The concept of free will implies the existence of a “self”. To be able to have a free will and make decisions freely, there must be an agent, an owner of this free will. To be able to say “I have a free will”, one needs to know who this “I” is.
How can we know, who we are?
In philosophy of the mind and in psychology, the idea has been developed that there is a minimal self and a higher cognitive self (1). Sometimes they are referred to as “pre-reflective” and “reflective” self. In order to establish a coherent minimal self-experience, a person needs to perceive signals from within their own body, i.e. proprioception and interoception – and identify these as their own. Proprioception refers to the position of own body parts; interoception describes perceptions like heat and cold, hunger and thirst, the desire to breath, as well as affective social touch (2).
During the development of a child, the first sensory perception is touch. Parents interact with their newborn mostly through touch, but even earlier the baby can perceive its own body and the outside world, i.e. everything that it non-self, through the tactile sense. It has been shown that already in the womb embryos show self-directed (sucking the thumb) and other-directed movements (kicking the womb or pushing a twin) (3).
By touching ourselves and by touching the humans and the world around us, we learn, where our body ends and where the outside world begins. It might be possible, that early disturbances of this tactile interaction with the world could lead to problems in differentiating between self and other. Many psychiatric disorders include symptoms in the self-domain. If we understand how our brain distinguishes between self and other – and what happens, if this distinction goes wrong – we might be able to develop novel treatment options to help patients establish a functional self-other boundary.
The brain differentiates between touch by ourselves and touch by others.
In my recently published study (4), I showed that the brain clearly differentiates between self-touch and other-touch. Our participants stroked their own arm or a researcher stroked their arm, while they were in the MRI scanner. When the researcher stroked the participants’ arm, we found activations in areas that are related to the processing of touch (somatosensory cortex, posterior insula), but also to the processing of social information (temporo-parietal junction, superior temporal gyrus). During self-touch, however, we only found activations in regions that were involved in the movement of the right hand, i.e. the hand that was stroking, but no activity that was related to the processing of the signal in the touched area on the left arm. What we found instead, was a widespread deactivation, in many different areas, including the insula and regions that are involved in very early processing steps, like the thalamus and the brainstem.
Since it was a surprise for us that we did not see any activation in the primary somatosensory cortex in response to the touch of the left arm, we asked our participants, where they felt the touch: in the touching right hand or in the touched left arm. They reported to feel it in both areas. We then tested their perception threshold for an additional tactile stimulus while they were either touching their own arm or being touched by someone else. During self-touch, the threshold for perceiving this additional stimulus was 100 times higher than during touch by somebody else. This indicates that the brain attenuates signals coming from the touched area specifically when we touch ourselves. This could be due to the fact, that the brain can predict the sensory perception during self-touch, and simply ignore it, as it is not relevant. Most of the time when we touch ourselves, we simply fidget around or perform self-grooming. The sensory information arising from self-touch is usually not relevant for us, therefore we do not need to pay attention to it. Touch by another person on the other hand is relevant and should be salient.
Participants also filled out a questionnaire called the self-concept clarity questionnaire (5), where they answer questions like “I am sure about what kind of person I am”. This was included, so that we were able to relate that minimal self-experience of touch on the own body to their higher-level self-concept. We did indeed find, that people who had a stronger difference in the neural signatures to self-touch and other-touch in the insula and the anterior cingulate cortex also had a clearer self-concept. This finding indicates that the basic self-experience of the self as a bodily “I” is intertwined with the more complicated self-concept, that “I” that we can reflect about.
Recent neuroscientific findings have led to the popular suggestion that the self and free will are an illusion.
It is argued that the brain “creates” this illusion of the self in charge of making decisions, even though low-level processes in the brain would have already decided, before a decision arises to consciousness. As our work suggest, this reflective self builds upon the pre-reflective, bodily self. The illusion argument only holds if we restrict the definition for “self” to the conscious, the reflective “I”, which excludes the bodily self. When including all parts, of which our self-perception is built, into our definition of “self”, it is no longer an illusion.
This argument changes the discussion about free will. If this self, that includes all its building blocks, makes a decision, even if it is at a pre-reflective stage, is this now not a free decision? One might argue that even such decisions are only driven by genes, previous life experiences, and environmental conditions. This, I believe, is a valid point – it is, however, not relevant for us in our daily life, as we can never access all information down to the spin of quanta necessary to calculate which decision somebody will make. And even if we could: if there is only one single time, where the probabilities for two possible choices are exactly fifty percent, and if then a decision is made, it would be a freely made decision.
1. Gallagher S (2000) Philosophical conceptions of the self: implications for cognitive science. Trends in cognitive sciences 4(1):14-21.
Gallagher S (2000) Philosophical conceptions of the self: implications for cognitive science. Trends in cognitive sciences 4(1):14-21.
2. Craig AD (2002) How do you feel? Interoception: the sense of the physiological condition of the body. Nat Rev Neurosci 3(8):655-666.
3. Castiello U, et al. (2010) Wired to be social: the ontogeny of human interaction. PloS one 5(10):e13199.
4. Boehme R, Hauser S, Gerling GJ, Heilig M, & Olausson H (2019) Distinction of self-produced touch and social touch at cortical and spinal cord levels. Proc Natl Acad Sci U S A.
5. Campbell JD, et al. (1996) Self-concept clarity: Measurement, personality correlates, and cultural boundaries. Journal of personality and social psychology 70(1):141.
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