3. Sensory Pathways

Sensory circuits (sight, touch, hearing, smell, taste) bring information to the nervous system from the outside world. Sensory organs—eyes, ears, skin, nose, tongue and proprioceptors (sensors in limbs)—and the associated brain pathways are set up during early development. Molecular cues are essential in establishing many basic cellular characteristics and the connections between all elements of a sensory pathway.¹⁷ The formation of sensory pathways begins in utero and continues in the early months after birth.

Cats that are congenitally deaf do not form the normal neural architecture associated with hearing. In deaf cats the brain’s hearing site is largely taken over by neurons and neural pathways involved in vision. Stephen Lomber, of the University of Western Ontario, found that if these cats are given hearing aids early in life, they are able to form a normal hearing section of the brain.¹⁸ The stimulation provided by the hearing aid at a critical stage of development maintained the normal architecture and function of the cats’ brains.

Next: 4. The limbic system pathways