[4] This appears to be comparable to the projective versus associative distinctions found in other forms of synesthesia.
The first type causes a person to feel sensations on the part of their body that mirrors the observed touch.
In most studies, participants are asked to observe someone else being touched and report what kind of synesthetic response they experience.
Approximately 30% of the normal population experience some form of this condition and around 16% of amputees report synesthetic pain after an amputation.
suffered a stroke and experienced paralysis along with loss of sensation on the left side of his body.
When touch is applied to the good arm, amputees have reported corresponding sensations in their phantom limb.
These cases can be considered mirror-touch synesthesia because a visual stimulus was able to elicit a tactile sensation.
Four amputees were recruited in a study and asked to observe an assistant's arm being touched at various angles.
Finally, one amputee experienced a cold sensation when observing ice cubes touching the assistant's arm.
[2] In most people, several parts of the brain are activated when observing touch, particularly in the motor system.
[11] The following is a list of regions where increased activation was seen: The fusiform gyrus, bilateral SI and SII, premotor cortex, and superior temporal sulcus is generally activated when observing touch to another person's head or neck.
In particular, the visual presentation of faces activates the fusiform gyrus and superior temporal sulcus.
Finally, when observing touch to the left side of a human face or neck, the right SI is activated, and when observing touch to the right side of a human face or neck, the left SI is activated.
It is also suspected that there is an area of the brain that is only activated in mirror-touch synesthetes when observing touch, but not in non-synesthetes.
The anterior insula is believed to mediate the conscious perception of touch and is involved with self-processing.
[11] The second theory proposes that the visual and somatosensory system in people with mirror-touch synesthesia are directly connected in such a way that is unique to these synesthetes.
The third theory involves bimodal cells in the parietal cortex, specifically in the intraparietal sulcus.
It is suggested that, when observing touch, bimodal cells for visual and tactile stimuli are activated above a certain threshold.
[11] Most studies on mirror touch synesthesia verify the existence of the condition through a variety of methods.
Mirror touch synesthetes showed significantly higher empathy quotient scores in emotional reactivity than in controls.
Thus empathy is multifaceted, and the tactile mirror system may not be fully responsible for the ability to empathize.
[7] Other ways of investigating the role of the mirror neuron system in empathy have been through pain and disgust.
The anterior cingulate cortex was also activated when observing people who would be painfully stimulated at a later time.