Variation in the throughput from single cortico-motoneuronal cells to electromyographic activity
Each column shows averages of rectified EMG from each of 13 muscles (rows) all triggered on the spikes discharged by neuron e0035_B during one of 8 different behavioral epochs. The trigger time is indicated by a vertical line in each column. All SpikeTAs are scaled vertically to fill the same height. SpikeTAs with highly significant effects are shown in red; those with effects of intermediate significance in blue; and those with no significant effect in black. Note that some muscles had highly significant SpikeTA effects (red peaks) during some behaviors, but no effect during others (black lines).
Certain neurons in the primary motor cortex make direct, monosynaptic connections to spinal motoneurons that drive hand and finger muscles. One might think that these constant connections to motoneurons would provide a constant throughput from the cortical neuron to muscle activity. Recently, however, we found that such throughput can change rapidly1. Now we are investigating factors that might produce such rapid changes.
The long-term goal of the present project is to understand factors that influence throughput from single neurons in the primary motor cortex to the motoneurons that drive muscles. The primary motor cortex, through its corticospinal projection, plays a major role in controlling movements of the body. Much of this control is achieved via direct connections from single motor cortex neurons to pools of spinal motoneurons. The throughput of these connections can be assessed in spike-triggered averages of rectified electromyographic activity recorded from muscles. By recording the activity of multiple motor cortex neurons and multiple muscles simultaneously during both natural and novel voluntary motor behaviors, and analyzing their spike-triggered average effects, the present application proposes to determine whether changes in neuron firing rate and ongoing electromyographic activity during voluntary behaviors produce systematic variation in the amplitude of throughput from the neuron to the muscle.
Because the firing rate of motor cortex neurons and the electromyographic activity of their target muscles often are correlated, the extent to which M1 neurons can be dissociated from that of their target muscles also will be investigated. Improved understanding of how the motor cortex controls muscles to move the body will lead to improved diagnosis, treatment and rehabilitation to functional recovery for patients affected by numerous neurological diseases including stroke, amyotrophic lateral sclerosis, multiple sclerosis, traumatic brain or spinal cord injury and cerebral palsy.
Davidson AG, Chan V, O'Dell R, Schieber MH (2007 Dec 21). Rapid changes in throughput from single motor cortex neurons to muscle activity. Science. 318, 1934-7.