excitatory, thus stimulating the sympathetic “fight-or-flight”
nervous response, people who participate in hypothermic
conditioning will experience a significant drop in
sympathetic activity and an increase in GABA after
acclimation. (Cold exposure also has the benefit of boosting
another neurotransmitter involved in learning and attention
called norepinephrine, which I’ll discuss momentarily.)
Avoiding consumption of added glutamate in processed
foods is another strategy for keeping this vital balance of
neurotransmitters. Monosodium glutamate (MSG), a flavor
enhancer often used in Chinese cooking, is one common
source, and aspartame, a noncaloric “diet” sweetener,
becomes excitatory, transforming into glutamate precursors
once inside the body.^10
Acetylcholine: The Learning and Memory
Neurotransmitter
Acetylcholine (pronounced ah-see-till-KO-leen) is a
neurotransmitter that is part of the cholinergic system, which
engages in many activities in the body but is mostly thought
of for its role in REM sleep, learning, and memory.
Low levels of acetylcholine are associated with
Alzheimer’s disease, where acetylcholine-producing
neurons become damaged. In fact, the second of the two
major classes of drugs currently used to treat Alzheimer’s
disease and other dementias works to increase acetylcholine
availability in the brain by preventing its enzymatic
breakdown at the synapse* (I’ve already mentioned the first