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Ku SP, Atucha E, Alavi N, Mulla-Osman H, Kayumova R, Yoshida M, Csicsvari J, Sauvage MM. Phase locking of hippocampal CA3 neurons to distal CA1 theta oscillations selectively predicts memory performance. Cell Rep 2024; 43:114276. [PMID: 38814781 DOI: 10.1016/j.celrep.2024.114276] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/09/2022] [Revised: 01/09/2024] [Accepted: 05/09/2024] [Indexed: 06/01/2024] Open
Abstract
How the coordination of neuronal spiking and brain rhythms between hippocampal subregions supports memory function remains elusive. We studied the interregional coordination of CA3 neuronal spiking with CA1 theta oscillations by recording electrophysiological signals along the proximodistal axis of the hippocampus in rats that were performing a high-memory-demand recognition memory task adapted from humans. We found that CA3 population spiking occurs preferentially at the peak of distal CA1 theta oscillations when memory was tested but only when previously encountered stimuli were presented. In addition, decoding analyses revealed that only population cell firing of proximal CA3 together with that of distal CA1 can predict performance at test in the present non-spatial task. Overall, our work demonstrates an important role for the synchronization of CA3 neuronal activity with CA1 theta oscillations during memory testing.
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Affiliation(s)
- Shih-Pi Ku
- Leibniz Institute for Neurobiology, Functional Architecture of Memory Department, Magdeburg, Germany.
| | - Erika Atucha
- Leibniz Institute for Neurobiology, Functional Architecture of Memory Department, Magdeburg, Germany
| | - Nico Alavi
- Leibniz Institute for Neurobiology, Functional Architecture of Memory Department, Magdeburg, Germany
| | - Halla Mulla-Osman
- Leibniz Institute for Neurobiology, Functional Architecture of Memory Department, Magdeburg, Germany
| | - Rukhshona Kayumova
- Leibniz Institute for Neurobiology, Functional Architecture of Memory Department, Magdeburg, Germany
| | - Motoharu Yoshida
- Leibniz Institute for Neurobiology, Functional Architecture of Memory Department, Magdeburg, Germany; German Center for Neurodegenerative Diseases (DZNE), Magdeburg, Germany
| | - Jozsef Csicsvari
- Institute of Science and Technology (IST), Klosterneuburg, Austria
| | - Magdalena M Sauvage
- Leibniz Institute for Neurobiology, Functional Architecture of Memory Department, Magdeburg, Germany; Otto von Guericke University, Medical Faculty, Functional Neuroplasticity Department, Magdeburg, Germany; Center for Behavioral Brain Sciences (CBBS), Magdeburg, Germany.
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2
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Friedenberger Z, Harkin E, Tóth K, Naud R. Silences, spikes and bursts: Three-part knot of the neural code. J Physiol 2023; 601:5165-5193. [PMID: 37889516 DOI: 10.1113/jp281510] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2023] [Accepted: 09/28/2023] [Indexed: 10/28/2023] Open
Abstract
When a neuron breaks silence, it can emit action potentials in a number of patterns. Some responses are so sudden and intense that electrophysiologists felt the need to single them out, labelling action potentials emitted at a particularly high frequency with a metonym - bursts. Is there more to bursts than a figure of speech? After all, sudden bouts of high-frequency firing are expected to occur whenever inputs surge. The burst coding hypothesis advances that the neural code has three syllables: silences, spikes and bursts. We review evidence supporting this ternary code in terms of devoted mechanisms for burst generation, synaptic transmission and synaptic plasticity. We also review the learning and attention theories for which such a triad is beneficial.
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Affiliation(s)
- Zachary Friedenberger
- Brain and Mind Institute, Department of Cellular and Molecular Medicine, University of Ottawa, Ottawa, Ontario, Canada
- Centre for Neural Dynamics and Artifical Intelligence, Department of Physics, University of Ottawa, Ottawa, Ontario, Ottawa
| | - Emerson Harkin
- Brain and Mind Institute, Department of Cellular and Molecular Medicine, University of Ottawa, Ottawa, Ontario, Canada
| | - Katalin Tóth
- Brain and Mind Institute, Department of Cellular and Molecular Medicine, University of Ottawa, Ottawa, Ontario, Canada
| | - Richard Naud
- Brain and Mind Institute, Department of Cellular and Molecular Medicine, University of Ottawa, Ottawa, Ontario, Canada
- Centre for Neural Dynamics and Artifical Intelligence, Department of Physics, University of Ottawa, Ottawa, Ontario, Ottawa
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3
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Chen R, Vakilna YS, Lassers SB, Tang WC, Brewer G. Hippocampal network axons respond to patterned theta burst stimulation with lower activity of initially higher spike train similarity from EC to DG and later similarity of axons from CA1 to EC. J Neural Eng 2023; 20:056004. [PMID: 37666242 DOI: 10.1088/1741-2552/acf68a] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2023] [Accepted: 09/04/2023] [Indexed: 09/06/2023]
Abstract
Objective. Decoding memory functions for each hippocampal subregion involves extensive understanding of how each hippocampal subnetwork processes input stimuli. Theta burst stimulation (TBS) recapitulates natural brain stimuli which potentiates synapses in hippocampal circuits. TBS is typically applied to a bundle of axons to measure the immediate response in a downstream subregion like the cornu ammonis 1 (CA1). Yet little is known about network processing in response to stimulation, especially because individual axonal transmission between subregions is not accessible.Approach. To address these limitations, we reverse engineered the hippocampal network on a micro-electrode array partitioned by a MEMS four-chambered device with interconnecting microfluidic tunnels. The micro tunnels allowed monitoring single axon transmission which is inaccessible in slices orin vivo. The four chambers were plated separately with entorhinal cortex (EC), dentate gyrus (DG), CA1, and CA3 neurons. The patterned TBS was delivered to the EC hippocampal gateway. Evoked spike pattern similarity in each subregions was quantified with Jaccard distance metrics of spike timing.Main results. We found that the network subregion produced unique axonal responses to different stimulation patterns. Single site and multisite stimulations caused distinct information routing of axonal spikes in the network. The most spatially similar output at axons from CA3 to CA1 reflected the auto association within CA3 recurrent networks. Moreover, the spike pattern similarities shifted from high levels for axons to and from DG at 0.2 s repeat stimuli to greater similarity in axons to and from CA1 for repetitions at 10 s intervals. This time-dependent response suggested that CA3 encoded temporal information and axons transmitted the information to CA1.Significance. Our design and interrogation approach provide first insights into differences in information transmission between the four subregions of the structured hippocampal network and the dynamic pattern variations in response to stimulation at the subregional level to achieve probabilistic pattern separation and novelty detection.
