Tickling is the act of touching a part of the body – typically under the arms, along the neck, bottoms of the feet, and along the ribs and stomach – which can cause an involuntary twitching response and incite laughter. It appears that the sensation involves signals from nerve fibers associated with both pain and touch – activating part of the brain that copes with pain.
Scientists in Germany’s Eberhard Karls Universität Tübingen, led by Dirk Wildgruber – whose study was published online in the journal PLOS ONE – have uncovered the reason why we laugh hysterically when we are tickled.
Tickling activates the part of the brain that anticipates pain, the fight-or-flight response, which explains perhaps why we haphazardly lash out. Additionally, laughter from tickling may be part of a defense mechanism to signal submissiveness, as laughter is part of a socially complex means of communication known to convey joy and happiness.
Fight-or-flight is an acute stress response – a physiological reaction of the sympathetic nervous system – that occurs due to a conscious or subconsciously perceived harmful event, attack, or threat to survival.
A hormonal cascade, triggered by the hypothalamus, prepares the body for either fight or flight as a means of instinctive defense.
The hypothalamus, located just above the brain stem, is responsible for certain metabolic processes and activities of the autonomic nervous system – synthesizing and releasing certain neurohormones. These in turn stimulate or inhibit the secretion of pituitary hormones. The hypothalamus controls body temperature, hunger and thirst, attachment behaviors, arousal, and circadian cycles (sleep).
Using 18 medication-free volunteers – nine men and nine women of average age 26 years – and a functional magnetic resonance imaging (fMRI) scanner, researchers examined the difference in tickling laughter verses social laughter elicited from a joke or a funny situation and taunting. Scans were monitored under situations of tickling and when participants found something genuinely funny.
Standard laughs did not provoke the hypothalamus to prep for a threat. But both tickling and laughing activated the part of the brain called the operculum that control facial movements and vocal and emotional reactions.
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