THE HIGH-ALTITUDE ADAPTATION OF THE ANDEAN HIGHLANDERS.

For thousands of years, high-altitude populations have inhabited plateaus in the Andean Mountains.
The first humans that lived on the highlands of the Andes arrived there for more or less than 12,000 years. High-altitude adaptation in animals and humans has been an instance of evolutionary process.
Since the time of the European arrival, which started in the early 1,500s, considerable genetic admixture has occurred with the Andeans, resulting in the introduction of 5% to 30% of European genes into the contemporary Andean gene pool.
At high altitudes barometric pressure is reduced and less oxygen is inhaled. As a result, the arterial oxygen content, being a measure of the oxygen carrying capacity, determined by hemoglobin concentration and oxygen saturation, is found higher in the Andean highlanders, compared to the sea-level population. That is, more oxygen per blood volume. This confers an ability to carry more oxygen in each red blood cell, making a more effective transport of oxygen in their body, while their breathing is essentially at the same rate.
The Andean highlanders are known to have their reproduction levels at a normal rate, without any effect in the giving birth or the risk for early pregnancy loss, which are common to hypoxic stress.
They have developmentally acquired enlarged residual lung volume and its associated increase in alveolar area, which are supplemented with increased tissue thickness. Though the physical growth in body size is delayed, growth in lung volumes is accelerated.
High-altitude environments can be debilitating to sea-level individuals exposed to elevations above 3,000m/9,843ft for periods ranging from several hours to days. Moderate symptoms induces substantial alterations in physiological and psychological parameters within a few hours. Immediately upon ascent to high altitude, there is a decreased blood oxygenation, which reduces the oxygen supply throughout the periphery and in the brain. With time the body compensates, at least in part, for the lack of oxygen, with a variety of responses.
High altitude then produces substantial impairments in a number of cognitive performances. Changes in psychomotor performance, mental skills, reaction time, vigilance, memory, and logical reasoning have all been measured at altitudes above 3,000m/9,843ft. Observed behaviors suggest that the initial mood experienced at altitude is euphoria, followed by depression. Individuals may also become quarrelsome, irritable, anxious, and apathetic.
Although disturbances in emotional control have been noticed since the time the first Europeans arrived to the highlands, there are few studies assessing mood changes at altitude.
In 1543, the anatomist Andreas Vesalius was the first to distinguish clearly between White Matter and the Gray Matter that overlay regions of the cerebral cortex. In the 19th century, the physician Jean Martin Charcot advanced in the understanding of White Matter's role with his studies of multiple sclerosis, a disease of young adults characterized by primary damage to the White Matter of the central nervous system. At the turn of the 20th century, the ascendancy of Sigmund Freud turned biomedical thinking toward psychoanalytic explanations of behavior, and for more than 50 years all of the brain- white and gray matter alike- was neglected. In 1965, Norman Geschwind, M.D., proposed that one mechanism underlying dysfunctional brain-behavior relationship rests on cerebral disconnection. He also advanced the view that the dense connectivity of the brain underlay its mental operations. Central to this concept was the idea that an intricate web of white matter pathways course exists within and between the brain's hemispheres.
The cerebral hemispheres work together to store memories, make judgments, form thoughts and learn new information. The left hemisphere of the brain controls writing, speech, comprehension and arithmetic. It is dominant in language and hand use in around 92 percent of people.
The distinct fissures of the brain made it be seen as divided into lobes. Both the left and the right hemispheres have 4 lobes: frontal, temporal, occipital and parietal. They have complex relationships, and they do not function alone. The frontal lobe is responsible for controlling speech, which involves writing and speaking. It also controls personality, behavior and emotions; problem solving, judgment and planning; intelligence, self awareness and concentration, and body movement.
On the other hand, the right hemisphere plays an important role in spacial processing and interpreting visual information.
Exercise promotes a greater demand for oxygen, so exposure to high altitude affects directly the neurotransmitter levels in the brain inducing a number of neurological and behavioral disturbances affecting the mood states of the individual. Cognitive performance is more vulnerable than psychomotor performance, then complex tasks are typically more affected than simple tasks. It manifests itself in increased errors, slowing of performance, or combination of these factors. Impairments occur in a graded manner.
Because human cognitive function is sensitive to changes in oxygen availability, exposure to high altitude should produce a continuum of effects as altitude level and duration increase.
Interestingly, some studies have reported that some of the changes in performance after exposures to extreme altitudes persist for up to a year after return to lower altitudes.