How Do We Smell? 91explain the exceptional capacity of the human brain, and overall olfactory
system, to identify and remember large numbers of smells. The multisensory
processes in which the neurons in the piriform cortex participate not only help
humans differentiate between one odor and another but also to discern the
meaning associated with a particular odor. The piriform cortex may not only
help one recall the pleasant smell of homemade bread but also evoke warm
feelings about the place and circumstances where the olfactory memories
originated. The same would be true of smells associated with highways, farms,
restaurants, poisonous cyanide seed or mudroom, and gardens.
An important passageway for information that enters and exits the hip-
pocampal formation, the entorhinal cortex seems to be particularly sensitive
to Alzheimer’s and other serious disorders. Its healthy functioning may
therefore be useful as a predictor or validator of developing or advanced
disorders. With regard to olfactory function, the entorhinal cortex (and espe-
cially the lateral entorhinal cortex) plays a vital role by accepting input from
the piriform cortex and the principal olfactory bulb. In animals, entorhinal
cortical response to odors is related to hunger and other internal states. In
cases where an animal anticipates a reward, such as food that is consistently
accompanied by a particular odor, the entorhinal cortex may actually be acti-
vated before a response from the olfactory bulb. This suggests that the odor
identification process, which typically has been regarded as a bottom‐to‐top
process, may at times be a top‐down process in which the piriform cortex
and olfactory bulb are catalyzed by anticipation‐driven signals emanating
from the entorhinal cortex.
Olfactory impairment also results when children are exposed to alcohol dur-
ing gestation. Heavy drinking during adolescence and in adulthood also leads
to olfactory damage. To compound the tragedy of fetal alcohol spectrum disor-
ders (FASDs), olfaction impairment may be accompanied by a lasting memory,
and even preference for, the smell of alcohol. This, besides the insidious example
of an alcohol‐abusing parent, can increase the probability of the continuity
of excess alcohol consumption across generations. Impulsive drinking by a
mother can, therefore, not only damage the olfactory system of the developing
fetus but later make it harder for that same child to avoid impulsive drinking.
Prenatal alcohol exposure has been widely studied and widely condemned due
to the cognitive and behavioral damage it inflicts. Many regions of the brain
affected by prenatal alcohol exposure have a simultaneous linkage to the pro-
cessing and identification of odors. Damage to these regions of the brain are
paralleled by documented neurological deficits associated with those same
regions. Children exposed to alcohol prior to birth through maternal drinking
were found to have significant olfactory deficits. Consequently, assessment of
olfactory performance may well contribute to more accurate and thorough
identification of persons at risk for deficits in cognitive and behavioral perfor-
mance. Alcohol is toxic to mothers and fetuses; so are many ingredients in