The Mental Health Social Worker

Might Aberrant Neuronal “Avalanches” Signal Mental Illness?

Even when we’re not doing much of anything, our brain’s cortex, or outer mantle, is bustling with activity. In fact, scientists for the first time have detected “avalanches” of cortex activity in awake monkeys at rest.

They’ve also discovered that these bursts of synchronous neuronal activity aren’t just random, but rather precisely ordered. Large avalanches are followed by smaller and smaller avalanches, much like the aftershocks of an earthquake. This type of ordering reveals that the normal state of cortex circuitry is at a tipping point: at the edge of instability — like rocks along an earthquake fault.

“Mental illness may involve disturbances in this delicate balance, and abnormal avalanche patterns are potentially detectable,” explained NIMH’s Dietmar Plenz, Ph.D. “Being in such a state of instability allows neurons to telegraph information optimally across varying distances and to quickly adapt to new challenges. This makes it possible for the cortex to grow through development and expand through evolution without changes in its architecture.”

Plenz and colleagues report on their study of neuronal avalanches online during the week of August 24, 2009 in the Proceedings of the National Academy of Sciences.

Background

Understanding the cortex’s complex functional architecture has posed challenges for researchers. Plenz’s earlier studies in cell cultures and brain slices suggested that cortex tissue is organized like grains of sand in a sand pile – with the potential for even a few grains to trigger large avalanches. Periods of relative calm are punctuated by the spontaneous, synchronous avalanches. To confirm these findings in intact, awake animals, Plenz and colleagues recorded electrical signals in different parts of the cortex of two monkeys that were resting in a chair.

Results of This Study

The researchers observed avalanches, synchronous bursts of neural activity across varying expanses of cortex, in a pattern that implies a specific structure. The neuronal avalanches seem to obey laws similar to those that characterize their geological counterparts. Again like earthquakes, smaller avalanches are more common than bigger ones. Their size can range from involving clusters of cells to widespread networks.

“Avalanches function at any scale, bridging a 1 mm distance in the same way as they bridge a 10 mm distance as the brain develops or evolves,” explained Plenz.

Significance

The state of instability appears to be a general property of cortex tissue. There are hints that disorders of thinking, such as schizophrenia, could involve a breakdown in this critical state, leading to aberrant neuronal avalanche activity, say the researchers.

What’s Next?

Plenz and NIMH colleagues are studying this possibility using a non-invasive technique called magnetoencephalography (MEG), which images electrical activity deep in the brain. They are comparing cortex activity in schizophrenia patients and healthy controls, looking for quantifiable neural signatures of abnormal avalanche activity.

“If a brain doesn’t show the normal, synchronous avalanche pattern, this could signal a brain disorder,” said Plenz.

Even though the monkey was just resting in a chair, neuronal avalanches were spontanously sparking in its brain’s outer mantle, or cortex. Electrodes (black dots) detected these synchronous bursts (colored circles) of neural activity. The diameter and color of the circles reflects the varying size of the avalanches, which occurred as disparate clusters of synchronous activity. Despite their irregular appearances, the avalanche patterns are highly organized in space and time obeying precise rules similar to those found for earthquakes. This suggests that the cortex is normally organized in a state with the potential for such critical activity.

Reference

Spontaneous cortical activity in awake monkeys composed of neuronal avalanches. Petermann T, Thiagarajan TC, Lebedev MA, Nicolelis MA, Chialvo DR, Plenz D. Proc Natl Acad Sci U S A. 2009 Aug 26.

WASHINGTON—The belief that healthy older brains are substantially smaller than younger brains may stem from studies that did not screen out people whose undetected, slowly developing brain disease was killing off cells in key areas, according to new research. As a result, previous findings may have overestimated atrophy and underestimated normal size for the older brain.

The new study tested participants in Holland’s long-term Maastricht Aging Study who were free of neurological problems such as dementia, Parkinson’s disease or stroke. Once participants were deemed otherwise healthy, they took neuropsychological tests, including a screening test for dementia, at baseline and every three years afterward for nine years.

According to the report in the September Neuropsychology, published by the American Psychological Association, participants were also given MRI scans at Year 3 to measure seven different parts of the brain, including the memory-laden hippocampus, the areas around it, and the frontal and cingulate areas of the cognitively critical cortex.

After examining behavioral data collected from 1994 to 2005 (with scans taken between 1997 and 1999 depending on when people entered the study), the researchers divided participants into two groups: one group with 35 cognitively healthy people who stayed free of dementia (average starting age 69.1 years), and the other group with 30 people who showed substantial cognitive decline but were still dementia-free (average starting age 69.2 years).

