Self-Tickle vs. Other-Tickle

Self-Tickle vs. Other-Tickle: Have your ever wondered why tickling yourself, doesn’t feel as nice as being tickled by someone else!? Here’s why …

It’s called Self-Tickle vs. Other-Tickle and the cause it doesn’t feel ‘right’ is that your brain is the one that ‘make you tingle’, not your senses …

Self-Tickle vs. Other-Tickle

It has been proposed that information about motor commands is used to distinguish the sensory consequences of our own actions from externally produced sensory stimuli, giving us the ability to monitor and recognize as our own, self-generated limb movements, touch, speech, and thoughts. This kind of mechanism can be used to maintain perceptual stability in the presence of self-produced movement. (Blakemore et al., 2000)

It is well known that you cannot tickle yourself

Figure 1. Active Interoceptive Inference Model (©2023 ADDspeaker.net)

This is because such attenuation of self-produced tactile stimulation [SELF-TICKLE] is due to the sensory predictions [PREDICTION] made by an internal forward model [ACTIVE INTEROCEPTIVE INFERENCE] of the motor system. A forward model [ACTIVE INTEROCEPTIVE INFERENCE] predicts the sensory consequences of a movement [PREDICTION] based on the motor command [SENSORY SIGNAL]. When a movement is self-produced [SELF-TICKLE], its sensory consequences can be accurately predicted [MATCH], and this prediction can be used to attenuate the sensory effects [SENSORY SIGNAL] of the movement [SELF-TICKLE]. As the discrepancy [PREDICTION ERROR] between predicted [PREDICTION] and actual sensory feedback [SENSORY SIGNAL] increases during self-produced tactile stimulation [SELF-TICKLE] there is a concomitant decrease [PRECISION WEIGHTING] in the level of sensory attenuation [PREDICTION] and an increase in tickliness [SENSORY SIGNAL]. Detecting the consequences of our own actions: We can readily distinguish between sensations that are produced by our own movements [SELF-TICKLE] and sensations that are caused by a change in the environment [OTHER–TICKLE]. This ability is important because it enables us to pick out stimuli that correspond to potentially biologically significant external events [OTHER–TICKLE] from stimuli that arise simply as a consequence of our own motor actions [SELF-TICKLE]. Prediction [PREDICTION] can also work in other sensory modalities [SELF-SPEECH, SELF-EMOTING, SELF-PLAY, SELF-MOTIVATING, SELF-ATTENTION, SELF-INHIBITION, and THOUGHTS] (Barkley, 2012), to alter sensory information, attenuating the component that is due to self-movement (re-afference) [SELF-TICKLE] from that due to changes in the outside world [OTHER–TICKLE]. In order to generate sensory predictions [PREDICTION], it is postulated that the central nervous system contains a central monitor or internal `forward model’ [INTERNAL MODEL]. Forward models [ACTIVE INTEROCEPTIVE INFERENCE] mimic aspects of the external world and the motor system in order to capture the forward [INFERENCE] or causal [EMPIRICAL PRIOR] relationship between actions [ACTION] and their outcomes [PERCEPTION]. (Blakemore et al., 2000)

Sensory consequences of movement

In order to generate sensory predictions, it is postulated that the central nervous system contains a central monitor or internal `forward model’. Forward models mimic aspects of the external world and the motor system in order to capture the forward or causal relationship between actions and their outcomes.

An efference copy of the motor command is used to generate continuously predictions of the sensory consequences (or corollary discharge) of the ongoing motor act. (Blakemore et al., 2000)

Figure 2. A model for determining the sensory consequences of a movement.

An internal forward model makes predictions of the sensory feedback based on the motor command. These predictions are then compared with the actual sensory feedback. Self-produced sensations can be correctly predicted on the basis of the motor command and are associated with little or no sensory discrepancy resulting from the comparison between predicted and actual sensory feedback.