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Affiliation(s)
- Ruiyi Chen
- Department of Biomedical Engineering, University of California, Irvine, CA 92697, United States of America
| | - Yash Shashank Vakilna
- Department of Biomedical Engineering, University of California, Irvine, CA 92697, United States of America
- Texas Institute of Restorative Neurotechnologies (TIRN), The University of Texas Health Science Center (UTHealth), Houston, TX 77030, United States of America
| | - Samuel Brandon Lassers
- Department of Biomedical Engineering, University of California, Irvine, CA 92697, United States of America
| | - William C Tang
- Department of Biomedical Engineering, University of California, Irvine, CA 92697, United States of America
- Department of Biomedical Engineering, National Taiwan University, Taipei 106319, Taiwan (ROC)
| | - Gregory Brewer
- Department of Biomedical Engineering, University of California, Irvine, CA 92697, United States of America
- Center for Neuroscience of Learning and Memory & MIND Center, University of California, Irvine, CA 92697, United States of America
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4
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Aoki Y, Yokoi T, Morikawa S, Kuga N, Ikegaya Y, Sasaki T. Effects of theta phase precessing optogenetic intervention on hippocampal neuronal reactivation and spatial maps. iScience 2023; 26:107233. [PMID: 37534136 PMCID: PMC10392074 DOI: 10.1016/j.isci.2023.107233] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2023] [Revised: 06/04/2023] [Accepted: 06/23/2023] [Indexed: 08/04/2023] Open
Abstract
As animals explore environments, hippocampal place cells sequentially fire at progressively earlier phases of theta oscillations in hippocampal local field potentials. In this study, we evaluated the network-level significance of theta phase-entrained neuronal activity in organizing place cell spike patterns. A closed-loop system was developed in which optogenetic stimulation with a temporal pattern replicating theta phase precession is delivered to hippocampal CA1 neurons when rats traversed a particular region on a linear track. Place cells that had place fields during phase precessing stimulation, but not random phase stimulation, showed stronger reactivation during hippocampal sharp-wave ripples in a subsequent rest period. After the rest period, place cells with place fields that emerged during phase precessing stimulation showed more stable place fields. These results imply that neuronal reactivation and stability of spatial maps are mediated by theta phase precession in the hippocampus.
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Affiliation(s)
- Yuki Aoki
- Graduate School of Pharmaceutical Sciences, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
| | - Taiki Yokoi
- Department of Pharmacology, Graduate School of Pharmaceutical Sciences, Tohoku University, 6-3 Aramaki-Aoba, Aoba-Ku, Sendai 980-8578, Japan
| | - Shota Morikawa
- Graduate School of Pharmaceutical Sciences, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
- Institute for AI and Beyond, The University of Tokyo, Tokyo 113-0033, Japan
| | - Nahoko Kuga
- Department of Pharmacology, Graduate School of Pharmaceutical Sciences, Tohoku University, 6-3 Aramaki-Aoba, Aoba-Ku, Sendai 980-8578, Japan
| | - Yuji Ikegaya
- Graduate School of Pharmaceutical Sciences, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
- Institute for AI and Beyond, The University of Tokyo, Tokyo 113-0033, Japan
- Center for Information and Neural Networks, 1-4 Yamadaoka, Suita City, Osaka 565-0871, Japan
| | - Takuya Sasaki
- Graduate School of Pharmaceutical Sciences, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
- Department of Pharmacology, Graduate School of Pharmaceutical Sciences, Tohoku University, 6-3 Aramaki-Aoba, Aoba-Ku, Sendai 980-8578, Japan
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5
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From representations to servomechanisms to oscillators: my journey in the study of cognition. Anim Cogn 2023; 26:73-85. [PMID: 36029388 PMCID: PMC9877067 DOI: 10.1007/s10071-022-01677-7] [Citation(s) in RCA: 8] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2022] [Revised: 07/20/2022] [Accepted: 08/09/2022] [Indexed: 01/29/2023]
Abstract
The study of comparative cognition bloomed in the 1970s and 1980s with a focus on representations in the heads of animals that undergird what animals can achieve. Even in action-packed domains such as navigation and spatial cognition, a focus on representations prevailed. In the 1990s, I suggested a conception of navigation in terms of navigational servomechanisms. A servomechanism can be said to aim for a goal, with deviations from the goal-directed path registering as an error. The error drives action to reduce the error in a negative-feedback loop. This loop, with the action reducing the very signal that drove action in the first place, is key to defining a servomechanism. Even though actions are crucial components of servomechanisms, my focus was on the representational component that encodes signals and evaluates errors. Recently, I modified and amplified this view in claiming that, in navigation, servomechanisms operate by modulating the performance of oscillators, endogenous units that produce periodic action. The pattern is found from bacteria travelling micrometres to sea turtles travelling thousands of kilometres. This pattern of servomechanisms working with oscillators is found in other realms of cognition and of life. I think that oscillators provide an effective way to organise an organism's own activities while servomechanisms provide an effective means to adjust to the organism's environment, including that of its own body.