That cognitive decline was measured by drops of at least 30 percent on two or more of six core tests of verbal learning and fluency, recall, processing speed, and complex information processing, and/or drops of 3 or more points, or scores of 24 or lower (raising suspicion for cognitive impairment), on the Mini-Mental State Examination screening tool for dementia.

In contrast to the 35 people who stayed healthy, the 30 people who declined cognitively over nine years showed a significant effect for age in the hippocampus and parahippocampal areas, and in the frontal and cingulate cortices. In short, among the people whose cognition got worse, older participants had smaller brain areas than younger participants.

Thus, the seeming age-related atrophy in gray matter more likely reflected pathological changes in the brain that underlie significant cognitive decline than aging itself, the authors wrote. As long as people stay cognitively healthy, the researchers believe that the gray matter of areas supporting cognition might not shrink much at all. “If future longitudinal studies find similar results, our conception of ‘normal’ brain aging may become more optimistic,” said lead author Saartje Burgmans, who is due to receive her PhD later this year.

The findings should caution scientists about drawing conclusions from brain studies that don’t screen participants over time, using precise and objective definitions, the authors added.

Article: “The Prevalence of Cortical Gray Matter Atrophy May Be Overestimated In the Healthy Aging Brain,” Saartje Burgmans, PhD student, Martin P. J. van Boxtel, PhD, MD, Eric F. P. M. Vuurman, PhD, Floortje Smeets, PhD student, and Ed H. B. M. Gronenschild, PhD, Maastricht University; Harry B. M. Uylings, PhD, Maastricht University and VU University Medical Center Amsterdam; and Jelle Jolles, PhD, Maastricht University; Neuropsychology, Vol. 23, No. 5.

Full text of the article is also available from the APA Public Affairs Office.

Saartje Burgmans can be reached by email or at (+31) 43 3881942.

WASHINGTON—Every March, most Americans welcome the switch to daylight saving time because of the longer days, but also dread losing an hour of sleep after they move their clocks forward. Now a new study shows that losing just an hour of sleep could pose some dangerous consequences for those in hazardous work environments.

The findings are reported in the September issue of the Journal of Applied Psychology, which is published by the American Psychological Association.

“One hour of lost sleep may not seem like a lot. But our findings suggest it could have an impact on people’s ability to stay alert on the job and prevent serious injuries,” said the article’s lead author, Christopher Barnes, PhD. Barnes and co-author David Wagner, PhD, were both doctoral students in organizational behavior at Michigan State University when they conducted this research.

They analyzed the number of injuries reported to the Mine Safety and Health Administration from 1983 to 2006. The U.S. Department of Labor requires all mine operators to investigate and report all mining-related injuries. The researchers also looked at the number of work days employees missed as a result of their injuries. Across the 24 years, there were 576,292 reported injuries on the job.

On average, there were 3.6 more injuries on the Mondays following the switch to daylight saving time compared to other days, and 2,649 more days of work were lost as a result of those injuries. That’s approximately a 68 percent increase in lost work days. In their analysis, the researchers controlled for weekends and holidays. Work experience did not appear to play a role in the number of injuries suffered.

The researchers also confirmed that people do sleep less in the days after they’re forced to turn their clocks forward. They looked at data from the Bureau of Labor Statistics’ American Time Use Survey, which measures the amount of time Americans spend engaged in various activities, including sleep. For this study, the researchers looked at data from 14,310 interviews from 2004 to 2006. Results showed that after the switch to daylight saving time, people slept an average of 40 minutes less on the Sunday night they switched to daylight saving time.

The researchers did not find any significant changes in the number and severity of workplace injuries on the Mondays after the switch to standard time, when people gained an hour. Further analysis of the American Time Use Survey showed that people had a much easier time adjusting their sleep schedules and did not, on average, sleep less or more after they changed to standard time. These findings would help explain why there were no significant effects, according to Barnes.

The study could have some important practical implications for employers, Barnes said. “We think managers and organizations can use this information to help improve safety in the days following the switch to daylight saving time,” he said. “They can schedule particularly dangerous work on other days, perhaps later in the week after employees have had more time to adjust their sleep schedules.” Another suggestion would be to implement extra safety precautions on those days.

Article: “Changing to Daylight Saving Time Cuts Into Sleep and Increases Workplace Injuries,” Christopher M. Barnes, PhD, and David T. Wagner, PhD, Michigan State University; Journal of Applied Psychology, Vol. 94, No. 5

(Full text of the article is available from the APA Public Affairs Office and at http://www.apa.org/journals/releases/apl9451317.pdf)

Contact Christopher Barnes by e-mail; his phone number is (517) 214-0438.

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