According to some recent research, flipping the bird is a lot of work, as far as moving your digits goes. Neuroscientists Claudia Wilimzig, Patrick Ragert, and Hubert R. Dinse, from Cal Tech and the Max Planck institute in Germany, have shown that the middle finger has the slowest reaction time of all five manual digits. Apparently, this is due to the simple fact that the middle finger is the finger in the middle.
The somatosensory cortices, which are higher order regions of the brain involved with sensation and movement, are imbued with “topographical maps” of the regions they represent. Everything but your guts has corresponding neurons in the sensory cortices, and regions with a more detailed sense of touch (i.e. hands and face) have more real estate in the brain (as represented by this famous, creepy image). What’s more, bordering parts of the body correspond to bordering sections of brain – if one region of skin sends information to one group of neurons, an adjacent region of skin sends information to an adjacent group of neurons.
Wilimzig and her team hypothesized that the reaction time of the blaspheming finger would be slowest, because it would be hampered by a kind of neuron “crossfire” from the four fingers surrounding it. Using a simple task where subjects saw their hands on a monitor and were prompted to move whichever finger lit up, the researchers found that the middle finger had the slowest reaction time, and the thumb the fastest. Their data even flipped them the bird:
The reason for this result, they argue, is that when the middle finger is prompted to move, the brain tells the four other fingers not to move. The “don’t move!” message is sent using chemical neurotransmitters that temporarily shut down neurons. Because the middle finger neurons are sandwiched between the other four fingers’ neurons on the brain’s map, some of these “turn-off” chemicals essentially leak into the middle finger neurons, which in turn makes their “move now!” message slower. And because all four other fingers are closer to the edge of this map, their leaking effect is smaller and reaction time lower.
Maybe this all explains the evolution of flipping the bird; it’s like saying, “you’re such a prick that I’m going to lift the particular finger on my hand that has to counteract the most inhibitory neurotransmitters of all my digits in order to initiate movement, in order to tell you how much of a prick you are. So, the next time someone cuts you off on the street, disrespects your grandmother, or you want to make a simple elegant point to the multitudes watching your super bowl halftime performance, show em’ your difficult finger as you dwell upon the wonders of neuroscience.