As the sensory discrepancy from this comparison increases (for example by increasing the delay or trajectory rotation between the movement and its sensory consequences) so does the likelihood that the sensation is externally produced. By using such a system, it is possible to cancel out the effects on sensation induced by self-motion and thereby distinguish sensory events due to self-produced motion from the sensory feedback caused by the environment, such as contact with objects. (Blakemore et al., 2000)

The Active Interoceptive Inference Brain

Figure 3. (Hutchinson & Barrett, 2019)

This prediction is then compared with the actual sensory feedback (re-afference) from the movement. Self-produced sensations can be correctly predicted on the basis of motor commands, and there will therefore be little or no sensory discrepancy resulting from the comparison between the predicted and actual sensory feedback. This accurate prediction can be used to attenuate the sensory effects of self-produced movement. In contrast, externally generated sensations are not associated with any efference copy and therefore cannot be predicted by the forward model. By removing or attenuating the component of sensory feedback that is due to self-produced movement it is possible to accentuate the feedback that is caused by external effects. This process therefore alters incoming sensory information for perhaps the more relevant component of information. (Blakemore et al., 2000)

The Active Interoceptive Inference Mind

Figure 4. (Hutchinson & Barrett, 2019)

The Helmholtz Eye Gaze Direction Model

For example, during eye-movements an efference copy of the motor command is used to predict the effects of the movement. In order to determine the location of an object relative to the head, its retinal location and the gaze direction must be known. As the eye muscles are thought to contain no sensory receptors used to determine the gaze direction, Helmholtz proposed that the gaze direction is determined by predicting the eye location based on the efference copy of the motor command going to the eye muscles. Using this estimate of eye position together with the object’s retinal location, the object’s true position in space can be determined. When the eye is moved without using the eye muscles (for example by gently pressing on the eye lid with the anger), the retinal location of objects changes, but the predicted eye position is not updated, leading to the perception that the world is moving. (Blakemore et al., 2000)

Forward models in schizophrenia

Frith proposed that a defect in this kind of central ‘self-monitoring’ mechanism might underlie auditory hallucinations and passivity phenomena, which are ‘first rank’ features in schizophrenia. Auditory hallucinations normally consist of hearing spoken voices. The essence of passivity experiences (or delusions of control) is that the subject experiences his or her will as replaced by that of some other force or agency: ‘My fingers pick up the pen, but I don’t control them. What they do is nothing to do with me… The force moved my lips. I began to speak. The words were made for me’. Frith has suggested that these abnormal experiences arise through a lack of awareness of intended actions. Such an impairment might cause thoughts or actions to become isolated from the sense of will normally associated with them. This would result in the interpretation of internally generated voices or thoughts as external voices (auditory hallucinations and thought insertion) and of one’s own movements and speech as externally caused (passivity of experiences). (Blakemore et al., 2000)

Brain areas involved in perception and action

In order for somatosensory cortex activity to be attenuated to self-produced sensory stimuli, these stimuli need to be predicted accurately. The cerebellum is a possible site for a forward model of the motor apparatus that provides predictions of the sensory consequences of motor commands. This proposal has been supported by computational, neurophysiological, and functional neuroimaging data. The results showed an increase in activity of the secondary somatosensory cortex (SII) and the anterior cingulate gyrus (ACG; Brodmann Areas 24/32) when subjects experienced an externally produced tactile stimulus relative to a self-produced tactile stimulus. The reduction in activity in these areas to self-produced tactile stimulation might be the physiological correlate of the reduced perception associated with this type of stimulation. The activity in the ACG in particular may have been related to the increased tickliness and pleasantness of externally produced compared to self-produced tactile stimuli. Previous studies have implicated this area in affective behaviour and positive reinforcement. While the decrease in activity in SII and ACG might underlie the reduced perception of self-produced tactile stimuli, the pattern of brain activity in the cerebellum suggests that this area is the source of the SII and ACG modulation. In SII and ACG, activity was attenuated by all movement: these areas were equally activated by movement that did and that did not result in tactile stimulation. In contrast, the right anterior cerebellar cortex was selectively deactivated by self-produced movement that resulted in a tactile stimulus, but not by movement alone, and was significantly activated by externally produced tactile stimulation. This pattern suggests that the cerebellum differentiates between movements depending on their specific sensory consequences. We suggest that the cerebellum is involved in predicting the specific sensory consequences of movements and in providing the signal that is used to attenuate the somatosensory response to self-produced tactile stimulation. (Blakemore et al., 2000)

