Homunculus reimagined

Homunculus redrawn

The brain area that controls neck muscles used to be between areas that control the thumb and the top of the head (black arrow) but a new study puts the neck between the shoulder and the trunk (red arrow). 

C. N. Prudente et al./Journal of Neuroscience 2015

The motor homunculus is a funny-looking fellow with a hulking thumb, delicate toes and a tongue that wags below his head. His body parts and proportions stem from decades-old experiments that mapped brain areas to the body parts they control. Now, a new study suggests that the motor homunculus’ neck was in the wrong place.

Hyder Jinnah of Emory University in Atlanta and colleagues used fMRI to scan the brains of volunteers as they activated their head-turning neck muscles. (Pads held participants’ heads still, so the muscles fired but heads didn’t move.) This head turn was accompanied by activity in part of the brain that controls movement. The exact spot seems to be between the brain areas that control the shoulder and the trunk — not between the areas responsible for moving the thumb and the top of the head as earlier motor homunculi had suggested, the team reports in the June 17 Journal of Neuroscience

Editor’s note: The caption was updated on June 18, 2015 to clarify the arrows pointing to the old and new locations of the brain area that controls neck muscles.

Laura Sanders

Laura Sanders is the neuroscience writer. She holds a Ph.D. in molecular biology from the University of Southern California.

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