentiate the repetition-suppression hypothesis from the nonlinear transduction model. By additionally varying the subjects movement speed and path lengths, the proposed protocol can distinguish conjunctive neuronal tuning (in which neurons respond to both speed and location or direction and location) from the other hypotheses. Crucially, if either the repetition-suppression or the nonlinear-transduction hypothesis holds, then the scale of the lattices will play a role. According to our analysis, hexadirectional signals should emerge only when a linear path segment is longer than half of the spatial lattice period. As grid cells with different scales are grouped into distinct modules along the dorso-ventral axis of the entorhinal cortex, this may make it possible to non-invasively measure the hierarchy of grid scales in the human brain.

neuroscience↗

bioRxiv2026

The lattice scales of grid-cell activity

Grid cells in the rodent medial entorhinal cortex (MEC) form a multi-scale representation of the animals environment and are thought to be a signature of continuous-attractor networks.Experiments suggest that grid scales are discrete and arranged in a geometric progression with constant scale ratios, as predicted by efficient-coding theories that posit that the grid-cell system is optimized for spatial resolution. This normative explanation has been challenged by a developmental theory whereby grid-cell modularity arises from pattern formation in a system with smooth parameter gradients. As a consequence, scale ratios should not be constant, but vary by module. However, as we show here, the experimental data chosen to support this mechanistic theory fail to do so. Publicly available large-scale grid-cell datasets could provide a clear benchmark and further our understanding of the neuronal basis of spatial navigation. We, therefore, reanalyzed such recordings and found that they refute the developmental theory. Instead, the measured scale ratios agree with the geometric-progression hypothesis and set strict bounds for any future grid-cell theory.

neuroscience↗

bioRxiv2025

A multi-ring shifter network computes head direction in zebrafish

From insects to fish to mammals, many species have an internal compass: a set of recurrently connected neurons that combine motor feedback, vestibular signals, and external cues to compute the animals heading direction. Whether the underlying mechanism is universal across different species is unresolved. In Drosophila, for instance, the central complex contains three connected, yet anatomically separate, functional neuron rings. Two rings receive countervailing velocity signals that shift neuronal activity bumps around all three rings. An alternative, classical continuous-attractor model invokes only one ring but requires velocity-modulated synaptic connections. A single-ring compass has been discovered in the anterior hindbrain of zebrafish. Using theory and experiments, we find, however, that three rings, including two shifter rings, are intermingled on the same anatomical scaffold. Zebrafish and Drosophila, therefore, use the same basic compass mechanism, suggestive of convergent evolution.

neuroscience↗

bioRxiv2025

Depolarizing afterpotentials in rodent mEC layer II neurons vary gradually across all principal cell types

Principal cells in Layer II (LII) of the rodent medial entorhinal cortex (mEC) often discharge in short burst episodes, whose biophysical mechanism and biological function are not fully understood. As shown by in vitro recordings in rats and in vivo recordings in mice, action potentials of stellate cells (SCs) and pyramidal cells (PCs) in mEC LII can trigger depolarizing afterpotentials (DAPs) that facilitate spike doublets and burst firing. In vitro recordings in mice confirm these findings for SCs and two additional cell types intermediate between SCs and PCs but suggest that mouse PCs generate minute DAPs only. To better understand the diversity and physiology of the intermediate LII mEC cell types, we performed slice experiments in Long Evans rats of both sexes and analyzed the data using clustering techniques. The analysis suggests four distinct cell clusters, reminiscent of previous observations in mice. On purpose, DAP properties were not used for the cluster analysis so that they could be studied post-hoc in an unbiased manner. Our results show that characteristic features of DAPs and other physiological markers are broadly distributed within each cell class and vary gradually from cluster to cluster, forming a continuum of biophysical properties.

neuroscience↗

bioRxiv2020

Burst activity plays no role for the field-to-field variability and rate remapping of grid cells.

Grid cells in rodent medial entorhinal cortex are thought to play a key role for spatial navigation. When the animal is freely moving in an open arena the firing fields of each grid cell tend to form a hexagonal lattice spanning the environment. Firing rates vary from field to field and change under contextual modifications, whereas the field locations do not shift under such "rate remapping". The observed differences in firing rate could reflect overall activity changes or changes in the detailed spike-train statistics. As these two alternatives imply distinct neural coding schemes, we investigated whether temporal firing patterns vary from field to field and whether they change under rate remapping. Focusing on short time scales, we found that the proportion of bursts compared to all discharge events is similar in all firing fields of a given grid cell and does not change under rate remapping. Mean firing rates with and without bursts are proportional for each cell. However, this ratio varies across cells. Additionally, we looked at how rate remapping relates to entorhinal theta-frequency oscillations. Theta-phase coding was preserved despite firing-rate changes from rate remapping but we did not observe differences between the first and second half of the theta cycle, as had been reported for CA1. Our results indicate that both, the heterogeneity between firing fields and rate remapping, are not due to altered firing patterns on short time scales but reflect location-specific changes at the firing-rate level.

neuroscience↗