Ah, the proverbial nightcap. The time-honored little nip before bedtime helps cast off the stresses and strains of the day and gently eases the mind and body into a peaceful night’s sleep. Get it right, and your brain waves are gently lulled into the correct rhythm for restorative sleep and memory retention. Get it wrong, and you’re tossing and turning all night, waking up grumpier than you were before you went to bed. And no, getting up in the wee hours to pour another two or three fingers of whiskey isn’t the answer!
What is the cause of this apparent paradox? Why does alcohol help us sleep and then wake us up out of our comfortable mattress? Why can’t it just put us to sleep and then wear off, allowing us to stay asleep until it is time to wake up naturally? The reason has to do with how the brain works. A nerve cell will either fire or not, depending on the balance between positive and negative ions in its internal environment with respect to outside the cell. Substances called neurotransmitters bind to nerve cells to control the flow of these ions. Stuff the cell with enough positive ions, the neuron fires an impulse. Add negative ions, and it takes more effort to excite it into generating an action potential. Glutamate is an example of an excitatory neurotransmitter, while GABA is an example of an inhibitory neurotransmitter.
As your small glass of sherry glides down through your digestive system and into your bloodstream, it finds its way into your brain, where it mimics the effects of GABA. Here, it diminishes neural activity by allowing negatively charged chloride ions into the nerve cells. You can remember the argument you had with your boss, but you can’t get excited about it. At the same time, alcohol is blocking the effect of the brain’s positive neurotransmitter, glutamate. You relax and go to sleep.
As the night goes on, GABA is absorbed back into the originating neuron. At the same time, it is being metabolized to, of all things, glutamate. As luck would have it, the region of the brain that is responsible for waking us up, the reticular system, is packed with glutamate-sensitive nerve cells. The art of the aspiring sleeper is to pour a large enough nightcap to help them drift off to sleep but not so large that it comes back to bite them later in the night.