Preserving Brain Functionality

Abstract
Sedentary behavior associated with reduced medial temporal lobe thickness in middle-aged and older adults
Atrophy of the medial temporal lobe (MTL) occurs with aging, resulting in impaired episodic memory. Aerobic fitness is positively correlated with total hippocampal volume, a heavily studied memory-critical region within the MTL. However, research on associations between sedentary behavior and MTL subregion integrity is limited. Here we explore associations between thickness of the MTL and its subregions (namely CA1, CA23DG, fusiform gyrus, subiculum, parahippocampal, perirhinal and entorhinal cortex,), physical activity, and sedentary behavior. We assessed 35 non-demented middle-aged and older adults (25 women, 10 men; 45–75 years) using the International Physical Activity Questionnaire for older adults, which quantifies physical activity levels in MET-equivalent units and asks about the average number of hours spent sitting per day. All participants had high resolution MRI scans performed on a Siemens Allegra 3T MRI scanner, which allows for detailed investigation of the MTL. Controlling for age, total MTL thickness correlated inversely with hours of sitting/day (r = -0.37, p = 0.03). In MTL subregion analysis, parahippocampal (r = -0.45, p = 0.007), entorhinal (r = -0.33, p = 0.05) cortical and subiculum (r = -0.36, p = .04) thicknesses correlated inversely with hours of sitting/day. No significant correlations were observed between physical activity levels and MTL thickness. Though preliminary, our results suggest that more sedentary non-demented individuals have less MTL thickness. Future studies should include longitudinal analyses and explore mechanisms, as well as the efficacy of decreasing sedentary behaviors to reverse this association.

"Of course, we need larger samples and better ways to measure patterns of sedentary behavior. But if you're sitting for long periods of time, it seems that that factor — not physical activity — becomes the more harmful or more significant measure of your fitness. Even for people who are physically active, sitting a lot seems to be bad for your brain."
"[That's consistent with studies of sitting's effects on such health measures as heart disease, diabetes and mortality.] Now we're finding it in brain atrophy."
Prabha Siddarth, biostatistician, quantum chemist, UCLA

Too much sitting, or other sedentary behavior, is associated with a thinning of a part of the brain important for memory, new research suggests. (Getty Images)

Those of the public interested in health studies will be aware that previous research has shown that sitting around for prolonged periods has been identified as shortening one's lifespan. The sheer act of surrendering movement and activity for too great a part of the day rather than remaining active as much as possible, is geared toward poor health, irrespective of age. Now a new study, one that breaks new ground, appears to conclude that people in their middle ages and beyond are actually harming their brain structure by prolonged sitting.

According to the study, that very portion of the brain linked to learning and memory in those spending more time standing and moving about is 'plump' as opposed to those who sit about when they could be in movement, whose brains in that specific area of the medial temporal lobe and subregions become thin. They lose critical brain cells, resulting in episodic memory (geared to recalling past events) fading, across the age spectrum.

While it is normal as one ages that the brain naturally loses volume in this region, premature thinning sounds an alarm bell. Dementia is known for shrinkage of the brain and its memory centres, and it is highly likely that what contributes to this malady is thinning of the cortex. With Alzheimer's onset the density and volume of the hippocampus and entorhinal cortex (memory-making structures at the centre of the medial temporal lobe) becomes pronounced.

Interviews and tests of 35 test subjects, cognitively healthy, between 45 and 75 years of age contributed to the findings. UCLA's Semel Institute and Center for Cognitive Neurosciences researchers queried these volunteers to clarify the patterns of their normal physical activities, then scanned their brains in an MRI. Self-reported sitting time or physical activity levels were gauged to determine how they corresponded to thickness in those critical brain structures.

Researchers found, using the reported average sitting times of three to 15 hours daily, and adjusting for age, that each additional hour of average sitting on a daily basis could be linked to a two percent decrease in the thickness of the medial temporal lobe, suggesting that compared to an individual who sits ten hours daily, someone of the same age typically sitting for 15 hours would see a ten percent thinner medial temporal lobe.

Study leader Prabha Siddarth, pointed out that the differential is representative of quite a substantial fading brain substance and outcome. The brain's total volume is frequently measured by neuroscientists; examining variations in the thickness of a particular structure is more revealing of the differences among individuals, according to the biostatistician and quantum chemist.

No correlation was found between the exercise habits of the subjects and the thickness of either their medial temporal lobe or its constituent structures, surprising researchers, since other work has concluded that people who work out more have greater brain volume and improved cognitive performance. Dr. Siddarth warns the lack of correlation in her study should not be taken as comfort. Instead it may suggest that inveterate sitters engaging in routine intensive exercise cannot depend on that to reverse the negative course of too much sitting.

Anyone concerned to maintain plump brains and sharp memories should heed the interpretation of this new study: Get up, and get moving. Whatever you're doing, if it can be done while moving, walking about, engage in that kind of double-tasking. If your work mandates sitting at a desk, take frequent, regular walking, standing, exercise-movement breaks. Much depends on it.

"With every hour of sitting each day there is a 2 percent decrease in thickness. If you are able to decrease it by five hours, there would be a 10 percent decrease."
"We're not trying to give message that physical activity doesn't help."
"It's possible if we didn't sit continuously for extended period of times, [preserving thickness of the brain region could be achieved by taking breaks.] None of the people were also asked about mentally active sitting -- like Sudoku. All those need to be worked out."
Prabha Siddarth, biostatistician, quantum chemist, UCLA

Reducing sedentary behaviour may be a possible target for interventions designed to improve brain health in people at risk for Alzheimer’s disease, said Siddarth.