https://doi.org/10.36866/pn.126.5

Dr Keith Siew
Scientific Editor, Physiology News

When first teaching students about sensory physiology, one of my favourite tasks is to split the class into two teams and hand out a few markers. The rules are simple, each sense can only be written up on the board once, and like a relay race, when done you must nominate a new teammate to take your marker to write up the next one on the board. One point for the common name, two points if you can give scientific designation (or name the sensory organ system) too.

Predictably there is an initial scramble and the usual suspects: sight, hearing, smell, taste, and touch all appear within seconds, but things slow dramatically as visual, auditory, olfaction, gustation and somatosensation gradually fill the board. At this point there is usually a pause… and I’m greeted with a sea of perplexed looks as I break the silence and exclaim: “What are you waiting for? There are oh so many more still to go!”.

It takes them a moment, but after some whispered mutters, eventually one brave soul thinks outside the box, will step forward and write something like… balance or pain on the board. A breakthrough! And with that spark the floodgates of ideas are once again open, eventually hunger, temperature, proprioception, baroception, chemosensation, thirst, acceleration, etc… all populate the board. And for bonus points a few even manage to come up with a smattering of “non-human ones” (or so we generally tend to think of them for now at least) like magnetoception, electroreception, echolocation, infrared sensing, etc.

The exact number of senses is a matter of debate, but we as physiologists can at least agree that it’s certainly not limited to five. And for our students, learning how real physical stimuli are transduced into neuronal signals that can be processed and responded to by our brains is perhaps one of the most fascinating areas of physiology they learn about.

It goes without saying that sensory physiology and its neuronal processing and modulation is a vast area of research, and in this special issue we’ve attempted to give you a broad flavour of some of the exciting work being carried out. From the evolution of our understanding of pain during development (a story beautifully told in five papers by our Honorary Fellow Member, Professor Maria Fitzgerald) to our recent recognition and redefinition of pain to include invertebrate species. Sensory research can have serious ethical, moral and legal implications for the ways our societies and scientific institutions will function going forward (see the comparative physiology of nociception by Dr Lynne Sneddon).

Not only that, but sensory physiology has the genuine power to radically improve lives (see how organisations like Royal National Institute for Deaf People support translating research into treatments). I can think of no better example than the amazing work by Dr Lore Thaler and colleagues, which shows that teaching our brains to process sensory signals in new ways can give us genuine superpowers! These amazing individuals with visual impairments can learn to navigate the world through echolocation (not unlike Marvel Comic superhero Daredevil). Even our furrier friends have evolved incredible adaptations that resemble Daredevil’s superpowers, with the blind desert golden mole being able to sense the seismic vibrations of wind passing through tufts of grass to navigate and search for food (learn more about Marvellous middle ears from Matthew Mason).

Even the study of perhaps less obvious sensory systems, like whiskers, can yield incredibly useful insights and drive technological innovation. With the aerodynamic shape of seal whiskers inspiring the latest generations of wind turbine blades or the utility of whisker-like probes for drone-like devices in sensitive areas like medical or archaeological environments being explored (see Robyn Grant’s article on whisker physiology).

Understanding how our brains process and respond to signals is itself an intriguing body of work, and the article by Kathleen Cullen on the role of the vestibular system and the cerebellum’s ability to generate models of our self-motion is an equally fascinating read. A computational marvel of our brains that’s pretty important if you want to distinguish between a sudden slip on the ice or a graceful flying sit spin.

It becomes even more wondrous when the processing of these signals can become mixed up or disagree with one another, leading to strange phenomena like synaesthesia where people may hear a C# and see purple, or hear their boyfriend’s name and taste bacon. There are even new senses being discovered like the gravitostat, whereby osteocytes in long bones can measure bodyweight and signal for its maintenance. There is a genuine plethora of material enough to fill a whole other issue! Who knows… maybe we will.