Gargalesis, also known as tickling, is a common sensation experienced by humans and other species. Yet, scientific understanding of tickling remains limited. For example, we still do not know why specific parts of the body are more ticklish, why we are generally unable to tickle ourselves, or why some people enjoy being tickled while others do not respond at all or are extremely sensitive.
Throughout human history, numerous theories about tickling have been proposed by prominent thinkers, including Aristotle, Galileo Galilei, Bacon, Darwin, Descartes, Erasmus, and Socrates. Tickling represents a complex interaction between somatosensory perception, motor function, and affective processing by making it relevant across multiple domains of neuroscience. Interestingly, tickling often begins in the first year of life and tends to stabilize as development progresses.
Tickling research has significant implications for comparative and evolutionary neuroscience, as species such as bonobos, orangutans, chimpanzees, and gorillas respond to tickling. It is particularly relevant to social neuroscience given that it typically occurs within familial or familiar social contexts. Some studies suggest that tickling evokes more reflex-like reactions and may even be effectively induced by machines, raising intriguing questions about the mechanisms involved.
The perception of tickling is an exciting challenge for neuroscientists, and the study of gargalesis, a sensation caused by mechanical stimulation, is difficult due to a lack of consensus in the medical and research communities. The term “tickle” was originally used to describe itch-like sensations resulting from mild mechanical stimulation, but it was later applied to describe the laughter-inducing sensation of tickling. Experimental studies often vary in the specific sensations they aim to induce and investigate, leading to potentially contradictory results.
The peripheral mechanisms of tickling remain unclear; some researchers have proposed links to interoceptive sensing. It is necessary to differentiate knismesis and gargalesis, as knismesis may act protectively, and the function of gargalesis remains unknown. Currently, there are no standardized procedures to elicit ticklish sensations, the body areas stimulated, and the properties of the applied stimulation vary. There are no standardized dependent variables to quantify gargalesis and only a small number of studies have collected physiological responses. Neuroscientists need to recognize that the neural mechanisms underlying tickle sensations are limited due to the scarcity of neuroimaging studies.
To enhance tickle research reliability and methodological rigor, future studies should document whether the aim is to induce gargalesis or knismesis, transition from manual tactile stimulation to automated administration by using haptic devices and robots, and consider self-reports alongside other variables. Automated stimulation could help identify the neural mechanisms of gargalesis at both peripheral and central levels by enabling controlled comparisons of stimuli that differ only in key factors influencing perceived ticklishness.
The study of human tickle perception faces multiple challenges, including the absence of consensus, standardized methods, and clear neural explanations. Future research must focus on identifying the physical triggers, neural pathways, and the variation between self and others. A close partnership between human and animal experimentation can give evidence for tickling’s protective or social bonding function. Achieving methodological standardization could lead to breakthroughs in our understanding of this fascinating and understudied phenomenon.
Reference: Kilteni K. The extraordinary enigma of ordinary tickle behavior: Why gargalesis still puzzles neuroscience. Sci Adv. 2025;11(21):eadt0350. doi:10.1126/sciadv.adt0350
