Deciphering hippocampal place codes in weak theta rhythms.

Local field potentials (LFPs) reflect the collective dynamics of neural populations, yet their exact relationship to neural codes remains unknown1. One notable exception is the theta rhythm of the rodent hippocampus, which seems to provide a reference clock to decode the animal's position from spatiotemporal patterns of neuronal spiking2 or LFPs3. But when the animal stops, theta becomes irregular4, potentially indicating the breakdown of temporal coding by neural populations. Here we show that no such breakdown occurs, introducing an artificial neural network that can recover position-tuned rhythmic patterns (pThetas) without relying on the more prominent theta rhythm as a reference clock. pTheta and theta preferentially correlate with place cell and interneuron spiking, respectively. When rats forage in an open field, pTheta is jointly tuned to position and head orientation, a property not seen in individual place cells but expected to emerge from place cell sequences5. Our work demonstrates that weak and intermittent oscillations, as seen in many brain regions and species, can carry behavioral information commensurate with population spike codes.

Computational analyses of in-vivo cerebral activity show that gamma oscillations in the olfactory cortex originate from local feedback inhibition following each sniff and serve to segregate competing odor representations through a winner-take-all process, providing an optimal window to decode odor.

Negative effects of interictal spikes on theta rhythm in human temporal lobe epilepsy

Previous studies have demonstrated that open-loop transcranial ultrasound stimulation (TUS) can modulate theta and gamma rhythms of the local field potentials (LFPs) in the mouse hippocampus; however, the manner in which closed-loop TUS with different pressures based on phase-locking of theta rhythms modulates theta and gamma rhythm remains unclear. In this study, we established a closed-loop TUS system, which can perform closed-loop TUS by predicting the peaks and troughs of the theta rhythm. Comparison of the power, sample entropy and complexity, and phase-amplitude coupling (PAC) between the theta and gamma rhythms under peak and trough stimulation of the theta rhythm revealed the following: (1) the variation in the absolute power of the gamma rhythm and the relative power of the theta rhythm under TUS at 0.6–0.8 MPa differ between peak and trough stimulation; (2) the relationship of the sample entropy of the theta and gamma rhythms with ultrasound pressure depends on peak and trough stimulation; and (3) peak and trough stimulation affect the PAC strength between the theta and gamma rhythm as a function of ultrasound pressure. These results demonstrate that the modulation of the theta and gamma rhythms by ultrasound pressure depends on peak and trough stimulation of the theta rhythm in the mouse hippocampus.

Theta rhythm and long-term potentiation (LTP) are 2 remarkable discoveries. The theta rhythm is an oscillatory neural activity of 3-10 Hz in the hippocampus. LTP is implicated as a cellular basis of memory, but the function of theta oscillation in memory is not clear. This review suggests that theta rhythm bestows optimal conditions for hippocampal LTP and memory encoding. Theta rhythm in hippocampal CA1 is generated mainly by 2 oscillating dipoles-somatic-inhibition and phase-shifted, distal dendritic excitation, with a smaller contribution by rhythmic proximal (CA3) excitation and distal inhibition. Our recent study showed that LTP of the excitatory synapses on the basal or apical dendrites of CA1 pyramidal cells peaked twice in a theta cycle, at the rising (R) and the midcycle (M) phase of the theta rhythm recorded at the distal apical dendrites. In contrast, evoked population spike excitability peaked at a single phase near the midcycle. We infer that R and M peaks of LTP correspond to maximal dendritic depolarization and maximal somatic depolarization of CA1 pyramidal cells, respectively. A ∼50° phase shift between LTP-versus-theta-phase functions suggests independent LTP at the basal and apical dendrites. It is argued that theta phase-dependent LTP occurs under physiological conditions, by pairing presynaptic activity with oscillating postsynaptic depolarization. Place cells, showing intrinsic membrane potential oscillations, are ideal LTP participants. It is suggested that theta phase-dependent LTP contributes to memory encoding, and disruption of either theta oscillation or LTP may disrupt memory in various neurological disorders, including epilepsy and Alzheimer's disease. (PsycInfo Database Record (c) 2021 APA, all rights reserved).

