Wednesday, July 8, 2009

'MORNING PEOPLE' AND 'NIGHT OWLS' SHOW DIFFERENT BRAIN FUNCTION



Are you an "early bird" or a "night owl?" Scientists at the University of Alberta have found there are significant differences in the way our brains function depending on whether we're early risers or night owls.

Neuroscientists in the Faculty of Physical Education and Recreation looked at two groups of people: "morning people," those who wake up early and feel most productive in the morning, and those who were identified as "evening people," who typically felt livelier at night.

Eighteen study participants were placed in two groups (nine morning people and nine evening people) after completing a standardized questionnaire about their habits. The participants were tested four times throughout the day: at 9 a.m., then in the afternoon at 1, 5 and 9 p.m., using three different techniques.

"We measured how much muscle force the two different participant groups could each generate during maximum contractions [and] we applied electrical stimulation to a nerve in the back of the knee to assess pathways through the spinal cord," said graduate student Olle Lagerquist, who came up with the original idea for the experiments.

"We also used trans-cranial magnetic stimulation-a magnet that we hold over the cortex-to stimulate brain cells to send a signal to different muscles."

The research team, made up of Lagerquist and fellow student Alex Tamm, technician Alejandro Ley and neuroscientist Dave Collins, made three major discoveries, the biggest of which was the difference in brain activity between the two groups.

"In morning people their cortical excitability actually decreased throughout the day. It was highest in the morning and lowest in the evening," said Tamm. "It was the opposite for evening people; their brain activity was highest at 9 p.m."

"[Before now] no one's been able to actually show that your brain has more excitability in the morning if you're a morning person and in the evening when you're an evening person," said Lagerquist.

Researchers were surprised by the result of the spinal-cord stimulation, which tested reflex response throughout the day. "We saw the spinal-cord excitability increase for both groups throughout the day," said Tamm.

The test that measured maximum muscle force found that morning people fared less well than evening people, who became physically stronger during day. Morning people didn't experience any change in the force they generated during maximum contractions throughout the day.

"We are suggesting that morning people may never reach their true maximum performance because their brain [activity] is going one way and their spinal cord activity is going the other, so it's offsetting," said Collins. "In evening people, both brain and spinal cord are at maximum in the evening and they get maximum performance at night."

Researchers are excited by these findings and the possibilities of future research in the area.

"We had a lot of measures and a lot of questions, and oftentimes when you do that, things come out very muddy," said Lagerquist. "The fact we could find something robust enough was a very nice surprise."

"As a next step, we may look at whether we can take morning people and evening people and [make morning people behave like evening people and vice versa]. No one has done that and then tested pathways through the brain and spinal cord the way we have, but it would be a very long, time-consuming process," said Lagerquist.

"It would have implications for shift work - and there are many questions. How quickly can we switch this? How difficult is it for an evening person to work a morning shift and be able to exist in that environment?"

(Photo: U. Alberta)

University of Alberta

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