How to Become Smarter (68 page)

Heart rate (effects are due to baroreflex)

Heating (that causes hyperthermia)
:
increases

Cold hydrotherapy (without hypothermia)
:
reduces

Metabolic rate

Heating (that causes hyperthermia)
:
increases

Cold hydrotherapy (without hypothermia)
:
increases

Appetite

Heating (that causes hyperthermia)
:
reduces

Cold hydrotherapy (without hypothermia)
:
improves or no effect (continuous exposure to cold increases food intake, but causes a weight loss)

Sweating

Heating (that causes hyperthermia)
:
promotes

Cold hydrotherapy (without hypothermia)
:
reduces

On free will.
Free will is closely linked with the concept of determinism in that determinists believe that the future is predetermined and authentic free will does not exist. In their view, what most people consider to be free will is merely an illusion. Determinism is most likely incorrect because at the quantum mechanical level (the world of electrons, atoms, and molecules, i.e. the microworld) the events are unpredictable and uncertain as postulated in the Uncertainty Principle. The latest developments in quantum physics suggest that, in the world of elementary particles, identical sets of circumstances can produce different outcomes (it all depends on probabilities of various outcomes). Therefore, the future most likely is not predetermined in the microworld. The
macro
world, i.e. the world of people, consumer goods, and houses, is the extension of the
micro
world. Therefore, in the macroworld (our world) the future is not predetermined either. Some things are more predictable than others; for example, changes of day and night are predictable (you can predict them with high probability). Other things, such as weather, are less predictable.

Nonetheless, although it is difficult to predict what will happen in the life of any given person, it is easy to predict what will
not
happen, with high probability. With respect to financial future of a person, it is easy to predict that a person with average net worth and income will not get into the top 0.1% of wealth in the population. The probability that this prediction will hold true is roughly 99.9%.

Returning to the subject of free will, human free will is limited because thoughts, desires, needs, emotions, and personality traits are the products of activity of the brain, and unfortunately, the vast majority of people has no control over their brains and cannot select their brains from a catalog before they are born. A person is stuck with the brain she was born with for life. (See
endnote Z
regarding the hegemony of the brain over the mind.) The government strictly regulates the substances that can allow a person to control some brain functions: depressants, strong stimulants, euphoriants, opioid painkillers, hallucinogens, and others. The law forbids healthy people from using these substances, with rare exceptions. Science has yet to explain the vast majority of brain functions, and it is unclear how a person can change these functions. Some of the examples are character traits and criminal behavior. Existing cognitive enhancement techniques (such as
Ritalin
®) can improve some mental functions but these techniques have their limitations. It is likely that individual differences in behavior and intelligence will continue to be substantial, even if proven methods of cognitive enhancement become widely available.

The arguments presented above suggest that most people have little free will and little control over their actions. This, however, does not mean that the criminal justice system should be abolished. Without going into a long discussion about ethics and moral responsibility, it makes sense for society to isolate dangerous people, regardless of whether they intentionally chose to be evil or are merely victims of their abnormal brain.

Mechanisms underlying the anti-fatigue effect of cooling
(L
AY
L
ANGUAGE
S
UMMARY
): We reviewed existing evidence of this effect in the
main text
. Possible mechanisms of the reduction of fatigue by body cooling can be the following: i) a reduction of the total level of serotonin in the brain, which is in agreement with a widely known theory of fatigue; ii) activation of the brain region responsible for wakefulness (the reticular activating system); iii) stimulation of the thyroid gland and the resulting enhancement of metabolism; and iv) increased dopamine activity in some areas of the brain.

1. Animal models of exercise-related fatigue have shown that prolonged exercise results in an elevated extracellular level of serotonin in certain areas of the brain, particularly, in the frontal cortex and hippocampus, which led some investigators to formulate the “serotonin hypothesis of central fatigue” [
   646
   ,
   672
   -
   677
   ]. Because serotonin plays a role in sleep, lethargy, and loss of motivation, some investigators hypothesized that accumulation of serotonin in certain areas of the brain may cause fatigue [
   646
   ]. The serotonin hypothesis of central fatigue was modified some time later to include the important role of dopamine in the development of fatigue [
   678
   ], as discussed in more detail below. Interestingly, animal studies suggest that exposure to cold reduces the level of serotonin in most regions of the brain [
   679
   ,
   680
   ] except rostral brainstem [
   660
   ], which is consistent with diminished fatigue according to the above theory [
   646
   ,
   676
   ]. In addition, studies on human subjects have shown that body cooling results in a drop of plasma concentration of prolactin [
   665
   -
   667
   ], which is also consistent with reduced serotonin activity (or level) in the brain because plasma prolactin is an indicator of cerebral serotonergic activity [
   677
   ]. Some reports have shown that exposure to cold activates serotonergic neurons in some raphe nuclei [
   659
   ,
   681
   -
   683
   ] and also increases the level of serotonin in this brain region [
   660
   ]. The decline, however, of the total serotonin level in the brain that was demonstrated on experimental animals [
   679
   ,
   680
   ] suggests that firing activity of
   the majority
   of serotonergic neurons is likely to be inhibited by systemic cooling of the body.
   
