Experiences in Nonvisual Senses Also Affect Neural Development

Development of the brain can be affected by early manipulation of nonvisual sensory inputs—a mouse’s whiskers, for example. Thomas Woolsey and collaborators (T. A. Woolsey and Wann, 1976; T. A. Woolsey et al., 1981) found a unique clustering of nerve cells in a region of the cerebral cortex of the mouse that receives input from the whiskers.

The arrangement of whiskers on the skin is distinctive, and whiskers are arrayed similarly in all animals of the same species. The region of the cortex in which the whiskers are represented contains clusters of cells, called whisker barrels because their arrangement makes them look like barrels squeezed together in the cortex. The layout of these cortical barrels corresponds to the map of the whiskers. Only whiskers that continue to send neural impulses to the brain keep their place in the cortex, as shown in Figure 1. There is evidence that sensory experience shapes the barrels by promoting synapse elimination and that this process continues past the neonatal period through puberty and even adulthood (Y. Zuo et al., 2005).

Figure 1  Cortical Barrels in Mice
(a) Representation of the body surface in mouse somatosensory cortex, showing the location of whisker barrels. (b) Each barrel (inset) receives its input from a single whisker on the opposite side of the mouse’s snout. (c, d) If a row or column of whiskers is destroyed shortly after birth (as indicated by the red dots), the corresponding barrels in the cerebral cortex later will be missing and the adjoining barrels enlarged. (e) If all whiskers are destroyed, the entire group of barrels will disappear. (Part a and photograph courtesy of T. A. Woolsey; b–e after Cowan, 1979.)

There are many other examples of early experience altering brain sensory systems. For instance, restricting salt intake in developing rats alters their later sensitivity to salty fluids (Thaw et al., 2000). And closing one nostril in newborn rats prevents the developing olfactory receptors on that side from being stimulated by odors, causing the olfactory bulb on that side of the brain to be reduced by about 25% (Brunjes, 1994).