My son took in a blind kitten four years ago. The cat now has extraordinarily long whiskers and eyebrows. She also has long hairs from the ears and scattered long ones over her body. The whiskers approach 60 millimetres and appear to be sensory compensation for sight loss. Is this likely, and how does it work?
鈥� I cannot compare the cat in question with any of its siblings, so this response is speculative to some extent.
The hair and whiskers of cats do vary dramatically, whether or not the animals can see. Cats have straight, non-woolly guard hairs that are extremely sensitive, especially at points such as the tips of their ears. Whiskers on the cat鈥檚 muzzle and wrists, and the ones forming its 鈥渆yebrows鈥�, are even more sensitive. Their stiffness has the effect of extending the cat鈥檚 reach and lends precision in assessing the position and texture of anything that they touch.
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Not surprisingly, the root of each hair has its own touch-sensitive nerve supply. Around a whisker follicle, the nerve tissue is exceptionally dense.
As a rule, sensory tissue atrophies if it receives little stimulation, but grows and becomes more complex if regularly stimulated by both the central nervous system and the environment.
Nerve fibres and the capillaries that supply them with blood tend to grow practically in unison. What鈥檚 more, increased blood supply and associated hormonal stimuli promote tissue growth. It is therefore plausible that whatever growth factors stimulate nerve development at the roots of tactile hairs in a blind cat might also stimulate both the activity and vigour of the follicles. The result is long, infrequently shed sensory hairs and whiskers.
鈥淲hatever stimulates growth of nerves at the roots of hairs might also stimulate the follicles鈥�
Jon Richfield, Somerset West, South Africa
鈥� A cat鈥檚 whiskers are regarded as tactile hairs or . As a rule of thumb, their tips extend out to span a distance equal to the width of the cat鈥檚 body. With their extreme sensitivity, these whiskers aid the feline in spatial awareness.
鈥淲ith their extreme sensitivity, whiskers aid the cat in matters of spatial awareness鈥�
Vibrissae are primarily found on the face, although they do grow elsewhere on the cat鈥檚 body 鈥� predominantly on the forelegs, with a few on the abdomen.
People with a sensory impairment commonly compensate by developing enhanced abilities in their other senses 鈥� blind people sometimes have better hearing than sighted people, for example. This phenomenon exists in many animals, too.
In 1995, Josef Rauschecker described an example in a study of cats that had been visually deprived from birth. He discovered that auditory and dominated the anterior ectosylvian cortex, a brain region that normally processes visual signals (Trends in Neurosciences, vol 18, p 36).
Interestingly, Rauschecker found that these cats had enlarged facial vibrissae, and in turn their brain鈥檚 somatosensory cortex differed from those in cats that could see. Rauschecker concluded that motor feedback had helped reorganise the processing of sensory stimuli. This would explain why the cat mentioned in the question has enlarged vibrissae.
Jessica Harvey-Cox, Colchester, Essex, UK