In many of these proposed studies, a double lesion approach could be very informative. We thank Amy Bastian, Pablo Celnik, Paul Cisek, Joern Diedrichsen, Trevor Drew, Michale Fee, Mickey Goldberg, Adrian Haith, David Krakauer, Pietro Mazzoni, Bence Olveczky, Steve Scott, Reza Shadmehr, Emo Todorov, and David Zee for fruitful discussions on the topic of this manuscript. Thanks to Sarah Mack for making the figure. The authors are supported by the following grants: NIH R01NS052804 (J.W.K.) and Machiah Foundation/Jewish Community Federation (L.S.). “
“A curious observer outside

of the field of motor neurophysiology might think that everything there is to know about the primary motor cortex (MI) has been learned. After all, MI is one of the Selleckchem I BET151 earliest cortical structures to be functionally studied beginning with the electrical stimulation experiments of Fritz and Hitzig in the late BKM120 solubility dmso 1800s (Fritsch and Hitzig, 1870). Motor cortical neurons have been designated historically as “upper motor neurons,” implying that they are perhaps one synapse away from the motor neurons in the spinal cord that activate muscles (Kandel et al., 2000). So, according to this viewpoint, MI can’t be any more complex or interesting than muscle drivers sitting in the brain instead of in the

spinal cord. As it turns out, however, the motor cortex is not so simple and its function remains elusive. First of all, despite extensive experimental and theoretical efforts for over fifty years, the exact computational and representational role played by the motor cortex remains unclear. Moreover, a number of recent studies have documented interesting sensory or sensory-triggered responses in the motor cortex that may require us to revise our understanding

of the functional role of the motor cortex. The use of the term “primary motor cortex” to define Brodmann area 4 is a designation that comes from the fact that movement can be most easily elicited through electrical stimulation of this area (Penfield and Boldrey, 1937). Moreover, it is known that approximately 30% to 50% of corticospinal projections originate from MI (Porter and Lemon, 1993). In addition, MI neurons typically begin modulating their firing rate up to several hundred milliseconds before ADP ribosylation factor a movement of the limb is initiated (Georgopoulos et al., 1982). Therefore, it is reasonable to consider this cortical structure as a primary motor area. However, this designation can obscure the fact that MI exhibits sensory responses and is part of a set of complex circuits that not only controls movement but also receives sensory inputs from the periphery. In the same vein, the designation of somatosensory cortex conceals the fact that this cortical structure also contributes to motor control as is evident in recent findings that the mouse barrel field controls retraction of the whiskers (Matyas et al., 2010).