Funded by: LJMU / Salford NHS Trust
There is a complex relationship between touch, and hence activity in low threshold mechanoafferents (LTMAs), and symptoms of pain (nociceptive, inflammatory and neuropathic) and itch. On one hand activation of LTMAs, by a light soothing touch or a transcutaneous electrical nerve stimulator for instance, can be positively reinforcing or even analgesic whereas in certain pain states innocuous light touch may be unpleasant and extremely painful (e.g. in dynamic mechanical allodynia). Similarly, mechanical skin stimulation (albeit typically at higher mechanoreceptor thresholds) during a scratch relieves symptoms of itch. However light touch adjacent to an area of itch is often itself felt as an itch (alloknesis, the itch equivalent of allodynia). Light mechanical stimulation on its own can also induce itch and the urge to scratch. Several disparate mechanisms at primary afferent, spinal and cortical level probably underlie this complexity. However, given the heterogeneity of anatomical and electrophysiological of LTMAs, it seems likely that activity in specific subtypes of afferent will have different, possibly divergent, effects on ongoing pain and itch. A detailed understanding of LTMA properties is vital to understanding these issues.
This project involves the use of microneurography, intraneural microstimulation and psychophysical techniques in humans to investigate how physical stimuli are transduced into neural code in low threshold mechanoreceptor afferent (LTMA) subtypes; and how such neural codes in specific LTMAs relate to and affect perceptual correlates such as pain, itch and paraesthesia.