Views Icon Views Article contents Figures & tables Video Audio Supplementary Data Peer Review Share Icon Share Twitter Facebook Reddit LinkedIn Tools Icon Tools Reprints and Permissions Cite Icon Cite Search Site Citation K. Tokuda, Y. Katori, K. Aihara; Modeling state transition of hippocampal local field potential between theta rhythm and large irregular amplitude activity by bifurcation between a limit cycle and chaotic dynamics. AIP Conference Proceedings 15 January 2013; 1510 (1): 134–137. https://doi.org/10.1063/1.4776514 Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentAIP Publishing PortfolioAIP Conference Proceedings Search Advanced Search |Citation Search

Kowalczyk et al. (Hippocampus 2014; 24:7-20) were probably the first to conduct a systemic study of posterior hypothalamic area (PHa) theta rhythm in anesthetized rats. They demonstrated that local PHa theta field potentials were tail-pinch resistant and could be generated in urethane-anesthetized rats independently of ongoing hippocampal formation theta rhythm. These in vivo data were also confirmed in PHa slice preparations perfused with cholinergic agonist, carbachol. In the current experiments we extend our earlier observations concerning PHa theta rhythm. Specifically, PHa field potentials were analyzed in relation to the ongoing local cell firing repertoire. Single-unit discharge patterns of cells localized in the posterior hypothalamic and supramammillary nuclei were characterized according to the criteria that was developed previously to classify theta-related cells in the hippocampal formation. The present study demonstrated that in addition to the earlier described theta-related cells (theta-on, theta-off and gating cells) the PHa also contains cells discharging in a very regular manner, which were labelled "timing cells". This type of neuron has not been previously documented. We suggest that "timing cells" form a part of the ascending brainstem synchronizing pathway, provideing a regular rhythmic signal which facilitates the transduction of tonic discharges of cells localized in the brain stem into theta-frequency rhythmic discharges. © 2016 Wiley Periodicals, Inc.

Brief optogenetic stimulation of thalamocortical axons evoked a 400 Hz wavelet, 'ripplet,' in the extracellular field potential in cortical layer 4, together with phase-locked spike bursts in fast-spiking inhibitory interneurons and alternating excitatory and inhibitory synaptic currents in excitatory cells.

The dorsal medial prefrontal cortex and basolateral amygdala exhibit social behavior-relevant neuronal oscillations, representing unified pathophysiological mechanisms underlying social behavioral deficits.

Place cells are hippocampal pyramidal cells that are active when an animal visits a restricted area of the environment, and collectively their activity constitutes a neural representation of space. Place cell populations in the adult rat hippocampus display fundamental properties consistent with an associative memory network: the ability to 1) generate new and distinct spatial firing patterns when encountering novel spatial contexts or changes in sensory input (“remapping”) and 2) reinstate previously stored firing patterns when encountering a familiar context, including on the basis of an incomplete/degraded set of sensory cues (“pattern completion”). To date, it is unknown when these spatial memory responses emerge during brain development. Here, we show that, from the age of first exploration (postnatal day 16) onwards, place cell populations already exhibit these key features: they generate new representations upon exposure to a novel context and can reactivate familiar representations on the basis of an incomplete set of sensory cues. These results demonstrate that, as early as exploratory behaviors emerge, and despite the absence of an adult-like grid cell network, the developing hippocampus processes incoming sensory information as an associative memory network.