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Place cells dynamically refine grid cell activities to reduce error accumulation during path integration in a continuous attractor model. Sci Rep 2022; 12:21443. [PMID: 36509873 PMCID: PMC9744848 DOI: 10.1038/s41598-022-25863-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2022] [Accepted: 12/06/2022] [Indexed: 12/14/2022] Open
Abstract
Navigation is one of the most fundamental skills of animals. During spatial navigation, grid cells in the medial entorhinal cortex process speed and direction of the animal to map the environment. Hippocampal place cells, in turn, encode place using sensory signals and reduce the accumulated error of grid cells for path integration. Although both cell types are part of the path integration system, the dynamic relationship between place and grid cells and the error reduction mechanism is yet to be understood. We implemented a realistic model of grid cells based on a continuous attractor model. The grid cell model was coupled to a place cell model to address their dynamic relationship during a simulated animal's exploration of a square arena. The grid cell model processed the animal's velocity and place field information from place cells. Place cells incorporated salient visual features and proximity information with input from grid cells to define their place fields. Grid cells had similar spatial phases but a diversity of spacings and orientations. To determine the role of place cells in error reduction for path integration, the animal's position estimates were decoded from grid cell activities with and without the place field input. We found that the accumulated error was reduced as place fields emerged during the exploration. Place fields closer to the animal's current location contributed more to the error reduction than remote place fields. Place cells' fields encoding space could function as spatial anchoring signals for precise path integration by grid cells.
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7
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Forro T, Volitaki E, Malagon-Vina H, Klausberger T, Nevian T, Ciocchi S. Anxiety-related activity of ventral hippocampal interneurons. Prog Neurobiol 2022; 219:102368. [PMID: 36273721 DOI: 10.1016/j.pneurobio.2022.102368] [Citation(s) in RCA: 8] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2022] [Revised: 10/04/2022] [Accepted: 10/18/2022] [Indexed: 12/04/2022]
Abstract
Anxiety is an aversive mood reflecting the anticipation of potential threats. The ventral hippocampus (vH) is a key brain region involved in the genesis of anxiety responses. Recent studies have shown that anxiety is mediated by the activation of vH pyramidal neurons targeting various limbic structures. Throughout the cortex, the activity of pyramidal neurons is controlled by GABA-releasing inhibitory interneurons and the GABAergic system represents an important target of anxiolytic drugs. However, how the activity of vH inhibitory interneurons is related to different anxiety behaviours has not been investigated so far. Here, we integrated in vivo electrophysiology with behavioural phenotyping of distinct anxiety exploration behaviours in rats. We showed that pyramidal neurons and interneurons of the vH are selectively active when animals explore specific compartments of the elevated-plus-maze (EPM), an anxiety task for rodents. Moreover, rats with prior goal-related experience exhibited low-anxiety exploratory behaviour and showed a larger trajectory-related activity of vH interneurons during EPM exploration compared to high anxiety rats. Finally, in low anxiety rats, trajectory-related vH interneurons exhibited opposite activity to pyramidal neurons specifically in the open arms (i.e. more anxiogenic) of the EPM. Our results suggest that vH inhibitory micro-circuits could act as critical elements underlying different anxiety states.
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8
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Lehr AB, Luboeinski J, Tetzlaff C. Neuromodulator-dependent synaptic tagging and capture retroactively controls neural coding in spiking neural networks. Sci Rep 2022; 12:17772. [PMID: 36273097 PMCID: PMC9588040 DOI: 10.1038/s41598-022-22430-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2022] [Accepted: 10/14/2022] [Indexed: 01/19/2023] Open
Abstract
Events that are important to an individual's life trigger neuromodulator release in brain areas responsible for cognitive and behavioral function. While it is well known that the presence of neuromodulators such as dopamine and norepinephrine is required for memory consolidation, the impact of neuromodulator concentration is, however, less understood. In a recurrent spiking neural network model featuring neuromodulator-dependent synaptic tagging and capture, we study how synaptic memory consolidation depends on the amount of neuromodulator present in the minutes to hours after learning. We find that the storage of rate-based and spike timing-based information is controlled by the level of neuromodulation. Specifically, we find better recall of temporal information for high levels of neuromodulation, while we find better recall of rate-coded spatial patterns for lower neuromodulation, mediated by the selection of different groups of synapses for consolidation. Hence, our results indicate that in minutes to hours after learning, the level of neuromodulation may alter the process of synaptic consolidation to ultimately control which type of information becomes consolidated in the recurrent neural network.
