Gamma oscillations

Recent advances in human intracranial recordings have significantly deepened our understanding of complex cognitive functions like working memory (WM) at the circuit level. While single-neuron analyses, primarily within the medial temporal lobes, have elucidated how individual neurons contribute to memory computation, the role of local field potential (LFP) dynamics in complementing single-unit activity during WM tasks remains poorly understood. To address this, we developed biologically plausible spiking recurrent neural networks (RNNs) trained on a delayed match-to-sample (DMS) task which in

…spatial features of neuronal oscillations and challenged the conventional view of global zero-lag synchrony as a basis of neuronal communication. More specifically, it revealed structured phase-offsets in superficial cortical singals corresponding to wave-like dynamics. Further investigation of single-c

Coherent oscillations of neural activity are ubiquitous across brain spatial and temporal scales and have been associated with the formation of sensory or behavioral representations [1]. Refined experimental techniques report today a new complexity of this oscillatory activity, especially in the gamma (30-100 Hz) band. Indeed, the frequency of these oscillations shows a large variability through time [2], questioning the classical view of γ oscillations being separated into different frequency bands. Oscillations appear instead in bursts characterised by rapid, synchronous neuronal firing. Thi

Coherent oscillations of neuronal activity are ubiquitous across brain spatial and temporal scales. Gamma oscillations (30-120Hz), detectable with Local Field Potentials (LFPs), are classically analyzed through massive trial averages. This approach leaves us with one average oscillation shape, one mean power and a view based on rigid frequency bands. Consistently, mechanisms based on biophysical models of neural networks typically predict periodic oscillations (e.g. PING models [1]). The functional role of oscillations have been largely investigated in the hippocampus, where, different gamma-f

…Specifically, evoked gamma oscillations through stimulation at 40Hz has been shown to rescue motor and cogniti

…challenge traditional views of brain oscillations as spatially stationary periodic sources. Understanding the spatio-temporal dynamics of cortical activity requires novel measurement and analysis methodologies. We recorded broadband local field potential (LFP) across the whole neocortex in freely behaving rats using high-density flexible surface and translaminar arrays using active transistors. 3D tracking and spatio-spectral analysis of recordings over long sessions enabled automatic and accurate brain and behavioral

Cognitive and motor functions of the human brain often display non-linear dynamics. Fractal dimension such as Higuchi’s fractal dimension (HFD) has been used as an effective method to probe these nonlinear dynamics and has been used to characterise different diseases. However, there is inconsistency in how HFD varies with age and disease in literature, which could be due to different computational techniques or frequency ranges used in these studies. To resolve this disparity, we investigated the frequency-dependant change of HFD with age for 64-channel electroencephalogram (EEG) data recorded

…modulations with envelopes of gamma oscillations from one zero to another zero with gaps. We are analyzing the dynamics of zeroes establishing local equilibrium. We found gaps staying close to the global average gap size of whole

Treatment-resistant depression is a global public health concern, leaving a significant portion of the population without effective remedies. To address this issue, innovative strategies are urgently needed. Psilocybin, a non-selective 5-HT2AR agonist, has been found to alleviate depressive mood in individuals with treatment resistant depression (Carhart-Harris et al., 2017) Ketamine exhibits robust and enduring antidepressant properties both in patients and preclinical models. (Krystal et al., 2013). Sleep patterns are often affected by depressive disorders, making wireless EEG a valuable too

Treatment-resistant depression is a global public health concern, leaving a significant portion of the population without effective remedies. To address this issue, innovative strategies are urgently needed. Psilocybin, a non-selective 5-HT2AR agonist, has been found to alleviate depressive mood in individuals with treatment resistant depression (Carhart-Harris et al., 2017) Ketamine exhibits robust and enduring antidepressant properties both in patients and preclinical models. (Krystal et al., 2013). Sleep patterns are often affected by depressive disorders, making wireless EEG a valuable

Spatial memory consolidation is supported by the coupling of hippocampus (HPC) and medial prefrontal cortex (mPFC) activities during sleep. The thalamic nucleus reuniens (NR), reciprocally connected to the HPC and the mPFC, is thought to play a key role in this process. In order to characterize the interactions of these structures during memory consolidation, we developed a new experimental protocol. On an automated maze, animals learn a daily trajectory to a reward and are tested for performance in subsequent sleep. During this protocol, we conduct high-density recording of the HPC, NR and mP

