XML Feed for RxPG News   Add RxPG News Headlines to My Yahoo!   Javascript Syndication for RxPG News

Research Health World General
 
  Home
 
 Latest Research
 Cancer
 Psychiatry
 Genetics
 Surgery
 Aging
 Ophthalmology
  Cornea
  Cataract
  Retina
 Gynaecology
 Neurosciences
 Pharmacology
 Cardiology
 Obstetrics
 Infectious Diseases
 Respiratory Medicine
 Pathology
 Endocrinology
 Immunology
 Nephrology
 Gastroenterology
 Biotechnology
 Radiology
 Dermatology
 Microbiology
 Haematology
 Dental
 ENT
 Environment
 Embryology
 Orthopedics
 Metabolism
 Anaethesia
 Paediatrics
 Public Health
 Urology
 Musculoskeletal
 Clinical Trials
 Physiology
 Biochemistry
 Cytology
 Traumatology
 Rheumatology
 
 Medical News
 Health
 Opinion
 Healthcare
 Professionals
 Launch
 Awards & Prizes
 
 Careers
 Medical
 Nursing
 Dental
 
 Special Topics
 Euthanasia
 Ethics
 Evolution
 Odd Medical News
 Feature
 
 World News
 Tsunami
 Epidemics
 Climate
 Business
Search

Last Updated: Aug 19th, 2006 - 22:18:38

Ophthalmology Channel
subscribe to Ophthalmology newsletter

Latest Research : Ophthalmology

   DISCUSS   |   EMAIL   |   PRINT
How Thalamic Neurons Grab Your Attention
Jul 12, 2006, 05:27, Reviewed by: Dr. Priya Saxena

The analysis supports a role for the thalamus in directing attention, and as the researchers explain, reveals that bursting could be used as a reliable signal to direct attention-related resources toward a behaviorally relevant area of the visual field.

 
Certain salient features in a visual scene grab our attention, such as a tiger emerging from a field of tall grass, after which we may spend more time taking in the details. Both ways of experiencing the world are automatic, and the neurons that make up the brain's visual system switch between these two modes continuously. But the exact neurons and mechanisms responsible are still a mystery to neuroscientists.

Based on their physiological properties and connectivity, neurons in the region of the brain known as the thalamus seem especially well-suited to responding dynamically to our visual world. The thalamus is considered the relay station for the brain, shuttling information between sensory neurons and the cerebral cortex. Thalamic neurons in the lateral geniculate nucleus (LGN) respond to visual scenes in two distinct modes: sustained and regular tonic responses and short, rapid bursts. Neuroscientists have long been curious about the role of these distinct firing modes in processing visual information, and whether certain features in a visual scene elicit them.

To better understand the function of bursts, Nicholas Lesica, Garrett Stanley, and colleagues investigate the interplay between external stimuli and intrinsic physiological membrane properties in modulating LGN burst responses. In a new study, they record LGN neuron activity in response to sequences of movies showing natural scenes that vary in luminance, then mathematically simulate the neurons' response properties under different intrinsic physiological states, and with or without the burst mechanism.

The researchers incorporated several well-established properties of LGN neurons into their model. For example, bursting is known to depend on a fundamental physiological feature, a neuron's membrane potential. The membrane potential refers to the electrical potential, or voltage, across the membrane resulting from a balance of negatively and positively charged ions, such as calcium. When neurons are at rest, they sit at a negative, or lower, potential; but when they are activated by a stimulus or other neurons, the potential becomes more positive, or higher. Once a certain positive voltage threshold is reached, the neuron fires an action potential. Lesica et al. designed “integrate-and-fire” model neurons with exactly this threshold property.

Similarly, bursting is also based on a threshold mechanism. Bursts are mediated by “T-type” calcium channels (T channels) that pass positively charged calcium ions into the cell; they become inactive at relatively higher membrane potentials. To model burst firing due to T channels, Lesica et al. combined a low-threshold, voltage-dependent current (channels open at relatively low voltage membrane potentials). The model also mimicked the spatial properties that activate LGN neurons. The model allowed the researchers to tweak the membrane potential of their simulated LGN neurons during the movies. And to understand how the bursting affected a neuron's response, they removed the burst-firing mechanism altogether.

By systematically changing the membrane potential, the researchers observed a strong relationship between resting potential, T channel threshold potential, and burst firing. The percentage of bursts in the LGN response was greatest when the resting potential was much more negative than the threshold potential. To characterize how luminance changes in the stimulus and membrane potential interact to evoke bursts, they analyzed the luminance features that preceded bursts for several hundred milliseconds. They found that when the resting potential was lower than the T channel threshold potential, an excitatory stimulus alone could trigger a burst. In contrast, at higher resting potentials, a prolonged inhibitory stimulus was required (to de-inactivate the T channels) before an excitatory stimulus could evoke a burst. In either case, they found that bursts mediated an enhanced detection of the stimulus, similar to a “wake-up call” to pay attention to the stimulus. When the researchers removed the bursting mechanism in their model neurons, they found that the tonic mode of firing was not able to induce the same level of enhanced responses. They suggest instead that tonic firing may be important for conveying the details of a stimulus.

The analysis supports a role for the thalamus in directing attention, and as the researchers explain, reveals that bursting could be used as a reliable signal to direct attention-related resources toward a behaviorally relevant area of the visual field. The mathematical simulations allowed Lesica et al. to test the role of bursting in a way that is not currently feasible with real neurons. And their findings pave the way for future experimental studies showing how LGN burst and tonic responses faithfully represent the dynamic visual world in behaving animals.
 

- Dantzker JM (2006) Bursting on the Scene: How Thalamic Neurons Grab Your Attention. PLoS Biol 4(7): e250
 

Read Research Article

 
Subscribe to Ophthalmology Newsletter
E-mail Address:

 

Written by Jami Milton Dantzker

DOI: 10.1371/journal.pbio.0040250

Published: June 13, 2006

Copyright: © 2006 Public Library of Science. This is an open-access article distributed under the terms of the Creative Commons Attribution License


Related Ophthalmology News

Master Proteins Dictate Retinal Differentiation Timetable
Yellow plant pigments lutein and zeaxanthin reduce risk of age-related macular degeneration
Objective way to diagnose diseases of colour perception
Onchocerciasis treatment reduces prevalence and intensity by 38%
Antioxidants may slow retinal degeneration
Hormone Therapy Does Not Affect Age-Related Vision Loss
Eating Fish Protects Against Macular Degeneration
Research Highlights Risk Factors For Age-Related Vision Loss
How Thalamic Neurons Grab Your Attention
FDA approves ranibizumab for the treatment of wet age-related macular degeneration


For any corrections of factual information, to contact the editors or to send any medical news or health news press releases, use feedback form

Top of Page

 

© Copyright 2004 onwards by RxPG Medical Solutions Private Limited
Contact Us