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Affiliation(s)
- Andrew B. Lehr
- grid.7450.60000 0001 2364 4210Department of Computational Neuroscience, University of Göttingen, Göttingen, Germany ,grid.7450.60000 0001 2364 4210Bernstein Center for Computational Neuroscience, University of Göttingen, Göttingen, Germany ,grid.7450.60000 0001 2364 4210Department of Computational Synaptic Physiology, University of Göttingen, Göttingen, Germany
| | - Jannik Luboeinski
- grid.7450.60000 0001 2364 4210Department of Computational Neuroscience, University of Göttingen, Göttingen, Germany ,grid.7450.60000 0001 2364 4210Bernstein Center for Computational Neuroscience, University of Göttingen, Göttingen, Germany ,grid.7450.60000 0001 2364 4210Department of Computational Synaptic Physiology, University of Göttingen, Göttingen, Germany
| | - Christian Tetzlaff
- grid.7450.60000 0001 2364 4210Department of Computational Neuroscience, University of Göttingen, Göttingen, Germany ,grid.7450.60000 0001 2364 4210Bernstein Center for Computational Neuroscience, University of Göttingen, Göttingen, Germany ,grid.7450.60000 0001 2364 4210Department of Computational Synaptic Physiology, University of Göttingen, Göttingen, Germany
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9
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Cariani P, Baker JM. Time Is of the Essence: Neural Codes, Synchronies, Oscillations, Architectures. Front Comput Neurosci 2022; 16:898829. [PMID: 35814343 PMCID: PMC9262106 DOI: 10.3389/fncom.2022.898829] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2022] [Accepted: 05/04/2022] [Indexed: 11/25/2022] Open
Abstract
Time is of the essence in how neural codes, synchronies, and oscillations might function in encoding, representation, transmission, integration, storage, and retrieval of information in brains. This Hypothesis and Theory article examines observed and possible relations between codes, synchronies, oscillations, and types of neural networks they require. Toward reverse-engineering informational functions in brains, prospective, alternative neural architectures incorporating principles from radio modulation and demodulation, active reverberant circuits, distributed content-addressable memory, signal-signal time-domain correlation and convolution operations, spike-correlation-based holography, and self-organizing, autoencoding anticipatory systems are outlined. Synchronies and oscillations are thought to subserve many possible functions: sensation, perception, action, cognition, motivation, affect, memory, attention, anticipation, and imagination. These include direct involvement in coding attributes of events and objects through phase-locking as well as characteristic patterns of spike latency and oscillatory response. They are thought to be involved in segmentation and binding, working memory, attention, gating and routing of signals, temporal reset mechanisms, inter-regional coordination, time discretization, time-warping transformations, and support for temporal wave-interference based operations. A high level, partial taxonomy of neural codes consists of channel, temporal pattern, and spike latency codes. The functional roles of synchronies and oscillations in candidate neural codes, including oscillatory phase-offset codes, are outlined. Various forms of multiplexing neural signals are considered: time-division, frequency-division, code-division, oscillatory-phase, synchronized channels, oscillatory hierarchies, polychronous ensembles. An expandable, annotative neural spike train framework for encoding low- and high-level attributes of events and objects is proposed. Coding schemes require appropriate neural architectures for their interpretation. Time-delay, oscillatory, wave-interference, synfire chain, polychronous, and neural timing networks are discussed. Some novel concepts for formulating an alternative, more time-centric theory of brain function are discussed. As in radio communication systems, brains can be regarded as networks of dynamic, adaptive transceivers that broadcast and selectively receive multiplexed temporally-patterned pulse signals. These signals enable complex signal interactions that select, reinforce, and bind common subpatterns and create emergent lower dimensional signals that propagate through spreading activation interference networks. If memory traces share the same kind of temporal pattern forms as do active neuronal representations, then distributed, holograph-like content-addressable memories are made possible via temporal pattern resonances.
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Affiliation(s)
- Peter Cariani
- Hearing Research Center, Boston University, Boston, MA, United States
- Department of Otolaryngology-Head and Neck Surgery, Harvard Medical School, Boston, MA, United States
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10
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Cheng K. Oscillators and servomechanisms in orientation and navigation, and sometimes in cognition. Proc Biol Sci 2022; 289:20220237. [PMID: 35538783 PMCID: PMC9091845 DOI: 10.1098/rspb.2022.0237] [Citation(s) in RCA: 18] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023] Open
Abstract
Navigational mechanisms have been characterized as servomechanisms. A navigational servomechanism specifies a goal state to strive for. Discrepancies between the perceived current state and the goal state specify error. Servomechanisms adjust the course of travel to reduce the error. I now add that navigational servomechanisms work with oscillators, periodic movements of effectors that drive locomotion. I illustrate this concept selectively over a vast range of scales of travel from micrometres in bacteria to thousands of kilometres in sea turtles. The servomechanisms differ in sophistication, with some interrupting forward motion occasionally or changing travel speed in kineses and others adjusting the direction of travel in taxes. I suggest that in other realms of life as well, especially in cognition, servomechanisms work with oscillators.
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Affiliation(s)
- Ken Cheng
- School of Natural Sciences, Macquarie University, Sydney, North Ryde, NSW 2109, Australia
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11
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Tomar A, McHugh TJ. The impact of stress on the hippocampal spatial code. Trends Neurosci 2021; 45:120-132. [PMID: 34916083 DOI: 10.1016/j.tins.2021.11.005] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2021] [Revised: 11/10/2021] [Accepted: 11/18/2021] [Indexed: 12/12/2022]
Abstract
Hippocampal function is severely compromised by prolonged, uncontrollable stress. However, how stress alters neural representations of our surroundings and events that occur within them remains less clear. We review hippocampal place cell studies that examine how spatial coding is affected by acute and chronic stress, as well as by stress accompanying fear conditioning. Emerging data suggest that chronic stress disrupts the acuity and specificity of CA1 spatial coding, both in familiar and novel contexts, and alters hippocampal oscillations. By contrast, acute stress may have a facilitatory impact on spatial representations. These findings encourage a fresh look at the documented stress-induced changes in hippocampal anatomy and in vitro excitability, and offer a new perspective on the links between stress and memory.
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Affiliation(s)
- Anupratap Tomar
- Center for Synaptic Plasticity, School of Physiology, Pharmacology, and Neuroscience, University of Bristol, University Walk, Bristol BS8 1TD, UK.
| | - Thomas J McHugh
- Laboratory for Circuit and Behavioral Physiology, RIKEN Center for Brain Science, 2-1 Hirosawa, Wako-shi, Saitama, Japan.
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12
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Vercruysse F, Naud R, Sprekeler H. Self-organization of a doubly asynchronous irregular network state for spikes and bursts. PLoS Comput Biol 2021; 17:e1009478. [PMID: 34748532 PMCID: PMC8575278 DOI: 10.1371/journal.pcbi.1009478] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2021] [Accepted: 09/24/2021] [Indexed: 11/21/2022] Open
Abstract
Cortical pyramidal cells (PCs) have a specialized dendritic mechanism for the generation of bursts, suggesting that these events play a special role in cortical information processing. In vivo, bursts occur at a low, but consistent rate. Theory suggests that this network state increases the amount of information they convey. However, because burst activity relies on a threshold mechanism, it is rather sensitive to dendritic input levels. In spiking network models, network states in which bursts occur rarely are therefore typically not robust, but require fine-tuning. Here, we show that this issue can be solved by a homeostatic inhibitory plasticity rule in dendrite-targeting interneurons that is consistent with experimental data. The suggested learning rule can be combined with other forms of inhibitory plasticity to self-organize a network state in which both spikes and bursts occur asynchronously and irregularly at low rate. Finally, we show that this network state creates the network conditions for a recently suggested multiplexed code and thereby indeed increases the amount of information encoded in bursts.
