Keeping it straight. Memory loss and learning difficulties in older people may result from weakening of the tiny vertical columns of neurons, known as microcolumns, that are found in the areas of the brain responsible for learning and remembering.
Researchers at BU’s Center for Polymer Studies, including College of Arts and Sciences Physics Professor Eugene Stanley, center director, and research associates Luis Cruz and Brigita Urbanc, Doug Rosene, a School of Medicine associate professor, and School of Public Health Assistant Professor Howard Cabral, recently studied brain structure and cognitive functioning in old and young rhesus monkeys. They concentrated on area 46 of the prefrontal cortex, an area of the brain known to be associated with age-related decline in memory and learning.
Microcolumns are stacks of about 100 neurons, each approximately 30 micrometers in diameter. Neurons within a single microcolumn are interconnected and are believed to be the fundamental computational unit of the cerebral cortex.
The studies of the monkey brains revealed no significant differences in the density of neurons; however, the strength of the microcolumns was significantly lower in the brains of the older monkeys. The researchers hypothesized that the microcolumns’ loss in strength is related to a misalignment of some of the neurons in the column. They created a mathematical model to test this, and found that moving a few of the neurons even slightly out of alignment significantly compromised the strength of the column. These structural changes, according to the researchers, adversely affect the ability of the microcolumn to function efficiently as an integrated unit, resulting in impaired ability to remember and learn.
Previous studies by Stanley and other researchers have established that disorder in the structure of microcolumns is found in the brains of people with conditions such as Alzheimer’s disease, Lewy body dementia, autism, dyslexia, and schizophrenia.
The researchers also looked at the relationship of the monkeys’ microcolumnar strength and their performance on tests of spatial working memory and recognition memory. Here, too, the lower the strength of the microcolumns, the poorer the monkeys performed on tests of memory and learning.
This research was published in the November 9, 2004, edition of the Proceedings of the National Academy of Sciences.
Catnapping. A cat snoozing in the sun may dream of different things than a person tucked into bed for the night, but according to another recent study from the laboratory of CAS Physics Professor Eugene Stanley, the patterns of brief sleep-wake transitions they experience as they sleep are remarkably similar.
The research team, led by former graduate student Chung-Chuan Lo (GRS’04) and including Plamen Ivanov, a research associate at the Center for Polymer Studies, as well as colleagues at Harvard Medical School and Philipps-Universitât in Marburg, Germany, examined the brief wake-sleep transitions that occur during the sleep of cats, mice, rats, and people.
The larger circadian rhythms of sleep and wakefulness are very different in these species. Adult cats spend two-thirds of their time sleeping, mainly in short periods scattered over 24 hours, mice and rats are nocturnal, and in general, adult humans sleep at night for a period of six to eight hours. Almost all animals, however, briefly awaken — for periods ranging from a few seconds to several minutes — many times throughout the entire sleep period. According to the authors, these awakenings may play a key role in the overall regulation of the sleep cycle.
The researchers mathematically analyzed the duration of sleep and wake episodes in the four species. They found that across all species the length of the short periods of wakefulness followed an almost identical pattern, known as a power-law distribution, in which short episodes of wakefulness were very common and long periods of wakefulness very rare. The duration of periods of sleep, however, was different for the four species. How long these periods lasted was related to the body and brain mass of the species.
This power-law distribution suggests that the process behind the timing of sleep-wake transitions is a phenomenon known in physics as “self-organized criticality,” which also describes the mechanisms of other natural systems, such as avalanches and earthquakes. In such a system, a point of critical change occurs as a result of internal rather than external forces. In the case of sleep patterns, the researchers surmise, it is likely the dynamics of the neural circuits themselves, rather than outside stimuli, that controls sleep.
Research team members believe that by understanding the mathematical patterns of these sleep-wake transitions, they can begin to model the complex interactions between neurons in the brain that govern sleep and wakefulness.
The research was reported in the December 14, 2004, Proceedings of the National Academy of Sciences. A description of a recent study from the Stanley lab on the relationship between cardiac rhythms and circadian cycles can be found at: http://
Briefs" is written by Joan Schwartz in the Office of the Provost. To read
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