Perception Leads Reality - The Effect of Temperature on Perception

Perception, defined as the organization and identification of sensory information in order to represent and understand our environment [1], is in a state of constant flux. It should come as no surprise then, that even our body temperature can affect our perception.

Experiments have shown that our perception of time speeds up when our body temperature is increased above normal and decreased when our body temperature is cooled below normal [2]. The most common hypothesis for this phenomenon is that we have a temperature-sensitive biological or chemical clock and that temperature manipulation produces changes in arousal. Perhaps this explains why when we have a fever our sense of time is also warped!
Hypothermia also seems to affect our visual perception. In an EEG study of face recognition, it was found that hyperthermia accelerates the early stages of visual perception. In this experiment, upright and inverted faces were presented to two groups of participants, a control and a hyperthermic group. The hyperthermic group had earlier latencies in the two EEG peaks of interest, the P1 and N170.  However, the specific face sensitive response, the N170 had a significantly smaller amplitude in the hyperthermia group when compared to the controls. Furthermore, the inversion effect of the faces on the N170 remained unaffected. This result suggests that although hyperthermia impairs the detection of faces in the visual field and their initial streaming to face-specific structural mechanisms, the subsequent face-specific configural processing remains unaffected [3].
With respect to odor and taste perception, while the exact effect of our body temperature on odour perception remains unexplored, we know that temperature or heating itself increases the odour of a substance due to the release of volatile molecules. Furthermore, odour ratings rise when the temperature increases when samples are sniffed. However, ratings made retronasally rise only for solids and not liquids. This is thought to be because liquids reach body temperature faster than solids when placed in the mouth. [4]. As the prominent English writer Aldous Huxley says, “There are things known and there are things unknown, and in between are the doors of perception.” 

[1] Schacter, Psychol, 2011
[2] Wearden and Penton-Voak, Q J Exp Psychol B,1995
[3] Sun et al, Int J Hyperthermia, 2012
[4] Delwiche, Food Quality and Preference, 2004

by Apoorva Rajiv Madipakkam, Alumni AG Sterzer
This article originally appeared 2013 in CNS Volume 6, Issue 3, Heat or Cold: What's Good for the Brain?

Keeping a cool Head: Hypothermia for Neuroprotection after Cardiac Arrest

Induced hypothermia (lowering the body temperature to ≤35°C) attenuates neuronal damage and provides neuroprotection mainly through lowering the rate of metabolism. It thus finds applications in ameliorating the secondary damage associated with traumatic brain injury, cardiac arrest, and stroke. This article will focus on therapeutic hypothermia after cardiac arrest.

Advantages of Hypothermia
For each degree centigrade decrease in body temperature, cellular metabolism is reduced by 5-7%, but the observed neuroprotective effect of hypothermia is much greater than can be explained by reduced metabolism alone [1].
During hypothermia the brain is exposed to fewer excitatory neurotransmitters and has more time to clear free radicals. It also reduces the average kinetic energy and hence the velocities at which free radicals travel, effectively lowering the likelihood that a free radical can damage vital cell parts before it gets neutralized by the endogenous antioxidative system.
Altogether, hypothermia induces a favorable shift in intracellular concentrations of ions and metabolites such as inorganic phosphate, lactic acid, Ca²⁺ and H⁺, hence slowing brain acidosis [1].

Hypothermia Studies
Animal studies of therapeutic hypothermia have shown profound neuroprotective effects [1]. Despite being the most used model, the small rodent brain is structurally, dimensionally, and metabolically different from the proportionally bigger and complex human brain. Therefore, it probably shows a greater response to neuroprotective efforts. Unlike with rodent models human studies must take into consideration different temperatures, duration of therapy, therapy onset/ending, cooling methods, and factors such as age, gender, and pre-existing illness [1,2]. Clinical studies of hypothermia after cardiac arrest have therefore produced strongly inconsistent results.
The two largest recent controlled studies on humans have shown significant improvements in patients’ neurological outcome and survival. The European study on “Mild therapeutic hypothermia to improve the neurologic outcome after cardiac arrest” showed a reduction in mortality by 14% and a 16% increase in patients with a good neurological outcome (able to live independently ½ year after cardiac arrest) in the hypothermia group. The 2002 Australian study on “Treatment of Comatose Survivors of Out-of-Hospital Cardiac Arrest with Induced Hypothermia” demonstrated a 26% increase in patients with a good neurological outcome [1,3].