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Affiliation(s)
- Filip Vercruysse
- Department for Electrical Engineering and Computer Science, Technische Universität Berlin, Berlin, Germany
- Bernstein Center for Computational Neuroscience, Berlin, Germany
| | - Richard Naud
- Department of Physics, University of Ottawa, Ottawa, Canada
- uOttawa Brain Mind Institute, Center for Neural Dynamics, Department of Cellular and Molecular Medicine, University of Ottawa, Ottawa, Canada
| | - Henning Sprekeler
- Department for Electrical Engineering and Computer Science, Technische Universität Berlin, Berlin, Germany
- Bernstein Center for Computational Neuroscience, Berlin, Germany
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13
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Abstract
Animals navigate a wide range of distances, from a few millimeters to globe-spanning journeys of thousands of kilometers. Despite this array of navigational challenges, similar principles underlie these behaviors across species. Here, we focus on the navigational strategies and supporting mechanisms in four well-known systems: the large-scale migratory behaviors of sea turtles and lepidopterans as well as navigation on a smaller scale by rats and solitarily foraging ants. In lepidopterans, rats, and ants we also discuss the current understanding of the neural architecture which supports navigation. The orientation and navigational behaviors of these animals are defined in terms of behavioral error-reduction strategies reliant on multiple goal-directed servomechanisms. We conclude by proposing to incorporate an additional component into this system: the observation that servomechanisms operate on oscillatory systems of cycling behavior. These oscillators and servomechanisms comprise the basis for directed orientation and navigational behaviors. Expected final online publication date for the Annual Review of Psychology, Volume 73 is January 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.
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Affiliation(s)
- Cody A Freas
- Department of Psychology, University of Alberta, Edmonton, Alberta T6G 2E9, Canada
| | - Ken Cheng
- Department of Biological Sciences, Macquarie University, Sydney, New South Wales 2109, Australia;
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14
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Zheng Y, Liu XL, Hsieh LT, Hurtado M, Wang Y, Niendam TA, Carter CS, Ranganath C, Ragland JD. Disrupted Modulation of Alpha and Low Beta Oscillations Mediates Temporal Sequence Memory Deficits in People With Schizophrenia. BIOLOGICAL PSYCHIATRY: COGNITIVE NEUROSCIENCE AND NEUROIMAGING 2021; 6:1157-1164. [PMID: 33862254 DOI: 10.1016/j.bpsc.2021.04.002] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/19/2021] [Revised: 04/01/2021] [Accepted: 04/01/2021] [Indexed: 11/27/2022]
Abstract
BACKGROUND People with schizophrenia (SZ) exhibit impaired episodic memory when relating objects to each other in time and space. Empirical studies and computational models suggest that low-frequency neural oscillations may be a mechanism by which the brain keeps track of temporal relationships during encoding and retrieval, with modulation of oscillatory power as sequences are learned. It is unclear whether sequence memory deficits in SZ are associated with altered neural oscillations. METHODS Using electroencephalography, this study examined neural oscillations in 51 healthy control subjects and 37 people with SZ during a temporal sequence learning task. Multiple 5-object picture sequences were presented across 4 study-test blocks in either fixed or random order. Participants answered semantic questions for each object (e.g., living/nonliving), and sequence memory was operationalized as faster responses for fixed versus random sequences. Differences in oscillatory power between fixed versus random sequences provided a neural index of temporal sequence memory. RESULTS Although both groups showed reaction time differences in late blocks (blocks 3 and 4), this evidence of sequence memory was reduced in people with SZ relative to healthy control subjects. Decreases in globally distributed prestimulus alpha (8-12 Hz) and beta 1 (13-20 Hz) power for fixed versus random sequences in late blocks were also attenuated in people with SZ relative to healthy control subjects. Moreover, changes in oscillatory power predicted individual reaction time differences and fully mediated the relationship between group and sequence memory. CONCLUSIONS Disrupted modulation of alpha and beta 1 electroencephalography oscillations is a candidate mechanism of temporal sequence memory deficits in people with SZ.
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Affiliation(s)
- Yicong Zheng
- Center for Neuroscience, University of California, Davis, Davis, California; Department of Psychology, University of California, Davis, Davis, California
| | - Xiaonan L Liu
- Center for Neuroscience, University of California, Davis, Davis, California; Department of Psychology, University of California, Davis, Davis, California
| | - Liang-Tien Hsieh
- Department of Psychology, University of California, Berkeley, Berkeley, California; Helen Wills Neuroscience Institute, University of California, Berkeley, Berkeley, California
| | - Mitzi Hurtado
- Department of Psychiatry and Behavioral Sciences, University of California, Davis, Davis, California
| | - Yan Wang
- Department of Psychology, University of California, Davis, Davis, California
| | - Tara A Niendam
- Department of Psychiatry and Behavioral Sciences, University of California, Davis, Davis, California
| | - Cameron S Carter
- Department of Psychology, University of California, Davis, Davis, California; Department of Psychiatry and Behavioral Sciences, University of California, Davis, Davis, California
| | - Charan Ranganath
- Center for Neuroscience, University of California, Davis, Davis, California; Department of Psychology, University of California, Davis, Davis, California
| | - J Daniel Ragland
- Department of Psychiatry and Behavioral Sciences, University of California, Davis, Davis, California.
