What is the Explanation Behind Tickles?
Tickle is a complex somatosensory phenomenon involving two distinct types: knismesis (light, feather-like sensation) and gargalesis (heavy, laughter-producing sensation), which arises from specialized touch processing that can be self-suppressed through GABAergic cortical inhibition.
Two Types of Tickle Sensation
Tickle manifests as two separate sensory experiences 1:
- Knismesis: A light, feather-type sensation that produces a noxious or irritating feeling without laughter
- Gargalesis: A heavy, pressure-based sensation that triggers laughter and withdrawal responses, representing the classic "ticklish" experience most people describe
These two sensations likely involve different receptors, neural pathways, and central processing mechanisms, though both originate from cutaneous stimulation 1.
Neural Mechanisms and Timing
The physiological response to tickling occurs remarkably fast 2:
- 300 milliseconds: Changes in thoracic circumference and joyous facial expressions emerge after tickle onset
- 500 milliseconds: Vocalizations (laughter) begin approximately 200 ms after the initial physical responses
- The timing and acoustic properties of laughter (speed, loudness, pitch) directly correlate with subjective ticklishness intensity 2
Somatosensory cortex activity drives tickling-evoked vocalizations in a somatotopic manner, meaning different body regions activate corresponding cortical areas 3.
The Self-Tickle Suppression Phenomenon
You cannot effectively tickle yourself because self-touch induces widespread GABAergic inhibition across the somatosensory cortex 3:
- Self-touch produces global cortical inhibition rather than the excitation seen with external touch
- This inhibition suppresses both vocalizations and cortical responses
- Self-touch can even suppress responses to simultaneous external tickling or direct cortical stimulation 3
- Blocking cortical GABA receptors with gabazine abolishes self-tickle suppression, confirming the inhibitory mechanism 3
The suppression operates through broad sensory attenuation of temporally coincident inputs rather than requiring a sophisticated "self versus other" distinction 2, 3.
Why Certain Body Areas Are More Ticklish
The distribution of ticklishness across body regions remains incompletely understood 1, 4. One hypothesis suggests that highly ticklish areas represent vulnerable or vital body regions that become exposed during dominance-submission social play 1. However, no definitive neuroanatomical or receptor-based explanation currently exists for regional ticklishness variation 4.
Social and Behavioral Function
Gargalesis functions primarily as a social behavior rather than a simple reflex 1:
- Facilitates mother-infant bonding and interaction
- Helps integrate children with peers and adults during play
- May serve as part of mating rituals or sexual foreplay in adults
- Contains elements of dominance and submission, with laughter and withdrawal serving as submission signals 1
Tickle anticipation produces ambivalent responses—rats will actively seek tickling (nose-poking for it) while simultaneously showing escape behaviors, freezing, and alarm calls, resembling the mixed excitement and anxiety ("Nervenkitzel") seen in children 3.
Machine vs. Human Tickling
The interpersonal nature of tickling is less critical than previously thought 5:
- Subjects respond equally to tickling from an automated machine versus a human experimenter
- Smiling, laughing, and wiggling occur at similar rates regardless of perceived source
- Self-reported ticklishness remains virtually identical between conditions 5
This supports a reflex-based model requiring unpredictability rather than an interpersonal model requiring human agency 5.
Clinical Relevance: Distinguishing from Tic Disorders
When patients report a "tickle" sensation, particularly in the throat or chest, this may indicate different pathophysiology 6:
- Subjects undergoing tussive (cough) challenge often report a "tickle" sensation at the top center of their chest, accompanied by the urge to cough 6
- Patients with chronic cough commonly describe this tickle sensation 6
- In habit cough or psychogenic cough, patients may report a "tickle" in the throat and adopt a "chin-on-chest" posture 6
- This respiratory "tickle" represents airway mechanosensitivity or chemosensitivity rather than cutaneous tickle sensation 6