Individuals with pronounced schizotypal traits are particularly successful in tickling themselves

It is well known that tickling oneself fails to elicit the sensations produced when tickled by someone else. Studies have confirmed that self-produced somatosensory stimulation results in less ticklishness than externally produced (but otherwise identical) stimulation.  For instance, a single tactile stimulus (such as a feather) used for tickling is felt to be less intense when it is self-applied than when applied by someone else. When we perform a voluntary act, our brain is thought to create ‘‘efference copies” of the outgoing motor commands and use them to optimize motor control. On this basis, it has been suggested that a ‘‘forward model” helps us to anticipate the sensory consequences of our actions. One aspect of this predictive process (which has obvious adaptive value) involves the sensory attenuation of voluntary action effects and thus enhancement of the salience of externally induced sensations. Efference copies reduce the cognitive load by decreasing the processing of predictable (and thus irrelevant) sensory stimuli. Consequently, an individual is more likely to focus on the rapid detection of unexpected and/or potentially threatening environmental stimuli. A second role may relate to the sense of agency, i.e. the sense that ‘‘I’m the one who is causing or generating an action”. More generally, a sense of agency enables events to be classified as being caused by oneself or by an external source. Consequently, impairment of the predictive process might reduce attenuation of the sensory consequences of voluntary actions and thus prompt the incorrect attribution of a self-generated event to an external cause. This is exactly what happens in people with schizophrenia. Firstly, the attenuation of self-applied stimuli normally observed in healthy subjects is absent. Secondly, some people with schizophrenia feel as if external agents are controlling their own actions; this has been referred to as a ‘‘passivity experience”. This abnormal, subjective, sensory experience might be critically involved in the emergence and persistence of delusions of control. This (first-rank) subset of symptoms (is closely related to the diagnosis of schizophrenia. The HighSchiz (high positive schizotypal traits) participants (but not the LowSchiz, low positive schizotypal traits participants) did not feel self-tickling to be less ticklish than tickling by a third party. This finding suggests that HighSchiz participants had less efficient predictive mechanisms and were less able to predict the sensory consequences of their own actions. Given that the sensory prediction mechanism is supposedly involved in differentiating between self-produced and externally-produced sensations, a loss of attenuation of tickling sensations in HighSchiz participants might be associated with a lesser sense of agency. This supposition was supported by the positive correlations between successful self-tickling, high positive schizotypal traits, and the frequency of self-reported passivity experiences. When considering a continuum ranging from the absence of a disorder to the full-blown symptoms of schizophrenia, our data provide a basis for understanding the illusions of control experienced by schizophrenic patients. (Lemaitre et al., 2016)

References

Barkley, R. A. (2012). Executive Functioning and Self-Regulation: Extended Phenotype, Synthesis, and Clinical Implications. In Executive Functioning and Self-Regulation: Extended Phenotype, Synthesis, and Clinical Implications. http://www.russellbarkley.org/content/ADHD_EF_and_SR.pdf

Blakemore, S. J., Wolpert, D., & Frith, C. (2000). Why can’t you tickle yourself? NeuroReport, 11(11), R11–R16. https://doi.org/10.1097/00001756-200008030-00002

Hutchinson, J. B., & Barrett, L. F. (2019). The power of predictions: An emerging paradigm for psychological research. Current Directions in Psychological Science, 28(3), 280. https://doi.org/10.1177/0963721419831992

Lemaitre, A.-L., Luyat, M., & Lafargue, G. (2016). Individuals with pronounced schizotypal traits are particularly successful in tickling themselves. Consciousness and Cognition, 41, 64–71. https://doi.org/10.1016/j.concog.2016.02.005