Neuropeptide Y (NPY) is the most abundant neuropeptide in the brain, co-expressed with other neurotransmitters. It is expressed mainly by interneurons in different regions, including the hippocampus (HP). NPY binds to five G-protein-coupled receptors (R), from which Y1 and Y2 R are the most numerous in the rodent brain. NPY is implicated in the regulation of stress and can exert anxiolytic or anxiogenic effects, depending on the specific brain region and receptor subtype being activated. HP and specifically its ventral portion, contributes to this processing with an important role in emotional

Changes in olfaction are emerging as early warning signs of several major neurological diseases. Neurological diseases are also associated with aberrant brain rhythms. Olfactory sensory neurons (OSN) deliver input from the nasal epithelium (NE) to the olfactory bulb (OB) and are key drivers of rhythmicity. Here, we examine the role of sensory input arising from the NE in the generation of electrophysiological rhythms in the OB. Rats were implanted with electrodes in the OB and post-surgery gadolinium/saline was infused bilaterally to both nares. Olfactory function was assessed using the hidden

The electrophysiological signal recorded from the brain shows rhythmic activity (oscillations) at different frequencies. One such rhythm, called gamma (~30-80 Hz), is modulated by high-level cognitive processes such as attention, memory, and meditation and, therefore, could provide clues about mechanisms underlying high-level cognition. Interestingly, gamma oscillations can be “induced” in the brain by presenting certain stimuli such as bars, gratings, and color patches (especially red hues). Moreover, these stimulus-induced gamma oscillations weaken with age and the onset of Alzheimer’s Disea

Gamma oscillations are believed to arise from the interaction between excitation and inhibition (E-I) in the neural circuitry. However, the dependency of gamma power on E-I interaction is not well characterized. Increasing the drift-rate of the visual grating, which changes E-I balance, increases the peak frequency of gamma while power initially increases and later attenuates. Importantly, this power versus drift-rate tuning curve is altered for subjects with autism or premenstrual dysphoric disorder. A recent MEG study in humans (Orekhova et al., 2020) examined the combined effect of contrast

Variations in brain states and behavioral profiles clearly influence neuronal activity in the visual cortex[1,2]. However, the mechanisms behind these influences and their consequent effect on sensory encoding remain to be determined. Here, we address this issue by analyzing simultaneous recordings of spiking activity and local field potentials (LFPs) from visual and subcortical regions of (N = 25) awake mice viewing a naturalistic movie. Applying a hidden Markov model (HMM) to cortical LFPs, we consistently identified three stable states in each mouse: a high-frequency state (dominated by gam

…circuit activity of high-frequency oscillations (HFOs) in theta and sharp wave-ripples (SWRs). By comparing HFOs occurring at times of SWRs (+/-50 ms) or during theta, we found using current-source density analysis that HFOs in different states are uniformly localized to layer 2/3 (L2/3) with current sources and sinks bridging the L1-L2/3 border. HFOs that occurred outside of SWR times where rhythmically locke

…for neural coordination are network oscillations, which dynamically synchronize neural activity across circuit elements. In MEC, theta and gamma oscill

Neural information processing in dynamic, natural environments requires the brain to flexibly allocate limited computational resources to varying task demands. One example is selective attention in the visual system, which allows to preferentially route signals from behaviourally relevant stimuli to downstream visual areas, while suppressing irrelevant visual information. It is an open question which neural mechanisms realize selective routing, and how this process is controlled. Here we propose that spontaneous synchronization in recurrent networks is the key mechanism for selective processin

It has been proposed that the visual cortex performs sampling-based probabilistic inference where neural responses represent stochastic samples from a posterior distribution. However, the highly-correlated nature of neural activity across time presents a computational ceiling on the effective sample size for any given time interval. Here, we show that auxiliary neurons, when implemented strategically, can speed up sampling rates in neural circuits to efficiently express an inferred posterior distribution. We train stabilized supralinear networks using a loss function that intrinsically rewards

Theta and gamma oscillations are believed to organise hippocampal activity and function. The current dominant view posits the existence of two gamma frequency sub-bands, occurring at different theta phases in CA1, produced by different generators and sub-serving exclusive cognitive operations. Such views are however grounded on averaging over many oscillatory events. Here, we explore agnostically the diversity of individual theta-gamma bursts and find, in striking contrast with the discrete sub-bands hypothesis, that gamma bursts with nearly every combination of frequency, amplitude and theta-

…variability, transient overshoots, and oscillations, that have so far escaped a common, principled theoretical account. We developed a unifying model for these phenomena by training a recurrent excitatory-inhibitory neural circuit model of a visual cortical hypercolumn to perform sampling-based probabilistic inference. The optimized network displayed several key biological properties, including divisive normalization, as well as stimulus-modulated noise variability, inhibition-dominated transients at stimu