A toughened individual welcomes novelty as a challenge, sees in it an opportunity for gain; an untoughened individual dreads it as a threat and sees in it nothing but potential harm. What is intriguing about research into toughness is the finding that to each of these attitudes–viewing novelty as a challenge or as a threat–there corresponds a distinctive physiological state.

Some scientists, recognizing that mental toughness corresponds to a physiological profile, have gone a step further and asked, can this toughness be trained? Scientists who think the answer is yes have built their research upon a curious finding–that resilience to stress comes from experiencing stress.

Sports scientists know, for instance, that to expand aerobic capacity athletes must endure a training process that shocks their muscles and taxes their cardiovascular systems, to the point of inflicting mild damage to tissues, and then punctuates this process with periods of rest and recovery. Stress, recovery, stress, recovery–when calibrated to exhaust an athlete’s resources, but only just, and then replenish them, the process can expand the productive capacity of a broad range of cells in the athlete’s body.

What the scientists studying toughening have found is that a somewhat similar process of challenge and psychological loading followed by recovery can tune our brain and nervous system so that we too approach stressors with resilience and an optimal mix of hormones, neuromodulators, and nervous-system activation.

Is there anything we can do once exhaustion, fatigue, anxiety, or stress have set in? To answer this question we must bear in mind that these conditions are messages sent from our body telling us what actions we should take, and we need to understand what they are saying. Quite often, though, we misunderstand these messages. A telling example can be found in our understanding of mental fatigue. Common sense tells us that it is a state of exhaustion, in which we have quite simply run out of energy, like a car running out of gas. The recommendation that naturally follows is a rest or vacation to replenish our energy reserves. Exhaustion of this kind certainly occurs. Run a marathon, and chances are you end up in a state of exhaustion; pull an all-nighter, and chances are you need some sleep. But more often than not, this is not the cause of mental fatigue. Often, mental fatigue disappears if we merely change activities, and that would not happen if we had exhausted our fuel.

A recently developed model in neuroscience provides an alternative explanation of fatigue. According to this model, fatigue should be understood as a signal our body and brain use to inform us that the expected return from our current activity has dropped below its metabolic cost. The brain quietly searches for the optimal allocation of attentional and metabolic resources, and fatigue is one way it communicates its results. If we are engaged in some form of search and have not turned up any results, our brain, through the language of fatigue and distractibility, tells us we are wasting our time and encourages us to look elsewhere.