Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Neuroscientists Examine Link Between Theta Rhythm and the Ability of Animals to Track Their Location

02.05.2011
In a paper to be published today [April 29, 2011] in the journal Science, a team of Boston University researchers under the direction of Michael Hasselmo, professor of psychology and director of Boston University’s Computational Neurophysiology Laboratory, and Mark Brandon, a recent graduate of the Graduate Program for Neuroscience at Boston University, present findings that support the hypothesis that spatial coding by grid cells requires theta rhythm oscillations, and dissociates the mechanisms underlying the generation of entorhinal grid cell periodicity and head-direction selectivity.

Theta Rhythm - The hippocampal theta rhythm is an oscillation that can be observed in EEG recordings from the hippocampus and other brain structures in numerous species of mammals including rodents, rabbits, dogs, cats, bats, and marsupials. In rats, the most frequently studied species, theta rhythmicity is easily observed in the hippocampus, but can also be detected in numerous other cortical and subcortical brain structures.

Hippocampal theta, with a frequency range of 6–10 Hz, appears when a rat is engaged in active motor behavior such as walking or exploratory sniffing, and also during REM sleep. Models have proposed a role for theta rhythm in spatial navigation and episodic memory function.

Grid cells and Self-Localization – Early studies on navigation revealed that most animals have an exceptional ability to keep track of their location, even in complete darkness. Research now suggests that this ability may involve computations in the entorhinal cortex. Single cell recordings from the entorhinal cortex during navigation have revealed a specific type of neuron that is able to track a rat’s position. These cells have been termed ‘grid cells’ based on the fact that they fire when the rat is at regularly spaced locations in the environment, forming a hexagonal ‘grid’ in the environment. These cells might allow animals to keep track of their current location.

Computational neuroscientists, including Michael Hasselmo, have demonstrated how these grid cells could generate this regular spatial pattern based on theta oscillations in models. The models proposed that theta oscillations in the entorhinal cortex provide a baseline clocking mechanism. The model requires input from other cells that respond based on the current head direction of the animal or its current running speed. In the model, running speed and head direction inputs modulate the frequency of other oscillators, such that when these oscillations interact to influence the firing of a grid cell, they cause the grid cell to fire systematically dependent on the location of the animal.

Brandon et al., support this theoretical model by demonstrating that grid cells in the entorhinal cortex need the theta rhythm as a clock to help keep track of the animal’s location. In the article, “Reduction of Theta Rhythm Dissociates Grid Cell Spatial Periodicity from Directional Tuning,” Brandon et al., report that grid cells recorded in the medial entorhinal cortex of freely moving rats exhibit firing at regular spatial locations and temporal modulation with theta rhythm oscillations (4 to 11 hertz). The researchers analyzed grid cell spatial coding during reduction of network theta rhythm oscillations caused by inactivation of the medial septum (MS) with the drug muscimol. During MS inactivation, grid cells lost their spatial periodicity, whereas head-direction cells maintained their direction signal. Conjunctive grid–by–head-direction cells lost grid cell spatial periodicity but retained head-direction specificity. All cells showed reduced rhythmicity in autocorrelations and cross-correlations.

This finding provides experimental support for the role of oscillations in coding spatial location by neural circuits. Consistent with this data, other laboratories have shown that the same manipulation of MS that reduces theta rhythm can severely disrupt the behavioral ability of a rat to remember the location of prior events. The alteration of oscillatory dynamics in the entorhinal cortex could underlie impairments in the ability to remember the spatial location of events in an episode. For example, drugs that cause amnesia may do so through an influence on theta rhythm oscillations, and a change in oscillations could contribute to the influence of Alzheimer’s disease on the formation of new memories.

The following Computational Neurophysiology Laboratory researchers contributed to this report: Mark P. Brandon, Andrew R. Bogaard, Christopher P. Libby, Michael A. Connerney,

Kishan Gupta, Michael E. Hasselmo.

The article, “Reduction of Theta Rhythm Dissociates Grid Cell Spatial Periodicity from Directional Tuning,” Science, can be found at http://www.sciencemag.org/content/332/6029/595.abstract.

