The labelled-lines principle of the somatosensory physiology might explain the phantom limb phenomenon

In the somatosensory system, various different sensory receptors capture different stimuli and convey them to the sensory cortex. Each type of receptor is specialised, that is, receives the stimulus to which it is predetermined to receive. Immediately as it is stimulated, the receptor sends a signal to the somatosensory cortex, via nerve fibres, and the area of the cortex that receives the signal determines the mode of the consequent perception. This mechanism is called principle of the ‘‘labelled’’ lines. The somatic receptors are the structures designated to receive stimuli, however, if their afferent fibres are stimulated at any point when approaching the cortex, the mode of perception by the cortex is the same as when the somatic receptor is stimulated directly. This occurs after the amputation of a limb, wherein the remaining fibres transmit to the cortex the mode of sensation for which they were specialised, despite the lack of somatic receptors at the beginning of the afferent pathway. However, the afferent pathway ends at the same cortex area as before the deafferentation. Since the somatic receptors and the integrity of afferent pathways are important to the regulation and modulation of the received stimuli, after the deafferentation the afferent pathway becomes anatomically and functionally abnormal. We believe these factors, involved in the pathophysiology of phantom limb (PHL), might be the explanation for this intriguing phenomenon.