Student: Proske and Gandevia in 2012 described an exafferent component as the “afferent signals generated by stimuli of an external origin”.
Professor: Well said; almost an exact quote.
Student: For me, running is mostly automatic, overlearned, rhythmic movement. How come I have no Sense of Effort during long periods of slow, easy running?
Professor: The simple answer is there is NO mismatch according to the theory cited byProske & Gandevia.
- That is, no error exists between the efference copy and the signal from motor command at the ” ‘difference’ calculator “.
- Proske & Gandevia further down the legend state, “if the predicted and actual sensory feedback match, the anomalous situation arises where there is no perception at all”.
Student: They even wrote that this instance is an ‘anomalous’ situation! So,
- Are they referring to voluntary contractions, perhaps using fine motor control or learning a gross motor pattern?
- Then again, there are well over-learned, automatic movements like running! Is jogging through the forest in Germany, only noticing the holes dug out by WWII bombs, just an ‘anomalous’ situation?!
Professor: Very interesting and intriguing questions. Then the answer is a sense of effort is to have A Mismatch!
Student: And what is the “motor command”?
- What if during some or many walking or running or cycling strides, no motor command signal was ‘issued‘?
- Or is there always a command signal coming down the efferent nerves to the active motor pool?
Professor: Let’s do some digging into the History of Motor Command and Control of Muscle Recruitment. Maybe we can find the answers to those questions, or at least get the ‘dogma’ scientists state about command signals.
Reference
Proske U, Gandevia SC. (2012) The proprioceptive senses: their roles in signaling body shape, body position and movement, and muscle force. Physiol Rev 92: 1651–1697.
