Homunculus reimagined

The motor homunculus is a funny-looking fellow with a big 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 says that the motor homunculus’s neck was in the wrong place.

Hyder Jinnah of Emory University and colleagues used functional MRI to scan the brains of volunteers as they activated their head-turning neck muscles by pushing against pads. Neck muscle firing 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 (red arrow) — not between the areas responsible for moving the thumb and the top of the head (black arrow) as earlier motor homunculi had suggested, the team reports in the June 17 Journal of Neuroscience.