Thursday, October 31, 2013

Tired Ideas

Have you ever wondered why it's difficult to concentrate for a prolonged period of time?  Most everyone has stories of working long nights, struggling to complete a project that must be done by morning.  We've all experienced the gradual decline in cognitive abilities and decreased levels of concentration.  But what is the biological cause of such fatigue?

Unfortunately, we're not quite sure yet.  However, we've got some pretty good ideas.

The simplest explanation for mental fatigue is known as the depletion model.  This model posits that the act of effortful thought consumes some resource (probably glucose) in the brain. As that resource is expended to the point of scarcity we then feel what we refer to as mental fatigue.  The depletion model is appealing in it's simplicity, but has become widely criticized in recent years and is currently thought unlikely to be an accurate representation of mental fatigue's cause.

One of the many problems with the depletion model is it doesn't seem to fit some subjective experiences well.  For example, most people have experienced waking up to a feeling of mental exhaustion.  If the depletion model is accurate than why would a relatively well rested brain have difficulty with resource depletion?  Situations such as these have led some people to attempt to create a wholly psychological model of mental exhaustion.  This paper discusses a psychological model wherein mental fatigue is viewed as a result of the opportunity cost of executive recruitment.  In other words, mental fatigue is caused by using your brain's higher functions to do something unpleasant such as difficult math problems or making conversation with an in-law.  The more you'd rather avoid the task, the more rapidly mental exhaustion sets in.

Psychological models often present interesting jumping off points and areas of discussion.  However, their lack of a biological mechanism limits their usefulness a great deal.  Without some sort of basis in neurobiology such models are little more than thought experiments in terms of application.

The most recent and well regarded models are in some ways the opposite of the depletion models.  Rather than focusing on the depletion of some neurological resource these models believe mental fatigue is caused by the accumulation of some excess product in the extracellular area (the area between cells).  Each time a neuron activates it releases chemicals into the extracellular space. While the brain has mechanisms to reclaim these chemicals, when present in excess (as during extreme mental exertion), these mechanisms may not be sufficient and an accumulation could occur.  This accumulation may then lead to a variety of effects including the activation of unintended astrocytes which we then experience as mental fatigue.

A growing body of evidence seems to support this recent model.  For example, a recent study has found that during sleep these reclamation mechanisms go into overdrive and clean these excess chemicals from the extracellular space.  This would explain why sleep is usually mentally reinvigorating. Studies have also shown that in cases of brain damage with mental fatigue as a symptom these systems are generally not working optimally due to inflammation.

Interestingly, while consensus seems to be moving towards these "excess" models, no one can seem to agree what exactly the brain is experiencing an excess of.  A recent study published in Science proposed that metabolites are the culprit while others suspect glutamate (a neurotransmitter) is the main cause.  Still, while the exact chemical responsible is a topic of debate most neuroscientists agree that an excess of something between cells is likely the cause of mental fatigue.

For the sake of brevity I have touched very lightly on each of these models. If you're interested in reading more regarding any of them the following links will be of interest:

Psychological/Opportunity Cost:

That's all for this week. Until next time stay safe and rationale.

Thursday, October 24, 2013

On the Science of Social Science

There have been rumblings of late in the economic's community about just how scientific economics really is. In particular Raj Chetty opined here that economics is indeed a science while Krugman rebutted here that while economics may or may not be a science, economists are rarely scientists.

The heart of the debate revolves around three issues in particular. Firstly, economists are often wrong. Secondly, economists predictions are often difficult to test. Finally, many economists cling to dogmatic ideas that the consensus agrees are unlikely.

I have applied this same line of thinking to meteorology and concluded that as goes economics so goes the science of weather. If one is deemed by the public to be a science then both shall be and vice versa.  After all, weather forecasts are often incorrect much like economic forecasts.  Even more damning, weather forecasts predict only a couple weeks ahead while economists are asked to predict events months or years ahead of time.

Additionally, meteorological models are supremely difficult to test. In fact, the only real evidence for their validity is the aforementioned often in error forecasts.  This is in no way the fault of meteorologists of course. It's simply prohibitively difficult (perhaps impossible) to create a lab large enough to create full size weather systems.  Similarly unless an council of economists comes to power over a decently sized nation macro level experimentation is impossible. Still, no one questions the validity of meteorology as a science and economics is constantly questioned.

And if a minority population clinging to outdated ideas is a reason to invalidate a discipline as a science then all sciences will soon be declared a farce.  It would not take much research to find physicists that still herald the idea of the aether, astronomers than believe in heliocetrism,  and biologists that decry evolution as a falsehood. In any science, minority opinions are not only normal but necessary and healthy. Claiming that some economists holding to their beliefs in the face of contrary evidence invalidates economics as a science is ridiculous.

The fact is that economics is a science.  It is true that many economists are not scientists, but that is a trend that is changing day by day.  It is only in the past several decades that the tools for large scale analysis has arisen and it takes a commiserate amount of time to train new economists to use these tools. A generation of economists rooted in theory and thought experiments is moving on and a new generation has begun to apply the modern tools of rigorous analysis and experimentation to a still growing discipline. Regrettably it appears many seem determined to keep their gaze fixed upon the past rather than the developing future of the science.

That's all for this week. Until next time stay safe and rationale.

Friday, October 4, 2013

A House Divided

If you're an American (and very likely if you're not) you know by now that the US government has shutdown over budget disagreements in the legislature.  What this "shutdown" entails is approximately 800,000 workers are neither working nor being paid.  However, "essential" workers continue to report for work and draw their paychecks.  The question is, "How big a deal is the shut down really?"

Economically speaking, as long as the budgetary problems are resolved relatively quickly there is unlikely to be a substantial impact.  Furloughed workers have historically received back pay upon their return to work during previous shut downs.  Thus, they will have as much money as usual during the upcoming holiday season.  Obviously all the work they would have accomplished during the shut down is lost forever, but in the grand scheme of the US economy their production is relatively small.  The larger economic impact is likely to be the continuing proof that the US political system is increasingly unable to get it's house in order.

For individuals however it's a very different story.  Nearly seventy five percent of the National Institute of Health's (NIH) staff has been furloughed.  Thus potentially life saving clinical trials have ground to a halt. Experiments that require daily monitoring have been hastily shelved in efforts to preserve cell lines. Grant moneys for federally funded projects are in many cases inaccessible to those receiving the awards. Even important federally maintained databases are either shut down or left unattended.

Similar stories are echoed throughout the research community. The Bureau of Economic Analysis and Census Bureau websites have been shutdown for the duration of the furlough. These organizations maintain databases that are valuable and essential resources for a great deal of economic research.  Without access to them many research projects will be unable to progress.

Of course, eventually the legislature will resolve their differences and such resources will become available again.  Among the hardest hit by a prolonged delay however will be NASA.  Due to the importance of certain celestial alignments any delay in mission launch schedules will set back missions by years as NASA waits for orbits to come together again.  The frustration of working on a mission for years just to be told a forced furlough would cause the launch window to be missed must be immeasurable.

The longer the shut down drags on the more profound the effects on research within our country will become.  Luckily the NIH grant cycle has just ended so there is a little time to resolve the congressional dispute without impacting the funding cycle too severely.  However, if an agreement is not reached within a few weeks funding for new and existing programs will very quickly begin to evaporate.  These programs are generally funded for the time being but require renewal which they'll be unable to acquire. We can only hope that wiser heads prevail in Washington and the shut down ends soon.

That's all for this week. Until next week stay safe and rationale.