Rhythmic activity in populations of neurons is associated with cognitive and motor function. Our understanding of the neuronal mechanisms underlying these core brain functions has benefitted from demonstrations of cellular, synaptic, and network phenomena, leading to the generation of discrete rhythms at the local network level. However, discrete frequencies of rhythmic activity rarely occur alone. Despite this, little is known about why multiple rhythms are generated together or what mechanisms underlie their interaction to promote brain function. One overarching theory is that different temporal scales of rhythmic activity correspond to communication between brain regions separated by different spatial scales. To test this, we quantified the cross-frequency interactions between two dominant rhythms-theta and delta activity-manifested during magnetoencephalography recordings of subjects performing a word-pair semantic decision task. Semantic processing has been suggested to involve the formation of functional links between anatomically disparate neuronal populations over a range of spatial scales, and a distributed network was manifest in the profile of theta-delta coupling seen. Furthermore, differences in the pattern of theta-delta coupling significantly correlated with semantic outcome. Using an established experimental model of concurrent delta and theta rhythms in neocortex, we show that these outcome-dependent dynamics could be reproduced in a manner determined by the strength of cholinergic neuromodulation. Theta-delta coupling correlated with discrete neuronal activity motifs segregated by the cortical layer, neuronal intrinsic properties, and long-range axonal targets. Thus, the model suggested that local, interlaminar neocortical theta-delta coupling may serve to coordinate both cortico-cortical and cortico-subcortical computations during distributed network activity. NEW & NOTEWORTHY Here, we show, for the first time, that a network of spatially distributed brain regions can be revealed by cross-frequency coupling between delta and theta frequencies in subjects using magnetoencephalography recording during a semantic decision task. A biological model of this cross-frequency coupling suggested an interlaminar, cell-specific division of labor within the neocortex may serve to route the flow of cortico-cortical and cortico-subcortical information to promote such spatially distributed, functional networks.

Hippocampal gamma and theta oscillations are associated with mnemonic and navigational processes and adapt to changes in the behavioral state of an animal to optimize spatial information processing. It has been shown that locomotor activity modulates gamma and theta frequencies in rats, although how age alters this modulation has not been well studied. Here, we examine gamma and theta local-field potential and place cell activity in the hippocampus CA1 region of young and old male rats as they performed a spatial eye-blink conditioning task across 31 d. Although mean gamma frequency was similar in both groups, gamma frequency increased with running speed at a slower rate in old animals. By contrast, theta frequencies scaled with speed similarly in both groups but were lower across speeds in old animals. Although these frequencies scaled equally well with deceleration and speed, acceleration was less correlated with gamma frequency in both age groups. Additionally, spike phase-locking to gamma, but not theta, was greater in older animals. Finally, aged rats had reduced within-field firing rates but greater spatial information per spike within the field. These data support a strong relationship between locomotor behavior and local-field potential activity and suggest that age significantly affects this relationship. Furthermore, observed changes in CA1 place cell firing rates and information content lend support to the hypothesis that age may result in more general and context-invariant hippocampal representations over more detailed information. These results may explain the observation that older adults tend to recall the gist of an experience rather than the details.SIGNIFICANCE STATEMENT Hippocampal oscillations and place cell activity are sensitive to sensorimotor input generated from active locomotion, yet studies of aged hippocampal function often do not account for this. By considering locomotion and spatial location, we identify novel age-associated differences in the scaling of oscillatory activity with speed, spike-field coherence, spatial information content, and within-field firing rates of CA1 place cells. These results indicate that age has an impact on the relationship between locomotion and hippocampal oscillatory activity, perhaps indicative of alterations to afferent input. These data also support the hypothesis that aged hippocampal place cells, compared with young, may more often represent more general spatial information. If true, these results may help explain why older humans tend to recall less specific and more gist-like information.

Retrosplenial cortex (RSC) is heavily interconnected with a multitude of cortical regions and is directly connected with the hippocampal formation. As such, it is a likely coordinator of information transfer between the hippocampus (HPC) and cortex in the service of spatial cognition and episodic memory. The current work examined three potential temporal frameworks for retrosplenial-hippocampal communication, namely, theta frequency oscillations (6-12 Hz), sharp-wave/ripple events, and repeating, theta phase-locked shifts from low (30-65 Hz) to high (120-160 Hz) gamma frequency oscillations. From simultaneous recordings of single units and local field potentials (LFPs) in RSC and HPC, we report the presence of prominent theta, low-gamma, and high-gamma oscillations in the retrosplenial LFP. Retrosplenial and hippocampal theta rhythms were strongly coherent and subgroups of retrosplenial neurons exhibited either spiking at theta frequencies and/or spike-phase-locking to theta. Retrosplenial neurons were also phase-locked to local low- and high-gamma rhythms, and power in these frequency bands was coupled in a sequential fashion to specific phases of hippocampal and retrosplenial theta rhythms. Coordinated activity between the two regions also occurred during hippocampal sharp-wave/ripple events, where retrosplenial neuron populations were modulated in their spiking and retrosplenial LFPs exhibited sharp-wave-like events that co-occurred with those observed in HPC. These results identify several temporal windows of synchronization between RSC and HPC that may mediate cortico-hippocampal processes related to learning, memory, and spatial representation. (PsycINFO Database Record (c) 2018 APA, all rights reserved).

