The brain doesn’t like it hot

An adequate body temperature is essential for our survival. The brain is especially vulnerable to temperature changes. It won’t display its usual top performance when temperature is too high. Cooling of the brain on the other hand seems to have healing effects under certain circumstances. There might even exist a link between brain temperature and emotion.

Humans have the ability to adapt to a great diversity of climates. Effective thermoregulation is reduced, though, in hot and humid environments. Temperatures above 40º C can be life threatening. The brain itself can’t tolerate temperatures above 40.5º C.

Brain section showing the hypothalamus, which is involved in regulating body temperature. (© designua - Fotolia.com)

Brain section showing the hypothalamus, which is involved in regulating body and brain temperature. (© designua – Fotolia.com)

The hypothalamus, a brain structure just above the brainstem, is an important player in regulating body and brain temperature. Sleep also appears to have thermoregulatory functions. Body and brain temperatures are reduced during sleep. Heating the hypothalamus in animals induces sleep. This may point to a cooling function of sleep. But sleep may also be necessary for heat retention. The body temperature of sleep-deprived rats falls dramatically and they die, even when they are allowed to sleep again.

Yawning may be linked to temperature regulation as well. It possibly serves to send cooler air to the brain to help it stay alert. Breathing through the nose contributes to the brain’s cooling system too. Cooling of the mucous membranes by nose breathing lowers blood temperature.

Cognition
A strong relationship exists between body temperature and performance. Cognitive function is improved by increasing temperature slightly above normal and reduced by a slight decrease. An increased temperature enhances working memory, subjective alertness, and visual attention as it results in faster transmission of information. These effects concern only very small changes within the optimal thermal zone. Further heating or cooling impairs performance.

Hyperthermia happens when the body produces or absorbs more heat than it can dissipate. It is usually caused by prolonged exposure to high temperatures. Experimentally, hyperthermia is used to treat some kinds of cancer. Raising temperature causes cell death. Hyperthermia therapy is applied locally to damage and kill cancer cells.

A body temperature sinking below the required temperature for normal operation may result in hypothermia. (© Tyler Olson - Fotolia.com)

A body temperature sinking below the required temperature for normal operation may result in hypothermia. (© Tyler Olson – Fotolia.com)

The opposite of hyperthermia is called hypothermia. This occurs when the body temperature sinks below the required temperature for normal operation. A slightly lower body temperature may have a positive effect, as chemical processes including ageing slow down. In a study, transgenic mice were given a gene that elevated temperature in the hypothalamus. This made the hypothalamus lower the body temperature by 0.3 to 0.5º C. The transgenic mice lived substantially longer than normal mice, males about twelve percent and females about twenty percent.

The effect on humans hasn’t been studied. Many stories are known of children fallen into cold water and revived even after being unconscious for over an hour. In cold water, metabolism is lowered and the brain can withstand a longer period of hypoxia, lack of oxygen. The low temperature appears to prevent cellular damage that occurs when blood flow and oxygen are lost for a time.

Therapeutic hypothermia is being used for medical treatments, although there is no consensus yet on its effectiveness. Cooling techniques include a cap that blows cold air across the scalp, a chilling nasal spray, and an icy lung injection. To obtain results, a drop in temperature of about 4º C is necessary.

Brain cooling appears to have therapeutic potential for epilepsy, stroke, asphyxia, and other neurological diseases. It also prevents brain damage after heart attacks and can control intracranial pressure after a stroke as it reduces swelling. Cooling is an interesting technique for treatment of focal epilepsy. When applied very close to the focus, it terminates seizures.

Emotion
Temperature has big impact on human emotion. This is most clear when ambient temperatures are high. They are known to generate more aggression. Heat waves result in elevated numbers of deaths, suicides and murders.

A high brain temperature may generate negative feelings. (© olly - Fotolia.com)

A high brain temperature may generate negative feelings. (© olly – Fotolia.com)

But there also appears to be a link between brain temperature and emotion. The hypothalamus has a function in both thermoregulation and emotion. Some behavioural and physiological aspects, such as shivering, panting, and sweating, occur not only during thermoregulation, but with certain emotions as well, for instance fear and anxiety or excitement. Thermo sensitive neurons in the hypothalamus also change their activity in response to emotional stimuli.

Facial muscles may play a role in this link between temperature and emotion. When they stretch or tighten, the blood flow changes. This raises or lowers the temperature of the blood flowing in the brain and activates neurons in the hypothalamus. Variations in the cerebral temperature might influence the release of emotion-linked neurotransmitters, the brain’s chemical messengers.

Blowing air in the nasal cavity gives an emotional response: warm air generates aversive feelings and cool air pleasant feelings. People with a nasal congestion feel discomfort. Blocking of the nasal airways results in severe distress in spite of the fact that sufficient oxygen is reaching the brain via mouth breathing. A failure to cool the brain via air intake in the nasal cavity may be the cause for these negative feelings.

Further research should give more insight into the contribution of brain temperature to emotion. There might also exist a link with depression. The neurotransmitter serotonin plays a role in both depression and thermoregulation. Maybe brain temperature in individuals suffering from depression is higher than normal, which would add to negative feelings.

So, there is a lot of truth in the saying “Keep your cool!”, not only figuratively, but also literally. And when you are in a hot environment, remember to breath through your nose to help your brain stay cool.

Image

Business man with fan © Tom Wang – Fotolia.com

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