About the Computational Neurophysiology Laboratory—The Computational Neurophysiology Laboratory addresses the cortical dynamics of memory-guided behavior, including effects of neuromodulatory receptors and the role of theta rhythm oscillations in cortical function. Neurophysiological techniques are used to analyze intrinsic and synaptic properties of cortical circuits in the rat, and to explore the effects of modulators on these properties. Computational modeling is used to link this physiological data to memory-guided behavior. Experiments using multiple single-unit recording in behavioral tasks are designed to test predictions of the computational models. Areas of focused research include episodic memory function and theta rhythm dynamics in the entorhinal cortex, prefrontal cortex and hippocampal formation. Research addresses physiological effects relevant to Alzheimer’s disease, schizophrenia and depression.

About Boston University—Founded in 1839, Boston University is an internationally recognized institution of higher education and research. With more than 30,000 students, it is the fourth largest independent university in the United States. BU contains 17 colleges and schools along with a number of multi-disciplinary centers and institutes which are central to the school's research and teaching mission.

Michael Hasselmo
Boston University
Computational Neurophysiology Laboratory
(617) 353-1397
hasselmo@bu.edu

Michael Hasselmo | Newswise Science News
Further information:
http://www.bu.edu

More articles from Life Sciences:

nachricht Could this protein protect people against coronary artery disease?
17.11.2017 | University of North Carolina Health Care

nachricht Microbial resident enables beetles to feed on a leafy diet
17.11.2017 | Max-Planck-Institut für chemische Ökologie

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: A “cosmic snake” reveals the structure of remote galaxies

The formation of stars in distant galaxies is still largely unexplored. For the first time, astron-omers at the University of Geneva have now been able to closely observe a star system six billion light-years away. In doing so, they are confirming earlier simulations made by the University of Zurich. One special effect is made possible by the multiple reflections of images that run through the cosmos like a snake.

Today, astronomers have a pretty accurate idea of how stars were formed in the recent cosmic past. But do these laws also apply to older galaxies? For around a...

Im Focus: Visual intelligence is not the same as IQ

Just because someone is smart and well-motivated doesn't mean he or she can learn the visual skills needed to excel at tasks like matching fingerprints, interpreting medical X-rays, keeping track of aircraft on radar displays or forensic face matching.

That is the implication of a new study which shows for the first time that there is a broad range of differences in people's visual ability and that these...

Im Focus: Novel Nano-CT device creates high-resolution 3D-X-rays of tiny velvet worm legs

Computer Tomography (CT) is a standard procedure in hospitals, but so far, the technology has not been suitable for imaging extremely small objects. In PNAS, a team from the Technical University of Munich (TUM) describes a Nano-CT device that creates three-dimensional x-ray images at resolutions up to 100 nanometers. The first test application: Together with colleagues from the University of Kassel and Helmholtz-Zentrum Geesthacht the researchers analyzed the locomotory system of a velvet worm.

During a CT analysis, the object under investigation is x-rayed and a detector measures the respective amount of radiation absorbed from various angles....

Im Focus: Researchers Develop Data Bus for Quantum Computer

The quantum world is fragile; error correction codes are needed to protect the information stored in a quantum object from the deteriorating effects of noise. Quantum physicists in Innsbruck have developed a protocol to pass quantum information between differently encoded building blocks of a future quantum computer, such as processors and memories. Scientists may use this protocol in the future to build a data bus for quantum computers. The researchers have published their work in the journal Nature Communications.

Future quantum computers will be able to solve problems where conventional computers fail today. We are still far away from any large-scale implementation,...

Im Focus: Wrinkles give heat a jolt in pillared graphene

Rice University researchers test 3-D carbon nanostructures' thermal transport abilities

Pillared graphene would transfer heat better if the theoretical material had a few asymmetric junctions that caused wrinkles, according to Rice University...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Ecology Across Borders: International conference brings together 1,500 ecologists

15.11.2017 | Event News

Road into laboratory: Users discuss biaxial fatigue-testing for car and truck wheel

15.11.2017 | Event News

#Berlin5GWeek: The right network for Industry 4.0

30.10.2017 | Event News

 
Latest News

NASA detects solar flare pulses at Sun and Earth

17.11.2017 | Physics and Astronomy

NIST scientists discover how to switch liver cancer cell growth from 2-D to 3-D structures

17.11.2017 | Health and Medicine

The importance of biodiversity in forests could increase due to climate change

17.11.2017 | Studies and Analyses

VideoLinks
B2B-VideoLinks
More VideoLinks >>>