The discussion of Self Comes to Mind on mirror neurons (102-04) in instructive. By the mere observation of another's action we activate the same motor processes as if one were doing the action. But we can also simulate our own pre-planned actions consciously by imagining and mentally rehearsing said action, which also activates the same motor processes. So I was wondering if there was any relation to motor neuron activation and the readiness potential noted in the Libet and subsequent experiments. And sure enough, according to this Kilner et al [1] there is indeed. After noting that mirror neurons operate similarly to when one actually performs an action they said:
"Here we show that the readiness potential (RP)--an electrophysical marker of motor preparation--is present when one is observing someone else's action. More importantly, when the nature and onset time of an upcoming action is predictable, the rise of the readiness potential precedes the observed movement's onset. This suggests that knowledge of a coming action automatically activates the motor system" (1299).
This still leaves some questions. Even if mirror neurons are operative in both one's own movements and in watching another's movement, and both correlate with the readiness potential, is this process conscious? Can consciousness cause the "automatic" readiness potential that precedes one's actions? Especially when our own action is "predictable," since we are consciously intending to make said action? He did say "when knowledge of a coming action automatically activates the motor system."
Indeed that is what Kilner et al investigated in another study.[2] They begin by defining action "as a sequence of acts or movements with a specific goal" that can be understood at four levels: "the intention level that defines the long-term goal of an action"; "the goal level that describes short-term goals necessary to realize the intention"; "the motor signals that describe the pattern of muscle activity through which the action is executed"; "the kinematic level that describes the" actual movement in space-time (621). And mirror neurons fire during this process.
Given the above work, it would appear reasonably feasible that a conscious intention of an action feeds the nonconscious mirror neurons and readiness potential, which precedes the actual movement. Our perception of the actual movement may coincide with the readiness potential, both of which precede the actual movement, and both of these seem automatic or unconscious. But neither Libet's study, or the recent one correlating the neural decision with one's perception of the "urge to move," [3] measure or tell us anything about the conscious intent of that movement, which according to the above precedes the automatic readiness potential.
1. Kilner et al (2004). "Motor activation prior to observation of a predicted movement." Nature
Neuroscience, 7(12): 1299-301
2. Kilner et al (2007). "The mirror neuron system: a Bayesian perspective." NeuroReport, 18(6), 619-23. PNAS,
3. Schurger et al (2012). "An accumulator model for spontaneous neural activity prior to self-initiated movement." PNAS, 109(42).
Another thing about the Libet experiment. Once the experimental parameters are disclosed to the subject he begins at that time to simulate and rehearse the experiment, thereby setting up mirror neurons and the readiness potential. This conscious preparation was not measured.
ReplyDeleteIt also explains why in the Schurger et al experiment the readiness potential by itself does not predict the movement, since they are seen whether one moves or not. We can simulate and rehearse the movement, which activates the RP, but we can also then choose not to move.
ReplyDeleteAlso recall from the Dehaene et al paper of 2011 (see previous blog post):
ReplyDelete"An original feature of the GNW model, absent from many other formal neural network models, is the occurence of highly structured spontaneous activity (Dehaene and Changeux, 2005). Even in the absence of external inputs, the simulated GNW neurons are assumed to fire spontaneously, in a top-down manner, starting from the highest hierarchical levels of the simulation and propagating downward to form globally synchronized ignited states" (209-212)."