Effects of attention and expectation on tickle sensation

Behavioral and Cortical Correlates of Self-Suppression, Anticipation, and Ambivalence in Rat Tickling

The relationship between tickling, sensation, and laughter is complex. Tickling or its mere anticipation makes us laugh, but not when we self-tickle. We previously showed rat somatosensory cortex drives tickling-evoked vocalizations and now investigated self-tickle suppression and tickle anticipation. We recorded somatosensory cortex activity while tickling and touching rats and while rats touched themselves. Allo-touch and tickling evoked somatotopic cortical excitation and vocalizations. Self-touch induced wide-ranging inhibition and vocalization suppression. Self-touch also suppressed vocalizations and cortical responses evoked by allo-touch or cortical microstimulation. We suggest a global-inhibition model of self-tickle suppression, which operates without the classically assumed self versus other distinction. Consistent with this inhibition hypothesis, blocking cortical inhibition with gabazine abolished self-tickle suppression. We studied anticipation in a nose-poke-for-tickling paradigm. Although rats nose poked for tickling, they also showed escaping, freezing, and alarm calls. Such ambivalence ("Nervenkitzel") resembles tickle behaviors in children. We conclude that self-touch-induced GABAergic cortical inhibition prevents self-tickle, whereas anticipatory layer 5 activity drives anticipatory laughter. VIDEO ABSTRACT.

Laterality of Tickle Sensation Produced by Self-Stimulation,

Numerous authors have reported that people cannot create a tickling reaction in themselves. However, Provine (2000) claimed that ticklishness was felt even if he stimulated his own leg with his fingers. Ticklishness was stronger when the hand and leg were on opposite sides of the body. Provine's findings were replicated with 30 university students. Two types of stimulus presentation methods were adopted: a participant's fingers and a paintbrush. Ticklishness was assessed by self-rating and evaluation by observers. Provine's claim was supported only by the self-rating of stimulation with the fingers.

Learning and the wisdom of the body

According to Spence, the learning researcher's task is to explain the relationship between experimental variables and behavior changes occurring with practice. Spence eschewed biological speculation. In contrast, for a biologist, "explanation" consists of ascertaining how the observed behavior increases reproductive success. Fundamental to achieving reproductive success is survival to sexual maturity, and such survival depends on homeostatic mechanisms attenuating the effects of physiological disturbances that threaten existence. Drugs are one way of disrupting homeostatic functioning, and studies of drug effects indicate that homeostatic mechanisms are engaged not just by pharmacological perturbations, but also by stimuli that signal such perturbations. Similarly, we attenuate the effects of a variety of nonpharmacological stimuli by such anticipatory homeostatic adjustments. The learning researcher is a homeostasis researcher.

Pavlovian conditioning of the tickle response of human subjects: temporal and delay conditioning

Previous studies of the human response to a tickle have demonstrated that subjects will respond to a gesture that signals the onset of a tickle in the same way as to a tickle. Researchers have described this anticipatory response as an "expectation." In the current study, we investigated, from the Pavlovian framework, the response to a verbal stimulus preceding the tickle stimulus. We exposed subjects to experimental phases which included the Neutral Stimulus Alone, 100% Pairing of the Neutral and Unconditioned Stimuli (tickle strokes to the foot), Random Presentation, Partial (75%) Reinforcement, and Temporal Conditioning. Pavlovian conditioning was observed in all phases, suggesting a parsimonious explanation for the expectation effect described by others.