2. Exposure to cold can activate some components of the reticular activating system also known as the diffuse modulatory system or brainstem arousal system [
   659
   -
   661
   ]. This system is a group of nuclei located in or near the brainstem and mainly responsible for control of the sleep/wake cycle [
   684
   ,
   685
   ]. Body cooling can activate serotonergic neurons of raphe nuclei [
   659
   ,
   681
   -
   683
   ] and noradrenergic neurons of the locus ceruleus [
   659
   ,
   686
   ,
   687
   ], the changes that can lead to enhanced somatomotor function of the brain and increased capacity of the CNS to recruit motoneurons [
   684
   ,
   688
   -
   692
   ]. Specifically, exposure to cold indeed can increase locomotor activity of laboratory animals [
   368
   ]. Conversely, reduced electrical activity in the diffuse modulatory system correlates with fatigue in laboratory animals [
   693
   -
   695
   ]. In polio survivors and in patients with multiple sclerosis, the presence of minor lesions in the reticular activating system correlates with severe chronic fatigue [
   696
   ,
   697
   ]. In laboratory animals, this type of lesions can cause lethargy [
   685
   ,
   690
   ,
   698
   ]. It should be pointed out that similar to cooling, psychostimulant drugs are also known to activate components of the reticular activating system, which is the likely mechanism of their fatigue-reducing and wakefulness-promoting effects [
   332
   ,
   370
   ,
   662
   -
   664
   ].
   
3. Hypofunction of the thyroid gland (hypothyroidism) is usually associated with fatigue [
   699
   ], whereas hyperthyroidism is associated with increased risk of hypomania and mania (but may also cause fatigue) [
   700
   ]. Exposure to cold activates the thyroid as evidenced by increased plasma levels of thyroid stimulating hormone, thyroxine, and triiodothyronine (the latter drives metabolism and thermogenesis) [
   701
   -
   704
   ]. High resting metabolic rate should accelerate recovery of fatigued muscle [
   705
   ,
   706
   ]. This is another possible mechanism of cold-induced reduction of fatigue. It is unclear whether repeated stimulation of the thyroid by body cooling can restore normal functioning of this gland. Patients with hypothyroidism usually have abnormal sensitivity to cold, which will make this treatment uncomfortable.
   
4. The fatigue-reducing properties of amphetamine (dopamine-norepinephrine reuptake inhibitor and a dopamine-releasing agent) have prompted the studies on the role of dopamine in central fatigue [
   707
   -
   710
   ]. Administration of amphetamine elevates the extracellular level of dopamine in many brain regions within 30 minutes [
   658
   ]. Several studies on laboratory animals indeed showed that dopamine may play a role in the development of fatigue. Particularly, the cerebral level of extracellular dopamine is decreasing during prolonged exercise [
   678
   ,
   711
   ]. These studies prompted some investigators to modify the serotonin hypothesis of central fatigue. The latest version states that the cause of fatigue is an increased ratio of cerebral serotonin to dopamine [
   646
   ,
   678
   ]. Surface cooling of the body can increase dopaminergic activity in some brain regions [
   472
   ]. Exposure to cold reduces the plasma level of prolactin [
   665
   -
   667
   ], which can be the result of reduced serotonergic activity or enhanced dopaminergic activity in the brain, or both [
   652
   ]. In all three scenarios, the decline of the prolactin level in blood plasma is consistent with reduced fatigue according to the serotonin hypothesis of central fatigue (reduced ratio of central serotonin to dopamine) [
   646
   ,
   678
   ]. As mentioned above, psychostimulant drugs reduce fatigue [
   332
   ] and reduce the plasma level of prolactin [
   668
   -
   670
   ].
   

Readers can find a more detailed discussion of this topic elsewhere [
671
].

Existing evidence of antidepressant effects of brief moderate cooling
(L
AY
L
ANGUAGE
S
UMMARY
): Moderate cooling of the body affects the activity of dopamine, norepinephrine, and serotonin in the brain, which is similar to the effects of some antidepressant drugs. There is also a resemblance with electroshock therapy, which is highly effective in depression.

In the main text we discussed several studies showing that cooling of the body has antidepressant properties [
376
,
385
,
387
]. There may be several mechanisms of the antidepressant effect of body cooling. Brief cooling of the body may produce physiological effects that are similar to the effects of some antidepressant drugs. In particular, animal studies suggest that exposure to cold can affect dopaminergic [
472
], noradrenergic [
659
,
686
,
687
], and serotonergic [
659
,
681
-
683
] pathways in the brain. These monoaminergic systems are targeted by various classes of antidepressant drugs, such as tricyclic antidepressants (mostly affect noradrenergic and serotonergic pathways [
712
]), monoamine oxidase inhibitors (target all three monoamine systems [
713
]), selective serotonin reuptake inhibitors (SSRIs), dopamine-norepinephrine reuptake inhibitors and serotonin-norepinephrine reuptake inhibitors.