Sometimes I imagine a more cerebral kind of Halloween theme party. Instead of dressing like your favorite drink (where guests come as a White Russian, Snake Bite, or Red-headed Slut, but beware of the friend who comes as a Blue Moon) or characters from 80s movies (with friends dressed as Indiana Jones, Marty McFly, and Princess Buttercup, but beware of younger guests who respond with bewildered looks to your carefully crafted Sloth costume), why not try something a bit more inventive? Why not encourage your friends to dress up as the part of the brain they resemble the most?
You could have news travel the old-fashioned way by telling your most gossipy friend, who, of course, should come as the thalamus. Just like your friend, the thalamus takes in almost all sensory information and distributes it to other parts of the brain. However, in a quirk of evolution, the nose has decided it walks to the beat of its own drummer and it bypasses the thalamus, preferring instead to send smelly signals to the olfactory bulb. If you have a friend who seems to always know something the usually omniscient gossip doesn't, a costume with two parallel swimming noodles protruding from her body (as the olfactory bulb looks a bit like antennae) would be just right for her.
The worry-wart in your crowd, who soaks in the social reports and finds most news items threatening, would be a perfect amygdala. Like the thalamus, this almond-shaped nugget of brain matter that rests on the hippocampus (we'll get to that later) is a member of the limbic system, or the emotional brain. The amygdala interprets the stimuli it receives from the thalamus and adjusts your body's current threat level accordingly. (Red alert! There is a fire and a loud bumping noise!)
While the amygdala is very good at making decisions in a flash, it is only capable of making decisions in a flash, based on the most cursory review of sudden stimuli. This is where the hippocampus, also a card-carrying member of the limbic system, comes in, and using its store of useful knowledge, calms the amygdala by explaining the fire is just a candle and the loud noise is just hip-hop music.
The hippocampus retains explicit memories, or memories you can decide to pick up, brush off, and put to good use. This slightly c-shaped swirl in the depths of the brain remembers candles are mostly safe and alarm clocks are only threatening to your dreams. This could be the pal who reminds the anxious amygdala of similar times when what the thalamus related seemed frightening, but turned out to be frivolous fodder.
Of course the limbic clique would not be complete without a hypothalamus. The pearl-sized hypothalamus controls emotion along with things like thirst, hunger, and the circadian rhythm -- your internal clock, which lets you know when it's time to snooze or rise and shine. I bet you can see one of your friends now in a hypothalamus costume, gliding through the mingling crowd, making sure everyone has had enough to eat and drink, while saying that, really, we should all be getting to bed soon.
She will not be able to get a word in edgewise next to Broca's area, though, your most talkative acquaintance. Hopefully, this friend would also be someone who enjoys being the first at things, for this was the first area in the mind associated with a specific function. In 1861, Paul Broca, a French physician, had a patient who went by "Tan," because that was the only sound he could make. Yet, Tan understood language (in this case, French) and had no injuries to his mouth or throat. Unfortunately, as this was before Magnetic Resonance Imaging, the patient had to die before Broca could open up the brain and discover the lesion in what would come to be called Broca's area (of course, it wasn't his area quite yet). A few more unfortunate demises later, and he had a theory and a flag staked in the human brain. This area is vital for knowing how to formulate and express words, a skill many people take for granted or abuse.
Shortly after Broca got a part of the brain, Carl Wernicke, in Germany, was perhaps a little jealous, so he went on to uncover the region of the brain responsible for deciphering language. Patients who have lesions in this area could speak, but they could only produce incoherent roaming rambles, and they did not seem to understand others. Thus, the best listener in your group could be Wernicke's area, the spot of the brain dedicated to decoding language.
Your oldest but, ironically, most immature friends could consider being parts of the hind brain, which in diagrams seems to serve as a stand for the rest of the brain and contains the cerebellum, brain stem, pons, and medulla oblongata. Also known as the reptilian brain, the hind brain has not evolved much in the last three-hundred million years (give or take a few million), when it existed in reptiles as they slithered across the earth's surface and you and I were not even apples in their eyes.
While these brain pieces are very old, they are not very sophisticated compared to the added features human brains have developed. We need the large, wrinkled cerebrum, the squishy mass that most people think of when they think "brain," that includes many of the aforementioned parts, in order to anticipate, plan, and think abstractly (about our own brains, for example). But that is not to say your old, immature friends aren't marvelous in their own, special way.
The cerebellum, also known as the "little brain," which I'm sure is good for its ego (or super ego?), serves as the conductor of a symphony composed of muscles. It directs them to work together so that you can tip-toe across a rocky creek bed, cut an onion and wipe your eyes in a fluid motion, or move from a downward facing dog into the child's pose with grace. This clearly is a costume opportunity for your most athletic friend, the one who actually can pull off yoga moves without ever falling on her cheek.
The medulla oblongata would be your friend who has a knack for ensuring the chip bowl is replenished, the paper napkins don't run out, and the stain on the carpet is cleaned up, all without you even knowing he is there. The medulla oblongata sets the pace for the blood that throbs through your veins, sustaining life for all your other organs. It also helps you breathe without you having to stop and say every two seconds, "Okay, time to breathe again." And finally, it ensures that your lunch travels through your intestines and delivers its calories and nutrients to your awaiting organs.
One more thing to consider before you start crafting invitations: most of your friends will need to be twins. The brain is made up of two hemispheres, so most of the brain parts mentioned above actually are not one piece, but two. It would also be preferable if one twin liked painting rainbows and the other was more inclined to play Sudoku, as the right brain has strengths in spatial abilities, music, and visual imagery, while the left side is good with numbers and language. For example, Broca's area and Wernicke's area are only on the left; a lesion on the corresponding right areas doesn't cause muteness or garbled gab.
So set out some brain food and decorate your house with red balls, wiry synapses, and other brain matter. But, while you wait in the dense neuron forest, preparing yourself to go easy on your wayward friend who may come as the figurative id and hoping that no brain-eating zombies crash the party, don't be surprised if the clock ticks past the start time and the doorbell remains silent. Admonishing your friends for not being twins and telling them they are immature, old, gossipy, or too talkative, will probably inspire them to have a drink-themed costume party the same night with one prominent absence from the guest list. Perhaps you could crash the party as a Sweet Surrender (a mimosa with some peach brandy splashed in). Don't forget to ask if anyone has invented a humble pie cocktail.