Introduction. Epilepsy is a common feature of mitochondrial disorders, including those associated with mutations in the POLG gene. Nevertheless, brain electrical activity features of POLG-related disorders in adult patients have not been adequately studied. Objective. To study the features and characteristics of the electroencephalography (EEG) pattern in adult patients with POLG-related disorders. Material and methods. Eight patients were examined: 7 with SANDO (Sensory Ataxic Neuropathy, Dysarthria, Ophthalmoparesis) syndrome, and 1 with MEMSA (Myoclonic Epilepsy Myopathy Sensory Ataxia) syndrome; median age was 32.5 years. All patients underwent routine EEG monitoring using a 19-channel electroencephalograph according to the generally accepted method. Results. Epileptic seizures were found in 3 patients, for 2 of them – as the first manifestation of the disease. In 6 patients, theta waves predominated in the occipital regions. Of those 6 patients, in 5 bilateral synchronous bursts of theta and delta wave groups were identified being more prominent in the frontocentral regions; 4 patients had transient non-lateralized delta activity in the occipital and parieto-occipital brain regions. In all patients, opening eyes led to the depression of rhythms and burst suppression. After photostimulation, in 2 cases bilateral synchronous bursts of delta and theta wave groups were recorded predominantly in frontal lobes. In 3 patients during hyperventilation an increase in delta activity in the occipital lobes and bilateral synchronous bursts of delta wave groups were observed. Epileptiform activity was recorded in 2 cases. Conclusion. In adult patients with POLG-related disorders, regardless of the clinical manifestation, typical EEG features include generalized background slowing, theta and delta bursts in occipital lobes with their suppression by opening eyes.

Event Abstract Back to Event Frequency scaling in local field potentials: A neuron population forward modelling study Henrik Lindén1*, Klas H. Pettersen1 and Gaute T. Einevoll1 1 Norwegian University of Life Sciences, Norway Extracellular field potentials are commonly used as a measure of activity in neuronal tissue. The signal is usually filtered into two distinctive frequency bands, one low-pass band below 500 Hz, referred to as the local field potential (LFP) and a high-pass band with frequencies above approximately 750 Hz, referred to as multi-unit activity (MUA). Whereas the MUA is believed to mostly represent spiking activity of neurons located near the electrode, the LFP is commonly assumed to reflect synaptic input to the neuronal population. The relation between the synaptic activity and the spectral content of LFP is however far from understood. It has been reported that the power of cortical LFP signals follow a 1/fα-scaling law, which is also evident in EEG recordings [1] . Bedárd et al. have shown that when the input to a neuronal population is Poissonian spike trains and synaptic filtering is taken into account, there is still a factor 1/f missing to account for the frequency attenuation seen in experimental LFP data [2] . They suggested that filtering effects in the extracellular medium may explain this frequency-dependent attenuation. However, in a more recent experimental study, no such frequency attenuation in the extracellular medium could be found [3] . Here we propose as an alternative explanation that the filtering effects arise in the neurons themselves due to a frequency-dependence in the typical separation between the synaptic input currents and the transmembrane return currents following synaptic activation. As a consequence, the current dipole length will shorten with increasing frequency and the contribution to the LFP will be correspondingly reduced. We have studied this filtering effect in detail by simulating synaptically activated populations of morphologically reconstructed neurons. The resulting transmembrane currents are then used to calculate the extracellular potential in a foward-modelling electrostatic scheme. We consider only passive membranes and current synapses so that the system is linear and can thus estimate the filtering properties in the frequency-domain by injecting sinusoidal synaptic model currents with different frequencies. We indeed find that for low input frequencies the separation between outward and inwards currents will be larger than for higher frequencies, effectively leading to a low-pass filtering of the LFP. To elucidate this effect we also consider a simplified dendritic stick model where analytic results allow for a more detailed qualitative understanding, in analogy with a previous study of low-pass filtering of extracellular action potential signatures [4].