Cooling Methods
Cooling must be accompanied by the use of sedatives and neuromuscular blockers, otherwise treatment will cause shivering and hence re-warming of the body with a counterproductive increase in energy/oxygen consumption. A good treatment protocol and adequate monitoring is required to successfully apply hypothermia.
Many adequate cooling methods are available and, with advancing medical technology, even more have become available. One such new device is an intravascular heat exchanger [3], which allows for rapid cooling and exact monitoring of blood flow and temperature. Another new internal cooling method is the intravenous infusion of iced isotonic fluid, such as saline solution [2,3]. Because saline solution is readily available even in a pre-hospital setting and safe to use regardless of age or gender, this is a suitable candidate for the early initiation of hypothermia. It is nevertheless necessary to maintain the cooled state with other methods later [2,3].
External methods include the application of ice packs to areas with a high heat exchange capability like the armpits, neck, groin or the head in the form of a cooling helmet [3,4]. However, proper placing of these devices requires a breach of privacy, especially when carried out in a pre-hospital setting. In addition the rate of cooling is relatively slow. Alternative methods include the use of cooling blankets or wet-evaporative cooling [4].
Hypothermia should be initiated as soon as safely possible but homeostatic imbalances induced by ischemia and the physical insult of reperfusion will persist for days. Hence there is a long time window (48-72h) to initiate and maintain hypothermia. Any one cooling method alone has shown lower efficacy than two or more methods combined. That and the rapid invention and inclusion of new cooling methods is one reason why an optimal therapy has not been developed and should therefore be researched and compared across qualified hospitals around the world.

[1] Poldermann, Intensive Care Med, 2004
[2] Peberdy et al, Circulation, 2010
[3] Nolan et al, Circulation, 2003
[4] http://bit.ly/13SyEz4


By Rick Cornell Hellmann, Alumni Medical Neurosciences, AG Spinal Cord Injury

Hyperthermia Impairs Memory Functions

On extremely hot summer days, can we really perform our everyday tasks with full efficiency? Can we focus our attention on what we want? Or should we, perhaps, take at least two months off because working during summer does not make any sense?

Image by stux via pixabay

 
Once again, scientists do not disappoint us by providing research on the influence of hyperthermia on cognitive processes. In a number of studies, healthy participants were exposed to high temperatures and then tested on their cognitive abilities in comparison to control groups. The results are consistent and point to the fact that hyperthermia does indeed impair short-term memory. More specifically, it influences reaction time during visual short-term memory performance, yet does not affect the accuracy [1]. Importantly, it enhances activity in bilateral dorsolateral prefrontal cortex and right intraparietal sulcus, regions important for task performance [1]. It is speculated that these activity changes are due to the higher occupation of cognitive resources in response to hyperthermia.
In other studies, it has been shown that heat exposure impairs complicated cognitive abilities, like the aforementioned visual short-term memory. However, it does not affect performance in simple tests, like attention tests [2,3]. Moreover, the authors showed beneficial effects of head cooling during hyperthermia, which preserved memory capacity, but appeared ineffective on visual recognition tests [3].
Armed with this knowledge, you always have a good excuse when something goes wrong on a very hot day. Jumping into a lake is nothing more than improving your cognitive skills! Just remember to keep a cool head, at all times! 

[1] Jiang et al, Int J Hyperthermia, 2013
[2] Gaoua et al, Int J Hyperthermia, 2011
[3] Racinais et al, J Physiol, 2008

by Filip Morys, Alumni Med Neuro
This article originally appeared 2013 in CNS Volume 6, Issue 3, Heat or Cold: What's Good for the Brain?