scholarly journals Boundary cells in the representation of episodes in the human hippocampus

2021 ◽  
Author(s):  
Hye Bin Yoo ◽  
Gray Umbach ◽  
Bradley Lega
Keyword(s):  
Generalized Linear Model ◽  
Theta Oscillations ◽  
Free Recall Task ◽  
Human Hippocampus ◽  
Mesial Temporal Lobe ◽  
Episodic Memories ◽  
Hippocampal Theta ◽  
Field Coherence ◽  
Fundamental Requirement ◽  
Separate Population

The representation of episodes is a fundamental requirement for forming episodic memories, but the specific electrophysiological mechanisms supporting episode construction in the human hippocampus remain unknown. Experiments in rodent models indicate that a population of neurons sensitive to edges of an environment, termed border or boundary neurons in spatial navigation, fulfills a role analogous to episode demarcation. We hypothesized that such boundary neurons could be identified in the human mesial temporal lobe, with firing rates sensitive specifically to the beginning and end of mnemonically-relevant episodes in the free recall task. Using a generalized linear model to control for factors such as encoding success and item onset times along with other variables, we found 44 Boundary neurons out of a total 736 single neurons recorded across 27 subjects. We distinguish boundary neurons from a separate population of ramping neurons, which are time-sensitive neurons whose activity provides complementary but distinct information during episodic representation. We also describe evidence that the firing of boundary neurons within the preferred windows (at the beginning and end of episodes) is organized by hippocampal theta oscillations, using spike-field coherence metrics.

scholarly journals Functionally distinct high and low theta oscillations in the human hippocampus

2018 ◽  
Author(s):  
Abhinav Goyal ◽  
Jonathan Miller ◽  
Salman E. Qasim ◽  
Andrew J. Watrous ◽  
Joel M. Stein ◽  
...  
Keyword(s):  
Cognitive Processes ◽  
Spatial Navigation ◽  
Theta Oscillations ◽  
Movement Speed ◽  
General Role ◽  
Theta Oscillation ◽  
Human Hippocampus ◽  
Multiple Frequencies ◽  
Hippocampal Theta ◽  
Anterior Posterior

AbstractBased on rodent models, researchers have theorized that the hippocampus supports episodic memory and navigation via the theta oscillation, a ~4–10-Hz rhythm that coordinates brain-wide neural activity. However, recordings from humans have indicated that hippocampal theta oscillations are lower in frequency and less prevalent than in rodents, suggesting interspecies differences in theta’s function. To characterize human hippocampal theta, we examined the properties of theta oscillations throughout the anterior–posterior length of the hippocampus as neurosurgical subjects performed a virtual spatial navigation task. During virtual movement, we observed hippocampal oscillations at multiple frequencies from 2 to 14 Hz. The posterior hippocampus prominently displayed oscillations at ~8-Hz and the precise frequency of these oscillations correlated with the speed of movement, implicating these signals in spatial navigation. We also observed slower ~3-Hz oscillations, but these signals were more prevalent in the anterior hippocampus and their frequency did not vary with movement speed. Our results converge with recent findings to suggest an updated view of human hippocampal electrophysiology. Rather than one hippocampal theta oscillation with a single general role, high-and low-theta oscillations, respectively, may reflect spatial and non-spatial cognitive processes.

Human hippocampal theta oscillations and the formation of episodic memories

Hippocampus ◽  
2011 ◽  
Vol 22 (4) ◽  
pp. 748-761 ◽  
Author(s):  
Bradley C. Lega ◽  
Joshua Jacobs ◽  
Michael Kahana
Keyword(s):  
Theta Oscillations ◽  
Episodic Memories ◽  
Hippocampal Theta

scholarly journals Hippocampal theta oscillations are slower in humans than in rodents: implications for models of spatial navigation and memory

2014 ◽  
Vol 369 (1635) ◽  
pp. 20130304 ◽  
Author(s):  
Joshua Jacobs
Keyword(s):  
Electrical Activity ◽  
Large Amplitude ◽  
Theta Rhythm ◽  
Spatial Navigation ◽  
Theta Oscillations ◽  
Mammalian Brain ◽  
Neural Basis ◽  
Human Hippocampus ◽  
Neurosurgical Patients ◽  
Hippocampal Theta

The theta oscillation is a neuroscience enigma. When a rat runs through an environment, large-amplitude theta oscillations (4–10 Hz) reliably appear in the hippocampus's electrical activity. The consistency of this pattern led to theta playing a central role in theories on the neural basis of mammalian spatial navigation and memory. However, in fact, hippocampal oscillations at 4–10 Hz are rare in humans and in some other species. This presents a challenge for theories proposing theta as an essential component of the mammalian brain, including models of place and grid cells. Here, I examine this issue by reviewing recent research on human hippocampal oscillations using direct brain recordings from neurosurgical patients. This work indicates that the human hippocampus does indeed exhibit rhythms that are functionally similar to theta oscillations found in rodents, but that these signals have a slower frequency of approximately 1–4 Hz. I argue that oscillatory models of navigation and memory derived from rodent data are relevant for humans, but that they should be modified to account for the slower frequency of the human theta rhythm.

