by Olivia Woodford-Berry, '19
Fainting spells can be a symptom of such health issues, from heart problems to neurological conditions. Though some patients with the mentioned symptoms may be shuffled from doctor to specialist, these symptoms may be a sign of something often overlooked. Before jumping to conclusions, consider some of the more basic questions: Are you drinking enough water?
Throughout human evolution, the brain has been molded to direct us towards higher odds of survival. When it comes to basic necessities, such as hydration, the brain’s primary function is to monitor what we need to do, when we need to do it, and as importantly, when we need to stop. In the brain, thirst is regulated by the hypothalamus, a region of the forebrain below the thalamus that also regulates hunger, body temperature, and the activity of the automatic nervous system. Still, though this aspect of our brain seems foundational to the human mind, there is relatively little known guidance towards understanding the biological basis of what reminds us to drink, and how these symptoms can be misdirected. A recent 2018 study from the California Institute of Technology demonstrated that excitatory neural populations in the lamina terminalis form an ordered circuit structure to regulate thirst. This mechanism includes signals from the thirst driving neurons in the subfornical organ (SFO) which are integrated into the circuitry of the brain by nitric oxide synthase-expressing neurons. Upon drinking, an inhibitory circuit, consisting of MnPO GABAergic neurons that express glucagon-like peptide 1 receptors (GLP1R), activates and inhibits the synaptic activity of the SFO thirst neurons.  That is to say, upon drinking water, the thirst signaling cells are quieted, resulting in a sense of immediate satisfaction.
This reaction is highly specialized to monitor drinking, for these inhibitory processes are activated only by liquids and are time-locked on the fluid consumption. In rat populations without functioning inhibitory cells, there is an “overly thirsty” phenotype that is a promising model for polydipsia, a syndrome that causes excessive thirst and may result in water intoxication.  Still, the exact mechanisms of these neural circuits and how they interact is not well understood.
In some cases, people have found ways around these problems despite our lack of scientific understanding. On the opposite side of the spectrum of polydipsia, there are people who don’t drink enough water. Though this problem is much more common, dehydration causes impaired physical performance, lower cognitive functions, and in some cases fainting.  As a result, many people have turned to technology. With the modern age a wave of apps has come telling us to eat better, exercise more, or in this case, drink more water. Whether we rely on ourselves our or phones, it is generally recommended that one consumes about 2.7-3.7 liters of water per day to be healthy. Thus, the creation of apps that do for us what our brains used to may speak to one of the lesser known ways that modern technologies allow us overcome our biology’s shortcomings.
1. Augustine V, Gokce SK, Lee S, Wang B, Davidson TJ, Reimann F, et al. Hierarchical neural architecture underlying thirst regulation. Nature. 2018.
3. Hillyer M, Menon K, Singh R. The effects of dehydration on skill-based performance. International Journal of Sports Science. 2015;5(3):99-107.