Cortico-motoneuronal cells in M1: muscles, movements, or functions

Summary

Date: 
May 12, 2015 - 1:00pm
Location: 
NW 243
About the Speaker
Name: 
Peter Strick (University of Pittsburgh)

This presentation will lay out the evidence to develop the following thesis–

1) The central control of movement is faced with an evolutionary constraint: Our
skeletomotor system is built on the framework of a relatively ancient spinal cord.

2) Most descending systems, including the corticospinal system, use the pattern generators
and motor primitives that are built into the spinal cord to generate motor output.

3) Cortico-motoneuronal (CM) cells (i.e., cortical neurons with axons that make
monosynaptic connections with motoneurons) are a relatively new phylogenetic and
ontogenetic development. Furthermore, CM cells are located in a separate part of the primary
motor cortex.

4) Thus, area 4 is split into 2 regions: a rostral region we have termed “Old M1” which has
disynaptic input to motoneurons; and a caudal region we have termed “New M1” which has
monosynaptic input to motoneurons.

In essence, Old M1 makes use of the circuits built into the spinal cord to generate motor
output. This region of the motor cortex enables the motor system to avoid the “curse of
dimensionality” and to solve the “degrees of freedom problem.” In contrast, New M1 uses CM
cells to bypass the constraints of spinal cord mechanisms. This region of the motor cortex
enables the motor system to use all of the available degrees of freedom to sculpt novel
patterns of motor output.

These arguments lead us to predict that the two regions of the motor cortex are differentially
involved in motor learning. We speculate that Old M1 is especially important during the initial
stages of learning a new skill by enabling the motor cortex to use existing spinal circuits to
rapidly construct new movement patterns. In contrast, New M1 may be especially important
during the later stages of learning a new skill by enabling the motor cortex to refine and
precisely specify patterns of motor output.