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15
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Tang W, Shin JD, Jadhav SP. Multiple time-scales of decision-making in the hippocampus and prefrontal cortex. eLife 2021; 10:e66227. [PMID: 33683201 PMCID: PMC7993991 DOI: 10.7554/elife.66227] [Citation(s) in RCA: 29] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2021] [Accepted: 03/05/2021] [Indexed: 02/07/2023] Open
Abstract
The prefrontal cortex and hippocampus are crucial for memory-guided decision-making. Neural activity in the hippocampus exhibits place-cell sequences at multiple timescales, including slow behavioral sequences (~seconds) and fast theta sequences (~100-200 ms) within theta oscillation cycles. How prefrontal ensembles interact with hippocampal sequences to support decision-making is unclear. Here, we examined simultaneous hippocampal and prefrontal ensemble activity in rats during learning of a spatial working-memory decision task. We found clear theta sequences in prefrontal cortex, nested within its behavioral sequences. In both regions, behavioral sequences maintained representations of current choices during navigation. In contrast, hippocampal theta sequences encoded alternatives for deliberation and were coordinated with prefrontal theta sequences that predicted upcoming choices. During error trials, these representations were preserved to guide ongoing behavior, whereas replay sequences during inter-trial periods were impaired prior to navigation. These results establish cooperative interaction between hippocampal and prefrontal sequences at multiple timescales for memory-guided decision-making.
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Affiliation(s)
- Wenbo Tang
- Graduate Program in Neuroscience, Brandeis UniversityWalthamUnited States
| | - Justin D Shin
- Graduate Program in Neuroscience, Brandeis UniversityWalthamUnited States
| | - Shantanu P Jadhav
- Graduate Program in Neuroscience, Brandeis UniversityWalthamUnited States
- Neuroscience Program, Department of Psychology, and Volen National Center for Complex Systems, Brandeis UniversityWalthamUnited States
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16
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Zakharova EI, Storozheva ZI, Proshin AT, Monakov MY, Dudchenko AM. Opposite Pathways of Cholinergic Mechanisms of Hypoxic Preconditioning in the Hippocampus: Participation of Nicotinic α7 Receptors and Their Association with the Baseline Level of Startle Prepulse Inhibition. Brain Sci 2020; 11:brainsci11010012. [PMID: 33374246 PMCID: PMC7824639 DOI: 10.3390/brainsci11010012] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2020] [Revised: 12/15/2020] [Accepted: 12/21/2020] [Indexed: 12/14/2022] Open
Abstract
(1) Background. A one-time moderate hypobaric hypoxia (HBH) has a preconditioning effect whose neuronal mechanisms are not studied well. Previously, we found a stable correlation between the HBH efficiency and acoustic startle prepulse inhibition (PPI). This makes it possible to predict the individual efficiency of HBH in animals and to study its potential adaptive mechanisms. We revealed a bi-directional action of nicotinic α7 receptor agonist PNU-282987 and its solvent dimethyl sulfoxide on HBH efficiency with the level of PPI > or < 40%. (2) The aim of the present study was to estimate cholinergic mechanisms of HBH effects in different brain regions. (3) Methods: in rats pretested for PPI, we evaluated the activity of synaptic membrane-bound and water-soluble choline acetyltransferase (ChAT) in the sub-fractions of ‘light’ and ‘heavy’ synaptosomes of the neocortex, hippocampus and caudal brainstem in the intact brain and after HBH. We tested the dose-dependent influence of PNU-282987 on the HBH efficiency. (4) Results: PPI level and ChAT activity correlated negatively in all brain structures of the intact animals, so that the values of the latter were higher in rats with PPI < 40% compared to those with PPI > 40%. After HBH, this ChAT activity difference was leveled in the neocortex and caudal brainstem, while for membrane-bound ChAT in the ‘light’ synaptosomal fraction of hippocampus, it was reversed to the opposite. In addition, a pharmacological study revealed that PNU-282987 in all used doses and its solvent displayed corresponding opposite effects on HBH efficiency in rats with different levels of PPI. (5) Conclusion: We substantiate that in rats with low and high PPI two opposite hippocampal cholinergic mechanisms are involved in hypoxic preconditioning, and both are implemented by forebrain projections via nicotinic α7 receptors. Possible causes of association between general protective adaptation, HBH, PPI, forebrain cholinergic system and hippocampus are discussed.
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Affiliation(s)
- Elena I. Zakharova
- Laboratory of General Pathology of Cardiorespiratory System, Institute of General Pathology and Pathophysiology, Baltiyskaya, 8, 125315 Moscow, Russia; (M.Y.M.); (A.M.D.)
- Correspondence: ; Tel.: +7-9199668657; Fax: +7-4991511756
| | - Zinaida I. Storozheva
- Laboratory of Clinical Neurophysiology, Serbsky’ National Medical Research Center for Psychiatry and Narcology, Kropotkinsky per., 23, 111395 Moscow, Russia;
| | - Andrey T. Proshin
- Laboratory of Functional Neurochemistry, P.K. Anokhin Institute of Normal Physiology, Baltiyskaya, 8, 125315 Moscow, Russia;
| | - Mikhail Yu. Monakov
- Laboratory of General Pathology of Cardiorespiratory System, Institute of General Pathology and Pathophysiology, Baltiyskaya, 8, 125315 Moscow, Russia; (M.Y.M.); (A.M.D.)
| | - Alexander M. Dudchenko
- Laboratory of General Pathology of Cardiorespiratory System, Institute of General Pathology and Pathophysiology, Baltiyskaya, 8, 125315 Moscow, Russia; (M.Y.M.); (A.M.D.)
