Rats found to mentally re-enact events
CAMBRIDGE, Mass., Sept. 2 (UPI) -- U.S. scientists say they have discovered rats engage in a mental re-enactment of their recent experiences when choosing what actions to take.
Massachusetts Institute of Technology researchers said they recorded the activity of single neurons called "place cells" in a brain structure -- the hippocampus -- that has been shown to be crucial for learning and memory. They found place cells are activated in a unique pattern and sequence for each specific location in a maze.
When examining the brain recordings, the scientists determined the same pattern and sequence of activation took place during pauses in activity, and when rats confronted a choice of routes in the maze. The researchers found while a rat is awake but standing still in the maze, its neurons fire in the same pattern of activity that occurred while it was running.
"This may be the rat equivalent of 'thinking,'" said Professor Matthew Wilson, who led the study. "This thinking process looks very much like the reactivation of memory that we see during non-REM dream states, consisting of bursts of time-compressed memory sequences lasting a fraction of a second. So thinking and dreaming may share the same memory reactivation mechanisms."
The researchers, who included Fabian Kloosterman and Thomas Davidson, say their findings might also reflect how memory systems fail in people with Alzheimer's disease and schizophrenia.
The study appears in the journal Neuron.
Seed implants better for prostate cancer
CHICAGO, Sept. 2 (UPI) -- Two studies say brachytherapy -- radiation seed implants -- is a superior treatment for early-stage prostate cancer, officials at a Chicago non-profit say.
The Prostate Cancer Foundation of Chicago and The Taussig Cancer Center at Cleveland Clinic say two independent studies show brachytherapy produces a superior disease-free survival rate among patients with early-stage prostate cancer.
The Prostate Cancer Foundation of Chicago analyzed 9,137 patients who were treated for prostate cancer with brachytherapy between 1997 and 2008 at Chicago Prostate Center. The study says 67.5 percent of the patients were regarded as low risk, 29.36 percent as intermediate and 1.01 percent as high. For those patients, overall cure rates were 96 percent, 84 percent and 75 percent for low-, intermediate- and high-risk patients, respectively.
When combined with external beam radiation therapy in intermediate- and high-risk patients, the brachytherapy results far exceed those of surgery, the study says.
Researchers at the Taussig Cancer Center at Cleveland Clinic say for low-risk prostate cancer patients, brachytherapy was equally successful as external beam radiation, but more successful than a radical prostatectomy -- prostate removal.
Nitrous oxide now top Earth emission
WASHINGTON, Sept. 2 (UPI) -- The National Oceanic and Atmospheric Administration says nitrous oxide has become Earth's largest ozone-depleting substance emitted through human activities.
NOAA scientists said they have, for the first time, evaluated nitrous oxide emissions in terms of their potential impact on Earth's ozone layer. Not only did they find nitrous oxide to be the top ozone-depleting substance, but they said they expect it to remain so throughout the 21st century.
The scientists said nitrous oxide -- also known as "laughing gas" and occasionally used by physicians and dentists for its anesthetic and analgesic effects -- is emitted from natural sources and as a byproduct of agricultural fertilization and other industrial processes. Calculating the effect on the ozone layer now and in the future, NOAA researchers found emissions of nitrous oxide from human activities have eroded the ozone layer and will continue to do so for many decades.
The study by A.R. Ravishankara, J.S. Daniel and Robert Portmann at NOAA's Earth System Research Laboratory appears in the Aug. 27 online edition of the journal Science.
Study: HIV subtype causes dementia risk
BALTIMORE, Sept. 2 (UPI) -- U.S. scientists say they've discovered patients infected with a specific subtype of the human immunodeficiency virus have an increased risk of dementia.
Johns Hopkins University researchers said they determined HIV Subtype D might be more likely to cause dementia than other subtypes.
HIV is the virus that causes AIDS.
The scientists said their finding is the first to demonstrate the specific type of HIV has any effect on cognitive impairment, one of the most common complications of uncontrolled HIV infection.
The researchers said HIV occurs in multiple forms, distinguished by small differences in the virus's genetic sequence and designated by letters A through K. Of the 35 million people living worldwide with HIV, the majority live in sub-Saharan Africa, where subtypes A, C and D dominate.
The research, led by Professor Ned Sacktor, is reported in the journal Clinical Infectious Diseases.
