Biology subjects

Fridman, G. Y.

Publications and source records attributed to Fridman, G. Y..

6 recordsLinked to original sources

bioRxiv2025

Spatiotemporal Abstraction Theory: Re-Interpretation of Localized Cortical Networks

The brain excels at extracting meaning from noisy and degraded input, yet the computational principles that underlie this robustness remain unclear. We propose a theory of spatiotemporal abstraction (STA), in which localized cortical networks integrate inputs across space and time to produce multi-scale, concept-level representations that remain stable despite loss of detail. We demonstrate how this principle explains a long-standing paradox of how cochlear implant patients can understand speech despite severely scrambled neural patterns. STA provides a unified framework that explains fundamental questions: Why do we have so many neurons that respond very similarly in one cortical location? Why do we have different inhibitory neurons? It also forces us to re-examine long-standing explanations of memory, creativity, illusions, attractor dynamics, excitatory-to-inhibitory balance, and the structure and purpose of the ubiquitous canonical circuits seen throughout the brain. We conclude with STA implications for improving neural implants and artificial neural networks.

neuroscience↗

bioRxiv2025

Why Meaning Survives Noise: The Spatiotemporal Abstraction Theory

The brain excels at extracting meaning from noisy and degraded input, yet the computational principles that underlie this robustness remain unclear. We propose a theory of spatiotemporal abstraction (STA), in which neural networks integrate inputs across space and time to produce multi-scale, concept-level representations that remain stable despite loss of detail. We demonstrate this principle using spectrograms of spoken sentences and their degraded analogs from cochlear implants, showing that as integration kernels widen, distorted input converges toward the original representation. This mechanism may explain how cochlear implant users comprehend speech despite severely scrambled afferent signals. STA provides a unified framework for understanding abstraction as an emergent property of cortical architecture, with implications for memory, neuroprosthesis design, and robust artificial systems.

neuroscience↗

bioRxiv2025

Volume Control for a Cortical Network

Conventional implantable neuromodulation relies on brief electrical or optical pulses that directly evoke action potentials in targeted neurons. While powerful, such approaches primarily impose activity rather than modulate how circuits process ongoing signals. Here, we introduce ionic direct current (iDC) delivered through non-penetrating, electrolyte-filled microcatheters on the cortical surface as an alternative strategy for neuromodulation that adjusts cortical gain without directly driving spikes. In rat primary somatosensory cortex, laminar recordings showed that cathodic iDC attenuated and anodic iDC amplified spontaneous and sensory-evoked activity while preserving the temporal structure of population responses. Computational modeling implicated polarization at the axon initial segment as the mechanism underlying bidirectional gain control. In awake animals, iDC modulation altered tactile sensitivity, demonstrating behavioral relevance. These findings establish iDC as a rapidly reversible, spatially precise method for modulating cortical processing, offering a fundamentally different mode of neuromodulation that bridges circuit physiology and behavior without overriding native neural dynamics. TEASERIonic direct current modulates cortical gain via subthreshold polarization, preserving native neural dynamics.

neuroscience↗

bioRxiv2023

Galvanic vs. Pulsatile Effects on Decision-Making Networks: Reshaping the Neural Activation Landscape

I.Primarily due to safety concerns, biphasic pulsatile stimulation is the present standard for electrical excitation of neural tissue with a diverse set of applications. While pulses have been shown to be effective to achieve functional outcomes, they have well-known deficits. Due to recent technical advances, galvanic stimulation, delivery of current for extended periods of time (>1s), has re-emerged as an alternative to pulsatile stimulation. In this paper, we use a winner-take-all decision-making cortical network model to investigate differences between pulsatile and galvanic stimulation in the context of a perceptual decision-making task. Based on previous work, we hypothesized that galvanic stimulation would produce more spatiotemporally distributed, network-sensitive neural responses, while pulsatile stimulation would produce highly synchronized activation of a limited group of neurons. Our results in-silico support these hypotheses for low-amplitude galvanic stimulation but deviate when galvanic amplitudes are large enough to directly activate or block nearby neurons. We conclude that with careful parametrization, galvanic stimulation could overcome some limitations of pulsatile stimulation to deliver more naturalistic firing patterns in the group of targeted neurons.

neuroscience↗

bioRxiv2023

Peripheral direct current for suppression of physiologically evoked nociceptive responses at the spinal cord

Electrical neuromodulation is an established non-pharmacological treatment for chronic pain. However, existing devices using pulsatile stimulation are not suitable for all types of chronic pain. Direct current stimulation is a recently developed technology which shows better selectivity for small-diameter fibres. We investigated if this selectivity could be applied to preferentially suppress nociceptive signalling. We applied direct current to the sciatic nerve of rats and compared its effects on spinal activity produced by physiological (non-electrical) stimuli delivered to the foot. Tests were performed across models of neuropathic and inflammatory pain to further clarify potential clinical applications. We found that direct current could effectively suppress activity relating to painful stimuli in both pain models tested. These findings strongly support the use of direct current neuromodulation for chronic pain relief, and suggest that it may be effective at treating a broader range of aberrant pain conditions than existing devices.

neuroscience↗

bioRxiv2021

The Rules of Pulsatile Neurostimulation

Electrical stimulation is a key tool in neuroscience, both in brain mapping studies and in many therapeutic applications such as cochlear, vestibular, and retinal neural implants. Due to safety considerations, stimulation is restricted to short biphasic pulses. Despite decades of research and development, neural implants lead to varying restoration of function in patients. In this study, we use computational modeling to provide an explanation for how pulsatile stimulation affects axonal channels and therefore leads to variability in restoration of neural responses. The phenomenological explanation is transformed into equations that predict induced firing rate as a function of pulse rate, pulse amplitude, and spontaneous firing rate. We show that these equations predict simulated responses to pulsatile stimulation with a variety of parameters as well as several features of experimentally recorded vestibular afferent responses to pulsatile stimulation. We then discuss the implications of these effects for improving clinical stimulation paradigms and electrical stimulation-based experiments.

neuroscience↗