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17
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Johnston M, Scarf D, Wilson A, Millar J, Bartonicek A, Colombo M. The effects of hippocampal and area parahippocampalis lesions on the processing and retention of serial-order behavior, autoshaping, and spatial behavior in pigeons. Hippocampus 2020; 31:261-280. [PMID: 33274822 DOI: 10.1002/hipo.23287] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2020] [Revised: 10/17/2020] [Accepted: 11/08/2020] [Indexed: 11/09/2022]
Abstract
We examined the role of the avian hippocampus and area parahippocampalis in serial-order behavior and a variety of other tasks known to be sensitive to hippocampal damage in mammals. Damage to the hippocampus and area parahippocampalis caused impairments in autoshaping and performance on an analogue of a radial-arm maze task, but had no effect on acquisition of 2-item, 3-item, and 4-item serial-order lists. Additionally, the lesions had no effect on the retention of 3-items lists, or on the ability to perform novel derived lists composed of elements from lists they had previously learned. The impairments in autoshaping and spatial behavior are consistent with the findings in mammals. The absence of impairments on the serial-order task may also be consistent once one considers that damage to the hippocampus in mammals seems to affect more internally-organized rather than externally-organized serial-order tasks. Together, the findings support the view that the avian hippocampal complex serves a function very similar to the mammalian hippocampus, a finding that is interesting given that the architecture of the avian hippocampus differs dramatically from that of the mammalian hippocampus.
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Affiliation(s)
- Melissa Johnston
- Department of Psychology, University of Otago, Dunedin, New Zealand
| | - Damian Scarf
- Department of Psychology, University of Otago, Dunedin, New Zealand
| | - Alysha Wilson
- Department of Psychology, University of Otago, Dunedin, New Zealand
| | - Jessica Millar
- Department of Psychology, University of Otago, Dunedin, New Zealand
| | - Adam Bartonicek
- Department of Psychology, University of Otago, Dunedin, New Zealand
| | - Michael Colombo
- Department of Psychology, University of Otago, Dunedin, New Zealand
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18
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Sanders H, Wilson MA, Gershman SJ. Hippocampal remapping as hidden state inference. eLife 2020; 9:51140. [PMID: 32515352 PMCID: PMC7282808 DOI: 10.7554/elife.51140] [Citation(s) in RCA: 48] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2019] [Accepted: 05/09/2020] [Indexed: 11/13/2022] Open
Abstract
Cells in the hippocampus tuned to spatial location (place cells) typically change their tuning when an animal changes context, a phenomenon known as remapping. A fundamental challenge to understanding remapping is the fact that what counts as a ‘‘context change’’ has never been precisely defined. Furthermore, different remapping phenomena have been classified on the basis of how much the tuning changes after different types and degrees of context change, but the relationship between these variables is not clear. We address these ambiguities by formalizing remapping in terms of hidden state inference. According to this view, remapping does not directly reflect objective, observable properties of the environment, but rather subjective beliefs about the hidden state of the environment. We show how the hidden state framework can resolve a number of puzzles about the nature of remapping.
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Affiliation(s)
- Honi Sanders
- Center for Brains Minds and Machines, Harvard University, Cambridge, United States.,Picower Institute for Learning and Memory and Department of Brain and Cognitive Sciences, Massachusetts Institute of Technology, Cambridge, United States
| | - Matthew A Wilson
- Center for Brains Minds and Machines, Harvard University, Cambridge, United States.,Picower Institute for Learning and Memory and Department of Brain and Cognitive Sciences, Massachusetts Institute of Technology, Cambridge, United States
| | - Samuel J Gershman
- Center for Brains Minds and Machines, Harvard University, Cambridge, United States.,Department of Psychology, Harvard University, Cambridge, United States
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19
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Xiao Z, Lin K, Fellous JM. Conjunctive reward-place coding properties of dorsal distal CA1 hippocampus cells. BIOLOGICAL CYBERNETICS 2020; 114:285-301. [PMID: 32266474 DOI: 10.1007/s00422-020-00830-0] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/17/2019] [Accepted: 03/25/2020] [Indexed: 06/11/2023]
Abstract
Autonomous motivated spatial navigation in animals or robots requires the association between spatial location and value. Hippocampal place cells are involved in goal-directed spatial navigation and the consolidation of spatial memories. Recently, Gauthier and Tank (Neuron 99(1):179-193, 2018. https://doi.org/10.1016/j.neuron.2018.06.008) have identified a subpopulation of hippocampal cells selectively activated in relation to rewarded goals. However, the relationship between these cells' spiking activity and goal representation remains elusive. We analyzed data from experiments in which rats underwent five consecutive tasks in which reward locations and spatial context were manipulated. We found CA1 populations with properties continuously ranging from place cells to reward cells. Specifically, we found typical place cells insensitive to reward locations, reward cells that only fired at correct rewarded feeders in each task regardless of context, and "hybrid cells" that responded to spatial locations and change of reward locations. Reward cells responded mostly to the reward delivery rather than to its expectation. In addition, we found a small group of neurons that transitioned between place and reward cells properties within the 5-task session. We conclude that some pyramidal cells (if not all) integrate both spatial and reward inputs to various degrees. These results provide insights into the integrative coding properties of CA1 pyramidal cells, focusing on their abilities to carry both spatial and reward information in a mixed and plastic manner. This conjunctive coding property prompts a re-thinking of current computational models of spatial navigation in which hippocampal spatial and subcortical value representations are independent.
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Affiliation(s)
- Zhuocheng Xiao
- Program in Applied Mathematics, University of Arizona, Tucson, AZ, 85721, USA
| | - Kevin Lin
- Program in Applied Mathematics, University of Arizona, Tucson, AZ, 85721, USA
- Department of Mathematics, University of Arizona, Tucson, AZ, 85721, USA
- Neuroscience Graduate Interdisciplinary Program, University of Arizona, Tucson, AZ, 85721, USA
| | - Jean-Marc Fellous
- Program in Applied Mathematics, University of Arizona, Tucson, AZ, 85721, USA.
