When describing his former teammate Joe Mauer’s hitting discipline, five-time MLB All-Star Jim Thome told ESPN, “Joe's the only teammate I've ever had who never gets fooled. And when I say 'never,' that's what I mean. Absolutely never." The fact that Mauer had more walks than strikeouts in 2012, while leading the league in on-base percentage, is not surprising to his Minnesota Twins’ manager Ron Gardenhire. "He takes (pitches) because he can," Gardenhire said. "Other guys aren't good enough."

Combine this knack of knowing when to swing with one of the sweetest strokes in baseball and the result is a three-time batting champion, a first for a catcher. Being able to unleash his trademark “quick swing” on just the right pitch has made Mauer into the model of brain-body coordination.

Now, Harvard bioengineer Maurice Smith has some new clues on how our brains are able to combine learned motor skills with all of the incoming cues from the external world.

When we map out an action, like a baseball swing, in our brain, we use two different types of representations, intrinsic and extrinsic. “An intrinsic representation is one that’s body-based and procedural. It relates to the complex series of muscle and joint movements your body has to make to complete a task,” Smith said in a Harvard press release. For baseball players, they practice that swing and its collective parts over and over so that it becomes automatic.

The key, of course, is being able to not just swing a bat but use it to hit a ball travelling at 90 mph. This requires an ability to interpret the ball’s flight and intercept its path with contact. “Your brain must represent that action plan extrinsically, as it is an activity based in the world,” notes Smith.

Those two representations seem to be two different processes, first evaluate the situation and absorb the outside inputs (the approaching ball), then execute the well-rehearsed motor sequence to swing the bat. However, Smith’s Neuromotor Control Lab at Harvard learned last year that the two representations may actually be intertwined.

“The predominant idea had been that in memory we maintain separate intrinsic and extrinsic representations of action and translate between the two when necessary,” said Smith. “But our work shows that memory representations are combinatorial rather than separate.”

Neurons store all of these different representations in a process known as gain-field encoding, which was thought to be just a common language interpreter between intrinsic and extrinsic. Not so fast, according to Smith.

In a unique experiment that tested volunteers ability to reach for a target with a cursor, the team was able to confirm that indeed the brain combines both types of representations internally. In baseball, that means the extrinsic model of the arriving pitch is stored alongside the intrinsic motor skill of swinging the bat.

“We found that this gain-field encoding, which leads to a combinatorial representation of space, is not simply an intermediary in the transformation between representations, but is in fact the encoding on which motor memories are based,” said Smith. “This suggests that the neurons which display gain-field encoding are the same ones that store the motor memories associated with the actions we learn.”

Their research is published in the Journal of Neuroscience.

Obviously, at Joe Mauer’s level, those motor memories have evolved to a world class level. Perhaps his cross-training in other sports contributed to his advanced status. He was, after all, the only high school athlete to ever be named the USA Today National Player of the Year in both baseball and football, not to mention averaging 20 points a game for his basketball team.

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