scholarly journals Supramammillary neurons projecting to the septum regulate dopamine and motivation for environmental interaction in mice

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Andrew J. Kesner ◽  
Rick Shin ◽  
Coleman B. Calva ◽  
Reuben F. Don ◽  
Sue Junn ◽  
...  
Keyword(s):  
Ventral Tegmental Area ◽  
Dopamine Neurons ◽  
Theta Oscillations ◽  
Mesolimbic Dopamine ◽  
Sucrose Consumption ◽  
Behavioral Interaction ◽  
Hypothalamic Structure ◽  
Hippocampal Theta ◽  
Substances Of Abuse ◽  
Stimulation Of

AbstractThe supramammillary region (SuM) is a posterior hypothalamic structure, known to regulate hippocampal theta oscillations and arousal. However, recent studies reported that the stimulation of SuM neurons with neuroactive chemicals, including substances of abuse, is reinforcing. We conducted experiments to elucidate how SuM neurons mediate such effects. Using optogenetics, we found that the excitation of SuM glutamatergic (GLU) neurons was reinforcing in mice; this effect was relayed by their projections to septal GLU neurons. SuM neurons were active during exploration and approach behavior and diminished activity during sucrose consumption. Consistently, inhibition of SuM neurons disrupted approach responses, but not sucrose consumption. Such functions are similar to those of mesolimbic dopamine neurons. Indeed, the stimulation of SuM-to-septum GLU neurons and septum-to-ventral tegmental area (VTA) GLU neurons activated mesolimbic dopamine neurons. We propose that the supramammillo-septo-VTA pathway regulates arousal that reinforces and energizes behavioral interaction with the environment.

scholarly journals Conceptualization and validation of an open-source closed-loop deep brain stimulation system in rat

2015 ◽  
Vol 5 (1) ◽  
Author(s):  
Hemmings Wu ◽  
Hartwin Ghekiere ◽  
Dorien Beeckmans ◽  
Tim Tambuyzer ◽  
Kris van Kuyck ◽  
...  
Keyword(s):  
Electrical Stimulation ◽  
Deep Brain Stimulation ◽  
Open Source ◽  
Brain Stimulation ◽  
Closed Loop ◽  
Symptom Control ◽  
Theta Oscillations ◽  
Open Source Hardware ◽  
Hippocampal Theta ◽  
Deep Brain

Abstract Conventional deep brain stimulation (DBS) applies constant electrical stimulation to specific brain regions to treat neurological disorders. Closed-loop DBS with real-time feedback is gaining attention in recent years, after proved more effective than conventional DBS in terms of pathological symptom control clinically. Here we demonstrate the conceptualization and validation of a closed-loop DBS system using open-source hardware. We used hippocampal theta oscillations as system input and electrical stimulation in the mesencephalic reticular formation (mRt) as controller output. It is well documented that hippocampal theta oscillations are highly related to locomotion, while electrical stimulation in the mRt induces freezing. We used an Arduino open-source microcontroller between input and output sources. This allowed us to use hippocampal local field potentials (LFPs) to steer electrical stimulation in the mRt. Our results showed that closed-loop DBS significantly suppressed locomotion compared to no stimulation and required on average only 56% of the stimulation used in open-loop DBS to reach similar effects. The main advantages of open-source hardware include wide selection and availability, high customizability and affordability. Our open-source closed-loop DBS system is effective and warrants further research using open-source hardware for closed-loop neuromodulation.

scholarly journals Event conjunction: How the hippocampus integrates episodic memories across event boundaries

2019 ◽  
Author(s):  
Benjamin James Griffiths ◽  
Lluís Fuentemilla
Keyword(s):  
Related Event ◽  
Gamma Model ◽  
Apparent Contradiction ◽  
The Past ◽  
Continuous Stream ◽  
Event Model ◽  
Episodic Memories ◽  
Hippocampal Theta ◽  
Conceptual Link ◽  
New Framework

Our lives are a continuous stream of experience. Our episodic memories, however, have a definitive beginning, middle and end. Theories of event segmentation suggest that salient changes in our environment produce event boundaries which partition the past from the present and, as a result, produce discretised memories. However, event boundaries cannot completely discretise two memories; any shared conceptual link will eagerly integrate these memories. Here, we present a new framework inspired by electrophysiological research that resolves this apparent contradiction. At its heart, the framework proposes that hippocampal theta-gamma coupling maintains a highly abstract model of an ongoing event and serves to encode this model as an episodic memory. When a second but related event begins, this theta-gamma model is rapidly reconstructed within the hippocampus where new details of the second event can be appended to the existing event model. The event conjunction framework is the first electrophysiological explanation of how event memories can be formed at, and integrated across, event boundaries.

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