- Department of Psychology, University of Arizona, 1503 E University Blvd, Suite 312, Tucson, AZ, 85721, USA.
- Neuroscience Graduate Interdisciplinary Program, University of Arizona, Tucson, AZ, 85721, USA.
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20
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Sokolova IV, Szucs A, Sanna PP. Reduced intrinsic excitability of CA1 pyramidal neurons in human immunodeficiency virus (HIV) transgenic rats. Brain Res 2019; 1724:146431. [PMID: 31491420 PMCID: PMC6939992 DOI: 10.1016/j.brainres.2019.146431] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2019] [Revised: 08/24/2019] [Accepted: 08/30/2019] [Indexed: 10/26/2022]
Abstract
The hippocampus is involved in key neuronal circuits that underlie cognition, memory, and anxiety, and it is increasingly recognized as a vulnerable structure that contributes to the pathogenesis of HIV-associated neurocognitive disorder (HAND). However, the mechanisms responsible for hippocampal dysfunction in neuroHIV remain unknown. The present study used HIV transgenic (Tg) rats and patch-clamp electrophysiological techniques to study the effects of the chronic low-level expression of HIV proteins on hippocampal CA1 pyramidal neurons. The dorsal and ventral areas of the hippocampus are involved in different neurocircuits and thus were evaluated separately. We found a significant decrease in the intrinsic excitability of CA1 neurons in the dorsal hippocampus in HIV Tg rats by comparing neuronal spiking induced by current step injections and by dynamic clamp to simulate neuronal spiking activity. The decrease in excitability in the dorsal hippocampus was accompanied by a higher rate of excitatory postsynaptic currents (EPSCs), whereas CA1 pyramidal neurons in the ventral hippocampus in HIV Tg rats had higher EPSC amplitudes. We also observed a reduction of hyperpolarization-activated nonspecific cationic current (Ih) in both the dorsal and ventral hippocampus. Neurotoxic HIV proteins have been shown to increase neuronal excitation. The lower excitability of CA1 pyramidal neurons that was observed herein may represent maladaptive homeostatic plasticity that seeks to stabilize baseline neuronal firing activity but may disrupt neural network function and contribute to HIV-associated neuropsychological disorders, such as HAND and depression.
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Affiliation(s)
- Irina V Sokolova
- The Scripps Research Institute, Department of Immunology and Microbiology, 10550 North Torrey Pines Road, La Jolla, CA 92037-1000, United States
| | - Attila Szucs
- The Scripps Research Institute, Department of Immunology and Microbiology, 10550 North Torrey Pines Road, La Jolla, CA 92037-1000, United States; University of California, San Diego, BioCircuits Institute, 9500 Gilman Drive, La Jolla, CA 92039-0328, United States; MTA-ELTE-NAP B Neuronal Cell Biology Research Group, Eötvös Lóránd University, Budapest, Hungary
| | - Pietro Paolo Sanna
- The Scripps Research Institute, Department of Immunology and Microbiology, 10550 North Torrey Pines Road, La Jolla, CA 92037-1000, United States.
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21
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GABAergic Medial Septal Neurons with Low-Rhythmic Firing Innervating the Dentate Gyrus and Hippocampal Area CA3. J Neurosci 2019; 39:4527-4549. [PMID: 30926750 PMCID: PMC6554630 DOI: 10.1523/jneurosci.3024-18.2019] [Citation(s) in RCA: 20] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2018] [Revised: 03/08/2019] [Accepted: 03/15/2019] [Indexed: 02/06/2023] Open
Abstract
The medial septum implements cortical theta oscillations, a 5–12 Hz rhythm associated with locomotion and paradoxical sleep reflecting synchronization of neuronal assemblies such as place cell sequence coding. Highly rhythmic burst-firing parvalbumin-positive GABAergic medial septal neurons are strongly coupled to theta oscillations and target cortical GABAergic interneurons, contributing to coordination within one or several cortical regions. However, a large population of medial septal neurons of unidentified neurotransmitter phenotype and with unknown axonal target areas fire with a low degree of rhythmicity. We investigated whether low-rhythmic-firing neurons (LRNs) innervated similar or different cortical regions to high-rhythmic-firing neurons (HRNs) and assessed their temporal dynamics in awake male mice. The majority of LRNs were GABAergic and parvalbumin-immunonegative, some expressing calbindin; they innervated interneurons mostly in the dentate gyrus (DG) and CA3. Individual LRNs showed several distinct firing patterns during immobility and locomotion, forming a parallel inhibitory stream for the modulation of cortical interneurons. Despite their fluctuating firing rates, the preferred firing phase of LRNs during theta oscillations matched the highest firing probability phase of principal cells in the DG and CA3. In addition, as a population, LRNs were markedly suppressed during hippocampal sharp-wave ripples, had a low burst incidence, and several of them did not fire on all theta cycles. Therefore, CA3 receives GABAergic input from both HRNs and LRNs, but the DG receives mainly LRN input. We propose that distinct GABAergic LRNs contribute to changing the excitability of the DG and CA3 during memory discrimination via transient disinhibition of principal cells. SIGNIFICANCE STATEMENT For the encoding and recall of episodic memories, nerve cells in the cerebral cortex are activated in precisely timed sequences. Rhythmicity facilitates the coordination of neuronal activity and these rhythms are detected as oscillations of different frequencies such as 5–12 Hz theta oscillations. Degradation of these rhythms, such as through neurodegeneration, causes memory deficits. The medial septum, a part of the basal forebrain that innervates the hippocampal formation, contains high- and low-rhythmic-firing neurons (HRNs and LRNs, respectively), which may contribute differentially to cortical neuronal coordination. We discovered that GABAergic LRNs preferentially innervate the dentate gyrus and the CA3 area of the hippocampus, regions important for episodic memory. These neurons act in parallel with the HRNs mostly via transient inhibition of inhibitory neurons.
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