Brain State Affects Memory Recall

A paper describing the work is published June 13 in the journal Proceedings of the National Academy of Sciences.
"It's been assumed that the process of retrieving a memory is cued by an external stimulus," said Charan Ranganath, professor at the UC Davis Center for Neuroscience and Department of Psychology. "But we found that the levels of brain activity before items came up were correlated with memory."
Graduate students Richard Addante and Andrew Watrous; Ranganath; Andrew Yonelinas, professor of psychology at the UC Davis Center for Mind and Brain; and Arne Ekstrom, assistant professor of psychology at the Center for Neuroscience, measured a particular frequency of brainwaves called theta oscillations in the brains of volunteers during a memory test.
Theta waves are associated with a brain that is actively monitoring something, Ranganath said. For example, rats show high theta waves while exploring a maze.
In the memory test, the volunteers had to memorize a series of words with a related context. They later had to recall whether they had seen the word previously and the context in which the word was seen.
High theta waves immediately before being prompted to remember an item were associated with better performance.
The work goes against the assumption that the brain is waiting to react to the external world, Ranganath said. In fact, most of the brain is busy with internal activity that is not related to the outside world -- and when external stimuli come in, they interact with these spontaneous patterns of activity.
It's not clear whether it is possible to deliberately put your brain into a better state for memory recall, Ranganath said. The laboratory is currently investigating that area -- with the hope that it might lead to better treatments for memory loss.

Sphingolipids

They belong to a class of lipids i.e. Membrane lipids. Sphingolipids come from the combination of sphingosine (a long chain base), which is an amino alcohol (and aliphatic in nature), and fatty acid.It is the simplest sphingolipid and is also referred to as sphingoid base. They have a head, which is polar in nature, and two tails, which are nonpolar.

The following mnemonic will help you a lot in remembering the structure of shingosine.



Sphingolipids are present in plasma membranes.

Types of sphingolipids:

1. Ceramide:
It consists of Fatty acid chain and sphingosine linked through amide linkage. It is ordinarily present in all sphingolipids.

These are the precursors of glycolipids and phospholipids having a wide range of function in the tissues.

2. Sphingophosphlipids
     a. Sphingomyelin
     It consists of Phosphoethanolamine or phosphocholine and 1-hydroxy group of a ceramide linked through ester linkage.Sphingomyelin is structurally similar to phosphatidylcholine but biologically and physically it is different.

3. Glycosphingolipids:

    a. Cerebrosides
    b. Sulfatides (Sulfated cerebrosides)
    c. Globosides
    d. Gangliosides

Fatty acids in Sphingolipids:
Fatty acids of sphingolipids are completely different from those of glycerolipids. They have very long chains and the number of carbon atoms may range from 25 to 35 in number.
Polyunstaurated fatty acids are rarely present in sphingolipids but sphingomyelins of testes and spermatozoa have this acid.
Monoenoic fatty acids and very long chain fatty acids are producd by specific elongases.
Free long chain fatty acids are converted in to free 2-hydroxy acids in vitro as a result of fatty acid 2-hydroxylase.It is an integral membrane protein of endoplasmic reticulum.

Synthesis of sphingolipids:

Synthesis of sphingolipids takes place in Endoplasmic reticulum. Following is the pathway for the synthesis of sphingolipids.

In the first step, Palmitoyl-CoA alongwith serine results into beta ketosphinganine to sphinganine to N-acylsphinganine to Ceramide containing sphingosine to Cerebroside and sphingomyelin.

Sphingomyelin cycle:
Sphingomyelin cycle is used to show a relationship between the metabolic products of sphingolipids.

Free sphingosine and certain other long chain bases work as mediators for many of the cellular processes. Sphingosine 1-phosphate and ceramide 1-phosphate increases mitosis.

Degradation of sphingolipids:
These are degraded by lysosomal enzymes.

Presence of sphingolipids in Micro-organisms:
Sphingolipids are also found in some genera of bacteria like sphingomonas and sphingobacterium.

Uses of sphingolipids:
They work as the site of adhesion of extracellular proteins. Sphingolipids are important in cell recognition and signal transmission/transduction.

Sphingolipids form the myelin sheath around the nerves in central nervous system.

Diseases in which sphingolipids are involved:

1. Microbial infections
2. Diabetes
3. Alzheimer's disease
4. Certain cancers
5. Some diseases of the respiratory and cardiovascular systems and
6. Some of the neurological syndromes

References:
Murray S. Webb, Marcel B. Bally, Lawrence D. Mayer, James J. Miller, Paul G. Tardi, Sphingosomes for enhanced drug delivery. Patent number: 5814335.

Further Reading:
Delivery System Handbook for Personal Care and Cosmetic Products : Technology, Applications and Formulations (Breakthroughs in Personal Care and Cosmetic Technology) by Meyer R. Rosen

Encyclopedia of Pharmaceutical Technology by James Swarbrick

Hannun, Y. A. 1994. The sphingomyelin cycle and the second messenger function of ceramide. Journal of Biological Chemistry, Vol. 269, No. 5.

http://lipidlibrary.aocs.org/lipids/introsph/index.htm

Copyright (c), 2008, jeepakistan.blogspot.com

Ceramide

Ceramides belong to a class of lipid molecules and are the principal component of intercellular lipids.
It is also found in the skin.

Structure:

Uses:
It is an important component in the cohesion of the cells of the skin i.e. holds the cells of the skin in a smooth and firm structure. Ceramide is used as an emollient in the products of hair care.