Specific brain regions in charge of fatigue-moderating efforts
Scientists have revealed that certain brain regions regulate bouts of fatigue – overcoming this clutch will help scientists find therapies that increase physical performance in healthy people as well as in those with physical/mental limitations. The findings were gleaned from a recent study at the Johns Hopkins University School of Medicine, US.
Dr. Vikram Chib, an assistant professor of biomedical engineering at Johns Hopkins, said, “We know about the physiologic processes involved in fatigue, such as lactic acid build-up in muscles, but we know far less about how feelings of fatigue are processed in the brain and how our brain decides how much and what kind of effort to make to overcome fatigue.”
He went on to develop a novel way to objectively quantify how people “feel” fatigue: 20 adult participants were asked to grasp and squeeze a sensor until fatigued and then make risk-based decisions. The participants quickly learned to associate units of effort with how much to squeeze, which helped to standardise the effort level among individuals.
The participants could choose a risky option based on a coin flip, offering the chance to exert no effort, or a predetermined set effort level. Here, the scientists were possibly mimicking the way participants’ brains and minds might decide how much effort to make. The scientists also used computerised programs to measure how participants felt about the prospect of exerting particular amounts of effort while they were fatigued.
“Unsurprisingly, we found that people tend to be more risk averse to avoid effort,” said Dr. Chib. Most of the participants (19 of 20) opted for the risk-free choice of a predetermined effort level. This means that, when fatigued, participants were less willing to take the chance of having to exert large amounts of effort.
Later, Dr. Chib’s team evaluated participants’ brain activity collected during the gripping exercises using functional magnetic resonance imaging (fMRI) scans. The fMRI would track blood flow through the brain and show which clusters of neurons were most active; they took a closer look at the motor cortex of the brain when the participants were fatigued as this region of the brain is responsible for exerting the effort itself.
They found that brain activity in the motor cortex was deactivated at the time participants “decided” between the two effort choices, and fewer signals are sent down from the brain to the muscles. However, participants whose motor cortex activity changed the least, in response to fatiguing exertion, were the ones who were most risk averse in their effort choices and were most fatigued.
This suggests that fatigue might arise from a miscalibration between what an individual thinks they are able to achieve and the actual activity in motor cortex. It may also advance the search for therapies that target this pathway to help people control conditions that are associated with fatigue.
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